1. Enhancing Carbohydrate Digestion
75% to 80% of the dry matter and 50% of the crude fiber in the feed are digested in the rumen of dairy cows. There is a symbiotic relationship between rumen microorganisms and host, rumen bacteria and ciliates. It is this symbiotic relationship that determines the ability of rumen microorganisms to digest large amounts of crude fiber feed. Volatile fatty acids (VFA), including acetic acid, propionic acid, and butyric acid, are produced by rumen fermentation of carbohydrates in feed, which is the largest energy source for ruminants.
Normally, acetic acid, propionic acid, and butyric acid account for 50%-65%, 18%-25%, and 12%-20% respectively. The ratio of VFA to VFA was affected by the ratio of concentrate to roughage and the form of roughage. When the proportion of roughage decreased or the roughage was too fine, propionic acid increased and acetic acid decreased. If the proportion of acetic acid drops below 50%, the fat content in milk decreases and body fat deposition increases, which is beneficial to feeder cattle. Because the glucose in ruminants can not participate in the molecule of milk fatty acid, it is harmful to dairy cows. Besides, the fermentable degree of carbohydrates, the length of the residence time of feed in the rumen and the amount of saliva secretion all affect the fermentation mode.
The concentrate of dairy cattle should not be too much and the roughage should not be processed too fine, but this does not mean that the longer the concentrate or roughage is, the better. It is reported that dairy cows fed with diets with high crude feed content can only get a lower yield. Because the digestible energy consumed is too little and the energy loss is large. If milk production is to reach 6000 kg to 7000 kg, more concentrate must be supplied to dairy cows, which accounts for at least 40% of the total nutritional value. The increase of concentrate and the decrease of roughage will lead to the decrease of the PH value of rumen contents, the change of normal rumen microflora, the increase of propionic acid ratio, the decrease of milk fat rate, and the decrease of PH value will easily cause a gastric ulcer, and sometimes even acidosis.
To adapt dairy cows to diets with high concentrate level and obtain high milk yield, and to avoid adverse consequences, the solution is to control rumen fermentation. For example, buffer compounds, sodium bicarbonate, and magnesium oxide were added to the diet to maintain the appropriate PH value of rumen contents and the appropriate proportion of volatile fatty acids.
2.Promoting Protein Digestion
Feed proteins can be divided into two categories according to their metabolism in the rumen, they are degradable proteins and non-degradable proteins. The former is decomposed into ammonia, which can be synthesized by rumen bacteria. The latter does not change. The proteins cross the rumen directly to the abomasum and small intestine are called undegradable protein. According to the size of rumen transit value, it can be divided into three categories: raw materials with low rumen transit value (less than 40%) such as soybean meal and peanut meal; raw materials with medium rumen transit value (40%-60%) such as cotton meal, alfalfa meal and corn; raw materials with high rumen transit value (more than 60%) such as fish meal, blood meal, meat meal and feather meal. There are both protein decomposition and protein synthesis in the rumen.
Protein fermentation in rumen is conducive to the conversion of poor quality proteins into bacterial proteins with high biological value, as well as the conversion of non-protein nitrogen such as urea into bacterial proteins. However, it is not conducive to the loss of feed protein, especially high-quality protein, by microbial decomposition to form a large amount of ammonia in the rumen. After calculating the utilization rate of rumen protein by 85%, the utilization rate of rumen protein is only about 50% by converting into bacterial protein and then absorbed by the intestine. Therefore, it is necessary to reduce the degradation of high-quality protein and synthetic amino acid in the rumen.
The purpose of stomach fermentation control is to reduce nutrient loss during fermentation. By changing fermentation types, diseases can be prevented and milk production and quality can be improved. Appropriate measures should be taken to direct nutrients, especially protein and starch, into the abomasum and small intestine through the rumen. Commonly used chemicals are ionic carriers, such as rumen hormone, which can increase the production of propionic acid, decrease the production of acetic acid and butyric acid, and reduce the degradation rate of feed protein. Halogenated compounds, such as polyhalogenated alcohols and polyhalogenated aldehydes, inhibit the production of methane in the rumen and reduce energy loss. Buffers, such as sodium bicarbonate and magnesium oxide, regulate acid-base balance and osmotic pressure stability in the rumen.
3.Improving the Digestibility of Roughage
Physical or chemical treatment, such as chopping, ammoniation or alkalization. Increasing nitrogen nutrition and adding NPN, such as urea and biuret, can increase the digestibility of cellulose, fermentable carbohydrates and control the content of fat when the crude protein content of the diet is low. Excess fat inhibits the digestion of cellulose in rumen. Adding inorganic salts can satisfy the nutrition of bacterial inorganic salts while maintaining the stability of rumen PH value, osmotic pressure, and dilution rate. The high proportion of concentrate (over 60%) affects the digestion of cellulose.