W2173: Impacts of Stress Factors on Performance, Health, and Well-Being of Farm Animals (from W1173)
(Multistate Research Project)
W2173: Impacts of Stress Factors on Performance, Health, and Well-Being of Farm Animals (from W1173)
Duration: 10/01/2011 to 09/30/2016
Statement of Issues and Justification
Animal agriculture is one of the fundamental cornerstones that has helped shape the development of United States. Over the last 100 years animal agriculture has changed dramatically. The implementation of new technologies and production techniques has enhanced the efficiency of production. An increase in production efficiency has enabled producers to produce more meat, milk, and eggs with fewer animals, while maintaining a high quality, safe food product at a low cost to the consumer. In order for production animal agriculture to continue to deliver a safe and low cost product to the consumer, abatement of animal stressors are fundamental animal husbandry components essential for optimizing animal health and productivity. Stressors relative to animal production include environmental, management and immunological factors that have been reported to decrease animal production (growth, reproduction, efficiency, etc.) and overall animal well-being. For example, adverse weather conditions, including both the effects of hot and cold climatic conditions are particularly difficult for grazing as well as confinement-fed animals housed in outdoor facilities. Prolonged hot or cold environmental conditions cause animals to metabolically compensate in order to cope with extreme climatic conditions ultimately compromising animal health and overall productivity.
Environmental and management stressors erode efficiency and cost livestock production enterprises billions of dollars annually in lost potential profitability. For example, in the absence of heat abatement measures, total losses across all animal classes averaged $2.4 billion annually (St-Pierre et al., 2003). Of the total, reduction in milk production potential represented a major portion of the losses to the dairy industry, averaging $897 to $1500 million (St-Pierre et al., 2003). Moreover, adverse weather conditions including the effects of both hot and cold climatic conditions, are particularly difficult for confinement beef cattle feeding enterprises. Over the past 10 yr, Mader (2003) reported that harsh climatic conditions cost the beef feedlot industry between $10 to 20 million annually. Both enteric and viral diseases of pigs, particularly in the nursery and grow-finish phase, erode performance efficiency costing the swine industry millions as a result of production inefficiency, and many of these diseases are exacerbated by management stressors (Dritz et al., 2002; Neumann et al., 2005). In addition, climate change is projected to have major impacts on weather patterns leading to increased stress on animal populations (Collier et al. 2009). Counteracting the impacts of climate change will require significant new contributions to our knowledge of assessing the stress response, genotype by environment interactions and new more effective ways to mitigate impacts of stress.
Moreover, the W-1173 members routinely share resources and expertise in research aims which have included evaluation of factors affecting evaporative heat loss in cattle, evaluation of thermal cameras as a predictive tool in thermal stress and disease, evaluation of thermal hysteresis during heat stress, evaluation of the bovine acute phase response, the evaluation of use of indwelling thermal loggers, evaluation of the slick gene impact on thermal tolerance, evaluation of the behavioral response to heat stress in four breeds of beef cattle and evaluation of various dietary supplements on response to various stressors. These have included niacin, omega-3-fatty acids, dietary seaweed, dietary selenium, dry yeast, citrus pulp, dietary potassium and sodium. Several members of the project were involved in development of a new reference text on Environmental Physiology of Livestock to be published in 2011 by Wiley-Blackwell.
In addition to climatic stressors, thoroughly understanding the impact of how stress affects the immune system and susceptibility of livestock to disease is extremely important because the majority of emerging animal diseases have proven to be zoonotic diseases, and therefore threaten public health. Likewise, it is important to understand the impact of different levels of stress and the interaction of multiple stressors on animal health and production efficiency. Finally, identification of the modes of adaptation to acute and chronic stress conditions, as well as recovery, will allow for improved future prediction of the impact of a changing environment on animal performance and well-being. The objectives outlined in the current proposal address both critical aspects of responses of livestock to environmental and management stressors, and examine viable management interventions and alternatives to mitigate the detrimental effects of these challenges. This collaborative group of scientists and engineers spans a broad range of disciplinary training, and the group proposes cross-station experiments that run the gamut from very basic cellular/molecular questions to very applied investigative aims. Thus, outcomes of this multi-state project can reasonably be expected to broadly impact production practices, animal comfort and wellbeing, and improve profitability across diverse livestock commodity sectors.
Related, Current and Previous Work
The W-1173 project formulated three primary objectives which were the focus of research and collaborative interactions during the previous 5 yr (2006 2011): (1) Identify strategies for developing and monitoring appropriate measures of animal stress and well-being. (2) Assess genetic components, including genomics and proteomics, of animal stress and well-being. (3) Develop alternative management practices to reduce stress and improve animal well-being and performance. Working under these three objectives, the W-1173 research group would contribute greatly to an enhanced understanding of stressors that impact animal performance, factors that act as intermediaries to stress responses, and how current and alternative management practices can influence the impact or manifestation of stress within the production environment. Detailed below by objective are specific examples and highlights of directed accomplishments from the previous 5 years (which is by no means all-inclusive), and demonstrates both the collaborative nature of this research group and the commitment to project objectives aimed at elucidating and alleviating the impact of stress in livestock production-management systems.
A search of the CRIS system was carried out to address any potential duplication using the terms stress, heat stress, cold stress, climate change and animal. There were no animal projects identified that had objectives which duplicated any of the efforts of this project. One project (NCDC 222) is a multistate research coordinating committee and information exchange group oriented around Adapting Agriculture to Climate Variability but do not yet have specific objectives. Another project (NC1029) Applied Animal Behavior and Welfare will examine some of the behavioral responses of animals to stressors and pain but their models are not similar to the environmental models employed in this project. However, the W-1173 project has held collaborative meetings in the past with the NC1029 group to discuss opportunities to improve estimates of animal responses to environmental stress and will likely continue to draw on their expertise in the future.
5.1 Identify strategies for developing and monitoring appropriate measures of animal stress and animal well-being.
Colorado conducted studies on steers to evaluated the effects of molybdenum (Mo) and copper (Cu) on the concentrations of hydrogen sulfide (HS) in the rumen gas cap. Data suggest that 100 mg/kg Mo from sodium molybdate in the diet reduced the HS without adversely affecting performance. Study 2 evaluated the genes involved in Cu regulation for pulmonary arterial tissue and liver tissue in different species: Angus crossbred steers, Nubian goats and Landrace pigs. These data suggest that genes involved in Cu homeostasis regulation in the arterial and liver tissue are different for different species.
Colorado and KS collaborated to study the effects of restraining methods (snare vs. sorting boards) on blood lactate concentration (LAC) in pigs (Kansas). Data showed the LAC was higher in groups restrained by snare versus sorting board. In both treatments, LAC increased with increasing duration of restrain. Sorting board would probably be the restraining choice for short duration with minimum effect on LAC.
Hawaii, Arizona and New York collaborated on a study to evaluate the effect of hot-dry vs. hot-humid conditions on sweating rates for high producing Holstein cows in the presence and absence of solar radiation at (550W/m2). The data suggest that sweating occurs in cyclic fashion(3-5min) and depends on the initiation and/or duration of solar exposure. Holstein has maximum sweating capability of around 600g/m2 and skin temperature drives the evaporative event.
Illinois studied the use of low cost GPS collar system for cattle coupled with handling and animal training (grooming and positive reinforcement with corn feeding). After two weeks of training and grooming, there was stark reduction in equipment damage and ease of handling of animals as demonstrated by the ease of approaching and working with the GPS system in 80% of the animals when they were in the field.
A collaborative study by NY, HI, MS, and Canada were able to develop continuous recording of vaginal temperature of dairy cows using data loggers with built in temperature sensors. Plastic anchors were designed and produced to hold data loggers inside the vagina of cows. The vaginal temperatures were compared to the rectal temperatures and the results matched to within 0.06 +/- 0.0150C(Hillman et al., 2009).
Primiparous sows were used in a study to evaluate reliable predictors of thermal stress. Results across all periods (3 weeks of gestation, farrowing, lactation and post-weaning) showed that skin temperatures at trunk (shoulder and rump) and at the extremities (ears and tails) were significant predictors of respiration rates and rectal temperatures(Missouri). A second study on the consumption of 40µg erogvaline/kg/day endophyte infected tall fescue effects on rumen temperature in Angus steers was evaluated under thermal neutral environment and heat stress environments. Endophyte consumption resulted in higher respiration rates and higher rectal temperatures but no significant differences in rumen temperature were detected. In a subsequent study it was determined that cattle with tolerance for fescue toxicosis did not showed body temperature differences related to site of origin (OK Angus vs. MO Angus). A fourth study examined the impact of ergopeptide alkaloids on vascular contractility using Angus of OK origin fed diets: control or 30µg ergovaline/kg BW/d in thermal neutral vs. heat stress conditions. The results affirmed the reduction of feed intake during heat stress and that animals fed ergovaline had lower feed intake. There were no differences in skin temperature during heat exposure but ergovaline treatment resulted in lower skin temperatures (ear and upper tail) in the thermal neutral environment supporting vasoconstrictor properties of ergopeptide alkaloids. The fifth study focused on the physiological responses of Angus (Missouri and Oklahoma origin) and heat tolerant Romosinouano in grazing conditions under mid-Missouri summer conditions. There were no differences in respiration rates and ruminal temperature between Angus of different origin but there was a breed difference between Angus and Romosinouano for both parameters. Both breeds shared similar pattern of adaptation from early to late summer periods.
Studies with sows with different parities (1-9) showed the emotional state of sows change with gestation stages. Sows in late gestation demonstrated more fearful behavior versus those in early gestation and there was no difference between parity(Minnesota). In a second study to determine housing (group versus individual pens) and parity on pre-weaning mortality, it was discovered that parity 1 sows had lower piglet mortality and weaned larger litters compared to multi-parity sows in a straw-bedded farrowing system.
Intrauterine infections in the bovine can have detrimental effects on reproductive performance, and Escherichia coli (E. coli) is a primary causative pathogen (Mississippi). Objectives were to characterize the photonic properties of E. coli-Xen14 (a stably transformed E. coli containing the lux operon), and conduct photonic imaging of E. coli-Xen14 from within the excised bovine uterus. Results indicated that DITI can be used to measure eye and muzzle temperatures in sheep as an indicator of body temperature in both the normothermic and febrile state. In cattle the relationship between muzzle temperature and rectal temperature was not apparent in the normothermic state, but eye temperature was correlated to rectal temperature. This study shows that DITI can be used as a non-invasive method of measuring body temperature in livestock.
Nebraska developed a model to understanding thermal hysteresis during heat stress. Heat stress studies of farm animals suggest that above a certain threshold body temperature (Tb) is driven by ambient temperature (Ta). When hysteresis is present, there are two values for Tb depending on whether Ta is increasing or decreasing. A theoretical delay-relay model is proposed to illustrate the hysteretic dynamics of the Tb-Ta relationship when Ta is cyclic. Treatment factors were significant for all parameters except the recovery inflection point. Significant pen and day interactions were found for the other six parameters.
Oregon determined that plasma concentrations of cortisol, acute-phase proteins and pro-inflammatory cytokines in halter-trained beef steers (Angus, 163+7.0 kg) following i.v. (0.1µg/kg BW) corticotrophin-releasing hormone infusion increased. In a separate study the relationship of temperament, an altered physiological state, and reproductive parameters in Bos taurus (Angus-Hereford cows) was evaluated. While no differences were detected in body condition score, haptoglobin and ceruloplasmin, excitable temperament led to lower pregnancy rates (89% vs. 94.0%).
The effects of environment conditions on shade utilization and pen distribution for dairy cows was studied using 186 cows over a 72h observation period (Texas). The results showed that cows tend to spend more time at the feed-bunk when the THI was low and during periods of cloud cover and high wind speed. Shade utilization increased with decreasing cloud cover and independent of THI. Soil temperatures under the shade was consistently cooler than open lots and the cows chose to lay down where it was cooler even in the night.
A collaborative effort by LIRU and Texas Tech University developed an indwelling rectal temperature probe that could be used in cattle that were group housed or individually penned. Use of this automated rectal temperature monitoring device in cattle research will enable more frequent sampling of rectal temperature, while also decreasing labor requirements; and will also decrease error introduced by human handling of cattle to obtain measurements.
A collaborative study was conducted LIRU, the USDA-ARS Subtropical Agricultural Research Station, the University of Missouri, the University of Florida, and Texas Tech University to elucidate the bovine acute phase response following an intravenous challenge with an endotoxin. Results indicate that maximum and minimum rectal temperature were positively correlated to the temperament of the animal, and that epinephrine tended to be positively correlated with maximum rectal temperature. Additionally, both stress hormones, cortisol and epinephrine, were positively correlated with the temperament of the cattle. Collectively, these data demonstrated that temperamental bulls had greater concentrations of cortisol and epinephrine and also had elevated rectal temperature compared to the calm bulls. Additionally, these data elucidate dynamic changes in rectal temperature to various stimuli including transportation and handling.
5.2 Assess genetic components, including genomics and proteomics, of animal stress and well-being.
Heat tolerance for 4 breeds (Angus, Charolais, MARC I and MARC III) of heifers with different hair coat color was evaluated (USDA-MARC). One group had accessed to shade while the other had no shade structure. It was determined that shade lowered the stress levels for all breeds with greater impact on the darker hair coat animals. The absence of shade had no effect on performance.
A single gene has been identified for expression of a phenotype in cattle characterized by a short, sleek hair coat and increased heat tolerance as measured by lower rectal temperatures and respiration rates (Virgin Islands). Introduction of this gene into populations could be used to mitigate heat stress in livestock in areas of high heat and humidity. This gene has been found in Senepol cattle and it has been determined that it has a simple dominance mode of inheritance. The objective of this trial was to compare the hair coat characteristics and body temperature measurements of the two genotypes. Hair samples were collected from the shoulder, over the ribs and rump in a 40.6 cm2 area using electric clippers. Surface temperature (ST) of a non-clipped area over the ribs was measured using an infrared thermometer. Rectal temperature (RT) was collected using a digital veterinary thermometer. Respiration rate (RR) was measured by counting breaths for 15 s and adjusting to breaths per minute (bpm). Individual hair weight was estimated by dividing the sample weight by number of hairs. There was no difference among locations on hair density or weight (P > 0.10) so data were pooled. There was no difference (P > 0.10) in RT or ST between NH and HH cows (38.6 ± 0.06 vs. 38.6 ± 0.06 °C and 34.8 ± 0.2 vs. 34.4 ± 0.2 °C, respectively). The NH cows had a higher (P < 0.0004) RR than HH cows (52.0 ± 1.5 vs. 43.2 ± 1.5 bpm, respectively). There was no difference (P > 0.10) in hair density between NH and HH cows (484.6 ± 41.9 vs. 420.5 ± 41.9 hairs/cm2 and 8.0 ± 0.8 vs. 6.0 ± 0.8 g/cm2, respectively). Individual hair weight was higher (P < 0.02) for NH cows than for HH cows (16.3 ± 0.8 vs. 13.4 ± 0.8 µg, respectively).
5.3 Develop alternative management practices to reduce stress and improve animal well-being and performance
A trial was completed by KS, GA and BC on a large commercial dairy in western Minnesota to evaluate the impact of using low profile cross ventilation (LPCV) in combination with evaporative pads on core body temperature (CBT) and resting behavior of lactating cows. No difference was detected in lying times and lying bouts between LPCV barns with and without evaporative pads. Cows housed in the facility with evaporative pads had lying times of 660 minutes/day and 12 lying bouts per day, whereas cows without evaporative pads had lying times of 654 minutes/day and 12.9 lying bouts per day. Time that CBT exceeded 102°F or 102.5°F tended (P = 0.06) to be greater for cows without evaporative pads. Core body temperature was above 102°F for 566 and 704 minutes/day and above 102.5°F for 321 and 378 minutes/day for cows with and without evaporative pads, respectively. These trends were evident even though the stocking density of the freestalls was greater in the facility with evaporative pads than in the facility without pads (123.4 vs. 113.1%).
A trial was conducted by KS on a cross ventilated dairy in Iowa to evaluate water usage of evaporative pads. Peak water usage was three time the average water usage. Total water consumption during the 31 day period was 1.82 ML (482,350 gal). The average daily water used per cow was 49 L (13 gal) per cow per day.
A replicated design with 24 multiparous high producing dairy cows (40 ±1.4 kg/d) was utilized to evaluate a dose range of dietary NI (0, 4, 8, or 12 g/d) in winter acclimated lactating dairy cows on body temperature indices, sweating rate, feed intake, water intake, production parameters and blood niacin concentrations under thermoneutral (TN) and heat stress (HS) conditions (Arizona). The HS environment increased skin, rectal and vaginal temperatures, respiration rate, sweating rate and water intake and decreased feed intake (4 kg/d, P<0.01), milk yield (3.4 kg/d, P<0.01), milk protein (0.18g/100ml, P<0.01). Sweating rate increased in HS (13 g/m2 h, P<0.01) compared to TN, but this increase in response to HS was 10 fold lower than reported in summer acclimated cattle. We did not detect evidence of an increase in sweating rate with supplemental NI. Heat stress reduced blood (7.82 vs. 6.63 ug/ml, P<0.01) but not milk niacin concentration. Dietary NI increased water intake in a linear manner (P<0.02) in both environments but the increase was greater during HS conditions (P<0.03). Dietary NI also increased skin temperature in both environments (P<0.01) in both shaved and unshaved skin in a dose-dependent manner (P<0.01) but the increase was greatest in shaved skin (P<0.04). This suggests that skin blood flow was enhanced with increasing NI dose. Results indicate that HS increases niacin requirements in lactating dairy cows and that NI supplementation partially restores blood niacin concentration during HS. Dietary NI increased water intake during HS and increased skin temperature. There may be seasonal differences in sweating rate responses to HS and NI.
Hawaii, New York and USDA-MARC evaluated the behavioral activities of four breeds of feedlot heifers: Angus, Charolais, MARC 1 and MARC III with distinct differences in hair coat, in shade and no shade pens. It was found that Angus (black) hair coat absorbed 98% of the solar load, MARC III with dark red hair absorbed 92% of solar load while Charolais only absorbed 37% of the solar load. Dark hair coat animals spend more time in shade vs. white hair coat and the core body temperature of the Angus animals increased at a rate 2x faster than other breeds when lying in the sun.
Studies conducted in laying hens facilities showed that different housing systems and different sites within a housing system (air, manure belts, water source, etc) yielded distinct microbial assemblages (Illinois). Detection of zoonotic pathogens also varied between housing and site of sampling suggesting that environmental factors as a consequences of housing types may influence pathogenic organism.
The impact of evaporative pads (EP) on core body temperature, duration of lying and lying bouts for Holsteins housed in cross-ventilation freestall housing was studied (Kansas). Lying times and lying bouts were similar for control (without EP) and treatment. However, EP reduced core body temperature significantly (38.90C vs. 39.20C).
A study to determine the effect of previous housing on aggression at the time of growing pig mixing showed that pigs with previous exposure to large groups were more tolerant to unfamiliar pigs (Minnesota). The less stressful conditions subsequently led to better growth performance.
Mississippi conducted a study to determine the potential of omega-3 fatty acid fortified supplements as an energy supplement to provide decreased mobilization of intramuscular fat deposition associated with cattle grazing forages and to enhance fatty acid content in meat tissue throughout the feedlot feeding period. Our data suggests that the energy supplement provided to the steers did decrease mobilization of intramuscular fat while grazing pastures. A study was conducted to develop a Comprehensive Climate Index (CCI) that has application under a wide range of environmental conditions and provides an adjustment to Ta for RH, WS, and RAD (Nebraska). Environmental data were compiled from nine separate summer periods in which heat stress events occurred and from six different winter periods to develop and validate the CCI. The RH adjustment is derived from an exponential relationship between temperature and RH with temperature being adjusted up or down from an RH value of 30%. At 35 ºC, the temperature adjustment for increasing RH from 30 to 100% equals approximately 10 ºC, while at -35 ºC temperature adjustments due to increasing RH from 30 to 100% average -2.0 ºC, with high RH values contributing to a lower apparent temperature under cold conditions. The relationship between WS and temperature adjustments were also determined to be exponential with a logarithmic adjustment to define appropriate declines in apparent temperature as WS increases. With this index, low WS results in the greatest change in apparent temperature per unit of WS regardless of whether hot or cold conditions exist. As WS increases, the change in apparent temperature per unit of WS becomes less. Based on existing wind chill and heat indices, the effect of WS on apparent temperature are sufficiently similar to allow one equation to be utilized under hot and cold conditions. The RAD component was separated into direct solar radiation and ground surface radiation. Both of these were found to have a linear relationship with Ta.
North Dakota examined the effects of exercise on resting blood oxygen levels and maternal behavior during pregnancy in Yorkshire gilts. Gilts were assigned to remain in gestation stalls or to undergo an exercise treatment. Treatment did not affect blood oxygen saturation; though a day effect was shown with saturation fluctuating every 2 wks. Exercise did not affect lying duration, but exercised gilts sat less and stood more. The control gilts tended to be more restless.
Effect of supplementation of polyunsaturated fatty acids(PUFA) in Angus steers 30 days prior to shipping to feedlot on average daily gain (ADG), dry matter intake and acute-phase response proteins studied. Not differences were observed in ADG in the pre-conditioning phase but the subsequent performance in feedlot, PUFA treatment resulted in greater ADG (Oregon).
Gastrointestinal nematode infections cause substantial economic losses in pasture-based sheep farming worldwide. Rhode Island evaluated the effect of vitamin E supplementation on naturally acquired parasite infection in lambs. Results indicate that biweekly injections of vitamin E at 15 and 30 IU d-a-tocopherol/kg BW, had no effect on parasitological parameters used in the study to assess gastrointestinal nematode infection.
A second study was run to determine the effect of vitamin E supplementation, using the newly revised recommendations of the National Research Council, on lymphocyte proliferation and immunoglobulin production in lambs (in progress). There was no effect of vitamin E supplementation on lymphocyte proliferation for all of the mitogens tested.
Texas determined the effects of transportation on plasma cortisol, corticosterone or dehyroepiandrostene (DHEA) in horses with no prior transport experience. All horses exhibited a pattern of elevation in cortisol and corticosterone during hauling but the levels returned to basal concentrations by 2h after transport. There were no differences between horses transported in individual stalls vs. loose group. ls did not appear to be useful in characterization of isolation or transportation stress in horses. A second study on the impact of housing, the utilization of shades and feeding regimens under heat stress environment was performed with dairy calves of age 1-3 days for 7 weeks period. Feeding regimen had no effect on shade utilization and calf activities. Activity (steps taken) were impacted negatively with high THI vs. low THI. Calves house outdoors were less active compared to calves housed indoors. It was observed that at 2 weeks of age, calves had learned to seek shade prior to lying down. Calf activity increased with age.
USDA-LIRU and Iowa State University conducted a study to determine the accuracy in the time spent at the waterer and the number of visits to the waterer by individually housed nursery pigs between human observers scoring video files using Observer software (OBS) and an automatic water meter Hobo (WMHOBO, control) affixed onto the waterline. In addition, the amount of water consumed and wasted by individual pigs provided with ad libitum access to a nipple waterer was recorded. Collectively, the data from this study indicated that the use of the traditional OBS method for quantifying drinking behavior in pigs can be misleading and that quantifying drinking behavior, and perhaps other behavioral events, via the OBS method must be more accurately validated in future research studies. Perhaps a definition of drinking behavior using actual water ingestion and the notion of bout would lead to a better accuracy with OBS, though we suggest that drinking behavior should not be recorded by human observers but by automatic recording devices.
Work at the University of Arizona and the Virgin Islands evaluated the impact of dietary Niacin on response to thermal stress in cattle. Results indicate that heat stress lowered plasma niacin and use of protected niacin (Niashure®) increased plasma niacin in heat stressed cattle. However, dietary niacin did not consistently reduce body temperature in heat stressed cattle.
Identify measures of animal stress and well-being and characterize factors affecting the biology of stress and immune responses
Identify and assess genetic components of animal stress and well-being
Development of management strategies and/or tools to enhance farm animal well-being under conditions of climatic change or other stressful environments.
MethodsWorking under these three objectives, the W-1173 research group would contribute greatly to an enhanced understanding of stressors that impact animal performance, factors that act as intermediaries to stress responses, and how current and alternative management practices can influence the impact or manifestation of stress within the production environment. 7.1 The following are collaborative research efforts proposed to address the first objective (item 6.1 above). Identify measures of animal stress and well-being and characterize factors affecting the biology of stress and immune responses. Dam Heat Stress( IN, HI, MO). Although many studies have focused on the effects of heat-stress on the dairy cow, limited literature on any species investigates the effects of pre-natal heat-stress on the neonate. An on-going study is underway to assess the effects of pre-natal heat-stress and its timing on calves' abilities to thrive. Additional, replications are needed to complete this study and a study in a temperature and humidity controlled environment will be necessary to target the importance of timing of the heat-stress event. Biological Measures of Stress Objectives at Oregon State focuses on determining the relationship of stress of handling and cattle temperament on productive and reproductive parameters. We accomplish these objectives by associating performance parameters, such as growth rates and reproductive efficiency, with physiological measures, such as circulating concentrations of hormones and other substances associated with performance, health, and the stress-response. A long-term collaborative effort involving scientists from the Livestock Issues Research Unit, the USDA-ARS SubTropical Agricultural Research Station in Brooksville, Florida, and the University of Missouri will continue to further elucidate the bovine innate immune response following an endotoxin challenge when beef cattle are exposed to heat stress conditions. Specifically, the upcoming objective will be to determine the differential physiological, endocrinological, and immunological responses of heat tolerant (Romosinuano) and heat susceptible (Angus) Bos Taurus cattle following LPS exposure during periods of heat stress. A collaborative study by scientists from the Livestock Issues Research Unit, Mississippi State University, and Texas Tech University will develop a shipping fever model in cattle that can be utilized to investigate the efficacy of various nutritional strategies that could potentially be utilized to reduce the incidence of morbidity and mortality of cattle associated with shipping fever. Additionally, development of this model will provide unique information regarding the behavioral responses of cattle during the progression of disease that could potentially be used to develop improved management practices Studies are to be undertaken (University of Nebraska) that will characterize effects of adverse climatic conditions on body temperature profiles and behavior attributes of feedlot cattle. Studies will be designed to determine stress threshold response curves based on animal parameters, including body condition, coat color and metabolizable energy intake. Adaptive responses of beef cattle to environmental stressors, such as heat stress, grass toxins, and feed and water restrictions, will be the focus of researchers at the University of Missouri in collaboration with KY-USDA-ARS, FL-USDA-ARS, TX-USDA-ARS, AR-USDA-ARS, and the University of Queensland, Australia. Long-term studies in the field environment will be conducted together with short-term, controlled laboratory stress tests to assess the temporal changes in specific processes related to thermoregulatory ability and animal health. In addition, the recovery from these stress conditions will be examined in terms of its impact on subsequent exposures to stressors. Another area will include the development of animal models of response to heat stress that take into consideration the response variances across populations and different levels of stress sensitivity. Use of telemetric temperature transmitters will allow monitoring of the differential responses to the rise and fall in the daily cycles of air and animal temperatures, and this information will be incorporated into the models. MS will address the development of relevant animal models and novel technologies for identifying and monitoring environmental and physiological stress in livestock (equine, cattle, swine and poultry). Specifically, these studies will utilize digital infrared thermal imaging, novel pressure and ocular sensors, non-invasive temperature and blood sampling devices, and in vivo/in vitro biophotonic markers for the development of animal models and non-invasive assessments of the effects of stress on production parameters. MS works with multi-state regional cooperators in MS, TX, USDA-ARS-TX, USVI and USDA-ARS-IN on these initiatives. Specific work addresses temperament indices in beef cattle, heat stress in sheep, dairy and beef cattle, biophotonic models of disease and gene regulation in swine and dairy cattle, and production-management physiology related to cow comfort and lameness in dairy cattle. While specific technologies are employed for model development and stress assessments, these are supported by blood hormone and immune parameter measures, environmental and climatic monitoring, and in vitro approaches for understanding physiological mechanisms of action in response to stressors. Technology development and stress factor elucidation is conducted in conjunction with research on reproductive physiology, nutritional management, and growth and development using traditional experimental designs and analysis approaches. Understanding Lactate Physiology of Swine to Help Reduce Industry Losses of Fatigued Pigs. Collaboration: (CO and KS). The physiological responses of finisher pigs to stress play a significant role in in-transit losses of slaughter pigs. KSU and CSU will collaborate to gain an understanding of the lactate physiology of swine. The initial phase of this project is a pilot study designed to test the repeatability and practicality of blood sampling and analysis techniques. It is hoped that a practical, low-stress, accurate technique can be adopted for use in the second phase of this project. The second phase of the project focuses on exploring various aspects of lactate kinetics (threshold, clearance) of finisher swine. Pigs will be exercised, simulating movement through a finisher barn during loading or at a packing plant, and blood lactate will be monitored (pre-, during, post- exercise). Evaluation and Application of Humane Hypoxia Euthanasia for Suckling and Nursery Pigs. Collaboration: (CO and KS). Humane euthanasia of sick or injured pigs raised in a commercial production facility is necessary when veterinary medical care and economic considerations deem that the animal cannot be rehabilitated. Humane euthanasia in a slow assent hypobaric chamber will allow swine producers to euthanize animals on-farm in a manner that is less stressful to the animal, consistent, and acceptable to the public, and less stressful for workers. It furthermore shows promise as a humane stunning method for slaughter, since the point is to produce hypoxia without asphyxia. Based on previous research conducted at Colorado State University (MacGregor, et al., 2008), the vision of the investigators is to have a low cost, on-farm slow assent hypobaric chamber that is safe to use, portable, easy to operate and delivers the most effective and humane form of on-farm euthanasia. Furthermore, it will help to alleviate distress to animal care takers when euthanizing sick or injured pigs. Piglets will be euthanized utilizing both hypobaric hypoxia and carbon dioxide to determine humaneness and effectiveness of both methods. Various physiological, behavioral and neurological parameters will be measured to characterize the stress induced by the euthanasia methods. 7.2 The following are collaborative research efforts proposed to address the second objective (item 6.2 above). Identify and assess genetic components of animal stress and well-being. Characterization of the physical and optical properties of animal hair coat and their effects on energy balance of cattle exposed to solar load. Collaboration: (NY,HI, MARC, FL and MS). The hair coat of animals which traps air to provide insulation in cold weather, becomes an obstruction for evaporative cooling by reducing the velocity and moisture gradients through the fur layer in hot and humid conditions (Gebremedhin et al., 2008). It is therefore imperative that physical and optical properties of the hair coat are accurately characterized for modeling heat and mass transfer through the hair coat. Hair coat physical and optical properties that represent present-day high milk-volume producing cows and changes in nutrition of animal feed is nonexistent in the literature. This study will develop an updated data base of physical and optical properties of hair coat of heifers and lactating cows. The specific objectives of this study are: (1) to measure the physical properties (hair length, hair diameter, hair-coat thickness, and hair-coat density) and optical properties (solar reflectivity and absorptivity) of various breeds of heifers and lactating cows, (2) to determine the difference in properties based on location on the body, breed and hair color, (3) to develop a database of hair-coat properties for different breeds of dairy cows, and (4) to characterize the data in probabilistic functions. Studies are to be undertaken (University of Nebraska) that will characterize effects of adverse climatic conditions on body temperature profiles and blood parameters of genetically diverse feedlot cattle. Studies will be conducted during periods of cold weather and hot weather with cattle of similar ages and on both steers and heifers. Data will be utilized to determine genomic profiles that are most conductive to possessing heat tolerance and cold tolerance. Determination of the relationship of the "slick hair" gene and evaporative cooling in known population of the Senepol breed and hair sheep. Collaboration: (VI;NY;HI;AZ). The genetic make-up of the the University of the US Virgin Islands Senepol herd that carry the the "slick hair" gene t has been determined. We proposed to study the relationship of this gene with evaporative cooling and extend the information to the hair sheep population in the research station. The specific objectives of this study are to determine: (1) sweating rates of heterozygous, homozygous and the absence of the "slick hair" gene population in the Senepol herd under heat stress conditions, and (2) correlate sweating and respiration rates to physiological responses (core body and skin temperature changes) and environmental parameters under stressful thermal conditions. The information learned from the experiment will be used to study the two breeds of hair sheep in the experiment station to determine their ability to cope with heat stress conditions in sub-tropics. Determination of genetic differences in stress responses. Oregon State will work on establishing an association between the extent of an animals response to stress factors (management procedures such as weaning, transport, and feedlot entry, as well as cattle temperament) with its genetic composition. The objective is to determine if the variance in physiological and performance response among animals to the aforementioned stress conditions are due to differences in genetic merit, whereas genetic composition can be used for selection of animals that are more resistant to the detrimental effects of stressful procedures. 7.3 The following are collaborative research efforts proposed to address the third objective (item 6.3 above). Development of management strategies and/or tools to enhance farm animal sustainability under conditions of climatic change or other stressful environments. Effects of Weaning Strategies on the Physiology and Performance of Pigs and Beef Calves. Collaboration: (TN; FL; CO; TX). Weaning is a stressful experience coincident with the animal eating little during the first days after weaning. The low food intake disposes them to weaning diarrhea and weight loss, which can result in increased incidences of morbidity and mortality. Activation of the major stress pathway, the hypothalamic-pituitary-adrenal axis, results in a significant release of the steroid, cortisol, from the cortex of the adrenal glands. Cortisol is a potent glucocorticoid with immunosuppressive effects that can lead to disease susceptibility. Corticosteroid-binding globulin (CBG) has a major influence upon the activity and availability of circulating cortisol, and thus is of relative importance in the animals biological response to a stressor. A reduction in CBG levels, subsequent to an elevation in cortisol, can result in an increase in the FCI (a surrogate measure of biologically active cortisol) especially in the acute stress phase, and within a week subsequent to the elimination of the stressor. Regulation of CBG synthesis by the liver, the principal site of production in most species studied, is not well known. Collaborative studies will be designed to examine circulating levels of total cortisol, CBG, FCI and measures of behavior, immune status and growth performance in pigs and beef calves in response to novel conditioning methods prior to weaning. Rubber Flooring to Increase Cow Comfort. Collaboration: (IN;TN). Dairy cattle show a preference for rubber flooring when they have it as an alternative to concrete. We have some evidence that concrete flooring is a chronic stressor, resulting in more peripheral blood mononuclear cells and cytokine changes that indicate chronic inflammation. We did not get clear indication with cortisol analysis reflecting an acute or chronic condition. We hypothesize that with additional analysis of bovine specific cortisol-binding protein, the cortisol responses might become better defined. Using Dietary Modulators to Enhance Immunity to Combat Nematode Infections and Enteric Pathogens. Collaboration: (RI; IN). Nematodes are problematic for sustainability of small ruminant farms, particularly in New England. The identification of natural anthelmintics for the control of parasites in small ruminants is essential. Beta glucan as well as the bioactive extract of cranberries have shown potential to enhance immunity. The impact of these extracts on several parameters of immune function will be tested with lambs. It is also possible that the bioactive cranberry extract will be a natural anti-microbial that would be useful for neonates (swine or cattle). Immune and microbial measures will be used to assess its efficacy with a Salmonella challenge. Dietary Strategies to reduce impact of stress. Oregon State will develop strategies that lessen the incidence of stress during common management procedures such as handling, weaning and transport, as well as alleviate the detrimental effects of such stressful conditions on cattle well-being and productivity. They will focus on nutritional management, more specifically inclusion of nutraceuticals into diets of cattle that will be exposed to such stresses, as well as strategies to improve the overall temperament of the herd. Collaborative studies will continue with scientists from the Livestock Issues Research Unit, the Food and Feed Safety Research Unit in College Station, and the University of Floridas Range Cattle Research and Education Center in Ona, FL to evaluate the effects of feeding citrus pulp to weaned pigs infected with Escherichia coli F18 and to young dairy calves infected with Salmonella Typhimurium. The objectives associated with these studies are: 1) develop a weaned pig diet that can prevent the incidence of post-weaning diarrhea associated with E. coli infection; 2) develop a diet for early weaned dairy calves that can prevent morbidity and mortality associated with Salmonella infection; 3) evaluate the feasibility of using citrus pulp as a means to reduce/eliminate fecal shedding of E. coli 0157 in cattle prior to slaughter. Development of thermal indices for lactating cows exposed to stressful thermal environments. Collaboration: ( NY; HI; AZ). Many of the environmental indices used for stress indications for livestock are either adopted directly from those developed for humans without making appropriate modifications (Thom, 1959, Hoppe, 1999), or were developed from empirical relationships of environmental factors (Buffington et al. 1981, Baeta et al., 1987, Armstrong, 1994). The existing equations for calculating thermal indices (a) do not either include all the environmental components, (b) and/or are not corrected with physiological responses of the animal, and (c) if they do, they account for a single physiological response (Eigenberg et al., 2005, Mader et al., 2006, Gaughan et al., 2008). New thermal indices will be developed based on physiological responses that reflect thermal environmental load. The specific objectives of this study are: (1) to develop thermal stress indices for lactating cows under stressful (hot and dry, hot and humid) conditions, (2) to categorize the thermal stress indices to different levels of stress on the animal, and (3) determine niacin effect on cooling / sweating. Modeling and experimental analysis of alternative udder cooling of dairy cows in stressful conditions. Collaboration: (NY, HI, MS). Milk is produced in the secretary epithelial cells of the udder. For the cells to perform their task, significant amounts of nutrients are supplied by the blood. About 400 to 500 liters of blood are required to produce one liter of milk (Mustafa, 2001). For the average cow, about 20% of output of the heart flows into the udder. Blood flow maintains the udder at a temperature near the core body temperature of the cow. This would suggest that the udder acts as a heat sink and that a large amount of heat would be transferred from the udder surface especially when considering its large surface area. Some studies have reported specific thermal parameters of the udder such as heat flux or temperature changes during and after milking (Janeczeck et al., 1995) but, to our knowledge, no study is available that has modeled the udder as a heat sink and consider it as a cooling system if kept wet. The specific objectives of this study are: (1) to develop a mathematical model that predicts heat loss from the udder, (2) to validate the predictions of the model against experimental data, and (3) to develop an evaporative cooling system for the udder and evaluate its effectiveness. Evaluate effects of geothermal cooling on lactating dairy cattle Collaboration: (.AZ, NY, HI,, KS). Geothermal cooling of cattle bedding has been shown to reduce core temperature and heat stress of cattle (Gebremedhin et al ). Geothermal cooling also has the potential to reduce cold stress during winter months. We will evaluate use of geothermal cooling of freestall and shaded lot bedding on heat parameters and performance of lactating dairy cows during hot summer months and cold winter months. Develop a model to evaluate cooling strategies for lactating dairy cows Collaboration: (AZ and KS). Dairy producers have multiple ways to minimize heat stress in dairy cattle. These methods include evaporative cooling of the air, evaporation of moisture from the skin surface and geothermal cooling of the resting area. The efficiency of these different strategies varies by climatic conditions. We will develop a model that will determine the ideal cooling strategy or strategies that should be used under different climatic conditions. Develop a practical and inexpensive method of cooling black feedlot cattle in regions of high temperature and solar load. Collaboration: (CO, NY and HI). Previous work by our group have shown higher absorption of solar radiation load by dark hair coat leading to higher core body temperature in these animals within a breed. In addition, we have determined that hair is a barrier to evaporative cooling and there are genetic variations of hair coat within a breed. There is increasing interest in the beef industry to supply dark hair coat animals (primarily with Angus influence) to feedlot. Hence, the objectives for this study are: (1) to assess the presence or absence (shaved) of hair coat to animals physiological ability to cope with heat stress by measuring respiration rate, core body temperatures, behavioral activities and panting score during peak heat stress period of the day, and (2) to develop a practical and inexpensive method of cooling black feedlot cattle. Studies are to be undertaken (NE) to characterize effects of adverse climatic conditions and mitigation strategies that are effective in sustaining animal comfort and productivity performance. In addition water consumption will be assessed. Models will be developed which characterize impact of adverse weather events and determine most effective and/or economical mitigation strategies to utilize. Develop dietary modulators that can improve vaccination efficacy and reduce vaccination-stress is nursery pigs (KSU). Peri-weaning pigs have immature immune systems and develop sub-optimal immune responses to vaccination. The growth performance of these piglets can be negatively impacted by vaccination. It has been a difficult task to simultaneously improve vaccination efficacy and growth performance in nursery pigs due to the extreme complexity of interactions between immune status, vaccination efficacy, and growth performance. The specific objective of this study is to develop novel dietary modulators that can improve nursery pig growth performance by reducing stresses associated with vaccination and weaning and can enhance vaccination efficacy in peri-weaning pigs.
Measurement of Progress and Results
- The W-1173 regional research project has enjoyed a long and productive history (established in 1985). Our project members have continued to expand their collaborations over the past five years since the previous project revision. Multiple new collaborations have evolved as well as expanded accomplishments from existing collaborative teams. The outputs of these efforts are documented through clear commitment to publication of research results. In the first four years of the current project, our members have published 196 peer-reviewed manuscripts and 390 other scientific papers in the form of abstracts, proceedings articles, book chapters, theses, dissertations and technical reports. Nearly all of these documents contain shared authorship among our participating project stations. The ongoing accomplishments of this group are a result of interactions among research scientists trained in a variety of disciplines (behavior, engineering, statistics, livestock management, endocrinology, immunology, etc.) with expertise in a broad range of livestock species. This comparative and multi-disciplinary approach among collaborating scientists is what facilitates the expansion of capabilities among individuals in the group which may not have been feasible by other means. Members of W-1173 are regular participants and/or invited speakers in special sessions and symposia on the biology of stress in livestock at national and international meetings /conferences. In 2010, Arizona organized an ADSA Discover Conference on: Effect of the Thermal Environment on Nutrient and Management Requirements of Cattle. The ADSA Discover Conference series was chosen as the suggested format for the meeting because its primary goal as stated in its Charter is to foster creativity, emphasize interaction and open discussion and focus on thrusts that will synergize the development and use of science for the benefit of food animal industries and society Moreover, the W-1173 members routinely share resources and expertise in research aims which have included evaluation of factors affecting evaporative heat loss in cattle, evaluation of thermal cameras as a predictive tool in thermal stress and disease, evaluation of thermal hysteresis during heat stress, evaluation of the bovine acute phase response, the evaluation of use of indwelling thermal loggers, evaluation of the slick gene impact on thermal tolerance, evaluation of the behavioral response to heat stress in four breeds of beef cattle, evaluation of various dietary supplements on response to various stressors. These have included niacin, omega-3-fatty acids, dietary seaweed, dietary selenium, dry yeast, citrus pulp, dietary potassium and sodium.
Outcomes or Projected Impacts
- Collectively, research directed toward the three objectives outlined in this proposal should advance the understanding of the biology of the stress response and important components and measures of animal well-being. This information will be utilized to develop new management practices for improvement of on-farm animal well-being The specific routes of information flow of these new practices to producers will include lay publications, extension publications, local and national extension meetings, the Large Herd Production Conference and national extension websites.
- Projected improvements for producers include improved methods for estimating environmental stress on animals. Improved predictions of production responses to given environmental conditions. Improved methods for reducing heat stress on cattle using conductive cooling approaches. Reduced energy costs and water consumption for cooling animals and improved nutritional practices for animals exposed to environmental stress. We expect this information to become more readily usable for direct application in animal production systems by disseminating information through lay publications and extension programs. . Such application will reduce animal stress and increase animal productivity and reproductive potential and performance resulting in increases in net income for the livestock industry. Furthermore, the application of management strategies to alleviate stressors would improve the image of livestock producers who are responsible and concerned for animal welfare and well-being.
Milestones(1):lestones are time-linked accomplishments with the majority of the discovery efforts in initial years followed by development of practical management strategies and then on-farm demonstrations. " Geothermal (ground water) cooled beds will be built on freestall and dry-lot shades dairies in Arizona, Texas, Kansas and California. Studies will begin to assess lactation and reproductive performance of dairy cows under hot summer conditions with and without additional cooling. " Measurements of environmental stressors and physiological responses (udder skin temperature, core temperature, respiration rate) of wetted udder only and wetted body of lactating cows. " Assess the many empirical equations on thermal indices of humans and animals that exist in the literature. " Determine sweating rate of Senepol cattle in relation to the Slick Hair gene in a tropical environment " Determine if hypobaric hypoxia is a viable method for on-farm euthanasia of swine. " Conduct animal study at Kansas State University to determine the molecular mechanism of vaccination-induced stress in peri-weaning pigs
(2):Geothermal cooling studies will continue on same dairies in Arizona, Kansas and California " Development of a mathematical model that predicts heat loss from wetted udder, and validation of model using the experimental data. " Organize and coalesce the environmental stressors and physiological responses data that we have collected to date and conduct additional experiments of exposing lactating cows to different levels of solar load. " Determine sweating rate of St Croix White and Dorper x St Croix White hair sheep under tropical conditions " Investigate swine lactate kinetics as it relates to in-transit losses of slaughter pigs. " Conduct animal study at Kansas State University to determine the effect of novel dietary modulators on vaccination efficacy and growth performance in nursery pigs.
(3):Geothermal cooling studies will continue on same dairies in Arizona, Kansas and California " Development of an evaporative cooling system for the udder and field test the system on limited lactating cows for effectiveness. " Development of new thermal indices that account for environmental stressors and physiological responses. " Determine sweating rate of St Croix White and Dorper x St Croix White hair sheep under tropical conditions " Determine if alternative handling procedures can decrease incidences of fatigued pigs " Conduct animal and in vitro studies at Kansas State University to determine the mechanisms of novel dietary modulators on vaccination efficacy and growth performance in nursery pigs.
(4):Geothermal cooling studies will continue on same dairies in Arizona, Kansas and California " Further refinement of the udder cooling system and field test on different breeds, udder sizes and environmental conditions. " Categorize the thermal indices into levels of stress they impinge on the animal. " Sweating rate studies will be summarized an published " Publish results of hypobaric hypoxia euthanasia of swine "
(5):Geothermal cooling studies will be summarized and published " Publish results of the effectiveness of udder wetting, prepare teaching module, and show and tell the udder cooling system to dairy farmers and extension agents via conferences. " Summarize and publish the new thermal indices and their level of impact on lactating cows, as well as prepare extension publications for extension agents. " Hair coat studies will be summarized an published " Publish swine lactate kinetic and handling experiments. "
Projected ParticipationView Appendix E: Participation
The collaborative efforts resulting from this project are expected to continue to produce multiple peer-reviewed scientific publications, as well as abstracts of research presented at national and international meetings, non-refereed research reports, extension publications and theses/dissertations. The committee has a long history of organizing and participating in scientific symposia. It is anticipated this activity will continue. However, the primary objective of the outreach plan is to use new information to develop practical on-farm management strategies which then can be disseminated through a variety of routes. Lay and extension publications will also be produced for producer use and local, regional and national meetings such as the Southwest Nutrition Conference, The Large Herd Dairy Conference, and state production conferences will also be venues for information exchange. Additionally, several of the project participants hold extension appointments at land-grant institutions Data and results generated from the current project that have practical application will be evaluated by extension personnel for appropriate dissemination at producer meetings.
The organization and supervision of the regional project will be by the Regional Technical Committee that will consist of a research administrator from an Agricultural Experiment Station in the region to act as the Administrative Advisor, one or more representatives from each cooperating Agricultural Experiment Station or cooperative Agricultural Research Service Station, and an advisory member representing the Cooperative State Research Service, USDA.
The Regional Technical Committee will prepare an annual report of the work being carried out under this regional project. In addition, it will be responsible for making periodic evaluations of the accomplishments of the project. It shall be the responsibility of the Executive Committee and Administrative Advisor to authorize, encourage, and assist in the preparation of suitable regional publications.
The Executive Committee of the Regional Technical Committee shall consist of the Chair, Secretary, and immediate Past-Chair. A new Secretary will be elected each year by the voting members of the Technical Committee. The previous Secretary will become the Chair for one year and then will move to the Executive Committee for an additional year. The Executive Committee will have the authority to act on behalf of the Regional Technical Committee. If any member of the Executive Committee resigns, the remaining member shall, with the advice and consent of the Administrative Advisor, appoint a member of the Regional Technical Committee to fill the vacancy. The term of the office will end at the adjournment of the regular annual meeting. The new immediate Past-Chair will prepare the annual progress report and submit it to the Administrative Advisor. The new Chair (previous Secretary) will prepare a set of minutes of the annual meeting and send it to the Administrative Advisor for distribution to the Regional Technical Committee.
Armstrong, D. V. 1994. Symposium - nutrition and heat-stress interaction with shade and cooling. Journal of Dairy Science, 77(7), 2044-2050.
Beata, F.C., Meador, N.F., Shanklin, M.D. 1987. Equivalent temperature index at temperatures above the thermoneutral for lactating cows. ASAE meeting paper,
Buffington, D. E., Collazoarocho, A., Canton, G. H., Pitt, D., Thatcher, W. W., & Collier, R. J. 1981. Black globe-humidity index (bghi) as comfort equation for dairy-cows. Transactions of the ASAE, 24(3), 711-714.
Cena, K. and J.L. Monteith. 1975a. Transfer processes in animal coats, I radiative transfer, Proc. R. Soc. Land., Vol. 188, 377-393.
Cena, K. and J.L. Monteith. 1975b. Transfer processes in animal coats, II conduction and convection, Proc. R. Soc. Land., Vol. 188, 395-411.
Collier, R.J., T. R. Bilby, M. E. Rhoads, L.H. Baumgard and R. P. Rhoads. 2009. Effects of Climate Change on Dairy Cattle Production. Annals of Arid Zone. 47(3 & 4): 1-12.
Davis, L.B. and R.C. Birkebak.1974. On the transfer of energy in layers of fur, Biophys. J., Vol 14, 249-268.
Dritz, S. S., M. D. Tokach, R. D. Goodband, and J. L. Nelssen. 2002. Effects of administration of
Antimicrobials in feed on growth rate and feed efficiency of pigs in multisite production
Systems. J. Am. Vet. Med. Assoc. 220:1690.
Eigenberg, R. A., Brown-Brandl, T. M., Nienaber, J. A., & Hahn, G. L. 2005. Dynamic response indicators of heat stress in shaded and non-shaded feedlot cattle, part 2: Predictive relationships. Biosystems Engineering, 91(1), 111-118.
Gebremedhin, K.G., P.E. Hillman, C.N. Lee, R.J. Collier, S.T Willard, J. Arthington,
and T.M. Brown-Brandl. 2008. Sweating rates of dairy cows and beef heifers in hot conditions. Transactions of ASABE 51(6): 2167-2178.
Gaughan, J. B., Mader, T. L., Holt, S. M., Lisle, A. 2008. A new heat load index for feedlot cattle. Journal of Animal Science, 86(1), 226-234.
Hillman, P.E., K.G. Gebremedhin, S.T. Willard, C.N. Lee and A.D. Kennedy. 2009. Continuous measurements of vaginal temperature in female cattle. Applied Engineering in Agriculture, ASABE 25(2):291-296.
Hoppe, P. 1999. The physiological equivalent temperature - a universal index for the biometeorological assessment of the thermal environment. International Journal of Biometeorology, 43(2), 71-75.
Mader, T. L. 2003. Environmental stress in confined beef cattle. J. Anim. Sci. 81:E110.
Mader, T.L., Davis, M.S., Brown-Brandl, T. 2006. Environmental factors influencing heat stress in feedlot cattle. Journal of Animal Science, 84(3), 712-719.
Janeczeck, W., B. Chudoba-Drozdowska, Z. Samborski, & A. Kusz 1995. Skin temperature
changes of the cow mammary gland and the heat flux from its surface before and after milking. Archivum Veterinarium Polonicum 35(1-2):35-44.
Mustafa, Arif. 2001. http://animsci.agrenv.mcgill.ca/courses/460/topics/3/text.pdf, Accessed
February 23, 2009.
Neumann, E. J., J. B. Kliebenstein, C. D. Johnson, J. W. Mabry, E. J. Bush, A. H. Seitzinger, A.
L. Green, and J. J. Zimmerman. 2005. Assessment of the economic impact of porcine
reproductive and respiratory syndrome on swine production in the United States. J Am
Vet. Med Assoc. 227:385.
St-Pierre, N. R., B. Cobanov, and G. Schnitkey. 2003. Economic losses from heat stress by US
livestock industries. J. Dairy Sci. 86:E52.
Thom, E. C. 1959. The discomfort index. Weatherwise, 12, 57-59.