The tropical region lies between the latitudes (tropics) of Cancer and Capricorn in the north and south of the Equator. By its geographical location, the region is expected to be uniformly hot all year round, but this is not so.
A number of environmental factors moderate the hotness of the region such that several micro-climates (mini pockets of climatic conditions) are created in certain places by factors such as distance away from the equator (the degree of latitude), altitude (height above sea level), soils and contours vegetation, ocean currents, wind, rainfall and distribution of land and water.
Differences between one micro-climate and another are noticeable by variation in such climatic elements as temperature, rainfall and to a lesser extent, humidity are the climatic elements of greatest influences in moderating conditions in a micro-climate.
Similarly, they also cause major effects on animal physiology, behaviour and productivity through their individual or separate effects but, more often, by their combinations with other environmental factors.
The influence of climate on animal production (including animal body functions, behaviours and productive abilities) may be direct or indirect.
Either way, systems of animal husbandry or management are also affected. A direct influence of climate on animal production and husbandry has to do with such influence on the animal itself, while indirect influence is on the animal’s environment each of these shall be
examined closely.
1. Direct Effect of Climate
It must be noted from the onset that responses of the individual animals to certain climatic conditions vary between individual animals of the same breed.
1) 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’ ranges from 10 to 27 while a tropical temperate cattle have 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 the length of day time grazing is related to the ambient temperature, and reduction in heat load improves grazing behaviour. Herders in the semi-arid and arid areas 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 at night and sprinkled with droplets of water during the day as means of alleviating heat load to improve feed intake and overall production.
(b) Effect of Temperature on Growth and other ProductivePerformance
High ambient temperature depresses appetite and reduces 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 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 the 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 an abrupt decline in egg production.
(c) Effect of Temperature on Milk Yield and Composition
Studies have indicated the effect of temperature on milk yield, butterfat and solids – not – fat. All these are depressed by high temperature, but usually by an indirect effect of temperature on
changes in feeding.
As much as between 44 percent and 55 percent differences in milk yield and butter fat production were noticed between twin heifers reared under sound tropical and temperature management conditions. With increasing air temperatures appetite is depressed, food intake is lowered, and heat production is 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.
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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 the temperature rises above 27-30.
(d) Effect of Temperature on Reproduction
Air temperatures do not seem to affect the reproductive cycle of cows, but bull fertility is markedly influenced. High testicular temperatures adversely affect spermatogenesis and the hormonal system.
Seminal degeneration and temporary infertility have been reported in Merino sheep exposed to a temperatures 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.
2. 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.
3) 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 exposedsuddenly 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 minimizing adverse effects of solar radiation such as grazing at night, clipping of excessive hair, grazing under shades in the daytime etc. Solar radiation may contribute or may even create more severe heat stress.
2. Indirect Effects of Climate
Effects of the climatic environment on animal production, biotic agents, and nutrition including the influence on animal feed supply and quality may be regarded as an indirect effect that does not bear on the 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 climatic factors such as precipitation and humidity. The rapid growth of plants results in the 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 the 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.
Studies have indicated the extreme sensitivity of cattle to heat stress. It is noted that the balance of acetate available for purposes other than heat production is increased as environmental temperature increases.
Ruminants in a hot climate are more sensitive to imbalances of protein-energy, which results in an increased heat production. High temperatures and high humidity provide favourable breeding environment for internal and external parasites, fungi and disease vectors.
There is high incidence of internal parasites in the humid tropics and in the wet season. In arid areas, and in dry season, the incidence of insect pests and external parasites remain a major health threat.
As much as the vegetation-type influences the incidence of insect pests/vectors of disease, so much is climate indirectly affects animal production.
Incidence of tsetse fly infestation and distribution between the humid and sub humid area explains the interaction between the climate and vegetation and their influence on an animal production. Heat / humidity stress may have all or some of the following effects:
• Increases the requirement for protein by the animal
• Decreases the efficiency with which metabolisable energy is utilised
• Heat stressed animals must reduce feed intake
• An unbalanced diet that leads to excessive metabolic heat production will compound the effects of heat stress due to climatic condition.
Tropical climate favours the rapid deterioration and increases the cost of handling animal products. In arid or humid climates of the tropics, substantial quantity of animal products have been lost to putrefying organisms which multiply rapidly under such conditions to cause deterioration, spoilage and ‘food poisoning’ of enormous economic value.
This indirectly affects animal production in terms of the high cost of generating electricity and provision of refrigeration on the farm to reduce the wastage of valuable animal products.
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