Rising temperatures and climatic changes have led to significant negative effects in the field of agriculture, and this is increasingly affecting livestock production. Climate change will have a major impact on animal husbandry and animal food production.
Cattle have an optimal temperature zone that allows them to maintain their body temperature without affecting their normal physiological functions. When the temperature increases, it can exceed this thermal neutral zone and cows may In response to this increase, metabolism, respiratory rate, heart rate, gasping and sweating are altered, and chemical and hormonal changes occur. These factors reduce their growth rate (weight and volume) and fat and negatively affect reproductive function, and there are many ways to lose heat. The rate of heat loss through evaporation is the highest in normal cases, and it depends on the surrounding air temperature, relative humidity, evaporation area, speed of air movement and its ability to lose heat by conduction is very weak. As for the heat loss by convection , it increases with the wind blowing on the animal, and if the heat loss increases by evaporation.Feed consumption: High temperatures and high humidity lead to a decrease in feed consumption for livestock.Water consumption: The impact of climate on water consumption of livestock has several aspects. Water is an essential food source for livestock, and on the other hand, it is a vehicle for heat loss and cooling through evaporation. So ocean warming increases livestock water consumption, but higher temperatures combined with higher humidity reduce the amount of water used and increase the number of drinking times livestock need.
Milk production usually decreases in the summer due to continuous exposure to heat, and it was found that an increase in temperature of 1 degree Celsius above the average prevailing temperature negatively affects about 10% of milk production during the stress period and about 8 to 10% of meat production during that period. Milk production is not only related to the intake of feed and its quality, but to the high temperatures that livestock are exposed to. With high temperatures, the physiological processes associated with breastfeeding are affected, in addition to a decrease in the level of thyroid hormone during the summer, and the components of milk change according to high temperatures. It was experimentally found that high temperatures Heat leads to a decrease in the amounts of fatty and non-fatty substances in milk. Daily milk production is strongly affected by climate change. An increase in temperature and humidity leads to a significant rise in temperature decrease in milk production. found lower values of milk fat content when the temperature–humidity index THI value was higher than 75.
Heat stress does not affect milk lactose, which is the main component of milk after water. Studies have shown that the ration of lactose in milk does not differ much between cows kept at temperature–humidity indexindex <75 and cows kept at temperature–humidity index> 75. Cow’s milk is rich in casein and makes up about 77% of the total milk protein. This is one of the important factors that make it enter the cheese industry.The milk protein content decreases when the temperature and humidity index value is higher From 75 (3.02 g/100 g) for temperature and humidity index < 75 vs. 2.89 g/100 g for temperature–humidity index > 75, respectively).
Meat production :
Heat stress in beef cattle may increase the risk of death.Heat stress has a significant detrimental effect on the qualities and characteristics of meat . It may reduce the degree of meat safety and may cause the transfer of pathogens because microorganisms are active at temperatures specific to each organism. Increasing the pH of the stomach increasesThe potential for foodborne pathogens (eg, Escherichia coli, Salmonella and Campylobacter) may be able to pass through the stomach and colonize distant gastrointestinal tract and secreted into the environment Moreover, animals that are under stress are more susceptible to injury For severe infections and inflammation, due to an increase in the secretion of stress hormones and an increase in mucosal permeability, animals may carry more pathogens in the gastrointestinal tract and associated lymphoid tissues. An important factor affecting meat quality is pH, which is one of the most frequently used chemical indicators that affect meat quality. Muscle pH can drop rapidly due to acceleration of anaerobic glycolysis in muscle during and/or after slaughter. Accelerated anaerobic glycolysis causes a series of chemical reactions to rapidly reduce the pH due to the conversion of glycogen to lactic acid in the muscles. Heat stress affects body weight, body size and carcass weight And the thickness of animal fat. Severe heat stress results in increased pH and darkness.This results in an adrenergic stress response that is activated. Peripheral vasodilation and muscle glycogenolysis are induced by adrenaline activity.
In response to various stressors, corticotropin-releasing factor (CRF) is released from the parvocellular neuron of paraventricular nuclei (PVN) of the hypothalamus into the hypophyseal portal vein to stimulate the corticotroph cells of the anterior pituitary gland which release adrenocorticotropic hormone (ACTH) in the systemic circulation .ACTH binds to the type-2 melanocortin receptor of the adrenal cortex, thereby releasing glucocorticoids mainly cortisol in the circulation.Mineralocorticoids :Chronic heat stress increases the secretion of mineralocorticoids via the Hypothalamo-pituitary axis HPA. It causes the retention of water and mineral balance in the body and helps to maintain blood volume and blood pressure.Thyroid Hormones : The body temperature and metabolic activity are regulated by thyroid hormones : triiodothyronine (T3) and tetraiodothyroxine (T4). Studies have shown that in heat-stressed animals T3 concentration gradually decreases while T4 concentration decreases , increases via Hypothalamo-pituitary-thyroid axis (HPT). TSH secretion is also inhibited by heat stress to reduce heat generation and Basal metabolic rate.
Egg production :
Heat stress is a condition in which chickens are unable to balance body heat production and heat loss. Heat stress is caused by the interaction of various factors such as high temperature, humidity and heat. The normal body temperature of chickens is 41-42°C, and the moderate temperature to maximize growth is between 18-21°C. Temperature above 25°C causes heat stress in poultry.When birds are exposed to a temperature higher than a suitable temperature for themBirds try to dissipate the excess heat produced inside the body, which is manifested by it Certain behavioral changes in birds. Heat-stressed chickens spend less time walking Standing, chickens consume less feed and more water, and they open their wings to try to reduce this stress. Their gasping rates also increase. egg shape is less affected by high temperature in old than in young hens. But the density of the white is affected by the severe heat stress (37 degrees Celsius) at the end of the egg-laying period more than the beginning of the egg-laying period. Periodic changes in temperature reduce the effect of heat stress by providing recovery periods for birds during cold periods. As for the genotype, the most productive genotypes are affected more than the less productive ones, and the genotypes of brown eggs, which are heavier in weight and more feathers, are more affected by heat stress than white eggs. There is a negative effect of heat stress on feed consumption as a 10% decrease was observed at 24°C, and for important production traits such as egg mass, egg production rate, egg weight and shell strength with a 5% loss at lower temperatures (24 to 29°C) .chicken diets which contain vitamins A and C improves live weight, egg weight, yolk weight, egg white weight, and eggshell weight under heat stress conditions. Antioxidant supplements can also be used under heat stress conditions.
Reccommendations to Prevent Heat Stress :
It is important to create awareness about climate-smart livestock projects for all those involved in livestock production. Climatic information and knowledge of its effects must be collected and then technical advice to help farmers and optimally manage climate risks and reduce the negative impact of drought on profit, and local species must be improved through cross-breeding with heat- and disease-resistant genotypes to ensure better adaptation and resistance to the breeds. The level of concentration of vitamins and minerals should be raised to enhance the health of livestock, and farmers should be trained in the use of supplemental hormones such as progesterone and the improvement of heat synchronization in females through GnRH to improve fertility efficacy.
- Wissam Dayoub, Msc. Animal Husbandry from University of Agriculture Faisalabad
- Mahvish Rajput, PhD. Parasitology from University of Agriculture Faisalabad
- Dr. Muhammad Sohail Sajid, Associate professor (Tenured) Dept. of Parasitology at
University of Agriculture Faisalabad