Adaptation to hot climate and strategies to alleviate heat stress in livestock production

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.

Dairy cattle in a temperate climate: the effects of weather on milk yield and composition depend on management

“…Models considering WS explained protein content best, while those containing sunshine, humidity and temperature also performed well. The importance of direct temperature metrics in explaining productivity is consistent with a wealth of studies on the impact of heat stress in dairy cattle (Renaudeau et al, 2012). Relatively few studies have assessed the impact of other weather variables on milk traits, but thermal indices that account for WS and solar radiation perform better than those that do not (Hammami et al, 2013).…”

“…As weather can have a delayed effect on biological processes, and the effects of weather depend on the timescale over which animals experience them (West et al, 2003;Renaudeau et al, 2012;Bertocchi et al, 2014), we explored the relationship between milk traits and all weather variables on the day the cow was milked ('test day' or TD), the preceding day (TD-1) and for the number of hours of sunshine, which was measured 0000 to 2359 h, 2 days before milking (TD-2). We calculated a 'moving' mean for each daily (0900 h) pointsample over the 3 and 7 days before (and including) the TD, and a moving minimum and maximum for the three variables for which 24 h summaries were available (ppt, T db and sunshine).…”

“…Milk yield in dairy cows, Bos taurus, is traditionally said to begin declining at around 72 THI units based on work carried out in subtropical regions (Armstrong, 1994;. Thresholds of 68 (Renaudeau et al, 2012;Gauly et al, 2013) or even 60 units (Bruegemann et al, 2012) may, however, be more characteristic of high yielding herds in temperate zones. The genetic relationship between heat tolerance and productivity is negative , and dairy cattle are becoming more sensitive to heat stress owing to optimisation of breeding and management practices for increased performance (Kadzere et al, 2002;West et al, 2003).…”

“…The genetic relationship between heat tolerance and productivity is negative , and dairy cattle are becoming more sensitive to heat stress owing to optimisation of breeding and management practices for increased performance (Kadzere et al, 2002;West et al, 2003). The reduction in productivity in heat stressed cows is largely a result of reduced feed intake, but high temperatures also have a direct effect on reproductive physiology and metabolism (Renaudeau et al, 2012). Cattle generate metabolic heat as a by-product of milk synthesis and so higher yielding animals experience heat stress at lower THIs than lower yielders (Kadzere et al, 2002).…”

Systems biology and livestock production

“…In broiler chickens the feathers comprise over 5% of the weight of the animal at slaughter (Cahaner et al, 2008) The nutritional input required to produce a plumage, and its insulating effect, are generally acceptable or beneficial in developed countries with temperate climates; the conditions under which the modern highly productive lines of poultry have been bred. However, in hot conditions poultry suffer heat stress, which decreases production of eggs and meat, and can be lethal (Renaudeau et al, 2012). The heat sensitivity of domestic chickens may appear unusual, given their tropical ancestry, but modern broilers gain weight much more rapidly than their antecedents, generating far more metabolic heat and having a bulkier body conformation that makes heat dissipation less efficient.…”