Nutritional regulation of dairy cows under normal production conditions mainly includes the best rumen fermentation, rumen microbial digestion rate, protein, fat regulation, anion and cation balance, feeding methods and other measures. cows under heat stress,DMITherefore, it is necessary to adjust the structure of the diet, increase the concentration of nutrients, add anti-heat stress substances and other nutritional measures to improve the intake of nutrients in dairy cows.

Increase energy concentration

Increasing the concentrate-to-roughage ratio can partially overcome the reduced production performance caused by insufficient feed intake, and increasing the amount of concentrate can increase the rumen passage rate and reduce the rumen fullness, stimulate feed intake, thereby increasing energy intake. The proportion of concentrate in the balanced diet of dairy cows is limited to the total dry matter mass.50～60% is more appropriate. Increasing the number of cow feeds can increase milk production and avoid health problems. Increase the number of feedings per day4Times and every day.1-2Compared with the second time, it can improve the milk fat rate.7.3%, milk production2.7％。

The supplementary fat in the diet contains high energy and less body heat. Supplementation to protect fat is beneficial to maintain the production performance of heat-stressed dairy cows. The addition of rumen bypass fat significantly increased the milk yield of dairy cows, and the composition of milk changed, in which the milk fat content increased.6.23%, the content of milk protein decreased4.25%. At the same time, the addition of rumen bypass fat significantly improved the body condition of lactating cows, which was of great significance to the cows with high yield and poor physical fitness.

Improve protein levels and quality

Increasing the crude protein content of the diet of heat-stressed dairy cows and increasing the level of true protein in the small intestine are the key factors to maintainDMIEffective measures to reduce protein intake. The study found that the high protein group (crude protein increased50%) milk production increased compared with the control group8.55%, feed utilization rate increased respectively2.9%, indicating that high protein can significantly improve the milk yield of dairy cows in summer. Add bean cake to feed330g/d, cow milk production increased18%, milk fat rate increased12.8％。

The degradation rate of protein in general high quality cake meal feed is higher50Therefore, in order to improve the level of non-degraded protein in the small intestine, it is necessary to protect some high-quality meal protein feeds with high degradation rate. Han Jifu and others reported that the addition of rumen bypass protein and propylene glycol in the diet of dairy cows can increase the concentration of propionic acid, and milk production has an increasing trend compared with the control group.

At present, the rumen protein treatment methods mainly include chemical treatment, heat treatment and physical coating protection.3kind of form. Chemical treatment and heat treatment methods have over-protection problems, and chemical treatment also has safety problems. There was no overprotection of protein in whole blood and other protein protection diets.

SupplementMineralsand adjusted dietary anion and cation difference

during heat stress, increasing dietary mineral concentrations to compensateDMIThe reduction and discharge of certain minerals is necessary. Potassium is the main mineral excreted through sweat, and the excretion of sodium in urine of heat-stressed cows increases. Supplemental potassium and sodium can improve milk production during heat stress. There are no suitable comparative studies to account for potential changes in the requirements of other major and trace elements during heat stress. The main physiological function of chromium is as an active component of glucose tolerance factor, which may play an important role in heat stress resistance. Chromium supplementation has an obvious effect on promoting the production performance of dairy cows.

The balance of anion and cation directly affects the acid-base balance, ion balance and enzyme system in the body. Application of negative ion diets produced moderate metabolic acidosis in dairy cows shortly before calving. So most of the cow's body“calcium storage”It exists in the form of positive ions, thereby reducing the occurrence of milk heat. Many trials have shown that increasing the dietDCABCan improve feed intake and production performance. The current results of the study, the most suitable lactating cattleDCABDIn-200～200mEq/KgDMBetween.

Use of vitamins and other additives

due to heat stressDMITherefore, it is necessary to consider not only the vitamin concentration of the diet, but also its absolute requirement. People usually raise vitamins in the diet of heat-stressed dairy cowsA,D,EandCconcentration, but less research on its role and mechanism. A large number of experiments reported that the daily addition of a certain amount of niacin per head in the diet of dairy cows can significantly improve milk performance and reproductive performance. The addition of nicotinic acid in the feed can improve the milk yield of dairy cows under heat stress in summer.

Organic acids in cows can be oxidizedCO2andHCO3-Therefore, it is possible to alleviate respiratory alkalosis and reduce the damage of high temperature stress to dairy cows. High temperature environment will also affect the activities of various enzymes in the digestive tract of dairy cows. The application of feed enzymes can improve the digestibility of energy and nutrients and reduce the emissions of organic matter, nitrogen and phosphorus in excreta, thereby improving the production performance of dairy cows.

Drink Water

Evaporative heat dissipation is an important way of heat dissipation during heat stress, and heat stress increases water loss. Temperature from10℃Elevated38 ℃The ratio of water intake to milk production is determined by4:1Rise26:1. Insufficient drinking water can reduce appetite, slow digestion, affect milk production and dry the mucous membranes in the cow's body, reducing the cow's ability to resist disease. As the temperature of drinking water decreases, the amount of drinking water of cattle decreases, but the cooling effect is greater. The temperature of drinking water affects the rectal temperature and respiratory rate of the milk.

Other measures to alleviate heat stress in dairy cows

A large number of data show that rectal temperature, respiratory rate,HBand erythrocyte potassium can be used as physiological indicators of heat resistance in cattle. Thyroxine and cortisol are related to the body's metabolism and can also be used as reference indicators for evaluation. According to domestic reports, the selection of heat-resistant varieties and local cows or cattle cross, is to improve the heat-resistant varieties of dairy cattle breeding, relieve stress and an important method.

In principle, the environmental control measures to prevent heat stress in dairy cows include three aspects: preventing solar radiation, reducing the cow's own heat production and increasing heat dissipation. The use of physical protection measures to reduce the heat stress of dairy cattle, can use air conditioning, evaporative cooling, pergola, ventilation and drinking cold water and other measures. However, genetic factors, environmental control level, climate factors and nutrient levels of dairy cows during heat stress affect the production effect of environmental improvement, and creating a suitable production environment and maximum production performance is not necessarily the best economic effect, thus limiting the application of environmental improvement in dairy production. Therefore, the use of physical protection measures must consider economic benefits.

In regions and countries with a high degree of intensive feed for dairy cows, dairy breeders arrange the dry milk period of some dairy cows in the highest temperature season in order to reduce the heat stress of dairy cows.