Genetic Component of Heat Stress in Dairy Cattle, Development of Heat Index Function.
TL;DR: Production data obtained from AIPL USDA included 119,337 first-parity, test-day records of 15,012 Holsteins from 134 Georgia farms collected in 1990 to 1997 and the temperature-humidity index calculated with the available weather information can be used to account for the effect of heat stress on production.
About: This article is published in Journal of Dairy Science.The article was published on 2000-09-01 and is currently open access. It has received 426 citations till now. The article focuses on the topics: Heat index & Weather station.
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TL;DR: Maintaining cow performance in hot, humid climatic conditions in the future will likely require improved cooling capability, continued advances in nutritional formulation, and the need for genetic advancement which includes selection for heat tolerance or the identification of genetic traits which enhance heat tolerance.
1,471 citations
Cites background from "Genetic Component of Heat Stress in..."
...Ravagnolo et al. (2000) reported that maximum temperature and minimum relative humidity were the most critical variables to quantify heat stress, and both variables are easily combined into a THI....
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...The authors concluded that THI can be used to estimate the effect of heat stress on production (Ravagnolo et al., 2000)....
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TL;DR: In this article, the authors estimate economic losses sustained by major US livestock industries from heat stress, including decreased performance (feed intake, growth, milk, eggs), increased mortality, and decreased reproduction.
1,397 citations
Cites background or methods from "Genetic Component of Heat Stress in..."
...Because current selection for production reduces heat tolerance in dairy (Ravagnolo et al., 2000), we lowered the THIthreshold of dairy cows from the traditional value of 72 established many years ago to a value of 70....
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...…and relative humidity were assumed counter-cyclical; thus, minimum THI (THImin) was calculated using minimum temperature and maximum humidity, whereas maximum THI (THImax) was calculated using maximum temperature and minimum humidity using the standard THI equation (Ravagnolo et al., 2000)....
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...…1974 Yalcin et al., 2001a Moore et al., 1992 Yalcin et al., 2001b NRC, 1981 Neuwirth et al., 1979 Ominski et al., 2002 Ravagnolo and Mitszval, 2000 Ravagnolo et al., 2000 Ray et al., 1992 Richards, 1985 Salah and Mogawer, 1990 Silanikove, 2000 Spain and Spiers, 1996 Strickland et al., 1989…...
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...…high natural and managerial sources of variation (du Preez et al., 1990c; Linvill and Pardue, 1992), plus other confounding factors, such as stage of lactation, breed, and age (Ray et al., 1992; Ravagnolo and Misztal, 2000; Ravagnolo et al., 2000), and carryover effects (Collier et al., 1982a)....
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TL;DR: The objective of this paper was to review the effective strategies to alleviate heat stress in the context of tropical livestock production systems and those involving genetic selection for heat tolerance.
Abstract: Despite many challenges faced by animal producers, including environmental problems, diseases, economic pressure, and feed availability, it is still predicted that animal production in developing countries will continue to sustain the future growth of the world's meat production. In these areas, livestock performance is generally lower than those obtained in Western Europe and North America. Although many factors can be involved, climatic factors are among the first and crucial limiting factors of the development of animal production in warm regions. In addition, global warming will further accentuate heat stress-related problems. The objective of this paper was to review the effective strategies to alleviate heat stress in the context of tropical livestock production systems. These strategies can be classified into three groups: those increasing feed intake or decreasing metabolic heat production, those enhancing heat-loss capacities, and those involving genetic selection for heat tolerance. Under heat stress, improved production should be possible through modifications of diet composition that either promotes a higher intake or compensates the low feed consumption. In addition, altering feeding management such as a change in feeding time and/or frequency, are efficient tools to avoid excessive heat load and improve survival rate, especially in poultry. Methods to enhance heat exchange between the environment and the animal and those changing the environment to prevent or limit heat stress can be used to improve performance under hot climatic conditions. Although differences in thermal tolerance exist between livestock species (ruminants > monogastrics), there are also large differences between breeds of a species and within each breed. Consequently, the opportunity may exist to improve thermal tolerance of the animals using genetic tools. However, further research is required to quantify the genetic antagonism between adaptation and production traits to evaluate the potential selection response. With the development of molecular biotechnologies, new opportunities are available to characterize gene expression and identify key cellular responses to heat stress. These new tools will enable scientists to improve the accuracy and the efficiency of selection for heat tolerance. Epigenetic regulation of gene expression and thermal imprinting of the genome could also be an efficient method to improve thermal tolerance. Such techniques (e.g. perinatal heat acclimation) are currently being experimented in chicken.
662 citations
Cites methods from "Genetic Component of Heat Stress in..."
...This approach was first developed in dairy cattle by Ravagnolo et al. (2000), who estimated genetic parameters for resistance to heat stress indirectly by regressing phenotypic performance on a THI value calculated from data coming from public weather stations....
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TL;DR: A better understanding of the adaptations enlisted by ruminants during heat stress is necessary to enhance the likelihood of developing strategies to simultaneously improve heat tolerance and increase productivity.
Abstract: Environmentally induced periods of heat stress decrease productivity with devastating economic consequences to global animal agriculture. Heat stress can be defined as a physiological condition when the core body temperature of a given species exceeds its range specified for normal activity, which results from a total heat load (internal production and environment) exceeding the capacity for heat dissipation and this prompts physiological and behavioral responses to reduce the strain. The ability of ruminants to regulate body temperature is species- and breed-dependent. Dairy breeds are typically more sensitive to heat stress than meat breeds, and higher-producing animals are more susceptible to heat stress because they generate more metabolic heat. During heat stress, ruminants, like other homeothermic animals, increase avenues of heat loss and reduce heat production in an attempt to maintain euthermia. The immediate responses to heat load are increased respiration rates, decreased feed intake and increased water intake. Acclimatization is a process by which animals adapt to environmental conditions and engage behavioral, hormonal and metabolic changes that are characteristics of either acclimatory homeostasis or homeorhetic mechanisms used by the animals to survive in a new ‘physiological state’. For example, alterations in the hormonal profile are mainly characterized by a decline and increase in anabolic and catabolic hormones, respectively. The response to heat load and the heat-induced change in homeorhetic modifiers alters post-absorptive energy, lipid and protein metabolism, impairs liver function, causes oxidative stress, jeopardizes the immune response and decreases reproductive performance. These physiological modifications alter nutrient partitioning and may prevent heat-stressed lactating cows from recruiting glucose-sparing mechanisms (despite the reduced nutrient intake). This might explain, in large part, why decreased feed intake only accounts for a minor portion of the reduced milk yield from environmentally induced hyperthermic cows. How these metabolic changes are initiated and regulated is not known. It also remains unclear how these changes differ between short-term v. long-term heat acclimation to impact animal productivity and well-being. A better understanding of the adaptations enlisted by ruminants during heat stress is necessary to enhance the likelihood of developing strategies to simultaneously improve heat tolerance and increase productivity.
640 citations
Cites result from "Genetic Component of Heat Stress in..."
...In a 2-year study conducted under field conditions, we recently found a decrease of 0.27 kg of milk per THI unit only if Holstein cows were exposed to THI higher than 68 (Figure 4), and similar results were reported by Ravagnolo et al. (2000)....
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TL;DR: Indices with higher weights on humidity were best in the humid climate, whereas indices with larger weights on temperature were the best indicators of heat stress in the semiarid climate.
523 citations
Cites background or methods from "Genetic Component of Heat Stress in..."
...This index has been used in studies on heat stress by researchers from the University of Georgia (Holter et al., 1996; Ravagnolo et al., 2000; Ravagnolo and Misztal, 2000, 2002a,b; West, 2003); and THI6 has been developed by the United States Weather Bureau to describe discomfort in humans....
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...Ravagnolo et al. (2000) described decline of milk production due to heat stress by a broken-stick function....
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...Ravagnolo et al. (2000) described decline of milk production due to heat stress by a broken-stick function....
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References
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TL;DR: Dairy cattle in areas with relatively moderate climates also are exposed to periods of heat stress, and the resultant decrease in milk production and reproductive efficiency can be offset by implementation of a program consisting of cooling through shades, ventilation and spray, and fans.
896 citations
TL;DR: Dairy emphasis should be to increase intake or to alter levels of proteins, amino acids or other nutrients to improve the conversion of feed units into production units to render animals more sensitive, in terms of productive efficiency, to environmental modifications that improve comfort.
Abstract: It is well documented that the stress of hot environments lowers productive and reproductive efficiency, in farm animals. Likewise, research information is available to aid in the management of livestock in such adverse conditions. However, practical methods to achieve the desired levels of productive and reproductive performance are lacking. Summer forages that will support a high level of productivity in subtropic and tropic regions are needed for ruminants. More critical information is needed on the total dietary needs of all farm animals in hot environments. Dietary emphasis should be to increase intake or to alter levels of proteins, amino acids or other nutrients to improve the conversion of feed units into production units. Increasing nutrient intake to support a higher level of production will render animals more sensitive, in terms of productive efficiency, to environmental modifications that improve comfort. This should be especially pertinent in the humid Southeast and other regions where production responses to environmental modifications have been variable. There is limited information on the effect of the night cooling cycle on productive efficiency and on the effect of severe heat stress on reproductive phenomena not related to conception.
490 citations
TL;DR: In this article, the authors quantitatively described the environmental profile of central Arizona using meteorological data between 1971 and 1986, and found that milk production is lower during heat stress compared to thermoneutral periods.
Abstract: The environmental profile of central Arizona is quantitatively described using meteorological data between 1971 and 1986. Utilizing ambient temperature criteria of hours per day less than 21° C, between 21 and 27° C, and more than 27° C, the environmental profile of central Arizona consists of varying levels of thermoneutral and heat stress periods. Milk production data from two commercial dairy farms from March 1990 to February 1991 were used to evaluate the seasonal effects identified in the environmental profile. Overall, milk production is lower during heat stress compared to thermoneutral periods. During heat stress, the cool period of hours per day with temperature less than 21° C provides a margin of safety to reduce the effects of heat stress on decreased milk production. Using minimum, mean and maximum ambient temperatures, the upper critical temperatures for milk production are 21, 27 and 32° C, respectively. Using the temperature-humidity index as the thermal environment indicator, the critical values for minimum, mean and maximum THI are 64, 72 and 76, respectively.
230 citations
Journal Article•
TL;DR: Overall, milk production is lower during heat stress compared to thermoneutral periods and the cool period of hours per day with temperature less than 21° C provides a margin of safety to reduce the effects of heat stress on decreased milk production.
216 citations
139 citations