Dairy: Not All Protein Sources Are Created Equal

In order to reach maximum milk production potential, cows need not only a sufficient amount of protein but a protein that provides the proper amino acid balance.  Amino acids are the building blocks of protein, and the quality of a protein is determined by its balance in term of essential amino acids.  Not all protein sources are created equal. 

A cow’s protein and amino acid requirements can be met by a protein source with an amino acid composition that closely matches the composition of what the cow is producing, such as milk protein and muscle.  By focusing on the amino acid composition of the protein supply to the cow, we can efficiently meet the cow’s protein requirements without overfeeding protein while meeting the correct amino acid balance.

Ruminants derive protein from two sources: microbial protein synthesized in the rumen and escape protein provided in feedstuffs.  Microbial protein provides 50 - 60 percent of the protein supply to the typical dairy cow.  Bacteria and protozoa in the rumen ferment carbohydrates and protein supplied from the ration into more bacteria and protozoa that will provide protein to the cow.  Microbial protein is a very high quality protein in that the amino acid composition matches that of milk protein. 

For high producing dairy cows, microbial protein alone will not provide a sufficient protein supply.  A feed source of protein is required to meet a high-producing cow’s protein requirements.  This protein must escape degradation in the rumen and will directly provide protein to the cow.  The amino acid profile of escape protein sources is critical to how well that protein can positively affect milk production and efficiency.

A study conducted at South Dakota State University by Dr. Javier Sabbia et al. (2012)¹ demonstrated the importance of proper protein nutrition as well as the application of a product designed to meet the cow’s requirements for amino acids.  YMP (DEMP^®, a yeast-derived microbial protein produced by Alltech, Inc.) is a source of high quality protein with an amino acid prodile that closely matches that of reference protein sources such as milk protein and microbial protein. The product is partially digested by the microbes in the rumen and supplies essential peptides (small proteins) and free amino acids that may maximize microbial protein synthesis.  In addition, the portion of YMP that escapes the rumen supplies the cow with a high quality protein directly from feed.  Research showed that YMP supports the protein supply to the cow by increasing microbial protein production and by supplying a feed source of high quality amino acids.

To examine the implications of a protein source on lactating dairy cows, Sabbia and colleagues replaced varying portions of soybean meal with YMP.  Plant proteins such as soybean and canola meal and distillers grains comprise most of the protein fed to ruminants in the United States.  By replacing equal amounts of soybean meal with YMP at 0, 300, 600, and 900 grams per cow per day, the researchers were able to compare how well YMP versus soybean meal met the amino acid requirements for a lactating cow. 

The cows were fed a typical Midwestern lactating TMR primarily composed of corn silage, alfalfa hay, ground corn and soybean meal.  The researchers found that milk production increased by replacing a portion of soybean meal with YMP at varying rates.  The rations containing 300 and 600 grams of YMP resulted in the most milk, 92 pounds compared to 87 pounds for the control (standardized to 4 percent fat and 3.2 percent protein).  Milk fat content increased by 0.09 to 0.13 percent with the inclusion of YMP. 

In addition to measuring performance parameters, the researchers at SDSU took measurements to determine the effect of treatment on rumen function, using both ruminally canulated cows as well as an in vitro procedure in the lab.  Rations including YMP resulted in lower rumen ammonia and branched-chain VFA concentrations.  Both of these parameters indicate protein degradation in the rumen; lower values for the YMP ration indicate degradation of feed protein was lower.

Together these variables indicate that YMP is less degradable in the rumen than soybean meal and will provide more high quality escape protein from feed to the cow.  Using an in vitro procedure developed to simulate rumen fermentation in the lab, researchers observed that true dry matter digestibility increased by 1.4 to 2.7 percentage units when YMP replaced soybean meal.  This observation supports the second hypothesis on YMP’s method of action: improving rumen efficiency thereby improving feed digestion and microbial protein flow. 

Improving protein supply to the cow by increasing the flow of high quality microbial protein from the rumen and providing a feed source of high quality protein can allow for increased milk production, as observed in the high producing cows used in the South Dakota State study.  The benefits of replacing common sources of plant protein with a high quality protein include increased milk production, higher efficiency of protein utilization, and the potential to feed lower protein rations. 

¹Sabbia, J.A., K.F. Kalscheur, A.D. Garcia, A.M. Gehman, and J.M. Tricarico.  2012.  Soybean meal substitution with a yeast-derived microbial protein source in dairy cow diets.  J. Dairy Sci.  95:5888-5900.

Amanda Gehman¹, Javier Sabbia^2,3, Ken Kalscheur², Alvaro Garcia², and Juan Tricarico⁴

¹Alltech, Inc., Nicholasville, KY

²South Dakota State University, Brookings, SD

³Biotech Uruguay, Montevideo, Uruguay

⁴Innovaton Center for U.S. Dairy, Rosemont, IL

Founded in 1980 by Dr. Pearse Lyons, Alltech improves the health and performance of people, animals and plants through natural nutrition and scientific innovation. With more than 3,000 employees and a presence in 128 countries, the company has developed a strong regional presence in Europe, North America, Latin America, the Middle East, Africa and Asia. For further information, visit www.alltech.com. For media assets, visit www.alltech.com/news.