Abstract Protective fat belongs to rumen-resistant fat. Adding protective fat in dairy cow diets can increase milk production, milk fat percentage and reproductive performance of dairy cows. Protective fats are suitable for high and middle-producing dairy cows, and the amount added in the diet is generally 3% to 5%. In the early period of lactation, as the milk production continues to increase, the energy requirement gradually increases. However, the increase in dry matter intake is limited. Cows at the peak of lactation, especially high-yielding dairy cows, often exhibit negative energy balance. . In order to increase the energy concentration in the diet, the traditional method is to add unprotected fat to the diet to change the negative balance of energy. However, the direct addition of unprotected fat has a strong inhibitory effect on the rumen, inhibits ruminal microbial activity, changes the type of ruminal fermentation, reduces the digestibility of cellulose, and decreases the ratio of methane, hydrogen, volatile fatty acids, and acetic acid/propionic acid. The rate also decreases, and rumen dysfunction and ketosis are easily caused. And because the long-chain fatty acids are easy to form insolubles, their use is reduced. The addition of treated protective fat, so that the fat does not dissociate and hydrolyze in the rumen, directly into the small intestine to be digested and absorbed, can effectively overcome the above drawbacks, improve the utilization of fat, thereby further enhancing the production performance of dairy cows. I. Types of protective fats and their protective principles Protective fats can supply energy to cows without inhibiting their ruminal fermentation. They are usually divided into two major categories: 1. The coated oils and fats are coated on the surface of fats and oils with some rumen-resistant materials that allow them to escape from the rumen fermentation and thus achieve the purpose of protection. They mainly consist of formaldehyde-protein complex coating and blood meal coating. Formaldehyde-protein complex coating is the earliest protected lipid, and its mechanism is that the formaldehyde-protein complex forming the protective film is reversible in the acidic environment. The protective film has a ph value of about 5-7 in the rumen. The environment will not decompose and the fat will not dissolve out. In the acidic environment with a true stomach pH value of about 2-3, the protective film is destroyed and the coated fat is dissolved, so it will not affect the digestion of fat in the digestive tract. Absorption, ashes (1979) experiments showed that the degree of protection of fat by formaldehyde-protein can reach 85%, but the micro-residue of formaldehyde in animal products is the main reason for limiting the promotion of this method. About blood-stained oils, as early as 1980, Orskov observed that the blood powder is completely insoluble in the rumen, and it forms a protective film on the feed surface. This protective film can prevent lipids from dissolving in the rumen. 2. Fatty Acid Compounds According to Jenkins (1993), free radicals are the main poisons for rumen microbes. Therefore, passivating carboxyl groups is an ideal method to protect lipids. The most studied fatty acids are calcium, which are composed of fat and calcium ions. The formed protective grease is a new type of energy feed additive. It is composed of saturated and unsaturated fatty acids combined with calcium ions. These calcium salts remain intact in the rumen neutral environment and dissociate immediately in an acidic environment. The calcium ions and free fatty acids are thus digested and absorbed by the small intestine. Second, the protective effect of protective fat on dairy cows Increase milk production and improve milk quality As a high-energy feed, protective fat can increase dietary energy concentration without affecting rumen fermentation, meeting the high energy needs of high-yielding dairy cows during early lactation, thereby increasing milk production. Wang Xiumei (1998) reported that adding 100-200g of long-chain fatty acid calcium to dairy cows' diets can increase the milk production of pre-lactating and even mid-later (230d) dairy cows; feeding 250g/d can prolong the milk production of high-producing dairy cows. The lactation peak period after 60 days kept the milk production at a stable high level. This is because long-chain fatty acid calcium is a protective fat. The rest of the research also showed that adding calcium fatty acid can significantly increase milk production in dairy cows. Kogers (1988) reported that the addition of 140g of fatty acid calcium increased milk production by 1.3kg; bondili (1993) reported that the addition of 200g of fatty acid calcium increased milk production by 10.60%; Zhang Zhongping (1993) reported that 350g of fatty acid calcium was added to produce milk. The volume increased by 26.60%. Although there was some inconsistency in the amounts added in each study, the addition of protective fats did have the effect of increasing milk production. Improve milk quality For lactating cattle, after protective fat is absorbed, it can be synthesized and secreted into milk through the mammary gland to increase the efficiency of milk fat synthesis. Therefore, after adding protective fat, the total milk and milk fat percentage in milk can be increased. The addition of protective fat can also significantly increase the flow of duodenal unsaturated fatty acids in ruminants and increase the content of unsaturated fatty acids in milk, especially linoleic acid and linolenic acid, thereby improving milk quality. In addition, after the fatty acid calcium is decomposed in the posterior segment of the digestive tract, the calcium in it is secreted into the milk and can increase the calcium ion content in the milk. Gao Tuzheng (1998) reported that the addition of 300 g/day to the dairy cow diet increased the milk production by 19.29%, the milk bloat rate by 13.16%, and milk fat, linoleic acid, linolenic acid and calcium in milk. Increase 18.20%, 25.55%, 29.60% and 17.25%, respectively. It shows that adding calcium fatty acid to the diet can not only significantly increase the milk production of dairy cows, but also increase the nutritional value of milk and improve milk quality. 2. The optimal temperature for reducing lactation in heat-stressed cows is 4-20°C. When the temperature is higher than 32°C, the body temperature of the cow increases, the breathing and pulse speeds up, the feed intake decreases, the feed utilization rate decreases, the milk yield decreases, and the milk fat percentage decreases. Adding protective fat to cow rations in hot weather can increase energy intake and reduce heat stress to a lower limit because protective fat does not participate in rumen fermentation and does not become a direct source of heat rise. . According to Liu Yanqin et al. (1999), the addition of fatty acid calcium to dairy cows' diet during hot summer has a certain degree of resistance to the heat stress of dairy cows, resulting in a decrease in respiratory frequency and pulse frequency, an increase in blood glucose concentration, and a significant increase in milk production. (p<o.05). Qin Lihu (1997) also found that it is appropriate to add protective fat in order to reduce body temperature in cows under heat stress. 3. Improve reproductive performance Adding fatty acid calcium can improve the reproductive performance of dairy cows, because after the addition, it alleviates the negative energy balance of dairy cows during lactation, inhibits postpartum weight loss of dairy cows, maintains good body condition, forms early estrus and has a high conception rate. In addition, linoleic acid, linolenic acid, eicosapentaenoic acid and docosahexaenoic acid in fat can improve the reproductive performance of dairy cows. Add protective fat to the early lactation diet of dairy cows. The interval between calving and re-pregnancies can be shortened. Experiments conducted by Boodilu (1993) showed that the rate of conception in cows fed with fatty acid calcium increased from 61% to 87%. Den also reported that after feeding dairy cows with fatty acid calcium, the pregnancy rate increased by 10% to 20%, the service life of dairy cows was extended by 0.5 to 1 year, and the incidence of mastitis decreased by 20% to 30%. 4. Increase body fat unsaturation Because protective fat does not degrade in the rumen, it can be directly digested and absorbed in the small intestine, so supplementing protective fats in the diet can increase body fat unsaturation. Tests have shown that 250 kg of cattle are fed with 3 kg of protective lipid per day to replace the same conventional feed. After 8 weeks, the content of unsaturated fatty acids in the oil can be increased from 1 to 2% to 20% or more (Wang Tangchen, Zhao Yuling, 1994). ). 5. Other effects of adding protective fat can increase energy intake, so as to avoid low-fat-lipid syndrome, dairy cow acidosis and other metabolic disorders caused by decreased intake of crude fiber due to high concentrate intake, and reduce the occurrence of metabolic diseases: In addition, the addition of protective fat can also reduce the energy loss by reducing the production of methane; it can also reduce the dust in the feed. Kronfeld et al. (1980) showed that the addition of animal protective fat in the diet of lactating dairy cows increased blood glucose levels and decreased the concentration of beta-hydroxybutyric acid and acetoacetate, which is of great significance in preventing the occurrence of early ketosis in high-yielding dairy cows. Third, the factors that affect the effect of the effect of 1. Types of Protective Fat Products Protective fats must be stable in the rumen without being dissolved, and they must be maximally digested and absorbed in the small intestine. The shorter the carbon chains in the protective fat products, the easier the fatty acids are to be absorbed, and the unsaturated fatty acids are easier to absorb than saturated fatty acids. j. i. Fernadez (1999) reported that in the calcium salt component, when the ratio of unsaturated fatty acids and saturated fatty acids is equal, it can be more effectively dissolved in the abomasum, and the absorption rate of fatty acids in the small intestine can reach 95%. Ketels et al. (1989) pointed out that in protective fatty products, the higher the ratio of unsaturated fatty acids, the higher the metabolic energy value. When the ratio of unsaturated fatty acids and saturated fatty acids is close to 4, the metabolic energy value reaches the maximum. When the fat is also the highest utilization rate. 2. Addition of fats Although protective fats have many benefits for dairy cows, if they are added excessively, they will reduce the dry matter intake of dairy cows and reduce the production performance of dairy cows. Generally, the added amount is: After the fat is added, the total fat content in the dairy cow's diet reaches 5% to 6%, and the utilization rate is the best. Palmquist (1993) reported that the best way to decide on supplements is that the total fat content in the dairy cow's diet should be equal to the amount of fat in the milk produced by the cow. For example, if a dairy cow produces milk of 40 per day, her milk fat percentage is 3.7%, then the total fat in milk is 1.48; the cow’s daily dry matter intake is 25kg, and the fat content is 3%. The total amount of fat in the grain is 0.75kg; thus, the amount of fat that needs to be added should be 0.73kg, which accounts for 3% of the whole diet, so 3% fat is more appropriate. As to how much protective fat is added in the end, it is not yet a unified standard, and it is generally reported as 3% to 5%. However, when the amount is less than 3%, the effect is not obvious; and when it is more than 5% to 6%, there will be side effects on the production of dairy cows. 3. After the time of calving, the dairy cow will have more physical exertion. At this time, any stress will affect its milk production performance, so it is not appropriate to add protective fat after the cow is born. Normally, it is better to start adding after 3 to 5 weeks of postpartum. After the addition, the milk production will decrease temporarily. However, the milk production will increase and the peak period of milk production will be longer. Therefore, the milk production during the whole lactation period will increase. . It has also been reported that it is effective when used in the prolific and hot summer months. In the late lactation, the effect is often not obvious. 4. Dietary composition added protective fat, quality hay in the diet, to provide adequate fiber, so that the amount of acetic acid produced in the rumen more, so as to make full use of protective fat, milk production and milk fat rate was obvious Increased. Studies have shown that dry matter crude fiber in dairy cow diets should be at a level of 17%, and acid washing fibers should be about zi%. In addition, after the addition of protective fats, there is a possibility that the rate of milk protein may be reduced, and therefore, it is necessary to increase the content of crude protein in the diet, but if it is combined with ruminal protein, this problem can be alleviated. 5. Dairy cow protective fats are suitable for high- and middle-produced dairy cows, and the effect on low-yielding cows is not obvious. For dairy cows whose milk fat percentage is less than 3.5%, the effect is obvious. When the milk fat percentage is higher than 3.5%, the effect of adding is often not obvious.
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