Sweat the small stuff with your dairy cow ration

By Dr. Silvia Onetti

However, those fine details can be immensely important, especially in high-producing dairy cow ration balancing.  Nutritionists no longer solely account for crude protein and net energy content of the ration.  They now focus more on the small (but very important) stuff within those categories, like amino acid balancing and specific, individual sources of energy.

Amino acid balancing
The focus of protein nutrition has shifted from balancing for crude protein (CP) to amino acids (AA).  Why?  Dairy cows do not have CP dietary requirements, but they do have AA requirements.  Amino acids are the building blocks of proteins and providing the herd with essential AAs maximizes protein utilization and lowers the amount of CP fed.  This translates into increased milk protein content and milk yield and less nitrogen waste in the environment. Additionally, research studies have shown successful AA balancing has several health and reproductive benefits.

Nutritionists also focus on providing sufficient levels of rumen degradable protein (RDP) and fermentable carbohydrates to maximize microbial protein synthesis. This, along with sufficient levels of rumen undegradable protein (RUP) – including bypass methionine and lysine sources – help optimize metabolizable protein (MP) supply.  Microbial protein and RUP account for the majority of the MP supply to the small intestine, and concentrations of lysine and methionine in MP will have a great impact on milk protein content and milk yield.

Energy concentrations
Typically, the energy content of feeds for dairy cows is determined at three times intake over maintenance, or NEl-3X.  Although this gives a good approximation, the focus on energy has shifted to evaluating the characteristics and intake of the major energy contributors, primarily neutral detergent fiber (NDF), starch, and fat.

Undigestible NDF and NDF degradation rates are used in ration formulation to predict the impact of NDF degradation on dry matter intake and milk production of cows.  Another critical component is the amount of physically effective fiber (peNDF) included in the ration to promote rumen function and health.

Although cows do not have a dietary requirement for starch, it is energy dense and highly digestible, which makes starch a key nutrient to maximizing milk production.  Some factors that can affect its digestibility are the type of endosperm, particle size, kernel processing, storage method and moisture content.  Nutritionists will often look at the types of protein in corn silage and high moisture corn to predict ruminal starch digestibility.

When fat is included in a lactating ration, the nutritionist should focus on the composition of the fat, especially the unsaturated fatty acid (FA) content because it can have profound effects on rumen fermentation, production responses, and milkfat synthesis. One tool adopted in ration formulation to determine how much fat can be fed to lactating cows is rumen unsaturated fatty acid load (RUFAL).  This is the sum of the main unsaturated free FAs – oleic (C18:1), linoleic (C18:2) and linolenic (C18:3) – in the ration. Forages and grains may account for the majority of the RUFAL intake, so don’t overlook them.

Don’t forget the cow
It’s important to focus on the fine details of high-producing dairy cow nutrition, but don’t forget the cows ultimately decide if the ration is correct for them.  Every piece of your ration could be precisely formulated, but if it’s not mixed and delivered properly, and the cows sort through it and don’t eat it, it won’t matter.  So sweat the small (but very important) stuff when it comes to your dairy ration, but do the same with cow comfort and management to optimize production with your nutrition program.

An extended version of this article was written for the October 1, 2016 edition of Progressive Dairyman. Click here to read that article.

About the author:  Dr. Silvia Onetti grew up in Cordoba, Argentina where she earned her bachelor’s degree in agriculture from the Universidad Nacional de Cordoba, Argentina.  After graduation, she worked at the National Institute of Agricultural Research in Argentina as a research assistant in dairy nutrition.  She received a Fulbright Scholarship, which influenced her decision to pursue her Ph.D. in dairy science at the University of Wisconsin-Madison.  Before being named Vita Plus director of nutrition, Onetti served as a member of the Vita Plus dairy nutrition and technical services team.  Currently, she is a member of the American Dairy Science Association and is active in the American Feed Industry Association.