Impact of Climatic Variables on Animal Production
The primary environmental factors that influence animals are ambient temperature (Ta), relative humidity (RH), radiation, precipitation, atmospheric pressure and wind velocity.
The high Ta and RH for long duration results in heat stress. Therefore, animals try to adjust their physiological means to conquer such stressful situations by compromising their production and reproduction. The Ta is among the primary factors associated with thermal stress and it is altered by wind, precipitation, RH and solar radiation. Animals adopt the adaptive mechanism to compensate within their limits on exposure to varied Ta by adjusting feed intake, metabolism and improving the heat loss mechanisms. The animals are able to maintain a relatively constant body temperature in a range of temperature limit by modifying behavioural and physiological responses. The escalation in the ambient temperature causes heat stress as a result of inefficiency of the animal to eliminate excessive heat load. The enhanced environmental temperature impacts production performances of farm animals like reduction in milk yield as well as changes in milk composition and reproduction. Hence, both the extremities of climatic conditions impact negatively on livestock welfare, performance and health.28.3.1 Temperature
Temperature is the degree of hotness or coldness measured on definite scale. The high ambient temperature beyond the animal’s physiological limit may impact its biochemical processes. The temperature alterations may affect the enzyme activities, protein synthesis, and degradation at the cellular level. The cellular components are directly affected by temperature changes, whereas the cell elements are negatively influenced. Ultimately, as a consequence of the cellular damage, the synthesis and production of heat shock proteins, molecular chaperones that protect cells during cold or heat stress, get activated.
At the same time, some species have the innate mechanism of surviving in extremely cold regions with low temperatures that often touch below freezing levels. For example marine species contain anti-freezing components within themselves that enables their survival.28.3.2 Solar Radiation
The animals receive solar radiation directly as are flection from clouds and surrounding surfaces and indirectly from terrestrial or long-wave radiation emitted by surroundings surfaces. The total impact of solar radiation on an animal depends upon the variance between the collective solar and long-wave radiation received and the long-wave radiation emitted by the animal. There are some factors that influence the total effect of solar radiation such as shade, ground cover, clouds, hair coat and insulation characteristics of animal. Generally, the net gain of heat by solar radiation exceeds the effective Ta during hot climatic conditions by 3-5 °C culminating in heat stress, whereas the increase in effective Ta in winter is highly beneficial. Thus, increase in Ta directly impairs the animal performance by disturbing the heat balance. In addition, environmental temperature hampers the animal’s heat exchange by convection and evaporation. As the temperature increases, the rate of evaporation is enhanced which develops as a vital means of heat dissipation. The reduction in feed intake due to elevated environmental temperature leads to a decrease in the secretory pattern of calorigenic hormones, particularly growth hormone, catecholamines and glucocorticoids which reduces the thermogenic processes of digestion and metabolism. The scientific committee on animal health and welfare set the upper critical temperature in calves at 30 °C and RH below 60%, and it should be below 27 °C when RH exceeds 80%. Further, temperatures between 15 and 29 °C in fluence growth performance; however, temperatures above 30 °C negatively impact daily weight gain.
28.3.3 Relative Humidity
Humidity is an essential element of environment and routinely expressed as relative humidity (RH). It is the ratio of the current absolute humidity relative to the maximum humidity at a specific temperature, representing the amount of water vapour in the air at that temperature. The moisture content of air impacts an animal’s heat balance, especially during warmer environmental conditions where the evaporative heat loss is critical for homeothermy. Higher environmental vapour pressure depresses the vapour pressure gradient from the skin and respiratory tract to the external environment, thereby decreasing rate of evaporation. The occurrence and prevalence of infectious diseases are sensitive to RH which favours growth of pathogenic organisms. Lower RH leads to dryness of the ocular mucosa and the stratum corneum of the skin along with reduced skin temperature. The suitable percentage of RH for mammals varies in the range of 30-70%.
28.3.4 Wind Velocity
The wind speed influences the amount of convective and evaporative heat dissipation mechanisms. The enhancement of heat loss or gain is maximum at low speed of air since air movement disturbs the closed air over the body. The effective air velocity suggested for dairy cattle is 1.8-2.8 m/s during hot environmental conditions. Further, wind velocity above 1.0 m/s cools animal very effectively during hot periods wherein the RH is high. However, increasing air velocity above 1.67 m/s has small extra benefit in the convective heat loss.
28.3.5 Precipitation
Animals occasionally encounter an extreme weather in combination of low temperature, wind and rain or wet snow which adversely affects its body heat balance. The logging of water in an animal’s fur or hair transfers still air, which decreases the external insulation. Further, precipitation also smooths the fur and decreases its depth, which results in reduced insulative value.
28.3.6 High-Altitude Environment
The high-altitude environment is characterized with extreme cold, mountainous terrain, reduced oxygen in the air, high solar radiation and short vegetations and/or herbage growing seasons.
The reduced partial pressure of oxygen at high altitude leads to decreased oxygen loading in lungs followed by insufficient oxygen supply to the tissues via the circulating blood. The reduced level of tissue oxygenation limits aerobic metabolism which may impact an animal’s feed and water requirements, locomotor activities and impair the internal heat production. However, in mammals, the modifications of haemoglobin function mediate an adaptive response to high-altitude hypoxia. The partial pressure of the oxygen is high when the atmospheric air enters into the alveoli of the lungs which facilitate the diffusion of oxygen across the respiratory membrane and arterial bloodstream. The oxygen in the arterial blood binds to haemoglobin and transported to the tissues wherein the haemoglobin discharges oxygen which disseminated into the cells across the capillary walls. At the same time, the carbon dioxide and other metabolic end-products get into the venous bloodstream which is delivered at the lungs.28.4