Over recent decades, genetic improvement and better management practices have dramatically increased dairy cattle milk production but, at the same time, managing fertility and conception rates has been difficult. Managing optimum productivity of dairy cattle in terms of quality milk production and efficient breeding plays a vital role in profitable dairy farming. Nutrition is one of the most important factors in their performance, health and welfare.
Many nutrients are utilised by the body for milk production, and increased nutrient demands for production can negatively impact reproduction in dairy cows.
High-yielding cows require special nutritional care, especially during periods of production stress. Modern, high-yielding animals are either in lactation or in advanced pregnancy, posing a regular metabolic stress to the body.
Meeting the nutritional needs of the high-yielding cow for optimum production and reproduction is a challenge for modern dairy producers. An adequately nourished cow will be healthy and capable of managing the stresses associated with high milk production.
Energy and protein feed ingredients, in addition to many trace elements and vitamins, play important roles in milk production and reproduction. It is not only the quantities of energy and protein source, but also their quality that plays a vital role for optimum production and reproduction.
Energy: additional supplementation a must for high-yielding cow
In lactating dairy cattle, milk yield usually peaks at four to eight weeks postpartum, but dry matter intake does not increase proportionately to meet energy requirements until 10-14 weeks postpartum. Consequently, high-yielding cows experience some degree of negative energy balance during the early postpartum period. High-yielding cows have a gap between energy supply and demand. To fulfil the higher energy need for milk production, animals utilize body reserves resulting in impaired health and frequent metabolic disorders.
Energy is the major nutrient required by adult cattle; and inadequate energy intake has a detrimental impact on milk yield and reproduction. Cows under negative energy balance have extended periods of anovulation. Postpartum anestrus, as well as infertility, is magnified by losses of body condition during the early postpartum period.
Strategy to increase energy intake
The extent and duration of postpartum negative energy balance is influenced by genetic potentiality for milk production, dietary energy density and dry matter intake. Nutritional management strategies can be employed to minimize the extent and duration of negative energy balance.
In view of the fact that dry matter intake during the early lactation period goes down, increasing energy density of the ration is the only available option to improve energy intake, which can be achieved through supplementation of grains or fat.
Diets containing high levels of grain may cause metabolic disturbances, such as rumen acidosis, and may ultimately result in low milk and milk fat production.
To avoid these problems, fat can be added to increase the energy density of the diet. Fat supplementation also has other potential benefits, such as increased absorption of fat-soluble nutrients and reduced dustiness of feed. In addition, feeding fat to dairy cows generally improves fertility.
Dietary supplementation with fat
Vegetable oils as such are not recommended for ruminants because the unsaturated fatty acids are toxic to rumen bacteria, especially to fibre degrading bacteria. Unsaturated fat supplementation reduces fibre 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 bypass 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.
Rumen-stable and rumen-protected fats
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, low pH values in feed and in 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, utilised by the body as an efficient source of energy.
Protein nutrients: essential for growth, maintenance and production
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.
Bypass protein: The best way to increase milk 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 rumen 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 feed. Rumen undegraded protein is assumed to be 100% true protein.
Chromium : Essential for energy metabolism
During the phase of negative energy balance, efficient utilization of energy results in higher productivity and better health. Chromium is an essential element that is required for the efficient utilisation of dietary energy. Glucose, produced from carbohydrates, is one of the major sources of energy. Insulin takes major part in the glucose metabolism. Chromium acts biologically as a component of glucose tolerance factor, which enhances tissue sensitivity to insulin and glucose utilization.
The transition period from 21 days prepartum to approximately 21 days postpartum is a critical period in regard to health and subsequent milk production of high-producing dairy cows. Supplementing high-producing dairy cows with chromium during the transition period can increase feed intake and milk production during early lactation. Chromium supplementation can also improve reproductive performance, cell-mediated and humoral-immune responses. Chromium helps reduce the effect of physiological stress.
Inorganic forms of chromium are very poorly absorbed. Chromium chelated with organic compounds greatly increases its absorption. Chromium nicotinate and chromium picolinate are usually considered the most available sources of supplemental chromium.
An unhealthy transition period, and subsequently negative energy balance during the early lactation period, not only reduces profit through reduced milk production, but often leads to metabolic disorders and impaired reproduction. Supplementing dairy cows, especially during the early lactation period, with rumen-stable fat, bypass protein and chelated chromium can reduce the extent and duration of the negative energy balance, and it can improve health, milk production, milk quality and reproduction performance.