Balancing dairy rations for rumen-protected amino acids is often an exercise in confusion. There are few hard and fast rules. Different ration formulation software programs give varying answers.
Some producers report gains in milk production; others see gains in components, particularly milk protein. Some see an increase in dry matter intake; others see an improvement in feed efficiency. It's enough to drive any rationally thinking producer to just forget about it.
That would be a mistake. With milk prices still in the doldrums and feed prices above the five-year average, improving rations is a win-win, say dairy nutritionists.
The reason? "The cost of feeding methionine and lysine is offset by feeding less rumen-undegraded protein,” says Chuck Schwab, the nation's leading amino acid expert. Schwab, professor emeritus at the University of New Hampshire, now consults with Adisseo.
"When amino acids are supplemented, you almost always make other changes to the diet and balance for rumen-undegraded protein,” he says. Supplementing the amino acids and lowering crude protein, Schwab says, can save up to 25¢/cow.
"Lowering protein in the ration without giving up milk production is especially helpful now,” says Rick Lundquist, a nutritionist who consults with large Southern dairies.
A 25¢/cow increase in income over feed costs yields a $65/cow to $75/cow gain, depending on herd average. On a 500-cow herd, that's an annual gain of $30,000 or more.
The science behind amino acid nutrition is still evolving, but the basics are firmly grounded. "Absorbed amino acids, not protein, are the cow's required nutrients,” Schwab says.
Amino acids are the building blocks for tissue and milk proteins. In dairy cattle, rumen microbes provide the bulk of protein and energy that are needed for maintenance, growth, milk production and reproduction. But in high-producing herds, particularly in early lactation, the rumen bugs simply can't meet all the cow's nutrient needs.
That's where rumen-bypass feeds come in. Typical legume protein sources such as alfalfa and animal byproducts are low in methionine.
"Methionine in milk and bacteria are 2.6% to 2.7% of crude protein; in soybean, blood, feather and meat meals, methionine is only 0.8% to 1.4% of crude protein,” Schwab says.
"Lysine is first limiting when corn and feeds of corn origin such as distillers' grains provide most of the rumen-undegraded protein. Lysine in milk and bacteria are 7.6% and 7.9% of crude protein, respectively, whereas in corn silage, corn, corn distillers' and corn gluten meal, lysine is only 1.7% to 2.8% of crude protein.”
Also, byproduct feeds used as bypass protein supplements are highly variable. In a recent Ohio State University study, blood meal samples ranged from 3.4 grams/lb. of digestible lysine to 42 grams.
Feeding commercially manufactured amino acids is likely more expensive. But they have much tighter quality control and far less variation.
A consensus on which cows will benefit is hard to come by. Some argue that lower-producing herds or groups will benefit if methionine and lysine are limiting.
"We don't see as great a response in later lactation other than milk protein and components,” Schwab says. "But we see an increase in the efficiency of use, so the benefit is there because the amino acid limitations without supplementation are there.”
Mike Hutjens, a University of Illinois Extension dairy nutritionist, says amino acid balancing is especially important above 80 lb. of milk in Holsteins, true milk protein yield of more than 2.4 lb., and herds that are 0.1 percentage point of true protein below breed average (below 3.0% for Holsteins, for example).
"I want a 2:1 benefit-to-cost ratio,” he says. "If I add 10 grams of amino acid at 2¢/gram, I want 40¢ more milk, milk fat and/or milk protein. With milk protein prices down, this makes adding amino acids tighter.”
Another critical component is measuring dry matter intake. "Fifty percent to 60% of the metabolizable protein [amino acids absorbed in the small intestine] is from protein synthesized in the rumen by microbes,” says Bob Patton of Nittany Dairy Nutrition in Mifflinburg, Pa.
"Unless we know how much the cow is eating, we cannot predict how much microbial protein will be produced. And if we do not know how much the greatest supply is, it is impossible to balance amino acids.”
A recent field trial involving a 3,200-cow Midwest herd supplemented with bypass lysine and conducted by Church & Dwight showed a positive response in milk, protein and fat yield.
Supplemented cows responded with 3 lb. more milk, 0.18 lb. more butterfat and 0.8 lb. more protein per day. That resulted in 54¢/cow/day in increased income.
Cost of the Megamine-L, fed at 1⁄3 lb./cow/day, was 23¢. The net income from the exercise was 31¢/cow/day, says Gene Boomer, manager of field technical services for Church & Dwight. Over the course of a year, that's a $75,000 bump in income.
However, such increases can be tough to measure without a control group, Boomer notes (see graph). The supplemented and control groups both showed normal day-to-day variation in milk weights over the three-month trial.
Without an unsupplemented control group, the only detectable difference would be a response to the amino acid in the first week of feeding. Even more problematic, not all herds show a milk response.
HOW MUCH DO COWS NEED?
While cows consume and utilize grams of amino acids, nutritionists often talk percentages and ratios. That's because cows consume nutrients through total mixed rations, increasing their dry matter intake as production increases.
At last year's Cornell Nutrition Conference, the optimal recommendation for amino acids was raised to 7.2% lysine and 2.4% methionine, a 3:1 ration. The prior recommendation had been 6.6% lysine to 2.2% methionine.
Current Status of Amino Acid Requirement Models for Lactating Dairy Cows
Arm & Hammer Animal Nutrition
Q&A with Jim Linn