Are you feeding too much dietary crude protein?
According to a 1998 survey of some of the highest-producing herds in
“We’ve done studies now which persuade me that, at least beyond the first part of lactation, there’s no need to feed these super-high protein levels,” says Glen Broderick, a dairy scientist with the U.S. Dairy Forage Research Center in
If you’re still feeding upward of 18 percent crude protein to lactating cows, here’s proof that you can feed less without jeopardizing milk production.
Milk peaks at 16.5 percent
The latest research from Broderick’s lab shows that you can trim crude protein from 18 percent or 19 percent to about 16.5 percent in mid-lactation diets, without harming milk production.
During one study, the research team fed five different levels of crude protein — 13.5 percent, 15 percent, 16.5 percent, 17.9 percent and 19.4 percent. The diets contained 25 percent alfalfa silage, 25 percent corn silage and 50 percent concentrate, comprised of high-moisture corn, roasted soybeans and soybean meal.
The results show a “hill-shaped” or quadratic response to increasing crude protein levels. In other words, milk production gradually climbed, peaked at a certain point and then began to descend as the crude protein level of the diet increased. (Please see “Crude protein affects milk yield” on page 40.)
The cows in this study achieved maximum milk production at 16.5 percent crude protein. Going beyond that level did not result in extra milk production. In fact, milk yield actually declined when crude protein exceeded 16.5 percent. “You may be shooting yourself in the foot by feeding more,” Broderick adds.
Several other studies also show that increasing crude protein beyond 16 percent or so does not result in more milk. (Please see “Don’t go beyond 16.5 percent” below.)
Don’t stray too much below 16.5 percent either. Broderick’s study also shows a drop in milk yield when crude protein falls below that level.
Trim crude protein cost
When cows eat more crude protein than what they need to make milk, they waste it. “Unused protein that does not go into milk finds its way almost totally into the urine,” Broderick says. That has environmental consequences, not to mention the fact that you’re forking out dollars unnecessarily.
But if you gradually trim the level of crude protein in the diet, you can keep more of those dollars in your pocket. For instance, let’s say you replace soybean meal with corn to lower total crude protein from 18 percent to 16.5 percent. If soybean meal is valued at $185 per ton, and corn grain is valued at $2.50 per bushel, you would save nearly 10 cents per cow per day by reducing crude protein by 1.5 percentage units. (Please see “Pencil it out” above.) So, if you trim crude protein during just the last 150 days of lactation, that’s a savings of roughly $1,500 per 100 cows.
The cost savings, not to mention the research, present a compelling argument for why you should gradually shave the level of crude protein in some lactating-cow diets to about 16.5 percent.
Less milk, more nitrogen wasted
Crude protein in excess of 16.5 percent does not boost milk yield, but it certainly increases urinary nitrogen loss, and that has environmental consequences. According to a study in the May 2006 Journal of Dairy Science, increasing dietary crude protein from 16.6 percent to 17.6 percent increased urinary nitrogen excretion by 54 grams per day.
Pencil it out
Here’s how much you can save by trimming dietary crude protein from 18 percent to 16.5 percent:
55 pounds dry matter intake per cow per day x 1.5% reduction in crude protein = 0.825 pounds crude protein.
0.825 divided by 0.44 (53% crude protein per pound of soybean meal minus 9% crude protein per pound of corn = 0.44) = 1.875 pounds of diet dry matter from either soybean meal or corn.
Cost per cow per day for soybean meal: 18.75 cents
Here’s the math:
$185 per ton divided by (2000 pounds in a ton x 89% dry matter in soybean meal) = 10 cents per pound dry matter in soybean meal.
10 cents x 1.875 pounds dry matter = 18.75 cents per cow per day.
Cost per cow per day for corn: 9.75 cents
Here’s the math:
$2.50 per bushel divided by (56 pounds in a bushel x 86% dry matter in corn) = 5 cents per pound dry matter in corn.
5 cents x 1.875 pounds dry matter = 9.75 cents per cow per day.
Cost you save per cow per day: 9 cents
18.75 cents – 9.75 cents = 9 cents
Calculations courtesy of Glen Broderick, U.S. Dairy Forage Research Center.
Don’t go beyond 16.5 percent
These studies also show that increasing crude protein beyond 16.5 percent
does not result in more milk, and, in some cases, actually decreases milk yield.
April 2003 Journal of Dairy Science Milk yield at Milk yield at
(Broderick) 16.7% crude protein: 75.2 pounds 18.3% crude protein: 75.2 pounds
December 2003 Journal of Dairy Science Milk yield at Milk yield at
(Leonardi et al.) 16.1% crude protein: 94.1 pounds 18.9% crude protein: 93 pounds
October 2004 Journal of Dairy Science Milk yield at Milk yield at
(Wattiaux & Karg) 16.2% crude protein: 109 pounds 17.1% crude protein: 107 pounds