General points in the nutrition of dairy cows:

1-Cows should be categorized based on the stage of lactation or the amount of production and fed according to their needs.

2-Throughout the year, use a nutritional program that is economical and balanced and can meet the animal's needs.

3-To maximize the amount of specialized feed, use diverse and high-quality feed items.

4-Adjust the frequency of feeding cows and act according to the program.

5-Cows have a particular preference for fresh and juicy forages, which should be used in feeding if available and inexpensive.

6-The composition of the nutrients in feed items is diverse and variable. Ensure the nutrient components of the formulated ration through laboratory analysis.

7-Provide clean and palatable water permanently for the cows.

8-Provide suitable environmental conditions, especially in the summer and winter seasons, for the cows.

9-Any changes in the diet should be made gradually.

10-Use mixed rations (concentrate – forage).

11-While the forage should be fibrous, ensure that the chopped pieces of forage are small.

12-Take necessary measures to minimize feed losses.

13-To ensure sufficient feed intake in the ration, consider the safety margin.

14-While assigning dedicated and responsible workers to manage the feeding of cows, do not frequently change the workers in this section.

15-Feed from aromatic materials should generally be done 0.5 to 2 hours after milking.

16-Do not store forage for long periods and ensure there is no mold, fungal growth, or foreign objects at the time of use.

17-To counteract the effects of potential foreign body ingestion, feed magnets or iron to the animals.

18-Strictly follow the parasite control program, especially for gastrointestinal parasites.

19-When using rations containing fine or powdery particles, use wetting and binding agents such as fat or molasses to improve feed efficiency and prevent respiratory losses.

- Dry period (last 2 months of pregnancy)

Nutritional programs are based on five stages of animal production as follows:

From calving to 80 days after

80 to 200 days after calving

200 to 305 days after calving

45 to 60 days before calving

The group of cows whose dry period is coming to an end will have specific nutritional programs implemented for increased production and the healthy maintenance of dairy cows based on these stages:

Nutritional programs in the first stage of production:

After calving, milk production rapidly increases and reaches its peak in 6 to 8 weeks, but food intake does not increase in proportion to production needs, such that the maximum dry matter intake will be 12 to 15 weeks after calving. Therefore, most dairy cows will be in a negative energy balance for 8 to 10 weeks. High-producing cows will likely remain in negative energy balance until the twentieth week or longer.

The lactating cow compensates for the energy deficit for milk production from body reserves, leading to weight loss during this period. The critical period for the nutrition of lactating cows is from calving to peak lactation. Each kilogram of milk increase during this period will result in an additional 200 kilograms of milk over the entire lactation period.

During this period, the following points are essential:

Avoid sudden and rapid changes in the diet that cause digestive disturbances and start gradual changes at least two weeks before calving.

Avoid increasing concentrates until the stress related to calving is resolved, and maintain the level so that the lactating cow receives a minimum amount (18 to 19 percent ADF) while maintaining digestive health and producing quality milk. The amount of concentrate intake should not exceed 2 percent of body weight. The frequency of concentrate feeding should be increased, and each time it should be fed in small amounts.

Pay sufficient attention to providing the necessary materials for the lactating cow and the correct ratio with energy, a significant portion of which comes from body fat reserves.

To reduce acidosis and other digestive disturbances, use chemical buffers such as sodium bicarbonate.

Stress factors such as vaccination, hoof trimming, tick baths, etc., should be postponed until after peak lactation.

The use of niacin supplements, which may have started during the dry period, should continue for high-producing cows, as this will likely increase food intake and reduce the likelihood of ketosis.

Increase energy intake by feeding high-energy supplements such as fat and molasses.

Nutritional management in the second stage of lactation:

During this period, the cow has passed the sensitive peak stage with maximum production, and the animal's reactions return to normal, allowing it to express its production capabilities if provided with a balanced diet. In this stage, the dairy management should assess the body condition of the cows in question, and if encountering abnormal cases such as excessive growth or extreme thinness, should seek to adjust the diet.

Nutritional management in the final stage of lactation:

Nutritional management of lactating cows in this stage is easier than in other stages because, at this stage, food intake exceeds the needs for milk production, and milk production is decreasing.

Points that dairy management should consider include:

The weight loss occurring at the beginning of the lactation period should be compensated so that the cow has an appropriate weight at the beginning of the dry period.

Maximum efforts should be made to maintain lactation as much as possible.

Young heifers have special needs for growth. Therefore, to promote growth in 2-year-old heifers, 20 percent and for 3-year-old heifers, 10 percent more feed than the maintenance requirement should be considered.

To dry off cows at the end of this stage, the feed intake can be restricted.

Nutritional management of dry cows

To prepare the cow for the next lactation, a dry period should be considered. Considering a 60-day dry period will optimize subsequent lactation for most cows. If the dry period is less than 40 days, the udder tissue will not have enough time to regenerate, resulting in suboptimal milk production in the next lactation. If the dry period exceeds 70 days, the cow becomes excessively fat, while milk production in the next lactation does not increase, and the difficulties of obesity will also follow. It is said that the efficiency of energy consumption for tissue building during lactation is higher than during the dry period.

Avoid excessive feeding of minerals, especially mixtures of sodium salts, and limit salt intake to a maximum of 28 grams per day.

Excessive salt intake can cause water retention in the body and edema in some cows, especially first-calf heifers.

The role of nutrition in the reproductive efficiency of cows

Sometimes farmers who have experienced reproductive problems in their herds are surprised that these issues are related to nutrition, although nutritional deficiencies or imbalanced rations are one of the causes of reduced reproductive efficiency. Failure in reproductive efficiency can result from disease, toxicity, and management-related issues. Heat and heat stress alone play the most significant role in reproductive inefficiency in herds using artificial insemination.

Despite all advancements in nutrition science, nutritional issues still overshadow reproduction. Cows require large amounts of nutrients at the beginning of the lactation period. During the first 120 days of lactation, cows produce nearly half of their total production, and nutrients are consumed for maintenance and milk production. If these needs are not met, reproduction takes a step back, and we witness a decrease in fertility rates. The key to bringing dairy cows to their maximum genetic potential for milk production while maintaining a reasonable and sufficient level of pregnancy is to prepare a balanced ration of quality forages and grains, as well as minerals and vitamins, and maximize the intake of this ration. Today, many experts consider dietary programs to be the main problem in the fertility issues of herds. Mineral deficiencies, insufficient vitamin levels, energy and protein imbalances, and excessive protein intake are recognized as factors of infertility and reduced reproductive efficiency.

When studying reproductive problems in herds, nutrition should always be considered. However, two truths about the relationship between nutrition and reproduction should always be kept in mind.

Nutrition is only one of the factors affecting reduced reproduction. Factors such as weaknesses in estrus detection or health issues in the dairy farm and the health of the cows themselves play a more significant role when nutritional problems are not apparent.

High-producing cows respond to insemination later than low-producing cows and require more open days.

Moreover, the frequency of insemination is also higher. This means that to solve fertility and reproduction problems, we need to pay more attention to physiology, nutrition, and management rather than genetics. Some nutritional factors affecting reproduction are as follows:

Energy

The energy intake in many herds is the most important factor affecting reproductive efficiency. Insufficient energy intake in heifers and lactating cows in the early period reduces fertility rates. Excessive energy intake in the late lactation period or during the dry period can lead to obesity in cows and reduced reproductive efficiency in the next period. Most high-producing cows at the beginning of the lactation period have a negative energy balance because they cannot consume enough feed to meet their high production needs. Thus, energy stored in body tissues is mobilized, leading to weight loss. Factors associated with this negative energy balance are considered reasons for fertility failures. The return to estrous cycle depends on the negative energy balance in the first three weeks of lactation. The greater the negative energy balance, the longer the interval until the first ovulation. Energy deficiency also increases the rate of silent estrus. Another point is that one of the factors influenced by negative energy balance that leads to increased calving intervals and reduced reproduction is weight loss in early lactation. Body condition score also plays a significant role in determining pregnancy rates (fat=5, thin=1), such that those with a body condition score slightly above one have longer calving intervals and lower pregnancy rates. On the other hand, excessive energy intake also drives cows towards obesity and leads to reduced reproductive efficiency, such that retained placenta is also observed in these cows to a relatively high extent. Similarly, ovarian cysts are also seen in them, all of which are factors reducing fertility rates.

Protein

Protein deficiency in dairy cows causes silent estrus and reduced pregnancy rates, leading to decreased milk production and feed intake. If protein is added to the ration, an increase in milk production can be observed after 2 to 3 days, and heifers are more sensitive to protein deficiency than mature cows and multiparous cows. When the amount of degradable protein in the rumen increases or the animal receives little energy, ammonia does not join the microbial protein system and is absorbed into the blood. Thus, this high level of ammonia and urea in the blood may lead to reduced fertility.

Minerals

Deficiency or imbalance of minerals is another nutritional factor that reduces reproductive efficiency. It is clear that sufficient amounts of these minerals should be provided in the ration, but there is generally disagreement about the minimum deficiency levels. Certainly, excess of them is also harmful.

Phosphorus: This element has the most significant association with reduced reproductive efficiency. Inactive ovaries, delayed sexual maturity, and low pregnancy rates are the results of phosphorus nutritional deficiency, such that receiving 70 to 80 percent of the required amount and reduced phosphorus in serum leads to an increase in the number of inseminations per pregnancy.

Calcium: Most studies regarding calcium and its effect on reproduction relate to the calcium-to-phosphorus ratio. Ratios of 1 to 1.5 and 1 to 2.5 of calcium to phosphorus do not have an effect on reducing fertility; however, it should be noted that the amount consumed by the cow is of great importance. For dairy cows, a sufficient amount of this element should always be provided, and for dry cows, the optimal and best level of calcium and phosphorus should be fed to reduce the occurrence of milk fever, as cows that suffer from milk fever require assistance during calving 2 times more than cows that do not have milk fever and are 2.4 times more likely to develop metritis. Therefore, efforts to reduce milk fever significantly contribute to maximizing pregnancy rates.

Selenium: Soil is one of the poor sources of selenium, so agricultural products grown in these soils also have this deficiency. This is especially evident when dairy farming is industrialized. Selenium deficiency is one of the causes of retained placenta, which can be prevented with vitamins. Feeding 1 milligram of selenium to cows that are selenium deficient can resolve this issue. Selenium deficiency can also be a cause of abortion.

Iodine: The effect of iodine on the thyroid gland can be effective in reproduction. It should be ensured that each cow receives 15-20 grams of iodine daily. Many problems associated with iodine intake include abortion, decreased resistance to diseases, and infections.

Vitamin A:

This vitamin promotes tissue health during pregnancy. In case of deficiency, delays in sexual maturity, abortion, stillbirths, retained placenta, and metritis occur. Cows receiving poor-quality or vitamin A-deficient forage should receive this vitamin as an oral supplement.

Among foods, green and fresh forages are sources of this vitamin. Alfalfa silage is also considered a source of beta-carotene, while corn silage is a poor source. Other problems that beta-carotene deficiency can cause in cows and heifers include:

- Delay in the return of the uterus to its normal state after calving

- Delay in the first estrus after calving

- Delay in ovulation

- Increase in ovarian cysts

- Abortion and fetal death in early pregnancy

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