Introduction
Protein forms the costly and critical component of the ration in cattle feeding.Considering this fact dairy farmers usually expect more returns from feeding additional protein in the cattle diets. But the question here is that is this additional protein used by the animal or is it excreted in the feaces.
Providing the dairy cows with essential amino acids are more important than satisfying the crude protein requirement. Crude protein is calculated after measuring the nitrogen content of a food, because amino acids are the building blocks used to make protein and it contains nitrogen. Looking at the total nitrogen content of the feed gives some insight about its protein content. As all of the nitrogen in the feed is not found in protein form. True protein is the actual protein after removing the non-protein nitrogen content in the feed and protein.
The efficiency of dairy cows to utilize nitrogen is low and most of the nitrogen is either excreted in urine or feces. In order to reduce the nitrogen excretion, scientists are balancing rations for improving the amount of metabolizable protein and also supplying adequate amount of amino acids that play a major role in milk synthesis. Noftsger and St. Pierre (2003), showed a 35% improvement in nitrogen efficiency, when a ration was balanced for methionine and lysine in metabolizable protein content.
Role of essential amino acids in animal
When essential amino acids are supplemented in such a way that they can be made available at the intestinal level, then it helps in the utilization of other amino acids present in feed, for the formation of required proteins by the animals. This clearly suggests that essential amino acids are needed for the effective utilization of other amino acids.
Milk protein production by the cow is limited by the particular amino acid that is in shortest supply in relation to the cow’s requirement for forming amino acid chains. Amino acid requirements can be expressed using either the factorial method or the ideal protein method.So, by balancing the metabolizable protein and supplying the essential amino acids at intestinal level of the cattle, the cost of production as well as loss of nitrogen from feces and urine can be avoided. As a matter of fact, more nitrogen is produced by the inclusion of more amount of crude protein and thus there is an inadequate availability of energy in the rumen which will increase the ruminal ammonia concentration. Unused ruminal ammonia enters into the portal blood system through the rumen wall and is transported to the liver, where it is detoxified by converting to urea. In addition to this, the ammonia which is derived from amino acids from post ruminal digestion is converted to urea in liver. Urea then circulates in the blood through kidneys and excreted in urine or it can enter into saliva through rumen and also into milk in case of lactating animals.
Milk or blood urea nitrogen is an indicator of diet adequacy and nitrogen utilization efficiency in lactating dairy cattle. As a management tool for dairy farmers i.e. monitoring of MUN(Milk Urea Nitrogen), dairy farmers can adjust dietary protein level to better match protein requirement of their cows and potentially increase profitability by reducing feed cost.
High dietary protein (nitrogen) intake resulting in BUN or MUN of greater than 19 to 20 mg/dL has been associated with an altered uterine environment and decreased fertility in lactating dairy cows and heifers (Elrod and Butler, 1993; Elrod et al., 1993; Ferguson et al., 1993; Butler et al., 1996). However, high protein intake and high BUN cannot always be associated with reduced reproductive efficiency (Carroll et al., 1988) and is therefore not a unique symptom. Apart from this, there is an energy cost associated with the conversion of excess ammonia to urea by the liver, which otherwise can be used for other productive purposes by the animal.
Role of limiting amino acids in true protein formation
Essential AA (EAA) refers to those AA that cannot be synthesized in animal tissues, or at least not at rates sufficient to meet requirements for protein synthesis. Therefore, they must be absorbed.
Methionine is considered as the first limiting amino acid in cattle diets. The metabolic requirement of methionine is high in dairy cows, in part because of its role as a methyl donor in transmethylation reactions in the synthesis of milk fat.On the other hand Lysine is considered to be the second limiting amino acid in cattle diets and has an essential role in milk synthesis in cattle.
The addition of rumen protected essential amino acids in the lactating animal diet can help to replace costly sources of protein with cheaper ones.
It has been a myth that the addition of rumen protected amino acids in the diet is expensive. If a dairy nutritionist can cautiously balance the ratio of the essential amino acids and the total amount of metabolizable protein in the diet, then the cost incurred on the feed can be optimized.
Many nutritionists suggest the optimum ratio of lysine and methionine to be 3:1.These ratios are in relation to the amount of metabolizable protein.
The Lysine requirement can be predicted for Lactating animals according to NRC is
RUPLys = Ef (DMIf X Cpf X RUPf X Lysf X 0.01)
where:
RUPLys = amount of Lys supplied by total diet RUP, g
DMIf = intake of DM of each feedstuff contributingRUP, kg
CPf =crude protein content of each feedstuff contributing
RUP, g/100 g DM
RUPf =ruminallyundegraded protein content of
each feedstuff contributing RUP, g/100 gCP
Lysf = lysine content of each feedstuff contributing
RUP, g/100 g CP
Equation to calculate Digestible Lysine in Lactating Animals.
dRUPLys = Ef (DMIf X Cpf X RUPf X RUPdigestibilityf X Lysf X 0.001)
where:
dRUPLys =amount of digestible Lys supplied by total
diet RUP, g
DMIf =intake of DM of each feedstuff contributing
RUP, kg
CPf=crude protein content of each feedstuff contributing
RUP, g/100 g DM
RUPf =ruminallyundegraded protein content of each
feedstuff contributing RUP, g/100 g CP as per NRC 2001.
Following points should be considered to balance these amino acids in the diet:
- one must know the exact requirement of metabolizable protein for an animal based on its body weight and milk production
- lysine and methionine concentrations in the diet must be balanced based on the amount of metabolizable protein needed by the animal. The general thumb rule would be that lysine is 7.2% metabolizable protein and methionine is 2.2% of the metabolizable protein
- If economics of the farm is prohibitive, thenreducing the grams of metabolizable Lys to meet a lower ratio of Lysine to Methionine rather than increasing the level of metabolizable methionine to meet this ratio may result in decreased milk yield and milk protein yield
Encapsulating Lysine or Methionine is not an easy task as it has an irregular shape which makes it difficult to apply a coating around and it is very hygroscopic in nature which makes it more difficult to handle. These challenges make it difficult to develop an efficacious product that can maintain the balance between having a high rumen bypass and high intestinal digestibility, while being able to withstand everyday stresses.
Lately, newer technology is developed to encapsulate products to protect it from rumen degradation. It is a proprietary method, utilizes aspects of controlled, but rapid solidification of the product embedded within a custom designed matrix of fatty acids. It allows for greater product functionality than which can be achieved with simple spray cooling methods.
To know more about technology, please contact at Sriharsha.KV@kemin.com
by Dr Sriharsha KV, Kemin South Asia Pvt Ltd
