Vegetable oils as such are not recommended for ruminants because the unsaturated fatty acids are toxic to rumen bacteria, especially to fiber-degrading bacteria. Unsaturated fat supplementation reduces fiber digestion, thereby defeating the major objective of increasing the availability of energy.
Therefore, the supplementation of fat for dairy cows is achieved by means of bypassing fats, which pass the rumen without any degradation. Rumen bypass fats can be either rumen-protected or rumen-stable fats.
These are inert in the rumen and are digested in the lower GI tract, hence they are not harmful to rumen bacteria.
The protected fats are mostly either calcium salts of long-chain fatty acids or saturated fats. Protection does not mean stability; usually, protection depends on the conditions of the rumen and its pH. Rumen-protected calcium-soap or calcium salts of long-chain fatty acids were developed to improve milk production. Being a chemical reaction product, they have many disadvantages.
Because of the pungent soap taste, there is usually poor acceptance of the feed. A further disadvantage is that larger amounts of feed concentrate, and low pH values in feed and the rumen, impair the stability of calcium soaps resulting in the release of the unsaturated fatty acids. These unsaturated fatty acids may negatively influence milk fat formation and may also disturb ruminal digestion, as described earlier.
A recent development in fat supplementation for dairy cows is rumen-stable fats, which are fractionated triglycerides, rich in saturated fatty acids, mainly palmitic acid. Rumen-stable fats are stable at various pH conditions. Their fatty acids are largely saturated so that they pass through the rumen almost unchanged. As a result, the fats reach the small intestine where they are broken down by enzymes and, subsequently, utilized by the body as an efficient source of energy.
Dairy cattle, like other animals, require essential amino acids that must be absorbed from the small intestine. Ruminants obtain amino acids from two sources – microbial proteins and bypass protein, or rumen undegraded protein.
Microbial protein: Microorganisms, especially bacteria, in the rumen assist in providing the total protein and individual amino acid requirements of ruminants. Rumen microorganisms are able to synthesize protein and amino acids from non-protein nitrogen compounds, such as urea and ammonia. The microorganisms in the rumen synthesize amino acids by combining ammonia and carbohydrates. These amino acids become part of the microbial protein. This microbial protein is then digested in the small intestine.
When the digestible energy content of the ration is high enough, one third or more of the total protein needs of many ruminant rations may be supplied by nitrogen from non-protein nitrogen sources. Growing and finishing cattle can effectively use non-protein nitrogen. Microbial protein production depends on the rumen conditions.
Microbial protein synthesis in the rumen depends largely on the availability of carbohydrates and nitrogen in the rumen. Rumen bacteria generally have the ability to utilise majority of ammonia that is released in the rumen from deamination of amino acids and the hydrolysis of non-protein nitrogen compounds. However, dietary conditions often occur in which the rate of ammonia release in the rumen exceeds the rate of uptake by ruminal bacteria. The condition may occur because of a surplus of rumen degraded protein or a lack of available energy, resulting in inefficient utilization of fermentable substrates and reduced synthesis of microbial protein.
High-yielding cows, however, have a much higher requirement of amino acids that cannot be fulfilled by rumen microbes, even at high rates of synthesis. The diet of such cows should include proteins of relatively low degradability in the rumen that will escape breakdown until they reach the intestine. This escape protein is known as bypass protein or rumen undegraded protein, which is digested in the intestine, and the amino acids are used for the synthesis of tissue and milk protein.
Diets for dairy cows should contain both rumina-degraded protein and rumen undegraded protein, at an ideal ratio of 65:35. Usually, reliance on feed proteins with a high content of digestible RUP is greatest in high-producing cows when most or all of the forage is provided by high-quality grasses and legumes. In these situations, the basal diet often contains adequate or more amounts of RDP but is deficient in RUP. Thus, protein supplementation should be limited to RUP to avoid excesses of RDP. Milk protein yield can be increased linearly by increasing RUP content in the feed. Rumen undegraded protein is assumed to be 100% true protein.