Effect of Environmental Heat Stress on Reproduction Performance of Dairy Cows- A Review

Abstract

Stress is the condition where there is undue demand for physical and mental energy due to excessive and aversive environmental factors (stressors) and cause deformations those are identifiable through physiological disequilibrium. Temperature stress imparts physical and economical losses to livestock production in temperate, subtropical and tropical regions of the world. Each species, breed or animal with its physiological state, has a comfort zone, in which the energy expenditure of the animal is minimal, constant and independent of environmental temperature. When environmental temperatures move out of the thermo-neutral zone (or comfort zone) dairy cattle begin to experience heat stress. Thermo-neutral zone depends on the age, breed, feed intake, diet composition, previous state of temperature acclimatization, production, housing and stall conditions, tissue (fat, skin) insulation and external (coat) insulation, and the behaviour of the animal. The ranges of thermo-neutral zone are from lower critical temperature (LCT) to upper critical temperature (UCT). LCT is the environmental temperature at which an animal needs to increase metabolic heat production to maintain body temperature. UCT is the environmental temperature at which the animal increases heat production as a consequence of a rise in body temperature resulting for inadequate evaporative heat loss. Heat stress negatively impacts a variety of dairy parameters including milk yield and reproduction and therefore is a significant financial burden in many dairy-producing areas of the world. Advances in management (i.e. cooling systems) and nutritional strategies have alleviated some of the negative impact of thermal stress on dairy cattle, but production continues to decrease during the summer. In this review an attempt has been made to bring forth the effect of heat stress and to discuss their impact on dairy cows.

Mitigation of the Heat Stress Impact in Livestock Reproduction

“…Incomplete dominance could result in ovulation of an aged follicle containing oocytes with reduced competence. Among other effects, incompetent oocytes become transcriptionally inactive by reaching a diameter of 110 μm and lose the ability to synthesize heat shock protein 70 (HSP70) in response to heat shock [36].…”

Impact of heat stress and hypercapnia on physiological, hematological, and behavioral profile of Tharparkar and Karan Fries heifers

“…Hot environment impairs production, reproduction, immune response, metabolic, and health status of livestock. Since the crossbred cattle are more sensitive to temperature rise than indigenous cattle, a rise of 2-6°C due to global warming will have more impact on growth, puberty, and maturity of crossbred cattle, and the negative effects of heat stress will become even more apparent in the future if climate change continues as predicted [2]. CO 2 is an asphyxiant gas, the physiological effects of acute CO 2 exposure are grouped together under the term hypercapnia, a subset of asphyxiation where breathing is too slow or shallow and causes respiratory acidosis while breathing too fast to the level of hyperventilation causes respiratory alkalosis.…”

Evaluation of Scrotal Temperature in Different Testicular Shapes by Infrared Thermography in Braford Bulls

“…The production of viable spermatozoa depends on testicular physiological mechanisms, especially thermoregulation, since the temperature of the scrotum should be maintained 2 to 6°C below the body temperature [11,13]. Any change in scrotal temperature may impact physical conditions and result in economic losses to livestock production in subtropical and tropical regions of the world [1,14]. The use of non-invasive methods, such as infrared thermography (IRT), is considered an effective tool in the characterization of the scrotal surface temperature in bulls [11][12][13]16].…”