Heat Stress in Small Animals (Sheep and Goat)
Rishi Kant1,R. P Diwakar2 and Pramod Kumar3
College of Veterinary Science and Animal Husbandry, Acharya Narendra Deva University of Agriculture and Technology, Kumarganj. Ayodhya (UP) -224229
Abstract
In this article we will come to know how various adaptive behaviors shown by Sheep and Goat during hot environmental conditions. High rise in ambient temperature leading to decline in production and various changes in normal behavior to cope up with the conditions. Sheep and goat both are well tolerant to heat but goats are more heat resistant in comparison to sheep. Various important adaptive behaviors shown by these two species are panting, evaporation and increase in water intake.
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Key words: Adaptive behavior, hot environment, panting, evaporation etc.
Introduction: Sheep and Goat are closely related species and living with human being since a long across the globe. Sometimes it becomes difficult to differentiate in between them. One of the important feature to distinguish in between is on the basis of tail, tail of goat turns upward where as it is not so in case of sheep. Both sheep and goat are considered as heat resistant but in general goats are more resistant to heat stress. Goats are more intelligent and curious in comparison to sheep. Various types of adaptation to hot temperature in sheep and goat can be categorized as under:
Heat Tolerance/Resistance: Sheep have well adaptations towards cold climatic conditions but they also have remarkable heat tolerance, though this tolerance is not up to the level of goats. When ambient temperature lies between 370C to 400C their body temperature remains normal. When environmental temperature rise beyond this level sheep maintain their body temperature by panting and evaporation from respiratory system. These two are most important mechanism for heat loss in sheep. Sweating also has some cooling effect mainly in shorn animals. Feed intake is reduced to minimize the heat production in body where as water intake increased. Rumination also slows down, respiration rate and respiratory volume increases.
By panting cooling of body in sheep occurs due to both central stimuli as well as loss of heat from peripheral blood supply to skin. Temperature of blood supply to hypothalamus also acts as central stimuli which ultimately results in thermoregulatory response. Loss of heat from peripheral receptors is more important in case of ram particularly in scrotum region and from udder of goat. Beside this, sweat glands also play some cooling role mainly in shorn animal. Discharge from apocrine sweat glands spread over the skin and has some cooling effect over skin accompanied by reduction in respiratory rate.
Shearing effect: Body temperature of shorn animals increase with a faster rate in comparison to unshorn animal, but it also cools rapidly in shade, wind and with decrease in environmental temperature. Respiration rate of shorn animal is also found to be less in shade. Shearing may increase heat tolerance in summer and decrease it in winter season.
Feed intake: Sheep on highly nutritive diet has higher chances of increase in respiration rate and heat production, where as animals on protein rich diet has less effect on respiration rate and heat production. Risk of heat intolerance also increases with highly nutritive diet, but when we compromise with the diet disturbance in thermoregulation mechanism may also occur. Therefore in high ambient temperature diet should be derived in such a way (Medium nutrient supply) so that it may not cause any alteration in heat tolerance process.
Water intake: Normal water requirement in sheep is 3-4 liters per day but may vary due to several factors such as size, age, activity, stage of growth, pregnancy, lactation and type of feed and amount of feed. Generally during heat stress water intake increases. Water consumption also increases with increase in dry matter intake. In hot environment evaporation from respiratory system increase to cool the body of animal and subsequently demand of water. Temperature of water also has little effect on water intake.
Regulation of body temperature in goat: Small ruminants like goats play a predominant role in the economy of million people, and have provided meat, milk, skin and fibre for centuries Regulation of body temperature is much similar to that of sheep. Two major mechanisms to maintain body temperature in goats are increase in respiration rate and heat loss by evaporation. Horn of goat also supposed to play a minor role in maintenance of body temperature by its supply to brain. Goats are non sweating animals. Goats are more abundant in tropical and subtropical regions reflecting that they are more heat resistant in comparison to sheep. Jamnapari goat and Bikaneri sheep graze normally even at a high temperature of 47.80C, where as Corriedale breed of sheep requires artificial cooling at this temperature. Goats are prolific breeders in tropical region showing their well adaptation in these hot conditions. Water intake increases with rise in ambient temperature. Goats are highly sensitive to cold environmental condition. They need more attention during winter season rather than in summer season. From the above discussed sections, it could be concluded that the changes in the biological functions of goats due to exposure to heat stress include depression in feed intake, disturbance in the metabolism of water, protein, energy and mineral balances, enzymatic reactions, hormonal secretions and blood metabolites also altered during hot ambient temperature.
Therefore, a variety of methods should be adopted by small ruminant producers/owners to overcome the negative effects of heat stress, including the use of shades, feeding and grazing strategies, providing water, handling time, the use of fans and evaporative cooling, and site selection of animals’ housing. Shade is the easiest method to reduce the impact of high solar radiation, and it is applicable under extensive conditions. Ration modifications can greatly help in reducing the negative effect of heat stress, and these adjustments may include changes in feeding schedules (feeding at cool hours, feeding intervals), grazing time, and ration composition such as dietary fiber adjustment, the use of high-quality fiber forage, increased energy density (supplemental protected fat) and use of feed additives [buffers (sodium bicarbonate), niacin, antioxidants and fungal culture (yeast culture)]. During summer, the feeding behavior for most of the animals changes and they tend to consume more feed during the cooler periods of the day. Therefore, feeding animals during the cooler periods of the day encourages them to maintain their normal feed intake and prevents the co-occurrence of peak metabolic and climatic heat load. Also, feeding animals at more frequent intervals helps to minimize the diurnal fluctuation in ruminal metabolites and increase feed utilization efficiency in the.
Thus we can say that both sheep and goat are well heat tolerant species and can be reared in tropical regions. By adopting these measures heat stress can be minimized and optimum production can be maintained. When both species are compared in terms of heat tolerance goats has little bit edge over sheep.
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