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The capacity of an animal to produce differs between species, breeds and strains as a result of genetic factors. However, a complex of inter-related factors in the animal husbandry will influence the animal's ability to utilize that capacity for growth, development and production.
Progress in breeding and feeding for further increase in production and efficiency can be limited by environmental factors. Research into these factors has therefore been increasing in recent years, especially in countries having intensive animal production.
Animal housing design is mainly concerned with the physical environment, in particular climatic and mechanical factors, but all other factors should also be considered in order to create a good layout, where healthy, high yielding animals can be provided with correct feeding, can be easily handled and can produce without stress or suffering physical harm.
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 and humans are given in Table 10.1.
Table 10.1 Normal Body Temperatures of Domestic Animals and Humans
|Dairy Cow||38.6||38.0 - 39.3|
|Beef Cow||38.3||36.7 - 39.1|
|Sheep||39.1||38.3 - 39.9|
|Goat||38.7 - 40.7|
|Chicken||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. 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 behaviour. 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. 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.
Figure 10. 1 Classification of factors influencing livestock production.
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.
Animal Moisture and Heat Production
Heat is produced centrally in the deep body. The surplus is conducted to the skin surface where it is given off to the atmosphere as sensible heat by means of convection, conduction and radiation and as latent heat by means of evaporation of moisture from the lungs and skin. Increasing ambient temperature, resulting in less temperature difference between the body surface and the air, will decrease the amount of heat that can be emitted as sensible heat. Instead a larger proportion is given off as latent heat, that is, heat employed to vapourize moisture.
Table 10.2 lists values for animal heat and moisture production at various temperatures. The heat and moisture produced by the animals confined in a structure must be removed by ventilation. In the tropics, sufficient ventilation flow is usually provided for by the use of opensided structures.
However, if an enclosed building is used, a range of ventilation flow rates must be provided for in the building design. The minimum ventilation rate should remove the moisture produced, but retain as much sensible heat as possible during cold periods. The maximum ventilation rate should remove enough of the sensible heat produced so that a small temperature difference, usually 2 to 4°C, can be maintained between inside and outside. It should be noted that ventilation alone can only maintain the building temperature at slightly above ambient. Ventilation is discussed in more detail in Chapter 7.
The over-riding environmental factor affecting the physiological functions of domestic animals is temperature. For most farm animals a mean daily temperature in the range 10 to 20°C is referred to as the "comfort zone". 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. At the upper and lower critical temperatures the 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.
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.
A 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.
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 heatstress.
Too low humidity in the air will cause irritation of the mucous membranes, while too high humidity may promote growth of fungus infections. High humidity may also contribute to decay in structures. If possible keep the relative humidity in the range of 40 to 80%.
The heat load on a grazing animal can be considerably increased by direct solar radiation and radiation reflected from clouds or the ground. A white hair coat will absorb less radiant energy than a dark, but the heat penetrates deeper in a white, loose coat. Air movements will dispel the heat and reduce the differences. Furthermore, solar radiation may adversely affect the animal's skin in particular breeds having unpigmented skin.
Heat gain by radiation can be effectively reduced by the provision of a shaded area. It must, however, be sufficiently large to allow space between the animals so that the heat loss by other means is not reduced. Grass covered ground in the surroundings of the shade will reflect less radiation than bare soil.
Air movements 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). In addition air movements are required to remove noxious and toxic gases and to supply the animal with fresh air for breathing. 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.
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.
Effect of Climatic Factors on Livestock Performance
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 species) there is usually a drop in production or a reduced rate of gain. 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. 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. 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 1 5 to 27° C and milk production begins to drop only when temperatures rise above 35°C.
Table 10.2 Animal Heat and Moisture Production
|Livestock||Weight||Ambient temperature*||Moisture g/h, animal||Sensible heat /animal||Total heat1 /animal|
|kg||°C||*°C||+25° C||*° C||+25° C||*° C||+25°|
|Sow one week prior to birth||180||+12||120||220||285||185||365||335|
|Sow with piglets||180||+16||175||300||340||245||460||450|
*Referring to temperature stated in the column "ambient temperature".
1Total heat equals sensible heat plus latent heat (latent heat equals moisture in g/h x 0.675 Wh/g).
It is important to note some of the physical differences between these two types of cattle that suits 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. 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. Although there is a considerable range in size within each bread, the Zebu is a relatively small animal, a fully grown bull rarely exceeds 700 kg, while the European cattle are large, reaching 1,000 kg liveweight. Figure 10.2 illustrates the configurations of the two types of cattle. Calves seem most sensitive to cold draughts and poor ventilation, but are quite tolerant of a wide range of temperatures.
Figure 10.2 Characteristic appearance of Zebu and [European type cattle.
Beef Cattle make their best gains at temperatures below 25° C. They can easily tolerate temperatures below 0° C if they have a good supply of feed.
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. 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.
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. 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.
Poultry. 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. With increasing environmental temperature there is a decrease in feedintake 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. 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. High humidities 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. 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.
Humans. In as much as the subject of rural housing is covered elsewhere in the book, human comfort zones will be discussed briefly. Man has the ability to become acclimatized to a constant temperature. Thus people living in cold climates easily tolerate low temperatures just as people living in tropical climates do not mind the heat. In temperate climates, most sedentary people dressed in light clothing find optimum comfort at approximately 26°C. However, a relative humidity of over 70% may produce discomfort. At 22°C people may feel cool regardless of humidity. Above 26°C they are likely to feel warm and as the relative humidity rises above 45%, discomfort increases. People who are dressed warmly and doing active work can be comfortable to temperatures of 0°C and below.
Disease remains a major profit-limiting factor in animal production in many tropical countries. Sanitary control measures should be incorporated in any building design, so that a good hygienic standard can be easily maintained. An animal which is well fed and watered and in good condition will have a high resistance to disease. Good management can do much to remove or reduce the effects of adverse environmental factors, such as climatic stress, which otherwise would weaken the body's natural defences.
New born stock should always receive colostrum (first milk), which contains antibodies. It takes time for an effective immune system to develop in an animal and therefore good hygiene is of special importance in facilities for young animals. Pens, in particular those for calving, farrowing, etc., should be constructed in easily cleaned and disinfected materials and be without corners and recesses where manure and dirt can accumulate.
The whole building should be cleaned and disinfected periodically and any pen that is emptied should be thoroughly cleaned before other animals are transferred to it. Rearing and fattening of young animals should be organised so that the building can be emptied, cleaned and disinfected between batches. This 'all-in, all-out' policy is particularly beneficial for disease control, where the animals are bought from outside the farm and in finishing units for pigs as well as broiler and layer houses.
Disease is transmitted in many ways including direct contact between animals, air-borne micro-organisms, biting insects and ticks, manure, soil, contaminated feed and water, birds and rodents and the stockman's boots. Direct contact between animals can be reduced by decreasing the number of animals in each group and by constructing solid partitions between pens. Solid walls may however obstruct air movements and thus contribute to heat-stress. Ideally, the waste handling system should prevent animals of different groups coming into contact with each other's manure. Especially young animals must be prevented from contact with manure from adult animals.
Good stockmanship includes regular observation of the animals to detect any change in behaviour, which could indicate disease. Sick animals should immediately be separated from the herd to prevent further spread of infectious disease and to allow the animal to rest. The sick animal should be isolated in a pen kept especially for this purpose and ideally in a separate building.
Newly acquired animals and animals returning from a market or other place where they may have been exposed to the risk of infection must be quarantined for an adequate length of time to detect any disease they may be carrying before they are allowed into the herd.
Other Environmental Factors
Acoustical factors will only, as far as known, have marginal effect on the animal's development and production. Nervous animals may, however, react adversely to intermittent sudden noises. Pig squeals prior to feeding can become a hazard to the stockman's hearing. Soft radio music in a milking parlour may have a smoothing effect on the cows.
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. Artificial light is used in the temperate zone to equalize egg production throughout the year. Additional hours of light before dawn and after dusk are recommended in hot climates to encourage the hens to eat during the cooler hours.
Dust can carry micro-organisms, which may cause an outbreak of disease.
Toxic and noxious gases are produced by manure which accumulates in buildings or storages. Especially in connection with agitation of manure slurry stored in a pit in a building, harmful amounts of gases can be released. However, problems with gases are not likely to arise in the open-sided buildings used in the tropics.
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