First, the composition of milk Milk is composed of a variety of ingredients, according to analysis confirmed that there are at least 100 kinds of chemical composition. But the main components are water, fat, protein, lactose, salts, and traces of other substances (such as phospholipids, vitamins, enzymes, pigments, gases, white blood cells, etc.). Milk can be roughly divided into water and dry matter (dry matter can also be divided into fat and fat-free solids).
Normal cow's milk content is basically stable, but each ingredient has a certain range of variation, of which the biggest change is milk fat, followed by milk protein, and the change of lactose is small. The inspection of milk is based on the content of each major component of the milk. Most of the milk composition is water (86%-89%), dry matter is 11%-14%, and the dilute and thick milk is mainly related to the dry matter content. The dry matter is directly related to the composition of his milk fat, milk protein, lactose, etc.
Second, the factors that affect the thick milk
The fat and protein content of milk is the most important two quality indicators of milk. The increase of fat and protein in milk not only increases the consistency of milk, increases the nutritional value, but also raises the acquisition standard for milk, which directly increases the economic benefits of cattle farmers.
The content of fat and protein in milk varies greatly depending on the type of cattle, breed, individual, lactation month, parity, feed type, and feeding level and season. Fat content in milk Milk fat percentage is one of the important indicators of milk quality. Protein content directly affects the yield of cheese.
(1) Beef breeds and breeds Each breed and breed of cattle is formed under certain natural climate and socio-economic conditions. Therefore, all breeds have their own inherent genetic characteristics and certain economically favorable traits. Therefore, the quality of milk is relatively low. Big difference.
(II) Due to the genetic differences between individuals, individuals in the same bovine species or breed have great differences in milk yield and milk quality even under the same feeding environment. This is also the charm of the breeding work.
(C) Age, parity and lactation The practice of raising cattle shows that with the increase of age and parity, the milk fat percentage and the milk protein rate of the milk produced have decreased slightly. Pre-lactating milk volume increased, milk fat percentage and fat-free solid body rate decreased; milk volume decreased during lactation period, and milk fat rate and fat-free solid-solidity rate increased.
(4) Feed and Feed Management Factors
1. Dairy cows' dietary concentrates are grossly inadequate. In order to pursue a high milk yield, the amount of concentrated feed is increased too much for dairy cows, and insufficient crude feed results in a decrease in ruminal acetic acid production and a decrease in milk fat percentage. Of the volatile fatty acids produced in the rumen of cattle, only acetic acid can be used as a source of energy for cow's milk fat synthesis. The source of acetic acid is cellulose in roughage, especially hay. In practice, when the hay content in the diet is between 1 kg and 2 kg, the fat percentage in the milk will be reduced by 0.3%-0.5%; the most suitable diet should contain 5 kg hay. In the diet, if straw is used instead of 40% of hay, milk production and milk fat percentage can be greatly reduced. Therefore, the quantity and quality of roughage are very important for improving milk fat percentage. When the proportion of crude feed in the diet fell below 40%, the milk fat content decreased significantly; when the proportion of crude feed was less than 10%, the milk fat content fell below 2% (normally 4%).
Concentrates are rich in carbohydrates. Feeding too much concentrate will alter the digestion process in the rumen, increase the formation of propionic acid, and reduce the content of acetic acid. Propionic acid cannot be used to synthesize milk fat, resulting in a reduction in milk fat percentage. It is recommended that milk cows produce 1 kilogram of milk per kilogram, and the fine material should not exceed 300 grams. The “material-for-milk†production method not only results in the waste of concentrates, increases the cost of raising the cows, but also affects the breeding of cows, which can easily lead to cancer acidosis, rumen retardation, etc., and reduce the benefit of cattle breeding.
2. The type of roughage is single and the quality is poor. According to the survey, the farmers implemented less than 20% of the whole plant with eared corn silage feeding cows; the farmer feeding corn straw silage accounted for about 30%; the farmer feeding corn stover, wheat straw accounted for more than 50%. The vast majority of dairy farmers do not grow pasture or carrots. The green feed of dairy cows depends on wild weeds on the roadside of the field, and they are supplied on a regular basis. Many dairy farmers give their dairy cows a diet mainly in the form of silage + concentrate or wheat straw + concentrate. Moreover, silage due to poor preservation of secondary fermentation and mold deterioration phenomenon, resulting in decreased quality of silage, dairy cow intake decreased, thus affecting milk production and milk quality.
3. The decrease in the crude protein content of the diet led to a decrease in the milk protein rate. When the crude protein content of diets decreased from 17% to 9%, crude protein decreased by 1% and milk protein decreased by 0.2%.
4. Dairy cows have poor feeding and management environments. The relative humidity of the cowshed is more than 90%, and the milk fat percentage will drop by 0.16-0.18%. If the ambient temperature is too high, the milk fat percentage will also decrease. When the weather is good in winter, exercise for cows can increase the milk fat rate by 0.17 to 0.24%. Due to poor sanitation conditions, dairy cows suffer from mastitis and the synthesis of milk ingredients is significantly reduced, resulting in a marked reduction in fat and fat-free solids; due to unbalanced feed intake, poor body condition, feeding of deteriorating feed, etc. As a result, the liver function declines, the nutrient supply to the raw materials converted into milk components is insufficient, the milk fat rate decreases, the synthesis of fat-free solids decreases, and the milk thins out.
5. Heat stimulation. Due to the hot weather, dairy cows have reduced appetite, insufficient feed intake, reduced dairy cows' physical strength, and reduced breast function.
6. Milking technique is incorrect. Poor preparatory work for milking, incorrect vacuum of the milking machine, and the number of pulsations are not only affecting milk production but also affecting the increase of milk fat percentage.
In addition, the sudden change of the environment, the destruction of the original feeding program, changes in the breeder, the milker, and the disease all have an impact on milk yield and quality.
(5) Mistakes in selecting and matching cows
1. One-sided pursuit of milk production, ignoring the increase in milk fat percentage. When choosing the species for breeding bulls, only the milk yield index was ignored and the milk fat rate index was ignored. Therefore, the bulls with high milk production and low milk fat percentage were selected. As a result, although the milk production of the daughters increased, the milk became thinner.
2. In order to become cheap, the use of unqualified bull (semen) breeding (even using inferior breeders without a breeding license) ultimately resulted not only in a lack of milk production by the daughter but also in the quality of the milk.
Third, improvement measures
(a) The correct selection of matching
1. The selection and allocation of bulls not only has a higher milk index, but also the milk fat index must be higher than that of the cows, so that the quality of future generations of milk can be genetically improved.
2. Eliminate the use of bull (semen) breeding that has not been determined by progeny; resolutely do not use “wild†bulls without pedigree and no breed licenses to avoid lowering the milk production performance and milk quality of future generations.
3. In view of the poor quality of milk produced by their own cows, bulls with good milk quality should be selected for improvement so that the quality of future milk production can be improved.
(2) Correct control of the proportion of refined roughage in rations Milk contains various nutrients such as fat, protein, sugar, minerals, and vitamins, and most of it is synthesized in the mammary gland by various precursors selected from the blood. For example, 90% of the protein in milk is synthesized in the mammary gland by the precursor in the feed, and 10% of the protein is carried directly by the blood. Therefore, if the precursors are insufficient, the normal composition of the milk content and the milk component cannot be ensured, and if too much of the precursor is used before, it will cause waste. Milk content generally fluctuates with production and dietary nutrient levels. The ratio of concentrates to coarses is roughly 50:50 (range 60:40 to 40:60), which is the proportion of feed that gives the highest milk composition. During the peak period of lactation, the nutrient requirement of dairy cows becomes larger, and the quality and feed structure of the diet should be fully guaranteed. When the quality is poor or the structure is not good, protein deficiency is often caused. When the amount of protein is insufficient, the amount of milk will decrease, the milk protein rate will decrease, and the milk will become thinner. In order to increase the energy of the diet, high-quality roughage should be fed while increasing the concentrate feed.
(3) Fully guaranteeing the quality of roughage The practice has proved that high-quality alfalfa hay can improve the milk yield from 800 to 1200 kg/year, and the quality of roughage can increase the milk fat percentage by 0.1 to 0.2% and the milk protein rate by 0.03 to 0.06%. Increase 0.02-0.04%, non-fat solids increase 0.05-0.09%. Low-quality roughages prevent high-yielding dairy cows from exerting high-yielding potential, deteriorate their physical quality, and reduce the quality of their milk, failing to meet the requirements for dairy processing, and directly reducing economic returns. For roughage with poor quality, physical, chemical, and microbial treatments can be used to improve its nutritional value, improve the quality of roughage, increase dry matter intake of dairy cows, optimize the rumen environment of dairy cows, and improve digestion and metabolism of nutrients in the body. To achieve the best use of roughage for dairy cows, and ultimately to reduce production costs and improve the quality of milk and cattle breeding benefits.
(D) attention to strengthen the cow's heatstroke cooling measures The optimum production temperature for dairy cows is 10-16 °C, and has the characteristics of cold and heat, especially Holstein cattle heat resistance is even worse. To this end, summer should pay attention to doing a good job:
1. Adjust rations and strengthen management. Improve dietary energy concentration and promote dairy cows to increase feed intake. Appropriately increase the amount of grain fed, add calcium fatty acid, and increase the palatability of succulent green feed, tubers, melons and so on. Add a feeding at night or early morning when the climate is cool. Strengthen drinking water to reduce the number of cows in order to facilitate heat dissipation. Change the concentrate powder into granules to improve the digestion and absorption of the concentrate.
2. Increase ventilation and spray cooling.
3. Greening environment. Around the barn, the playground must be greened.
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