Q&A with Jim Linn

May 3, 2010 06:00 AM

Editor's note: Jim Linn is an Extension dairy nutrition specialist and chairman of the Department of Animal Science at the University of Minnesota. He also authors Dairy Today's Nutrition column.

At what level of milk production does balancing amino acids become important?

Linn: In theory, it pays at any level of production because we can decrease the amount of total crude protein in the diet, increasing the efficiency of nitrogen usage. However, I would think in most herds the early-lactation and high-production groups will benefit most from amino acid balancing. If you needed a number, I would say 75 lb. of 3.8% milk or higher.

Where do you see the biggest benefit?

Linn: When herds are one-dimensional protein supplement feeding. In herds where there are several protein sources being fed, amino acid balancing is probably occurring by default and the response to amino acid balancing will be limited.

Best opportunities are when the protein content of the diet is high and amino acid balancing can reduce it or when the protein content of the diet is already low and the right amino acid balance can increase milk production and components. Herds that are balanced close to NRC requirements for protein and have a couple of different protein sources are probably the least likely to see a benefit.

In the rations you typically work with, do you feel lysine or methionine is first limiting?

Linn: In herds with a lot of byproducts in the diet, particularly corn-based, lysine is usually first limiting. In haylage, corn silage, corn grain and soybean meal herds, methionine is probably the most limiting. If rumen fermentation can be optimized, methionine will be the first limiting in most cases.

If early and first-lactation diets are the most critical, when do you start adding amino acids to the ration? Close-up? Post-fresh?

Linn: I would say post-fresh. We need a lot more research on balancing amino acids on dry cows and close-up cows before we recommend amino acid additions to these groups.

How do you know amino acid-balanced rations are working? More milk? More milk protein? Better repro?

Linn: Better milk components -- both fat and protein. High milk production usually follows.

At what point in the lactation do you take amino acids out, assuming you have multiple groups?

Linn: See the first answer, but I would say anytime after 250 days is OK to remove. With high-quality forages and good feed management, we should have good rumen fermentation and enough microbial protein produced to support good milk components and production to 75 lb. of milk.

Any thoughts on cost/benefit?

Linn: I haven't figured this out, but the best return will be when milk protein yield is increased. Milk yield and milk fat yield are important, but the dollar return on milk protein yield places it at the top. We probably need close to a 0.2% increase in milk protein at 75 lb. to 80 lb. of milk to break even, but this is a very quick swag estimate.

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