The Models Used to Formulate AA Balanced Rations

Basic knowledge of amino acid (AA) nutrition for lactating cows has significantly advanced in the last 50 years. However, only recently has that wisdom been harnessed into models that can be used on a day to day basis.

In the U.S., the three basic models currently used are NRC 2001, CNCPS and CPM. Over time, they have all evolved and changed to include improved equations that predict the cow’s responses with better accuracy. In 2001, NRC published its latest version, the last version of CPM (v.3) was released in 2003, and CNCPS released its latest version (v.6) in 2007. Each model has its own set of equations (i.e. “biology”) to predict the amino acid profile of the metabolizable protein (MP).

Each model also has its own methodology to evaluate the nutritional "quality" of the feed’s proteins. These differences have a direct impact on the predicted grams of MP and individual AAs the cow has available to fulfill her requirements.

The protein of any feed is partitioned into fractions A, B or C in the NRC model, or into fractions A, B1, B2, B3 and C in the CPM and CNCPS models:


Besides some differences in how these fractions are defined in each model, CPM and CNCPS have different degradation rates (Kd) for each fraction. In general, the Kds for the B1 and B2 fractions are lower for CNCPS v.6 versus CPM v.3. Hence, each model will provide a different prediction of MP supply and the AA profile of the MP.

In the next Technical mail we will discuss the impact of these differences and how we interpret each model’s output to optimize the AA utilization for maximal milk output.

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

Is MetaSmart® better than Smartamine® M?

MetaSmart and Smartamine M are often compared to one another because they both supply methionine to the cow, but it is important to note that they are different products. MetaSmart is the isopropyl ester of HMB (methionine analog) and Smartamine M is based on a coated, true dl-methionine. The mode of action of the two products differs:

A) MetaSmart benefits rumen function and provides metabolizable methionine to the cow.
B) Smartamine M is solely a source of metabolizable methionine to the cow.

A trial with 70 cows was conducted at the University of Wisconsin with several objectives in mind. One of them was to compare (head-to-head) the impact each product would have on milk production and composition when fed to high-producing cows.¹

The cows were fed the same diet and either MetaSmart or Smartamine M was added to provide the estimated grams of required metabolizable methionine to maximize milk production and composition according to the NRC. This meant that 40 grams of dry MetaSmart or 15 grams of Smartamine M were added such that:

A) MetaSmart delivered 9 grams of HMB for ruminal use and 9 grams of HMB as a metabolizable methionine source to the cow.
B) Smartamine M delivered 9 grams of metabolizable methionine to the cow.

The cows fed MetaSmart produced 0.9 lbs. extra milk with .16% extra fat and .04% extra protein. To facilitate interpretation of those results, we recommend integrating these changes into a single number by calculating the Energy Corrected Milk (ECM). The cows fed MetaSmart produced 1.8 extra lbs of ECM; furthermore, they had lower Milk Urea Nitrogen than the cows fed Smartamine M.

a,b: Values with a different superscript are statistically different (P < 0.05)

The results from this research show that MetaSmart is just as good as Smartamine M as a metabolizable methionine source with the added benefit of improving rumen function.

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