The dairy industry in general has become increasingly precise in identifying and meeting the protein requirements of dairy cows. Most notable part being focusing on the diet's content of crude protein to metabolised protein and now to amino acids.
The challenge remains for nutritionist - understanding the current concepts in protein and amino acid nutrition and converting them into more cost efficient filled bulk tanks for the clients.
Crude Protein
In the olden days, optimal protein requirements were determined through dose-response measurements.
Performance was measured for groups of cows fed a single diet.
The only variation was the level of supplemental protein fed.
Milk production level was observed for a while. If it increased, the diet with lower protein concentration was considered insufficient.
On the other hand, if the removal of protein from diet failed to reduce performance of the cows, the supply of protein was too much.
Different mathematical and statistic model were used to determine the protein requirement.
The 2001 NRC for example, estimated that 23% dietary crude protein was required for optimal milk production.
Today, nutritionist know that these levels are too high and any excess crude protein consumed by the cows will be excreted via urine.
The major weakness of formulating diets on a crude protein basis is that it does not take into account the type of crude protein consumed.
Metabolised Protein
Burroughs metabolisable protein system recognizes that not all crude protein in the ration is available for absorption as amino acids.
The amount of dietary nitrogen solubilised in the rumen and available for microbial protein synthesis was characterised as such.
With the Burroughs system, calculations include the amount of total digestible nutrients available to support microbial growth.
In order to determine this, the calculated microbial protein was added to the amount of dietary protein that escaped ruminal degradation.
The calculation will require 3 things:
Amount of protein in feeds converted to ammonia in the rumen.
Amount of feed protein that escaped ruminal breakdown.
Total digestible nutrient value for the feeds.
Burroughs system also introduced many new terms which are crucial to describe the protein requirements of the cows:
Rumen degradable protein (RDP) - the feed protein degraded in the rumen by the ruminal microbial population.
Rumen undegraded protein (RUP) - the feed protein that remains undegraded in the rumen and it passes to the small intestine for digestion as well as absorption.
Metabolised protein (MP) - the total sum of absorbable amino acids provided from ruminal microbial protein and the RUP digested in the small intestine.
The metabolisable protein model will allow farmers to accurately meet the animal requirements.
One way is by fractionating crude protein into RDP and RUP and formulating to meet the MP requirements of the animal.
There is the potential to lower the total amount of crude protein fed without decreasing milk production.
With that being said, the goal is not to lower ration crude protein but instead it is to meet the MP requirements of the animal while lowering the feed cost.
Amino Acids
Of the nitrogen fed to the cows, only about 21 - 38% is actually exported as milk or meat. The rest of it is excreted in urine and feces.
We are able to increase the efficiency of nitrogen utilisation by amino acid balancing.
Amino acid balancing provides more opportunity for the dairy to profit.
Ideally, each amino acid's supply and requirements would be identical matches.
However, the amino acid composition of milk protein differs from the amino acid composition of feed ingredient protein.
Due to this mismatch, it often results in deficiencies of amino acids in dairy rations which causes lost in production and profit.
When amino acids are supplied below the cow's minimum requirements, milk production is decreased.
The 2 amino aids which are typically first limiting are methionine and lysine.
It is crucial that these 2 amino acids make up a certain portion of the dietary protein content.
Without them, the dairy cows simply would not be in peak condition.
Nutritionist today also use amino acid balancing to help improve milk components and milk production levels, while at the same time protein utilisation and lessen the dairy's environmental impact.