There are differences in heat stress between varieties and individuals. Cattle with low erythrocyte potassium content are relatively heat-resistant than cattle with high cellular potassium content. When improving the selection of dairy cows, we should pay attention to the selection of dairy cows with strong heat resistance from calves and adult cows, which can get certain genetic progress. In order to speed up the establishment of heat-resistant strains of dairy cows in China, we can consider introducing them from Israel, which is located in the tropical desert area and has the largest annual milk production in the world, which has attracted the attention of experts.
2. Strengthen heatstroke prevention and cooling.
In hot summer, you can open all the doors and windows of the cowshed for ventilation in the morning and evening; Close all the doors and windows of the barn from 10 to 16 every day to prevent the invasion of hot air. Plant shade trees or build sheds around cowsheds and sports fields to avoid the sun and rain of cows. Cowhouses and places where cows are tied must be kept dry and clean, and there can be no water and mud. The relative humidity should be kept below 85%. It is strictly forbidden that excessive humidity will hinder the heat dissipation of cattle, make them feel stuffy and reduce the metabolic function of the body. The cowshed should be in the north-south direction. Exhaust fans should be installed on the north wall of the cowshed or ceiling fans should be installed every 3~5 cows in the cowshed. The wind should blow to the cow's body and head, so as to discharge the dirty heat in time. Attention should be paid to air convection when spraying water in cowshed to cool down. Self-employed individuals who raise a small number of cows can lead the cows to ventilation pipes or shady places and tie them up. When cows are found to have symptoms such as breathing with their mouths open, sweating and spitting out their tongues, they should immediately pour cold water on their heads and bodies, and at the same time feed cold mung bean soup or sauerkraut soup; Apply essential balm on the forehead, temples and nose of cattle to eliminate heat stress.
3. Adjust the composition and structure of diet
Cows mainly feed on roughage, with high crude fiber content, large intake and large heat consumption, which increases the heat dissipation load. Feed fermentation in rumen not only produces methane, but also produces heat. Synthetic milk will further increase heat production. 1 Dairy cows with milk volume of 20kg on the first day have 50% higher calories than dry cows. The higher the milk yield, the more heat is produced. With the improvement of individual production performance, food intake and milk synthesis will inevitably increase, which will lead to the increase of heat production. This is the reason why high-yield cattle are more sensitive to heat stress in summer and the milk yield decreases faster. Under heat stress, dairy cows' appetite decreased, total dry matter intake decreased, energy and protein intake decreased, and production performance decreased. Oil has the characteristics of less heat production, and most of the energy can be directly used for production, which is different from other nutrients. Under heat stress, detoxified cottonseed is often used as fat to feed dairy cows to lower their body temperature. Feeding fat to cows will not raise their body temperature. On the contrary, cows can be directly used as metabolic energy. Protein decomposes amino acids in rumen of dairy cows. When the supply of amino acids exceeds the demand and the required energy cannot be met at the same time, amino acids will be decomposed and used as energy, and the heat generated at this time will also increase accordingly. Therefore, under heat stress, it is necessary to eliminate unnecessary nitrogen, but the energy in dairy feed should be fully guaranteed. Most of the energy of straw roughage is directly used to maintain normal body temperature. With the increase of roughage proportion, the heat production of dairy cows will also increase accordingly. Under heat stress, it is more beneficial for dairy cows to feed more concentrated forage than roughage. During the heat stress period, the concentrate and green roughage of dairy cows must be less and better. The feeding amount of concentrate is about 20% higher than usual, and the feed must contain crude fiber 17%.
4. Ways to change feeding methods
The optimum temperature range for Holstein cows to produce milk is-1.1~15.6℃, and the optimum temperature is 10~ 15℃. The most comfortable temperature is about 65438 00℃, and the milk yield begins to decrease above 20℃, above 28℃ by more than 50%, and below -5℃, the milk yield begins to decrease. When the outside temperature exceeds 27℃, the cow's body temperature rises, and its breathing is accelerated, showing obvious heat stress. The milk yield at 10℃ was 100%. When the temperature rose to 2 1. 1℃, 26.7℃, 29.4℃ and 38.0℃, the milk yield decreased by 1.7%, 24.8% and 30% respectively. With the global temperature rising, the output of dairy cows has increased significantly, and the impact has become more serious. This is why most of the high-yield core groups of Holstein cattle in China are concentrated in the north, and there are few left after crossing the Yangtze River. It is not that the south bought low-yield cattle, but that the high-yield production potential could not be brought into play. When feeding cows, we should appropriately increase the feeding times and increase the feeding amount in the cool morning to maintain the supply of fresh green feed, melons, aquatic plants and other juicy feeds. You can also add some concentrate to the porridge to improve the palatability of dairy cows and increase their food intake, which is beneficial to the heat dissipation and hydration of dairy cows during the heat stress period. You can also feed more green feed or appropriate cold water thinner at night. At the same time, pay attention to supplement appropriate vitamins and salt to dairy cows during the heat stress period.
5. Reasonable arrangement of breeding time
Heat stress causes gonadal hypoplasia and secondary sexual characteristics of young animals; Adult cattle gonadal atrophy, loss of libido, sperm and egg dysplasia, etc. In hot climate, the estrus cycle of dairy cows is prolonged, the estrus performance is not obvious, the estrus time is shortened, the conception rate is reduced, the elimination rate is increased, and the early embryo death is increased, especially when it is subjected to heat stress before and after mating. Weight loss of calves born to parturient cows; Heating in the second trimester can easily lead to miscarriage. Calving in summer will reduce the milk yield of each cow by 500~ 1000kg. It is of positive significance to properly adjust the calving season of dairy cows to make them calve seasonally, so as to reduce the number of calving in summer, prevent postpartum diseases, reduce yield and avoid the influence of heat stress on lactation peak and the whole lactation period. So the breeding is concentrated in 1 February and1month every year, and calving is carried out in September and1month of the following year. The lactation period of 10 month is in autumn, winter, spring and early summer, which is suitable for the requirements of dairy cows on environmental temperature, while the drying period of the next two months is just in July and August, which has no effect on the annual milk yield of dairy cows. Breeding in summer can be arranged in the afternoon-morning when the temperature is cool, so as to improve the conception rate of dairy cows. In the process of embryo transfer, adding 50M glutathione or taurine to the culture medium is beneficial to improve the heat stress resistance of embryos.
6 Ensure fresh and sufficient drinking water.
Heat stress occurs in the high temperature season in summer. Because of the high temperature, cows consume a lot of water. If drinking water is insufficient, it will reduce appetite, slow down digestion, affect milk yield of dairy cows, dry mucous membranes in dairy cows and reduce disease resistance. Insufficient drinking water for a long time will also cause metabolic disorder of dairy cows, and even cause death of dairy cows in serious cases. The daily water consumption of dairy cows is 3~5 times of the daily milk production. During the heat stress period, the water supply should be increased accordingly, and some salt should be added to the drinking water. In hot summer, it is best to bathe the cows with cold water before each feeding or milking, so as to lower the body temperature and improve the intake and lactation of the cows.
7 keep the environment clean and tidy.
The pollution of feces, urine and sewage to dairy cows not only affects the hygiene of milk, but also affects the normal metabolism of dairy cows, which is not conducive to the discharge of heat and the health of dairy cows. During the period of heat stress, attention should be paid to keeping the cattle body and its surrounding environment clean and hygienic. At the same time, 1.0% ~ 1.5% trichlorfon solution can be sprayed in the cowshed and the surrounding environment to kill mosquitoes, flies and other pests, so that cows can have a good rest environment and reduce heat stress.
8 Brush cows regularly.
Brushing dairy cows can accelerate the metabolic function of dairy cows' skin, which is beneficial to the heat dissipation of dairy cows. Brush once every morning and evening, and 30% of the total calories of cows can be distributed by brushing cows. During the heat stress, the cows should be bathed and scrubbed regularly with clean water. Milking at noon should be avoided to ensure that cows have enough rest. Scrubbing nipples with warm water before milking and bathing breasts with 0. 1% potassium permanganate solution after milking can reduce bacterial infection and prevent breast diseases.
9. Do a good job in the diagnosis and treatment of heat stress
Trim cattle hooves at least once a year to reduce the occurrence of hoof rot. Inject epidemic (bacterial) vaccine regularly to prevent infectious diseases. In high temperature season, it is necessary to clean up cow dung and urine in time, eliminate mosquitoes, flies and mice regularly, do a good job in environmental sanitation, and minimize the occurrence of diseases in dairy cows. For delivery cows and aborted cows, brown sugar bran soup or amniotic fluid should be given in time to promote early discharge of fetal membranes. If lochia is discharged for a long time, antibacterial and anti-inflammatory treatment should be carried out to prevent uterine inflammation. When the body temperature rises above 40.0℃, the breathing is shallow and fast, reaching 60-80 beats/min, or heavy, eating slowly or stopping, mental excitement or depression, skin temperature burning, nasal hyperhidrosis, foaming at the mouth, serous runny nose, conjunctival flushing or dendritic congestion, and the milk yield decreases, the jugular vein bleeds1000-2000. Sodium caffeine 20 ~ 30 ml, intramuscular injection, twice a day; Compound aminopyrine injection 20ml, intramuscular injection, twice a day; Mannitol or calcium gluconate can be used for intravenous injection in individual patients with excitement and brain edema.