The reproductive performance of dairy cows is directly related to the production level of dairy cows. Many factors are affecting the reproductive performance of dairy cows in actual production, and there are very complex relationships among them, including breed, age, genetic factors, diseases, feeding management, environment, and nutrition.
1. Effect of Energy on Reproductive Performance
Energy plays an important role in the growth and development of dairy cows and normal production. It is the first nutrient needed by dairy cows. Appropriate energy level can ensure the normal physiological function of dairy cows and is the basis for obtaining the best breeding benefits. The inappropriate dietary energy, whether too high or too low, will have a more serious negative impact on the reproductive performance of dairy cows.
The excess energy of dairy cows, especially in the 2-3 months before dry milk, if the energy level provided to dairy cows is too high, excessive energy will be converted into fat, which will make the fatness of dairy cows too good. Over-fattening will easily lead to a decline in the intake of dairy cows, fat will also accumulate in the breast, reproductive organs, liver, and other organs, affecting the health of dairy cows, which can easily lead to problems such as dystocia, placenta retention and mastitis in dairy cows. This is more serious for dairy cows with low milk production and poor hereditary performance, which will lead to obesity after parturition, decrease the quality of eggs, and abnormal ovulation and estrus.
When the cow lacks energy, if it happens before delivery, it will make the cow's fatness worse and the follicles develop slowly and dysplasia, and affect ovulation so that the fertility rate of mating declines. Besides, it will also cause the cow to easily appear the disease of retaining the placenta and not exhausting lochia after delivery. After delivery, the intake of dairy cows began to decline, and at this time the cows are at the peak of lactation. The cows will inevitably use their physical energy to meet the needs of high lactation. It is very easy for the cows to have a negative energy balance, and the energy level affects the level of reproductive hormones of the cows, thus affecting the reproductive performance of the cows so that dairy cows have delayed estrus, follicular growth retardation, estrus abnormality and so on. Negative energy balance is more obvious in high-yielding dairy cows and more serious in overweight dairy cows before delivery. Therefore, attention should be paid to the nutritional level of dairy cows in the diet. When the intake of dairy cows decreases, the energy level in the diet should be properly increased to avoid negative energy balance, which will harm the reproductive performance of dairy cows.
2. Effect of Protein on Reproductive Performance
To improve the milk production of dairy cows, breeders often increase the protein level in the diet, but it will lead to the decline of the reproductive performance of dairy cows. Proteins in dairy cattle feed include rumen degradable protein and rumen-passing protein. When excessive protein is fed to dairy cattle, ammonia content in rumen and urea content in the blood increase, which changes the liquid composition in the uterus. This results in different degrees of toxicity to eggs, fertilized eggs, and embryos. It also reduces the synthesis of prostaglandins and the depth of progesterone and delays the time of estrus and ovulation. Besides, in the case of dietary high levels of protein, cows need to consume too much energy to metabolize excessive nitrogen and add negative energy balance, which seriously affects reproductive performance. When the supply of protein is insufficient, it will affect the development of follicles. Dairy cows have abnormal ovulation and estrus and are prone to postpartum diseases such as placental retention.
3. Effects of Minerals on Reproductive Performance
Postpartum calcium will flow out with a large amount of milk, especially for high-yielding dairy cows. It is easy to produce milk fever. The calcium content in the blood is very low. When the calcium concentration in blood decreases, the digestive function of dairy cows and the intake of dry matter decrease, which leads to negative energy balance in dairy cows. At the same time, the increase of lipid catabolism can easily lead to fatty liver and ketosis. The decrease of uterine muscle peristalsis can lead to dystocia and postpartum placenta retention. The level of phosphorus in the diet has an important effect on calcium absorption. Therefore, to meet the normal growth, lactation and reproduction of dairy cows, the appropriate level of calcium and phosphorus in the diet should be increased.
4. Effect of Vitamin on Reproductive Performance
Although the amount of vitamins in the diet is very small, it has an important effect on the reproductive performance of dairy cows. Vitamin E, also known as tocopherol, can increase the secretion of lutein hormones, so that the fertilization process can be completed smoothly, and can also reduce the risk of early embryo death and abortion of embryo. Besides, dietary vitamin E supplementation can also reduce the incidence of placenta retention and mastitis. Vitamin A is a vitamin closely related to the reproductive performance of dairy cows. When dairy cows lack vitamin A, problems such as embryo dysplasia, abortion, placenta retention, and uteritis will occur.
5. Effect of Trace Elements on Reproductive Performance
Zinc and copper are involved in the composition of various enzymes and proteins in animals and reproduction of dairy cows, and also protect cells. Free from the harm of oxidative metabolism, zinc deficiency will affect the formation of sperm and weaken the function of corpus luteum, while copper deficiency will inhibit the estrus of cows, make cows not estrus or estrus abnormality. Selenium mainly plays an antioxidant role, can protect the membrane structure of organisms, maintain the normal reproductive function of the body. If the cow body lacks selenium, there will be diseases such as placenta retention, uterine inflammation, ovarian cyst, etc. Besides, selenium is necessary for sperm production. If lacking selenium, sperm formation will be affected.
Iodine is an important substance to synthesize and regulate energy metabolism. It can promote the synthesis of vitamin A. If iodine deficiency obstructs fetal growth and development, it will also increase the probability of retaining the placenta of dairy cows after delivery and decrease reproductive performance. Manganese participates in the synthesis of vitamins and plays an important role in maintaining the normal reproductive function of dairy cows. Lack of manganese can easily cause recessive oestrus of dairy cows, decrease the rate of mating and conception, and easily lead to abortion of dairy cows and increase the deformity rate of newborn calves.