Can Amino Acid Balancing of Dairy Rations Improve N-Utilization?

Feeding strategies to improve the utilization of the nitrogen (N) in a diet are important to reduce N excretion to the environment. Amino acid (AA) balancing presents the opportunity to do so, without negatively impacting milk performance. By concentrating the levels of the limiting amino acids methionine and lysine in the diet, less metabolizable protein (MP) and crude protein (CP) needs to be fed. This creates space in the ration to incorporate other beneficial feed ingredients:

A) Keep feed costs down by feeding less of expensive protein sources.
B) Enhance production by feeding more fermentable carbohydrate.

A trial with 70 cows was conducted at the University of Wisconsin with several objectives in mind; one of them was to improve the N efficiency by feeding an AA balanced ration. All cows were fed a diet containing 60% forage on a dry matter basis (58% corn silage - 42% alfalfa silage); the diet of one group of 15 cows was supplemented with ground shelled corn, high moisture shell corn, soybean meal, dried molasses, Energy Booster, a pre-mix with minerals and vitamins and 40 grams of dry MetaSmart®. Another group of 15 cows was fed a higher protein ration where corn distillers and Soyplus was also included in the formulation. The diet with MetaSmart was formulated according to NRC guidelines to provide:

A) A lower supply of MP (2450 grams vs. 2590 grams), reducing the CP concentration (15.7% vs. 16.8%) of the ration.
B) A higher NFC concentration (47.0% vs. 43.6%).

The cows fed MetaSmart produced 2 lbs extra milk with .08% extra fat and .14% extra protein, an increase of 3.5 extra lbs in Energy Corrected Milk (ECM). In addition, the cows fed MetaSmart had lower MUN, PUN and higher N efficiency.

a,b: Values with different superscript in the column are different (P < 0.05)

The results from this research show that by AA balancing rations using MetaSmart, MP supply can be reduced, improving N efficiency and still enhance ECM production.

¹Effect of feeding different sources of rumen-protected methionine on milk production and N-utilization in lactating dairy cows Chen et al., 2011 - J. Dairy Sci. 94:1978–1988