Open days of dairy cows is one of the factors affecting the reproduction of cows. Open days of a dairy cow is the number of days from calving to re-pregnancy.
The reproductive performance of dairy cows has many aspects and is the result of the complex and interactive effects of nutrition, genetics, and also under the influence of management practices and other environmental factors. This performance is often dependent on the previous performance of the animal and can change with the age of the cow. The decrease in reproductive performance of dairy cows has been widely reported in various studies in the world.
Recent research shows that there is significant genetic variation in the fertility of female cows. There is extensive research in this field of the existence of a negative correlation between milk production and fertility. It should be noted that various factors affect the open days of dairy cows. In this article, an attempt is made to discuss the nutritional factors affecting dairy cows.
Various factors affect the open days of dairy cows, including nutritional factors including protein, energy, vitamins, and minerals that make up animal feed rations.
Nutritional effects on reproduction (especially open days of dairy cows)
Pre- and post-partum feeding, especially when dairy cows are increasing their milk production, can affect reproductive performance and subsequently herd profitability. In general, the increased metabolic demands of high-yielding cows along with reproductive and health needs have made the interaction between nutrition and reproduction (especially postpartum) an important issue in the dairy industry. Recent research has confirmed the important role of nutrition in reproduction, and in most cases severe nutritional deficiencies have led to reproductive problems and diseases. Also, the nutritional mechanism that affects reproductive performance is very complex and cannot be clearly identified. Nevertheless, the role of nutritional factors such as protein or energy balance and their mechanism of action on reproduction has been better known in recent years.
Nutritional factors can inhibit the ovarian cycle, but in general, as long as the ovarian cycles are normal, they have no effect on how estrus occurs. In many cases, the correct energy balance has a significant effect on the resumption of ovarian cycles after parturition, such that a negative energy balance delays the occurrence of postpartum estrus.
Here is a review of the nutritional factors that affect dairy cow days:
• Diet energy and its relationship with dairy cows’ open days
Dietary energy is one of the important factors affecting reproductive efficiency. Inadequate energy intake in heifers and mature lactating cows during early lactation reduces reproductive efficiency. On the other hand, receiving too much energy at the end of the lactation period or during the dry period can cause obesity and reduce the reproductive efficiency of cows in the next period. Most productive cows are in a negative energy balance because they cannot get enough feed to meet their needs during the lactation period. In this way, the energy available in body tissues (fats) is called and weight loss occurs. Factors related to this negative energy balance are the reasons for failure in fertility. The return to the estrous cycle depends on the negative energy balance during the first three weeks of lactation. The greater the negative energy balance, the longer the interval until the first ovulation. A lack of energy also leads to an increase in silent estrus.
Paying attention to the body condition score also has an effective role in detecting the pregnancy rate (obese = 5, thin = 1), so that animals whose body condition score is slightly more than one have a longer calving interval and a lower pregnancy rate. On the other hand, excessive intake of energy also leads cows to fattening and reducing reproductive efficiency, so that in these cows, retained placenta is seen in a relatively large amount, and ovarian cysts are also seen in them. All of these factors reduce fertility.
Dietary energy is one of the important factors affecting reproductive efficiency. Inadequate energy intake in heifers and mature lactating cows during early lactation reduces reproductive efficiency. On the other hand, receiving too much energy at the end of the lactation period or during the dry period can cause obesity and reduce the reproductive efficiency of cows in the next period.
By using the recommended amount of Dynalac and Omega 3 fat supplement of UFAC, England, both the amount of energy needed by the animal is provided at the time of negative energy balance, and by having essential fatty acids and a balanced ratio of Omega 3 and Omega 6, as well as the presence of two EPA fatty acids. And DHA in omega-3 supplements, which have a direct effect on the rate of asthenia and increase fertility, cause a significant reduction in open days and reduce the costs incurred due to the increase in open days.
• Dietary protein and its relationship with dairy cow open days
Livestock feed containing high protein, in general, has a better taste and increases feed consumption, in most dairy farms, more protein is eaten than the animals need. These diets containing high amounts of protein can reduce reproductive efficiency. In most studies, the increase in raw protein in the diet is considered to be the reason for increasing the time until the first ovulation after parturition and increasing the number of inoculations per pregnancy or the number of open days of dairy cows. In general, protein substances differ in the degradable parts of their proteins. For example, two diets containing 18% protein may differ in the amount of degradable and non-degradable protein in the rumen. Imbalances in the supply and requirements of animals for degradable and non-degradable protein in the rumen may each affect reproduction.
Because of the similarity of hormonal changes in cows fed high crude protein diets to those occurring in energy-deficient cows, many of these interactions are caused by the energy factor (rather than amino acids or nitrogenous by-products of metabolism). rumen) originates. Diets containing high amounts of protein or diets containing excessive amounts of degradable protein can exacerbate the negative energy balance by increasing milk production.
In general, the effect of dietary protein on fertility appears to be very complex, as various factors such as age, energy, non-degradable protein in the rumen, and uterine health may influence the response to changes in protein intake. In order to reduce the economic losses caused by ineffective feeding and excess protein on production and reproduction, animal feed rations should be adjusted based on providing appropriate amounts of degradable and non-degradable protein in the rumen. For example, for high-yielding cows and cows in early lactation, 35% of crude protein should be in the form of undegradable protein in the rumen. Therefore, it is necessary to replace some sources of transitional protein, especially in diets that are based on alfalfa (as alfalfa protein is highly degradable).
Protein deficiency in dairy cows leads to silent estrus and reduced pregnancy, so that a decrease in milk production and food consumption is also observed. If protein is added to the animal feed ration, the increase in milk production can be observed after 2-3 days, and of course, heifers are more sensitive to protein deficiency compared to mature and multi-calved cows. Heifers that face a severe protein deficiency, their skeletal growth is reduced, especially in the pelvis. These heifers start the estrous cycle late and have problems with calving and may be affected in terms of lactation and may not produce significant milk. Excessive protein in the diet (more than 17% of crude protein) leads to a decrease in pregnancy percentage and an increase in the frequency of insemination per pregnancy and open days of dairy cows. Of course, researches have not shown a single result and it may depend on the amount and type of proteins and the amount of energy in the animal feed ration (and not the amount of raw protein). When the animal is given a large amount of ruminal degradable protein or the animal receives little energy, ammonia is not incorporated into the microbial protein system and absorbed into the blood, and thus this high amount of ammonia and urea in the blood may decrease. lead to fertility. In some studies, it has been shown that blood urea nitrogen (BUN) more than 100 mL/200 mg reduces the possibility of pregnancy.
• Dietary minerals and its relationship with dairy cow open days
Deficiency or lack of balance of minerals in animal feed is one of the nutritional factors that reduce reproductive efficiency. It is clear that a sufficient amount of these substances should be provided through the diet, but in general there is a difference of opinion about their minimum threshold. Of course, too much of them is also harmful.
•Phosphorus: This element is most closely associated with reduced reproductive efficiency. Inactive ovaries, late sexual maturity and low pregnancy rate are the result of phosphorus deficiency.
• Calcium: Most of the studies on calcium and its effect on reproduction are related to the ratio of calcium and phosphorus. Ratios of 1 to 1.5 and 1 to 2.5 have no effect on reducing fertility. However, it should be noted that the amount of each of these consumed by the cow is very important. Sufficient amounts of this element should always be provided for dairy cows, and for dry cows, the optimal level of calcium and phosphorus should be fed to reduce the incidence of milk fever. Because cows that are infected with milk fever need 2 times more help during childbirth than cows that are not affected by milk fever and are 2.4 times more likely to get uterine infection, so try to reduce milk fever. , helps to maximize the pregnancy rate.
• Selenium: Usually, agricultural products are selenium deficient. This is especially evident when cattle breeding is a form of cultivation and industry. Selenium deficiency is one of the causes of placental abruption, and by eating this food along with vitamin E, this complication can be prevented. Feeding 1mg of selenium to cows suffering from selenium deficiency can solve this problem. Selenium deficiency can also cause miscarriage.
•Iodine: The effect of iodine on the thyroid gland can be effective in reproduction. It should be ensured that each cow receives 15 to 20 mg of iodine daily. Consuming a large amount can lead to problems such as miscarriage, reduced resistance to disease and infections.
• Potassium: Many studies have shown that receiving high amounts of potassium may lead to delayed puberty, delayed ovulation, weakening of the corpus luteum, and lack of estrus.
• Copper: Copper deficiency leads to early fetal death, decreased ovarian activity, decreased estrus, decreased pregnancy rate, increased placental abruption, and increased hard birth.
• Zinc: Zinc deficiency in bulls leads to lack of sperm production and in female cows to delayed sexual maturity and uterine abnormalities.
• Vitamins in the ration and its relationship with the open days of dairy cows
The vitamins needed by cows are provided through their production in the rumen, intestines and tissues, as well as through the feeding of animal feed. Below is a review of each of the vitamins and their effect on reproduction.
• Vitamin A: It is a vitamin that promotes tissue health during pregnancy. Deficiency of this vitamin leads to delayed sexual maturity, miscarriage, stillbirth or weak fetus, placental abruption and uterine infection. The recommended amount of vitamin A for dairy cows is 50,000 to 80,000 international units (IU). Cows that receive low-quality or low-vitamin A forage should receive these vitamins in the form of oral or injectable supplements.
Among foods, green and fresh fodder are a good source of vitamins. Alfalfa silage is also considered as one of the sources containing beta-carotene. While corn silage is one of the poor sources of beta-carotene. Other problems that beta-carotene deficiency can cause in cows and heifers include:
• Delay in the return of the uterus to its original state after childbirth
• Delay in the first estrus after childbirth
• Delayed ovulation
• Increasing the amount of ovarian cysts
• Miscarriage and fetal death at the beginning of pregnancy
As can be seen, the above factors all increase the number of days open for dairy cows.
• Vitamin D: This vitamin is needed for the metabolism of calcium and phosphorus, and of course, its deficiency is rarely seen in industrial cattle farms because the animals get enough of it with sunlight. The animal’s need for this vitamin is 10,000 (IU) per day.
• Vitamin E: There is still no clear and convincing evidence on the effect of its deficiency on reducing reproductive efficiency, and the level of its need is not known correctly.
The correct balance of the animal feed ration can ensure the provision of quality feed, although we should not be overly sensitive in this case. This means that if one amount of food is enough for the animal, double it is not only not useful but can be harmful.
Constant consultation with an experienced specialist can also guarantee the health of the animal, and if the above items are not followed and considered only when a problem occurs, the pregnancy yield will decrease and the days between birth and pregnancy (open days) will increase. Depletion of the herd, which is associated with a decrease in the profitability of dairy cows, will be inevitable.