1 Selected varieties and individuals
There are great differences in milk yield and milk fat rate among different breeds of cattle. The milk yield of carefully selected breeds such as Holstein cattle is obviously higher than that of local breeds. There is a negative correlation between milk yield and milk fat rate. The higher the milk yield, the lower the milk fat rate. However, the milk swelling rate of high-yield milk varieties can still be improved through planned breeding. Although different individuals of the same breed are at the same growth stage, under the same feeding and management conditions, their milk yield and milk fat rate will still be different. For example, the milk yield of Holstein cows ranges from 3000 to 12000.
Kg, and the milk fat rate was 2.6% ~ 6.0%. Breeding excellent varieties and individuals and constantly improving them is an effective way for high quality and high yield of dairy cows.
2. Choose high-quality feed
The volatile fatty acid in rumen metabolites of cattle is acetic acid. The proportion structure of propionic acid and butyric acid has great influence on milk yield and milk fat rate of dairy cows. After being absorbed, acetic acid is transported to mammary gland through blood, and a series of short-chain fatty acids are synthesized in milk fat. Propionic acid is absorbed and transported to the liver to become the raw material for synthesizing glucose; Butyric acid is a short-chain fatty acid in milk fat, and can also be condensed with acetic acid coenzyme A to form higher fatty acids. Increasing the ratio of acetic acid to butyric acid is beneficial to improve the milk fat rate of dairy cows.
Milk fat is synthesized by two basic types of precursors, of which about 50% is synthesized by mammary gland with acetic acid and acetic acid produced by rumen fermentation as raw materials, and the rest is supplied by feed fat or fat accumulated in the body (directly forming milk fat in the form of long-chain fatty acids). Different feed ingredients have great influence on the in vivo synthesis of breast distension.
2.l crude fiber
Crude fiber content has the greatest influence on milk fat in feed. Fiber decomposes in rumen to produce acetic acid, while starch can enhance rumen fermentation, reduce pH value and promote the production of propionic acid. The milk fat percentage is positively correlated with the ratio of acetic acid and propionic acid in rumen. If the forage in the diet is less than 50%, or ADF (acid-washed fiber) is less than 19%, or the total feed crude fiber is limited to 13%, the ratio of acetic acid to propionic acid will decrease due to the decrease of dietary fiber content, thus reducing the milk fat content.
2.2 Fat
The positive function of fat is high energy, which can directly provide fatty acids for milk fat synthesis. About 50% of milk fat must be provided by dietary fat. When cows are in positive energy balance, it is difficult to utilize body fat and transport it to the mammary gland, so dietary fat is the only source of milk fat during lactation. The negative effect of fat is unsaturated fatty acid produced by unsaturated fat metabolism, which combines with hydrogen in rumen to promote propionic acid production and reduce milk fat content; Due to the addition of hydrogen, the generated transfer monounsaturated fatty acids can also inhibit the synthesis of fat in the breast. According to the above dual functions of fat, in order not to hinder rumen fermentation and other characteristics, it is appropriate to add 3% ~ 6% fat to feed. Free oil often reduces the milk fat content, but the whole oilseed has no such effect. Soybean oil or whole beans can reduce milk protein content, but cottonseed oil and cottonseed have little effect. Adding unsaturated fat or high dose of fat often leads to the decrease of milk fat rate, mainly because of its influence on rumen fermentation. Therefore, people try to reduce the negative effects of fat by some measures, such as feeding whole or crushed oil cakes, treating fat with formaldehyde to avoid tumor fermentation, and using calcium saponifiers. These technical measures have different effects in maintaining and improving the milk fat rate. Gao Gao (1998) reported the addition of fatty acid calcium 300.
Compared with the control group, G/d head can significantly increase the milk fat rate (P < 0.05), and the contents of linoleic acid, linolenic acid and calcium in total fat and essential fatty acids are significantly increased (P
2.3 Energy and protein
When the dietary energy level increases, the milk protein content increases, but it may reduce the milk fat rate. Increasing the protein content in the diet usually does not increase the milk protein content, but when the protein is lower than the necessary amount, it may decrease the milk protein. Only when cows are in a state of extremely low nutrition or long-term malnutrition can energy and protein affect the milk fat rate.
2.4 inorganic salts
When the rumen pH value is kept in the normal range, the formation of acetic acid is easier than propionic acid. Due to the increase of acetic acid, the feed intake, milk yield and milk fat rate of dairy cows will be improved. Adding alkalizing agent to fermentable feed such as high moisture grain and silage corn can achieve ideal effect, but adding alkalizing agent to feed such as hay and silage fresh grass with ADF accounting for more than 20% has no obvious effect. The most commonly used alkalizing agent is sodium bicarbonate or sodium carbonate, and the ratio of magnesium oxide and sodium bicarbonate is 1: 2, so the alkalizing effect is better. Zeolite can increase rumen pH value, but at the same time it may reduce milk fat and milk protein content. Han (1986) reported that feeding sodium acetate can increase the milk fat rate during rumen propionic acid fermentation.
2.5 Other feed additives nicotinic acid can improve the milk fat rate or milk yield. It is reported that feeding cows with 6 g nicotinic acid every day during postpartum 120 d can improve milk yield.
1 1.9%, the effect of adding nicotinic acid to dairy cows in the middle lactation period is far worse than that in the early lactation period, which may be due to the negative energy balance of dairy cows in the early lactation period. Due to the decrease of feed intake, the change of diet composition and the change of rumen microbial population after delivery, the niacin supplied in diet and synthesized by rumen microorganisms decreased, resulting in niacin deficiency in dairy cows. In the middle lactation period, the rumen microbial population of dairy cows is stable, and the milk yield gradually decreases. Cows can meet the needs of metabolism and production by relying on feed and nicotinic acid synthesized by themselves, so the effect of adding nicotinic acid in early lactation is obviously higher than that in middle lactation. Therefore, the factors such as milk yield, lactation stage and feed conditions should be considered when adding nicotinic acid to dairy cows, and it should not be added blindly.
For high-yield dairy cows, in order to ensure that dairy cows consume enough energy, the intake of roughage should be limited. Relevant data show that in this case, adding a proper amount of sodium acetate or sodium diacetate into the feed can promote and improve the balance of electrolytes in the body, stimulate the liver, kidney and intestinal mucosa, and thus increase the milk fat rate. In addition, when the concentrate-feed ratio is increased to reduce the milk fat rate of dairy cows, it can be supplemented by 450 per day.
G sodium acetate or sodium butyrate to improve the milk fat rate.
Lasalin and monensin plasma carriers can reduce the milk fat rate, because these antibiotics can increase the production of propionic acid in rumen.
3 scientific and standardized feeding management
3. Reasonable proportion of concentrated feed and roughage
In dairy cow's diet, concentrate should not be overemphasized, but high-quality roughage such as juicy green feed and green hay should be given priority. After coarse feed such as high-quality green hay is fully supplied, the insufficient energy is supplied by concentrate, and the feed should be coarse before fine, and the concentrate should be fed as few times as possible to avoid ingesting a large amount of concentrate at one time. Poewll(l939) first found that feeding dairy cows with high-precision and low-coarse diets would lead to a decrease in milk fat percentage. When the concentrate ratio in the diet is high, the ratio of acetic acid in rumen decreases and the ratio of propionic acid increases. On the contrary, when the proportion of coarse material is large, the proportion of acetic acid increases. It can be seen that feeding roughage is beneficial to improve the milk fat rate. However, roughage can not provide raw materials for dairy cows to synthesize milk protein, which will affect their production. Milk quantity. Therefore, the dairy cow's diet should be reasonably matched, which should not only provide a proper amount of concentrate and juicy feed to ensure the high yield of dairy cows, but also ensure a certain proportion of roughage to improve the milk fat rate. In production, cows are often fed roughage first, then concentrated feed or mixed with concentrated feed, and the proportion of roughage is generally not less than 40% of the diet.
3.2 Pay attention to the digestibility and substance form of diet.
Soest( 1963) confirmed that the milk fat percentage is related to dietary fiber through a large number of dairy experiments, and concluded that the influence of dietary fiber content and source on milk fat percentage may be directly related to fiber length. Pay attention to the digestibility of diet when feeding cows. The digestibility of high-yield dairy cows should not be lower than 65%, and attention should be paid to the digestibility of concentrate and roughage. Barley and sorghum are easy to degrade in concentrate, corn is relatively poor, grass green hay is easy to degrade in roughage, and other grasses are relatively poor. At the same time, we should pay attention to the physical form of diet. Concentrate seeds are best broken or crushed, while green roughage is not easy to break too much, generally 8.
The best is about cm, silage can be longer, which can increase the time of feed in digestive tract, thus improving the digestibility of crude fiber and dry matter, and then improving the milk fat rate.
3.3 supplement fat
Generally, the fat content of dairy cows' diet is about 3%. Relevant data show that when the fat content in the diet is 5% ~ 6%, the nutritional utilization rate of dairy cows is the highest. Therefore, adding a certain amount of rapeseed or protective fatty acids to the diet can effectively improve the milk fat rate, but the addition amount should not be too high, and the fat content in the diet is about 5% ~ 6%.
3.4 Strengthen the management of dry milk period
The dry lactation period of dairy cows is the stage when the fetus needs more nutrition for its rapid growth and development. Improving the nutritional status of dairy cows is also beneficial to the next lactation period and prepares the necessary conditions for prolonging the production period. At the same time, the cessation of mammary gland secretion during dry lactation is a necessary preparation stage for the normal secretion of secretory epithelial cells in the next lactation period. Therefore, the milk fat rate can be effectively improved by supplementing adequate nutrition in the dry milk period and combining with scientific feeding management (such as strengthening breast massage in the middle and late dry milk).
3.5 Master the correct milking method
Correct massage and milking operation can enhance milk ejection reflex, improve milk yield and milk fat rate. Standardizing and improving milking techniques to make the milk in breast cells as clean as possible every time can not only increase the milk yield (the increase rate is 10% ~ 20%), but also increase the milk fat rate by 0.2 ~ 0.4 percentage points. Master the milking speed and try to finish milking within 5 minutes.
3.6 Proper exercise
Cows fed in the house exercise less. If given proper exercise, it can not only exercise physique, strengthen metabolism and improve health, but also improve milk yield and milk fat rate. Under normal circumstances, cows should exercise freely for no less than 6 hours every day. According to reports, driving cows 3 kilometers a day can effectively improve the milk yield and milk fat rate, but the exercise should not be intense and the time should not be too long, depending on the physiological and nutritional status of cows. Excessive exercise sometimes leads to negative energy balance and ketosis.
4. Strengthen the prevention of mastitis in dairy cows.
Mastitis is an important factor affecting milk yield and milk fat rate of dairy cows, especially mastitis caused by Streptococcus lactis, Escherichia coli and Pasteurella multocida. The milk will be watery and the milk fat rate will be significantly reduced. Because the etiology of mastitis is complex and there are many influencing factors, it is difficult to prevent it. To prevent mastitis, we must start from all aspects, take comprehensive measures, and implement the policy of putting prevention first and combining prevention with treatment. In daily management, we should do a good job in environmental and animal hygiene, especially breast hygiene; Pay attention to milking hygiene and milk correctly; Regular subclinical mastitis or DHI test, if the test results show "++"and above, timely medication for subclinical mastitis; Attach importance to and adhere to the work of nipple medicated bath. The nipple immersion liquid requires strong sterilization, low pressure, stable performance and long action time. Commonly used are 0.3% ~ 0.5% chlorhexidine solution and 0.5% ~ 1% iodophor. It is necessary to isolate sick cattle and eliminate chronically ill cattle in time.
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