Heat Stress and its Management in Goat
INTRODUCTION
Small ruminants play an important role in the economy of millions of people who earn their livelihood by rearing these animals in different climatic conditions and they are considered the major source of the rural economy. Sheep and goats are among the most successful animals with a wide geographic distribution playing a significant role in the agricultural revolution and the progress of human civilization. The two animal species play a major role in the subsistence of poor families, particularly in rural areas. Sheep and goats derive their popularity from their versatile ability to supply meat, milk, skin, offal, horn, fuel dung, wool and fibre. Furthermore, these animals are well suited to different geographic and environmental conditions, including extreme and harsh climates, and perform better than other domesticated ruminants. However, goats have a tendency to tolerate more warmth better than sheep.
The goat is present in almost all villages and plays an important role in the nutrition, revenue generation and employment of rural populations. They produce food and fibre at a relatively low cost based on unconventional raw materials. This is why the term “poor man’s cow” is used to describe the larger picture of small and marginal farmers. The economic importance of goat production has increased especially in countries which are regularly exposed to severe climates, as they are more efficient than other domestic ruminants. The smaller size of native goat breeds is a genetic adaptation strategy synchronized with the available nutrient resources compared to exotic and crossed goats. Goats with loose skin and floppy ears are more heat tolerant, indicating proper breed selection is a very valuable tool for sustaining goat production under an increasingly challenging environment that is heat stress.
THERMO-REGULATION
Sheep and goats are homeothermal animals and can keep body temperature close to constant in a wide range of environmental conditions. The temperature range in which the animal does not require extra energy to maintain its body temperature is called the thermo-neutral zone. The animals function more effectively in their thermo-neutral zone, while over and under the lower critical temperatures, the animals are stressed and limits the production process. The thermo-neutral zone is about 12–32ºC for sheep and 12–24°C for goats in the hot regions of the world. Heat Stress occurs in animals when there is a mismatch between heat production in the body and its dissipation. Increased body temperature and breathing rates are the most important signs of thermal stress in goats. As a response to stress, animals use physical, biochemical and physiological processes to counteract the harmful effect of Heat stress and maintain thermal equilibrium. Exposure of goats to high ambient temperature induces an increase in the dissipation of excess body heat to offset the excessive heat load. The first layer of defense protecting the goats from direct sunlight is provided by the fur, and this protection varies depending on the color of the fur, the depth and the length. Dark furry goats absorb more heat radiation and are more prone to heat than light-colored goats. Long hairs provide heat insulation, providing a capillary buffer zone between the outside environment and the body of the animal. The animal has a set of mechanisms to counter heat stress by dissipating heat in the environment and reducing metabolic heat generation. The animal dispels body heat by different mechanisms, i.e. Conduction, Convection, Radiation and Evaporation. Multiple behavioural adaptation mechanisms, such as finding shade and cooler surfaces, shifting the pattern of feed and water intake, and changing posture and reducing muscle activity, also play a key role. Exposure of goats to elevated ambient temperature increases thermoregulation by increasing respiratory rate, sweating, heart rate and rectal temperature. When animals are exposed to HS, they experience a variety of effects, including decreased feed intake production and consumption, disruptions in water, protein, electricity, and mineral balances, enzymatic reactions, hormonal secretions, and blood metabolites, and a decline in faecal and urinary water loses.
HOUSING MANAGEMENT
Altering the environment to improve the heat dissipation mechanism is one of the most common approaches to reducing heat stress. It includes the provision of shade, a system of evaporative cooling with water in the form of mist, mist or spraying of natural or forced air, and possibly cooling pools. Amongst these, shading is the simplest and most economic method. Offering shade to goats decreases rectal temperature and respiratory rate. The proper choice of animal housing site is critical to reducing long-term exposure to solar radiation.
NUTRITIONAL MANAGEMENT
Changes to rations will significantly minimise the negative effects of heat stress. Lower DMI during heat stress decreases the supply of nutrients for absorption, and the nutrients that are consumed are used less effectively. During the summer season, feeding should be performed during cooler times of the day to allow them to maintain their daily feed consumption and to avoid the climatic heat load. Furthermore, feeding at more regular intervals tends to reduce the diurnal fluctuation of ruminal metabolites and, as a result, improves feed consumption efficiency in the rumen. Reduced forage-to-concentrate ratios can result in more digestible rations that can be eaten in larger quantities. Feed with a low fibre content is favoured during heat stress because heat output is more closely associated with acetate metabolism than with propionate metabolism. During the heat stress season, nutrient-dense diets are normally recommended. During the summer, dairy goats supplemented with 4% fat had lower rectal temperature, increased milk production efficiency, and yield. Feed additives, such as the inclusion of live yeast, enhance nutrient digestibility by modifying the production of volatile fatty acids in the rumen, decreasing the production of ruminal ammonia, and increasing the population of ruminal microorganisms. Antioxidants, such as vitamin C and E, protect the body’s protection mechanism against excessive free radical production, reduce rectal temperature and respiration rate during heat stress, and thereby stabilize the animal’s health status. Another effective way to relieve heat stress is to have plenty of safe and cool drinking water.
Poonam Yadav, Nutan Chauhan, Jitendra Kumar
Ph.D Scholar, Animal Physiology ,NDVSU, Jabalpur
Ph.D Scholar, Animal Nutrition ,NDRI,Karnal
Ph.D Scholar, Animal reproduction Gynaecology and obstetrics ,NDVSU, Jabalpur
