1. Physical characteristics of high-yielding dairy cows
In general, cows with milk yield of more than 7 500 kg, milk fat rate of 3.4%~3.5% and milk protein rate of 3%~3.2% during lactation are called high-yielding cows. The milk yield of individual dairy cows in lactation period is more than 8500 kg, and that of multiparous dairy cows is about 9000 kg. High-yielding dairy cows should have the characteristics of high milk yield and good milk quality, including high milk fat rate and milk protein content, and normal reproductive performance. In addition to producing high-quality milk, high-yielding dairy cows should have a healthy physical condition, exuberant appetite, developed digestive system and strong metabolic function. And there are no metabolic diseases.
High-yielding dairy cows have obvious dairy characteristics, such as breasts like bathtubs, extending forward and backward, compact attachment, and thick mammary veins. Generally, the height is over 1.4m and the length is over 1.7m. Ruminant time is longer than low-yielding dairy cows, and the number of rumen peristalsis is relatively more. Therefore, in the process of feeding and management, high-yielding dairy cows should be given enough time to ruminate and breathe, otherwise, the digestive system will be disordered, and the milk production and health of dairy cows will be adversely affected.
The physiological characteristics of high-yielding dairy cows are high basal metabolic rate, and physiological indexes such as respiration and heartbeat are faster than those of low-yielding dairy cows. Most of the milk is water, so high-yielding dairy cows have a large amount, a long time and many times to drink water. The average amount of drinking water per cow can reach 62 kg. Because of the high-yielding dairy cow's large feed intake and strong metabolism, the time of defecation is longer and the amount of defecation is large. The amount of defecation is thinner. The daily amount of defecation is 38-49 kg, and the amount of urination is 40-68 kg.
The amount of bacterial protein synthesized by rumen microorganisms of high-yielding dairy cows is limited. Protein in diet alone can not meet the needs of lactation, and protein feed should be added to meet the needs of high-yielding dairy cows. Although the nipples of high-yielding dairy cows are looser and the lactation rate is lower than that of low-yielding dairy cows, the daily milk production of high-yielding dairy cows is much higher than that of low-yielding dairy cows, so the daily milking time is longer than that of low-yielding dairy cows.
High-yielding dairy cows have a strong ability of nutrient transformation, which can effectively digest nutrients contained in various feedstuffs. In the process of milk production, the nutrients in feedstuffs are transported to the breast. The ability to convert it into nutrients is particularly strong, and the ability of low-yielding dairy cows is relatively poor compared with it. In actual production, feeding high-yielding dairy cows with a large amount of concentrate can lead to ketosis. Therefore, the proportion of roughage should be increased during feeding. Buffers can also be added to the diet to buffer the appearing of gastric acid in the rumen of dairy cows caused by eating a large amount of concentrate, to keep the pH value in the rumen stable and effectively prevent acidosis and ketosis.
2. Nutritional needs of high-yielding dairy cows
High-yielding dairy cows need to maintain high nutritional requirements, and also consider the proportion of concentrate and roughage in the diet to ensure the appropriate ratio of fermentable nitrogen to rumen protein in fermentation products, and to avoid the occurrence of metabolic diseases. Therefore, the nutritional needs of high-yielding dairy cows are relatively complex.
Energy is an important nutritional factor for dairy cows. Higher intake is an important factor to meet the energy needs of dairy cows. The proportion of roughage and concentrate in the diet affects the intake of dry matter. The proportion of roughage in the diet of high-yielding dairy cows is 30%, which can maintain the normal function of the rumen and ensure that the milk fat rate does not decrease.
Carbohydrate is the main energy source in the diet of high-yielding dairy cows, accounting for 60%~70% of the diet of dairy cows. It can provide energy for rumen microorganisms and maintain the health of the intestinal tract. Roughage plays an important role in the nutritional needs of dairy cows' lactation. It is the main energy feed. When the milk production increases in the year, it is difficult for the roughage to provide enough energy to maintain the need for lactation. At this time, the combination of high-energy feed plays a key role.
The protein requirements of dairy cows are divided into rumen fermentable nitrogen and absorbable amino acids. When milk production increases, rumen fermentable nitrogen can not meet the needs, which requires increasing the amount of absorbable protein and ensuring its quality. Additional non-degradable protein supplements are needed in the diet. Fish meal, meat and bone meal are the main protein supplements used in production. Attention should be paid to the quality of protein supplements in use. Different kinds of protein supplementary feeds are not effective, and fish meal is generally better. This is because the amount of rumen degradable protein decreases while the rumen protein is increased, thus changing the mode of absorbable amino acid. Fish meal can play a better balance role. It is noteworthy that the proportion of protein in the diet should be moderate. The excessive protein levels in the diet will have adverse effects on the reproductive performance of dairy cows.
Minerals are very few in dairy cows, but they play an important role. For example, calcium is an important mineral component in the skeleton. Calcium is especially important for dairy cows, because the content of calcium in milk is high, and the nutrition of calcium is related to cow milk fever. Milk fever is a major metabolic disease of dairy cows. When it occurs, intravenous calcium preparations can effectively treat the disease.
Therefore, adult dairy cows should feed a low-calcium diet before delivery and high-calcium diet after delivery to avoid cow milk fever. Apart from participating in the composition of bone, phosphorus is also an indispensable substance for material metabolism in cows. The insufficient supply of phosphorus will affect the growth rate of cows and the utilization rate of feed, and make cows produce milk fever. The proportion of calcium and phosphorus should be considered when supplementing phosphorus in the diet. Besides, other mineral elements also play an important role in the feeding of dairy cows. When they are added, attention should be paid to the amount of added mineral elements. Excess mineral elements will cause antagonism(definition) between them, which is harmful to the growth, reproduction, and lactation of dairy cows.
Vitamins can be divided into fat-soluble and water-soluble, which play an important role in body regulation and tissue metabolism. Vitamin deficiency can lead to many diseases, such as night blindness caused by vitamin A deficiency and rickets caused by vitamin D deficiency. Supplementation of nicotinic acid to high-yielding dairy cows can reduce the occurrence of stress reactions and play an important role in milk production, milk quality, and ketosis control.