Direct Effect of Climate

It must be noted from the onset that responses of individual animal to certain climatic condition vary between individual animals of the same breed. Temperature All domestic animals are homeotherms or warm blooded. In other words, they maintain their body temperature within a range most suitable for optimal biological activity. The body temperature range is relatively constant and is higher than the environmental temperature. The ambient temperature on the other hand varies with changes in the climatic elements at a particular time. The animal body temperature ranges within certain limits defined as the ‘comfort zone’ is a temperature range within which no demands are made on the temperature regulating mechanism. For a typical tropical breed of cattle, the ‘comfort zone’ range from 10 to 27 while a tropical temperate cattle has between -1 and 16. If there is a change in ambient temperature beyond either the upper or lower limit, the body mechanism for

regulating animal body temperature is triggered to action to enable the body remain or return to normal. However, thermo regulative mechanism may begin to fail, resulting in abrupt rise in rectal temperature, decline feed intake, an increase in water intake, a decrease in productive process such as growth and milk/egg production and perhaps a loss in body weight. Sometime the composition of milk produced may be affected. This partly explains the deterioration of highly productive cattle imported from temperate area to the tropics. Other behavioural and physiological responses of animal to excessive high temperature or heat load include sweating, panting, wallowing in mud or pool of water, reduction in physical exercise and mating activities. Let us examine a few of these effects of temperature on animal conducts.

Effect of Temperature on Grazing Activity (a) The Effect of High Air Temperature on Cattle is Reflected in their Grazing Behaviour; Studies have shown that length of day time grazing is related to the ambient temperature, and reduction in heat load improves grazing behaviour. Herders in semi-arid and arid area have adopted the act of grazing at night to improve both intake and length of grazing in hot seasons. Fast growing broiler birds are often fed in the night and sprinkled with droplets of water in the day as means of alleviating heat load to improve feed intake and overall production. (b) Effect of Temperature on Growth and other Productive Performance: High ambient temperature depress appetite and reduce feed intake and grazing time which may also diminish production as measured by growth, milk yield and milk solids production. Experimental evidence has shown that there is a partial correlation with growth rate when body weight is constant. However, under good management conditions where feeding and management are adequate, high ambient temperatures do not appreciably affect growth rates. Temperate type sheep in the tropics of Australia that are exposed to high air temperature often have a low lambing percentage and give birth to small weak lambs that have a high post-natal mortality. Lambs born in early summer and reared through hot summer are usually smaller at birth than lambs born in the cool months of early dry season. In poultry light breeds and young chicks are more resistant to heat than heavy breeds and adult birds. High temperatures predispose laying birds to abrupt decline in egg production. (c) Effect of Temperature on Milk Yield and Composition: Studies have indicated the effect of temperature on milk yield, butter fat and solids – not – fat. All these are depressed by high temperature, but usually by indirect effect of temperature on changes in feeding. As much as between 44 per cent and 55 per cent differences in milk yield and butter fat production were noticed between twin heifer reared under sound tropical and temperature management conditions. With increasing air temperatures appetite is depressed, food intake lowered, and heat production reduced. The exact mechanism of temperature effect on milk and milk composition is not known. Either the high temperature directly affects appetite, thus decreasing feed intake productivity and heat production or the need to reduce heat production forces down appetite and hence lower feed intake. The direct effect of temperature is further appreciated in a study that defines optimum temperature (0C) for milk production as 21- 27 in Jersey and Holstein 29-32 in Brown Swiss and higher in tropical breeds of cattle. Similarly, milk constituents namely; butter fat, chloride, lactose and total nitrogen are affected when temperature rises above 27-30. (d) Effect of Temperature on Reproduction: Air temperatures do not seem to affect reproductive cycle of cows, but bull fertility is markedly influenced. High testicular temperatures adversely affect spermatogenesis and hormonal system. Seminal degeneration and temporary infertility have been reported in Merino sheep exposed to temperature above 330C over a length of time. Both sizes of egg and thickness of its shell decline when laying fowls are exposed to high temperatures. Egg productivity decline has been experienced in poultry farms in Nigeria. However, incubation and brooding are favoured under high temperature. Humidity As stated earlier, it is difficult to separate or single out the effect of temperature, precipitation and humidity on animal production. Evaporation is one of the important channels of heat loss. It depends on ambient air temperature, the amount of available moisture in the atmosphere (humidity), area of evaporating surface and the degree of air movement. The amount of available moisture partly affects the rate of evaporative heat loss from the skin and respiratory system of an animal. High humidity adds to the heat load of the animal by depressing evaporative heat loss with declining effect on feed intake and productivity as demonstrated under temperature effects. Solar Radiation The quantity of solar radiation received in tropical region differs profoundly from the temperate. For tropical breeds of animal, solar radiation effects are scarcely noticeable because of their skin and eye that are pigmented. When temperate breeds are exposed suddenly to solar radiation of the tropics they suffer from sun burns or skin cancers, epithelioma (eye infection from solar radiation) and other photosensitive disorders. Solar radiation correlates with air temperature and thus partly contributes to the ambient temperature which is a principal climatic element affecting animal production. Management systems adopted in the tropics are a means for minimising adverse effects of solar radiation such as grazing in the night, clipping of excessive hair, grazing under shades in the day time etc. Solar radiation may contribute or may even create a more severe heat stress. 3.3 Indirect Effects of Climate Effects of the climatic environment on animal production, biotic agents, nutrition including the influence on animal feed supply and quality may be regarded as indirect effect that does not bear on immediate conduct of the animal but on its environment. Effect on Feed Supply: Climate affects the quantity and quality of feed available to the animal. Temperature, precipitation, daylight and humidity limit plant growth and affect feed quality more drastically than other climatic factors. In humid and sub humid areas where there is sufficient rains, plant exhibit seasonal growth, hence seasonal availability of forage. In the dry season when plant experience slow growth or complete growth seizure, available grazing stuff declines and animals lack enough to eat. In the arid and semi-arid zone lack of sufficient grazing material results in seasonal movement in search of forage feed in the wetter areas. The pattern of distribution of rainfall in which tropical region experience torrential rainfall in a short duration also partly explain rapid growth of plants within a short while followed by fast decline in biomass and other nutritional qualities. Nutritional quality of feed has to do with proportion of constituent nutrients, availability and balance of these nutrients in the ratio needed by the animals. Feed quality is most influenced by the climatic factors as precipitation and humidity. Rapid growth of plants results in production of high fibrous content of the forage feed as quality deteriorates with age. Tropical forage compared with that of temperate matures quicker, such that at same age the fiber content is higher; and digestible protein and total digestible nutrients lower. Thus stocks in the tropics usually have to digest more fibrous feeds and this may add to their heat load.