A cow with her calf.
Cows Could Be Getting Too Much Protein
Peabody November 23, 2004
It's not just consumers who are contemplating the effects of
high-protein diets: dairy farmers are, too. Dairy cows need adequate protein
for milk production, so farmers need to supplement their animals' diets with
But an Agricultural Research
Service scientist has found that while a certain amount of dietary protein
is necessary for lactating dairy cows, too much can contribute to nitrogen
pollution and, in some cases, decreased milk yield.
Broderick, with the agency's
Dairy Forage Research Center in Madison, Wis., found that the optimal
percentage of protein in the dietwhich minimizes urinary nitrogen
excretion without reducing milk productionis 16.5 percent. This is
compared to the 18 to 19 percent often provided by many in the industry.
To meet the protein requirement, Broderick fed lactating cows a diet
of alfalfa silage, corn silage and high-moisture corn, plus soybean meal as the
main protein supplement.
A dairy cow has numerous microorganisms at work in its rumen, one of
the animal's four stomach compartments. Many of these bacteria convert crude
protein in the diet into a form that's well-balanced in amino acids for cows.
But the bacteria will also degrade good-quality protein, leading to an overall
net loss. Farmers compensate for the loss by feeding their cows high levels of
protein supplement. But these higher-quality protein meals add to feed costs.
The extra protein isn't always utilized by the cow, so the animal
excretes it as urinary nitrogen. In many farm settings, this very unstable form
of nitrogen will be converted to ammonia, which turns into a vapor. Ammonia
that's released into the atmosphere in this way can form acid rain, return to
the Earth and fuel unwanted plant growth. Large amounts of nitrogen lost from
concentrated dairy operations also have the potential to contaminate surface
and ground waters.
According to Broderick, if just 1 percent less dietary protein were
fed to dairy cows in the United States, urinary nitrogen could be reduced by
about 60,000 tons per year.
ARS is the U.S. Department of
Agriculture's chief scientific research agency.