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EFFECTS OF THE TROPICAL ENVIRONMENT ON ANIMAL PRODUCTION

At the end of this unit, you should be able to: 
• identify the geographic limits of the tropical environment and its peculiarities 
• explain the direct effects of three climatic elements on animal production and productivity in the tropics 
• discuss the indirect effects of the tropical climate on animal production 
• describe effects of altitude and soil fertility on animal production system.

3.1 The Tropical Environment and its Moderating Factors

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. 
In either way, systems of animal husbandry or management are also 
affected. 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. 

3.2 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. Seminaldegeneration 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. 
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 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 which 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 high cost of generating electricity and provision of refrigeration on the farm to reduce wastage of valuable animal products. 

3.4 Effects of Altitude and Soil Condition on Animal Production 

Altitude refers to height of a place over and above relative to the sea level which is usually measured in metres. Three plateaux in Nigeria exhibit micro-climatic conditions that differ slightly from the general tropical environment in terms of relatively lower ambient temperature, 
temperate vegetation and sometimes precipitation. This distinct condition confers on the Obudu Hill, Jos and Mambilla Plateau temperate like micro-environment on these places located within the tropical Nigerian climate. As such, production of cattle and other 
livestock may take the semblance of the temperate system of animal production. Some of the environmental stress conditions earlier enumerated may be unnoticed or moderated in the elevated places. 
Physiological responses of animals supported by favourable micro climatic condition tend to stimulate improved animal performance in terms of intake and metabolism of nutrients, growth and reproductive activities. Federal and state governments, organizations and wealthy individual scramble to establish livestock farms on Obudu Hill, Jos and Mambilla Plateau as well as other unique environments in Nigeria to take special advantage of the modified climate in such places for improved animal production and tourism. The emerging growth in dairy production in Kenya is partly attributed to high productivity of dairy cattle located on high altitudes and highlands of the country. The geographical principle of “the higher the relative altitude of given place, 
the cooler it becomes” is characteristic of the micro-climatic phenomenon experienced in most tropical highlands, which has led to improved animal productivity. 
The effect of soil condition on animal production is more or less indirect. The nutrient composition in food and forage, and possibly water depends on the soil content of micro and macronutrients. Relative balance of the required nutrients available for growth, production and 
reproductive performance in the body system of farm animal derive primarily from soil fertility and retention of nutrients in crops and forage which the animal consume. Palatability of certain forage feeds has been ascribed to the fertility of the soil. Forage and crop residue upon which tropical livestock survive are known to deteriorate rapidly in nitrogen and biomass contents, and lack in P, Ca and Na partly as a result of soil fertility factors, and these impact seriously on tropical livestock productivity. A few soil borne bacterial diseases such as anthrax and 
blackleg in contaminated sites may constitute a major problem on animal health. 

3.5 Effect of Tropical Climate on Animal Parasites, Vectors and Diseases 

In the vast tropical regions characterised by marked dry seasons and periodic droughts, climate is often the most prominent factor influencing animal health. It determines seasonal loss of body conditions, production and periodic starvations in years or times with exceptionally poor rains. Apart from this, the tropical climate stimulates proliferation of infectious and parasitic diseases through recurring provision of a 
favourable environment for development, growth and spread of such diseases and their agents. The resulting problems they cause livestock vary between various climatic regions, systems of management and between breeds or populations of animals. 
Climatic differences between regions have profound effects. It is obvious that worm eggs survive far better in humid climates than in the deserts, although surprisingly favourable conditions may occur locally 
around water points in a dry area. In Africa, tsetse flies thrive in warmer 
lower regions, while the tick vector of East Coast fewer prefers cooler, higher areas of greater altitude. As a general rule, animal populations tend to be adapted to the local diseases in the area in which they lived many generations, especially as they are kept under traditional, extensive management. Problems tend to crop up or increase, when they are kept in crowded conditions, favourable to intensive disease transmission and to concentrations of helminthes, eggs, coccidia and ectoparasites. 
Major climatic effect on animal diseases and parasites arise when European cattle are introduced into the tropics. Quite apart from the tropical climatic stress that further compound the poor health condition, exotic breeds such as dermatophilosis, theileriosis, trypanosomiasis, babesiosis, cocodiosis, tick infestation and a host of other diseases than are populations of local cattle in the areas in which such diseases are endemic. It is thus clear that co-evolution of host and parasite tend to 
result in natural selection of greater resistance on the part of the host. 
Quite often it is not so much a matter of breeds or species, but more of populations locally selected by natural disease pressure. 
Worm infestations are less spectacular than acute bacterial, viral or protozoan diseases, and their harmful effects, loss of production or sub optimal performances, are often underestimated. Acute rise in the degree of worm infestation during the rainy season in the tropics has been 
reported. The use of existing knowledge on the epidemiology and immunology combined with use of drugs have assisted a great deal to limit infestations to levels where they are harmless or nearly so. 
Eradication is hardly possible due to major part of the worm population occurring in the environment in form of eggs and larvae. 
Ectoparasites infestations apparently take over from the internal parasites as rainfall diminishes into the dry season. Ectoparasites inflict irritation, wounds and abscesses by their biting habit on the host. Thus resulting in painful bites, restlessness, reduced production performance, damages to hides, loss of blood, teat and part of the udder, causing 
considerable economic waste. The conditions further predispose animals 
to various parasitic and disease attack. Beside climatic conditions that permit the prevalence and proliferation of the ectoparasites, alternative hosts, especially wild beasts and domestic animals, harbor different stages of the biological cycle of the parasites. Certain pocket of micro environments also provides suitable places for breeding of the ectoparasites, making eradication much more cumbersome where such programme exists. 

4.0 CONCLUSION 
Virtually all production aspects of animal agriculture are affected or influenced by the unique tropical climate. It is very clear that the climate impinges directly on the biological functions of the body system, animal behaviour and production performance through such overbearing and moderating influence of temperature, humidity, solar radiation, and indirectly on feed supply, parasites and diseases, storage and handling of animal products. Progress in animal production has for age long being dependant on adjusting production system to suit the influence of the climate or changing the body physiological functions and behaviour to 
fix-up with climatic dictates. These fundamental factors underlie the various systems of production, systems of housing, feeding, reproduction and the overall management practices that are often adopted, modified or imposed. 

5.0 SUMMARY 

The review has indicated the divergent effects of the tropical climate on the production system, animal behaviour, productivity, feed production, and animal healthcare with implications for management practices required to reduce negative or enhance positive influence of the climate. 
The knowledge of the production environment in the tropic are tools for 
management practices in animal production. Students need to pay great 
attention in undertaking theoretical and practical course in the subject area. 

6.0 TUTOR-MARKED ASSIGNMENT 
1. Enumerate direct effects of tropical climate on animal production and discuss their management implications. 
2. Of what significance are the indirect effects of the climate on animal productivity in Nigeria, giving specific examples? 
3. Pinpoint rationales for restriction on importation of European cattle breeds into Nigeria, citing associated climatic, 
environmental health risks and their implications. 

7.0 REFERENCES/FURTHER READING 

Anonymous (1990). “Livestock Pests and Diseases of Tropical Region.” 
In: Preston, T.R., Mauricio, R. and Tang, H (Eds.). Integration of Crop in Response to Increasing Population Pressure on 
Available Resources. Proceedings of Seminar held on July11-14, 1989, in Mauritius. 
Payne, W.J.A. (1990). An introduction to Animal Husbandry in the Tropics. Fourth Edition. New York, U.S.A: Longman Scientific & Technical (Publ.).

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