Proteins are chains of amino acids and are found in all the cells of the body as structural components (especially muscle) but are also broken down to be used in DNA, enzymes, hormones, the immune response, blood cells etc. They are important building blocks for most of the body and its functions.
When we talk about protein in cattle diets, we usually refer to it as crude protein(CP) (measured as Nitrogen (N) x 6.25) as nitrogen is incorporated into protein and the rumen bugs utilise it to create protein. It is an effective indicator of N availability for dairy cows.
Dairy cows require a variable amount of crude protein but Table 1 can be used as a basic rule of thumb, remembering however that New Zealand pastures range in CP from 9 - 35% depending on the time of year and growing conditions.
There are many factors that will affect these requirements so only use the information in table 1. as a guideline. Things that will affect these levels are:
- Energy status
- Milk production levels
- Metabolisable Energy (ME) levels in the diet
- Amino acid components of the protein
- Ambient temperature
- Exercise levels
More is not always better when you consider supplementing with protein due to the cost involved in feeding higher protein feeds. They are always generally more expensive than the basic energy feeds and it is often the energy that is the production limiting side to the diet. Work undertaken by John Roche (DairyNZ technical series notes 2011) looking at protein supplementation by modelling against different energy level diets, showed that only in certain circumstances where the diet was very low in CP (less than 12%) would cows benefit from protein supplementation. In most of these cases, use of cheap protein supplements such as grass silage or palm kernel extract can be used to overcome these deficits without the need for more expensive protein supplements (i.e. soya bean meal).
Before looking at supplementing with proteins it is well worth considering undertaking pasture analysis to see what it is that you are feeding to your cows. Knowing how much and of what quality is being fed is an important part to understanding what is going to be required. Similarly looking at how we are feeding supplements will have a significant effect on how they are utilised. We need to remember that we are feeding the bugs in the rumen first, they in turn are feeding the cow when it comes to protein in the form of microbial CP. They need energy in the rumen however to make use of the protein that is being delivered with every mouthful of grass.
Using energy supplements correctly, maintaining rumen health whilst acting to substitute for pasture intake, will help to relieve pressure on pastures and hopefully reduce the impacts of the weather conditions on pasture demands and availability. Protein supplements need to be considered in certain circumstances but on pasture based systems the requirement for this may often be limited.