Dairy Cows Do Not Have a Crude Protein Requirement
Aug 28, 2014
Focus your attention on metabolizable protein for more accurate results and improved nitrogen utilization.
By Dr. Elliot Block, Research Fellow, Arm & Hammer Animal Nutrition
Dairy cow feedstuffs contain many different proteins at various levels and quality. For years crude protein content was used for formulating dairy diets as one way to overcome this variability.
But crude protein has no relation to what is supplied to the animal that is useful for productive functions. Crude protein values only measure the nitrogen content of a feedstuff, which is the building block of proteins. It does not indicate if the nitrogen is an amino acid, non-protein nitrogen, the bioavailability or degradability of the nitrogen in the rumen, how much of the nitrogen escapes the rumen or if it is bound-nitrogen.1
In short, there is no dietary requirement for crude protein, yet this value still plays a significant role in dairy ration ingredient use and purchase decisions.
Crude protein is worth monitoring for a number of reasons, but it should no longer be the target value for ration balancing.
It is what’s in the protein and its impact on the cow, rumen and/or bacterial output performance that really matters.
A combination of rumen bypass protein, endogenous protein and bacterial protein reaches the intestine and is available for absorption. This is metabolizable protein—it is what the animal needs, and should be the protein basis used to formulate rations.
Metabolizable protein supplies the amino acids the cows need for growth, to maintain body condition, produce milk and support fetal growth. Metabolizable protein is defined as the true protein that is digested postruminally, along with its amino acid components that are absorbed by the small intestine. Absorbed amino acids are used for the synthesis of proteins, which are essential for an animal’s growth, reproduction and milk production.
The Dairy National Research Council (2001) has suggested moving to a metabolizable protein system to better define and refine protein formulation and utilization, says Dr. Larry Chase, extension dairy nutrition specialist at Cornell University. "This system fits with the biology of the cow," he adds.
Stop Overfeeding Protein
Of utmost concern to dairy producers should be that when they base diets on crude protein, they are likely over- or underfeeding protein to cows. Either way, cows do not receive what they need.
For example, a ration may meet a cow’s metabolizable protein needs at varying crude protein levels—you can meet needs at 15% crude protein and/or 18% crude protein depending on the ration and feedstuffs included.
Plus overfeeding protein results in cows excreting excessive nitrogen. This has environmental impacts for dairies in regard to the release of nitrogen and ammonia emissions—both of which are under increasing scrutiny.
Furthermore, when buying feedstuffs based on crude protein, producers are not being efficient with their feed dollars, as shown by the chart below.
As you can see, rations with similar crude protein levels can deliver vastly different metabolizable protein levels. Note that the values shown here are based on the increase in metabolizable protein predicted in CPM Dairy (v5.0) by adding one pound of each supplement to a high-producing cow’s diet. Furthermore, it was assumed that the price per ton of soybean meal, FERMENTEN™, blood meal and canola were $500, $650, $1,000 and $375, respectively.
What’s Stopping You?
Balancing rations based on metabolizable protein is increasing in the dairy industry, but not everyone is doing so yet.
The challenge is that this system is not as simple as it is with crude protein, and requires the use of ration balancing programs to calculate both metabolizable protein requirements and the metabolizable protein supplied by feeds and microbial protein synthesized in the rumen, explains Chase. Still, he says, the industry is changing to a metabolizable protein approach.
Successful implementation will require working more closely with nutritionists and other nutritional partners to determine the metabolizable protein value of feedstuffs under consideration for ration inclusion. It also means working with these partners during purchase decisions to help producers make the most economical decisions when determining which feed ingredients to buy.
Don’t let this change in this relationship throw you. "This system should provide an opportunity to improve the efficiency of protein use in dairy cattle," Chase concludes. That improvement can have long-lasting impacts on your dairy’s productivity and profitability.
1 Varga G. Why Use Metabolizable Protein for Ration Balancing. eXtension.org. Available at: http://www.extension.org/pages/26135/why-use-metabolizable-protein-for-ration-balancing#.UqDduZWA1dg. Accessed November 17, 2013.