Effect of heat stress on reproductive parameters of buffaloes
March 27, 2013
Muhammad zubair, Dr. Maqbool Ahmad Associate Professor Department of Theriogenology University of Agriculture, Faisalabad.
Dr.Sajid Mahmood Sajid lecturer Faculty of Veterinary Sciences, University of Poonch Rawlakot.
Buffalo is playing a leading role in the national economy by producing milk, meat and draught power in Pakistan. Out of total milk produced in the country, buffalo contributes about 68 %, followed by cattle (27%) and sheep/goat/camel (5%).Due to high fat contents of buffalo milk; it is the most preferred species in Pakistan. There are 26.3 million buffaloes in Pakistan. Due to its versatile qualities they are rightly called as Black Gold of Pakistan.
Buffaloes are perfectly suited to the hot and humid climates and muddy terrain, although they exhibit signs of great distress when exposed to direct solar radiation or when working in the sun during hot weather. Such phenomena are due to morphological, anatomical and behavioral characteristics.
Morphologically, buffaloes have a good coat of soft hair like that of cattle at birth and during early calfhood. The hair on the body becomes sparser and almost devoid of hair as the animal grows. The amount of hair coat retained varies considerably, depending on the breed, season and housing practices and because of its exposure to water and mud. The colour of the hair may be black, dun, creamy yellow, dark, light grey or white.
Anatomically, buffalo skin is covered with a thick epidermis and the basal cells which contain many melanin particles that give the skin surface its characteristic black colour. The melanin particles trap the ultraviolet rays and prevent them from penetrating through the dermis of the skin to the lower tissue. These rays are abundant in solar radiation in the tropics and subtropics, and excessive exposure of animal tissue could be detrimental, perhaps even resulting in skin tumors. This beneficial characteristic is reinforced by well-developed sebaceous glands, with greater secretary activity than in cattle. These glands secrete the sebum, a fatty substance emerges on the skin’s surface and covers it with a lubricant, making it slippery for water and mud. The skin of buffalo is usually black and heat absorbent and is only sparsely protected by hair. Also, buffalo skin has one-sixth of the density of sweat glands that cattle skin has, so buffaloes dissipate heat poorly by sweating. If worked or driven excessively in the hot sun, a buffalo’s body temperature, pulse rate, respiration rate and general discomfort increase more quickly than those of cattle.
Heat stress is the state at which the mechanisms activates to maintain animal’s body thermal balance, when exposure to elevated temperature. Elevated body temperature is due largely to a reduction in the temperature gradient between skin surface and the environment. The effects of exposure to ambient elevated temperature are controlled by the external environment through a chain of reactions involving thermo receptors, photoreceptors, sensor capacities, the hypothalamus and central nervous system
Heat stress has a pronounced effect on the estrus behavior of the female animals as heat stress reduces the length and intensity of estrus. Summer anestrous is an important condition is buffaloes contributing to infertility in buffaloes. Changes caused by heat stress reduce the likelihood of estrus detection. Heat stress causes increased cortisol secretion and this hormone blocks estradiol-induced sexual behavior. Effect of heat stress on estrous behavior also includes actions independent of the pituitary-adrenal axis reducing the ovarian activity and follicular development. Heat stress causes a reduction in peripheral concentrations of estradiol at estrus. Moreover reduced physical activity is also probably an adaptive response that limits heat production and reduced estrous behavior. Heat stress during the follicular growth period potentially compromises the oocyte, either because of direct actions of elevated temperature on the oocyte or because of alterations in follicular function that will compromise oocyte. Heat stress at the beginning on the day of ovulation reduces the diameter and volume of the dominant follicle of the estrous cycle. Secretion of the hormones regulating reproductive tract function is also altered by heat stress. These changes lead to variable changes in steroid hormone concentrations in peripheral blood. This reduced action of steroid hormones on reproductive tract tissue during heat stress eventually impairs uterine and oviductal functions.
The heat stress shortens lactation length in summer as compared to spring.
Effect of heat stress on embryonic survival and development during early stages of pregnancy is more pronounced as there is decrease in embryo survival in early stages of development due to heat stress. Disruption of early embryonic development results from actions on the embryo itself or on the oviductal or uterine environment in which the embryo resides. It is also found that heat stress shortens the life of corpus leutum which is necessary for the maintenance of pregnancy due to production of cortisol from adrenal gland. Heat stress also causes abnormalities in the ova.
Exposure of buffaloes to the hot conditions evokes a series of drastic changes in the biological functions that include depression in feed intake, efficiency and utilization, disturbances in metabolism of water, protein, energy and mineral balances, enzymatic reactions, hormonal secretions and blood metabolites. Such changes result in impairment of reproduction and production performances.
EFFECT OF HEAT STRESS ON BREEDING BULL
Nutrition, climate, diseases and weather conditions influence reproductive performance of the bull. The most susceptible parts to heat stress are testis. Testis plays an important role for production of sperm and testosterone.
Nature is pretty ingenious in keeping the testicles cool; the bull has three avenues to help regulate their temperature. The scrotum itself has the ability to have a thick or thin wall. It can relax or contract to control the thickness of the wall, to serve as insulation when thick or to more effectively allow heat to escape when thin. The scrotal wall is thick in winter when the muscle is contracted, and thin in summer when it’s relaxed. Then the cremaster muscles raise or lower the testes within the scrotum itself. When it’s cold, the testes are pulled up next to the body for warmth, and when weather is warm they are suspended farther away from the body.
The third mechanism the bull has is a very interesting series of blood vessels called the panpiniform plexus. As blood is on its way to the scrotum and testes, it is at body temperature. But in the panpiniform plexus the blood is also leaving the testes and that blood is cooler. As the warm blood comes into the testes, it goes right next to the blood vessels carrying away the cooler blood, so there’s a heat transfer. This countercurrent heat exchange insures that the blood leaving the testes gets warmed back up to normal body temperature before it gets back into the body, and that the warm blood coming into the testes gets cooled down before it gets there,” he says. The testes (scrotum) and the body are necessary for cooling of the testes (3-4 °C below body temperature) and facilitate spermatogenesis to proceed normally.
Socrtal circumference and testicular consistency, tone,size and weight, which are excellent indicators of sperm producing capacity and spermatogenic functions, decrease in hot summer in the sub tropics to the extent that they become lower than those of the same breeds reared under temperate environmental conditions The reduction in testicular measurements (testes weight and length) by exposure to heat stress is due to degeneration in the germinal epithelium and to a partial atrophy in the seminiferous tubules. This is reflected in the adverse effects on the average number of testicular cells, especially the secondary spermatocytes and spermatids of types B, C and D, the ratio of steroli cells to other cells and the diameter of the seminiferous tubules. In addition, any conditions that cause high temperature in the animal such as long hair cover, over condition (too fat) and lack of adaptation, are likely to have adverse effects on spermatogenesis.
High temperature usually affects inversely the processes of spermatogenesis and metamorphosis of sperms that cause sperm degeneration. Seasonal differences, with minimal spermatogenesis occurring during summer months that is usually referred to as “summer sterility which is due to reduction of steroidgenic function of the testes and to the decrease of the blood flow through the testes. Despite the thermoregulatory mechanism of the testes, sexual desire (libido) is negatively affected by high environmental temperature. Such phenomenon, altogether with the adverse effects on ejaculate volume, live sperm percentage, sperm concentration, viability and motility.
Reaction time (libido)
The reaction time (libido) generally shorter in summer season than the other seasons. The shortest time (9.4±0.6 minutes) is recorded during summer and the longest (15.9±1. 5 minutes) in autumn.
Chemical characteristics of semen
Seminal plasma contains many organic compounds which are not found elsewhere in the body at such high concentrations. Such compounds are fructose, total phosphorus, total nitrogen, citric acid, sodium, potassium, calcium, sorbitol and spermine. These substances are produced by various accessory glands in response to testosterone .These chemical parameters of semen are adversely affected by heat stress.
Generally, elevation of ambient temperature affects male reproductive functions deleteriously. Such phenomenon leads to testicular degeneration and reduces percentages of normal and fertile spermatozoa in the ejaculate of males. The ability of the male to mate and fertilize is also affected. The biological backgrounds of such phenomena include disturbances in each of sexual activity, endocrine and testes functions, spermatogenesis and physical and chemical characteristics of semen. Most of anabolic and thermogenic hormones such as thyroxine, triiodothyronine, insulin, growth hormone, cortisol and aldosterone decrease appreciably under hot climatic conditions in an attempt by the animal to decrease its endogenous heat production to tolerate heat. The adrenal function is also reduced in heats tressed animals and this may allow the animal to cope with the environment because of the calorigenic actions of glucocorticoids.
Heat stress can be reduced by following management methods.
a) Artificial Shade
b) Evaporative Cooling Pads and Fans
c) High Pressure Foggers
d) Sprinkler and Fan Cooling Systems
e) Sprayers in Parlor Exit Lanes
f) Cooling Ponds
g) Antioxidant therapy like vitamin A, E and C.