Climatic elements have direct effect on the system of animal production, body physiology and animal behaviour, feed supply and quality, proliferation of pests and parasites as well as preservation of animal products (Samson et al., 2011) A number of climatic elements such as temperature, rainfall, humidity, radiant energy, air movement, light, altitude etc. greatly influence and interact with the performance of livestock production. 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.
The over-riding environmental factor affecting the physiological functions of domestic animals is temperature. Temperature is measured using the instrument called thermometer, which are of various types. 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 (Samson et al., 2011). In this range the animal’s heat exchange can be regulated solely by physical means such as constriction and dilation of blood vessels in the skin, ruffling up the fur or feathers and regulation of the evaporation from lungs and skin.
For a typical tropical breed of cattle, the ‘comfort zone’ range from 100 C to 270 C while a tropical temperate cattle has between -10 C and 160 C (FAO, 1986). If there is a change in ambient temperature beyond either the upper or lower limit, physical regulation will not be sufficient to maintain a constant body temperature and the animal must, in addition, decrease or increase its metabolic heat production. The body mechanism for regulating animal body temperature is triggered to action to enable the body remains or return to normal (Samson et al., 2011). However, a further decrease or increase in temperature will eventually bring the temperature to a point beyond which not even a change in heat production will be sufficient to maintain homeothermy, hence, thermo-regulating mechanism may begin to fail, resulting in one or more of the following as elucidated by Samson et al., 2011: i.Abrupt rise in rectal temperature.
ii. Decline feed intake i.e. loss of appetite.
iii. Increase in water intake.
iv. Decrease in productive process such as growth and milk/egg production
v. Loss in body weight i.e. emaciation.
vi.Change in composition of milk produced.
This partly explains the deterioration of highly productive cattle imported from temperate area to the tropics. However, very young animal, lacking fully developed temperature-regulating mechanisms, particularly the ability to increase heat production by increased metabolism, is much more sensitive to its thermal environment and requires higher temperatures. Other behavioural and physiological responses of animal to excessive high temperature or heat load include:
iii.Wallowing in mud or pool of water as in pigs.
iv.Reduction in physical exercise and mating activities.
As mentioned earlier that all domestic livestock are homeotherms; that is, they maintain relatively constant internal body temperatures, usually within a 1 to 2° C range. Normal body temperatures of some domestic animals are given in Table 1.
Table 1: Normal Body Temperatures of Domestic Animals (FAO, 1986).
Dairy Cow 38.6 38.0 – 39.3
Beef Cow 38.3 36.7 – 39.1
Pig 39.2 38.7- 39.8
Sheep 39.1 38.3 – 39.9
Goat 38.7 – 40.7
Horse 37.9 37.2- 38.2
Chickens 41.7 40.6 – 43.0
The body temperature of most domestic animals is considerably higher than the environmental temperature to which they are exposed most of the time. They maintain their body temperatures by balancing internal heat production and heat loss to the environment. The hypothalmus gland acts as a body thermostat by stimulating mechanisms to counteract either high or low ambient temperatures (FAO, 1986). For example, increased conversion of feed to-heat energy is used to counteract low ambient temperatures, while for example increased respiration (rate and volume) and blood circulation in the skin counteracts high ambient temperatures.
Varying temperature also results in changed behavior . Most animals reduce their level of activity in a hot environment and, for example, pigs lie clustered in a heap at low temperatures, while they lie spread out with extended limbs at high temperatures (FAO, 1986). This would suggest increased space requirement for pigs held in a warm, tropical climate. The body can tolerate short periods of heat stress, but if the ambient temperature exceeds the body temperature for an extended period, it may prove fatal. When feed is converted by the animal’s metabolism for the production of milk, eggs, meat, off-spring etc., heat is produced as a by-product. An increased production level and thus feed requirement will therefore result in increased internal heat production. High yielding animals are consequently more likely to suffer from heat stress in a hot climate than are low yielding ones.
Feeding fibre-rich, low digestible feed stuffs like hay will result in high heat-production because of increased muscular activity in the alimentary tract and, in ruminants, increased micro-organism activity in the rumen. An increased share of concentrates in the feed may therefore reduce heat stress in an animal under hot climatic conditions (FAO, 1986).
Effects of Temperature on Animal Activities
Quite a number of animal activities are affected by ambient temperature ranging from grazing activities and feeding behaviour, growth and productive performance, milk yield and composition, reproduction etc. These effects are elucidated below:
(a)The Effect of High Ambient Temperature Feeding Behaviour in Animals: 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. However, in the case of monogastric animals such as broiler birds, they are often fed in the night and when to be fed during the day, their feeds are sprinkled with droplets of water as means of alleviating heat load to improve feed intake and overall production (Da Silva, 2007).
It should be noted that feeding fibre-rich, low digestible feed stuffs like hay will result in high heat-production because of increased muscular activity in the alimentary tract and, in ruminants, increased micro-organism activity in the rumen (FAO, 1986). An increased share of concentrates in the feed may therefore reduce heat stress in an animal under hot climatic conditions. In contrast, when the ambient temperature is low, the animal will increase conversion of feed to-heat energy is used to counteract low ambient temperatures, hence resulting to increase in feed intake (FAO, 1986).
(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 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 (Da Silva, 2007). 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% and 55% differences in milk yield and butter fat production were noticed between twin heifer reared under sound tropical and temperature management conditions (Samson et al., 2011). With increasing air temperatures appetite is depressed, food intake lowered, and heat production reduced (Vercoe, J.E.).
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 (Vercoe, J.E.). The direct effect of temperature is further appreciated in a study that defines optimum temperature for milk production as 210 C – 270 C in Jersey and Holstein 29-32 in Brown Swiss and higher in tropical breeds of cattle (Da Silva, 2007). Similarly, milk constituents namely; butter fat, chloride, lactose and total nitrogen are affected when temperature rises above 270 C – 300 C (FAO, 1986).
(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 330 C over a length of time (FAO, 1986). In poultry, 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.
As stated earlier, it is difficult to separate or single out the effect of temperature, precipitation and humidity on animal production. Humidity is measured using the instrument called hygrometer. 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 (Samson et al., 2011). The amount of available moisture partly affects the rate of evaporative heat loss from the skin and respiratory system of an animal. Poultry do not have sweat glands, so all evaporative heat loss must originate from the respiratory tract.
Other livestock species have varying abilities to sweat and in descending order they are as follows: Horse, donkey, cattle, buffalo, goat, sheep and pig. In a hot-dry climate evaporation is rapid, but in a hot humid climate the ability of the air to absorb additional moisture is limited and the inadequate cooling may result in heats tress. Too low humidity in the air will cause irritation of the mucous membranes, while too high humidity may promote growth of fungus infections (Da Silva, 2007). High humidity may also contribute to decay in structures. High humidity also 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. If possible keep the relative humidity in the range of 40 to 80%.
SOLAR RADIATION OR RADIANT ENERGY
The quantity of solar radiation or radiant energy received in tropical region differs profoundly from the temperate. Solar radiation is measured using the instrument called Photometer. The heat load on a grazing animal can be considerably increased by direct solar radiation and radiation reflected from clouds or the ground (Samson et al., 2011). For tropical breeds of animal, solar radiation effects are scarcely noticeable because of their skin and eye that are pigmented (Mahadevan, 1966).
A white hair coat will absorb less radiant energy than a dark, but the heat penetrates deeper in a white, loose coat (FAO, 1986). In contrast, 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. Furthermore, solar radiation may adversely affect the animal’s skin in particular breeds having unpigmented skin. 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 as means of minimising adverse effects of solar radiation include: i.Grazing in the night.
ii.Clipping of excessive hair. iii.Provision of a shaded area for animals or grazing under shades in the day time. However, the shade should be sufficiently large to allow space between the animals so that the heat loss by other means is not reduced (FAO, 1986). Solar radiation may contribute or may even create a more severe heat stress, hence, all measures must be taken to reduce direct impact of solar radiation on animals.
Altitude refers to height of a place over and above relative to the sea level which is usually measured in metres. Altitude is measured using the instrument called Altimeter. Illustratively, three plateau 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 (Samson et al., 2011). Temperate-like micro-environment on these places located within the tropical Nigerian climate makes the production of cattle and other livestock to 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 microclimatic condition tend to stimulate improved animal performance in terms of intake and metabolism of nutrients, growth and reproductive activities (Khalifa, 2003). 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 (Samson et al., 2011)
Air movements involve wind direction and wind velocity but the most important is the wind velocity or speed. These will assist in heat loss by evaporation and by conduction/ convection as long as the air temperature is lower than the skin temperature. When the air temperature approaches the skin temperature rapid air movements are experienced as comfortable, but at low temperatures it will lead to excessive cooling of unprotected skin areas (cold draught) (Mahadevan, 1966).
In addition air movements are required to remove noxious and toxic gases and to supply the animal with fresh air for breathing (Samson et al., 2011). A wind velocity of 0.2m/s is generally regarded as a minimum requirement, but it can be increased to 1.0m/s, when the temperature is nearing the upper critical, or more when it goes beyond that (Da Silva, 2007). Wind speed is measured using the instrument called Anenometers while wind direction is measured using Wind Vane.
PRECIPITATION OR RAINFALL
Heavy rain my penetrate the fur of an animal and decrease its insulation value. A strong wind can in such circumstances lead to excessive cooling. However, a naturally greasy hair coat will resist water penetration and with the provision of a shelter for the animals the problem may be avoided altogether (Samson et al., 2011). It should be noted that increase in precipitation result in consequent in increase in relative humidity. Rainfall is measured using the instrument called Rain gauge.
Light which dictates day length or photoperiod varies with latitude and season and has a direct influence on animal performance, especially on the breeding season for sheep and egg production of poultry. Under natural conditions, there is a correlation between length of day and rate of laying (Samson et al., 2011). Artificial light is used in the temperate zone to equalize egg production throughout the year (Mahadevan, 1966). Additional hours of light before dawn and after dusk are recommended in hot climates to encourage the hens to eat during the cooler hours.
INDIRECT EFFECTS OF CLIMATIC ELEMENTS ON LIVESTOCK PRODUCTION
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. These indirect effects include:
(a) Effects 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 (Samson et al., 2011). 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 (Khalifa, 2003). 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 (Samson et al., 2011). 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(Mahadevan, 1966). 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 (Samson et al., 2011).
(b) Effects on Animal Disease, Vector and Parasites
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.
(c) Effects on Storage and Handling of Animal Products
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 (Samson et al., 2011). 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.
EFFECTS OF CLIMATIC FACTORS ON THE PRODUCTIVE PERFORMANCE OF VARIOUS LIVESTOCK SPECIES
In tropical and subtropical countries, an animal may often be under heat stress when the environmental temperature exceeds the upper critical level (18 to 24°C, depending on the livestock specie) there is usually a drop in production or a reduced rate of gain (FAO, 1986). Furthermore, when the temperature falls outside the comfort zone, other climatic factors assume greater significance. Humidity becomes increasingly important as do solar radiation and wind velocity.
Dairy cattle show a reduced feed-intake under heat stress resulting in lowered milk production and reduced growth. Reproduction is also adversely affected. There are, however, important differences between breeds. European cattle (Bos taurus) produce well at temperatures ranging from 4 to 24° C even at high humidity (FAO, 1986). Much lower temperatures (-10°C) have little effect as long as fluctuations are not too rapid or frequent. On the other hand, a drop in milk production results with temperatures exceeding 25°C (Vercoe, J.E.). The drop may be as much as 50% at temperatures of 32°C or higher. In contrast, Zebu cattle (Bos indicus), which are native to warm climates, have a comfort zone of 15 to 27° C and milk production begins to drop only when temperatures rise above 35°C. In addition, beef cattle make their best weight gains at temperatures below 25° C (FAO, 1986).
They can easily tolerate temperatures below 0° C if they have a good supply of feed. It is important to note some of the physical differences between these two types of cattle that suit each to its climate of origin. The Zebu is characterized by a hump, large ears and loose, thin skin including a prominent dewlap. These characteristics promote heat loss by convection and evaporation and thus efficient body temperature regulation under hot climatic conditions (Khalifa, 2003). In addition, the Zebu has less subcutaneous fat, a lower body volume for the surface area, and short smooth hair all of which contribute to the animal’s comfort under hot conditions. The European breeds on the other hand have thick skin held tightly to the body, long hair and a large amount of fat which serve as insulators, traits desirable for cold or temperate climates (Da Silva, 2007). Calves seem most sensitive to cold draughts and poor ventilation, but are quite tolerant of a wide range of temperatures.
Pigs require a change in ambient temperature as they age and grow, and like cattle, they show a decreased feed intake when under heat stress. Piglets survive and develop best at 30 to 32°C initially followed by a gradual reduction to 20°C over the first three weeks. Feeder pigs (30 to 65 kg) make good gains in the temperature range of 10 to 25°C with 24°C reported optimum. The optimal ambient temperature for pigs weighing 75 to 120 kg is 15° C (FAO, 1986). Brood sows do well at 15°C but suffer badly at 25°C and above since they do not perspire when hot. Reproduction rates fall under heat stress and sows are more apt to trample their baby pigs in the discomfort of hot weather (Da Silva, 2007).
Sheep can tolerate a wide range of temperatures but should be protected from wind and rain. However, a long period of high ambient temperatures inhibits reproduction. Heat stress also reduces lambing percentage, decreases the incidence of twinning, and decreases the birth weight of lambs (Khalifa, 2003). When temperatures are below 7°C at breeding time, ewes show improved reproductive efficiency.
Goats are affected by temperature, humidity and rain. In hot climates, goats need shelter from intense heat during the day. In humid areas they need protection from prolonged heavy rain. Excessive wetting from rain can cause pneumonia and an increase in parasitic infestation.
The environmental requirements for poultry vary with age. Chicks should be started at 35° C. After one week the temperature is reduced gradually to 24°C by the fifth week. Broilers and young turkeys reared at ambient temperatures below 18°C are heavier than similar stock reared within the 18 to 35°C range, but their feed conversion efficiency will be less. Laying birds produce the greatest number of eggs and the largest sized eggs at 13 to 24° C. The best feed conversion efficiency is achieved between 21 to 24° C (FAO, 1986). With increasing environmental temperature there is a decrease in feed intake and alterations in behaviour. Within the temperature range of 5 to 30°C there is a reduction of about 1.6% in feed intake for every 10°C increase in ambient temperature (FAO, 1986). Above 24°C there is a reduction in egg production and egg size. A continued rise in temperature to 38°C or more may prove lethal (Da Silva, 2007). High humidity at high temperatures create conditions that are more likely to be lethal because of a breakdown in body cooling through respiration.
Rabbits are affected most by sun and heat, wind, rain and draughts. Sunlight is of benefit to breading stock and the growing young, but it will also fade the coat of coloured rabbits and discolour a white one. While rabbits enjoy the sun, they must have the chance to get out of the direct rays. Because of their thick fur coats they tolerate cold better than extreme heat, but they are susceptible to chilling from draughts. Rabbits also need protection from rain and dampness.
Horses do not require warm surroundings, but they do not easily tolerate draughts, dampness and high humidity. When exposed to high temperatures and vigorous exercise, horses sweat and the evaporation of this perspiration cools the skin and helps to maintain normal body temperature (FAO, 1986).
Virtually all production aspects of animal agriculture are affected or influenced by these unique climatic factors. 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, air movement, altitude, precipitation, light 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
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