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Fine-tuning calf nutrition could reduce nitrogen pollution

03.03.2005


Milk prices dairy farmers received in 2004 were higher than in recent years but dairying, like all forms of agriculture is a vicious treadmill, demanding ever more increased efficiency to stay in place, said a dairy nutritionist with the Texas Agricultural Experiment Station.



"And an accelerated calf growth program is one way they are looking to increase efficiency and productivity," said Dr. Barry Lambert, who has a joint appointment with the Experiment Station and Tarleton State University.

But current accelerated growth programs run the risk of not only overfeeding some nutrients, which is a waste of money, but also increasing the amount nitrogen the calf excretes. More nitrogen in the manure increases the potential for nitrogen finding its way into streams and rivers.


The increase in nitrogen output per calf may not be that large. But with nine million dairy calves born in the United States yearly, it can add up to something environmental groups can literally raise a stink over. Lambert, however, believes feed rations in accelerated calf growth programs can be fine-tuned so the growth rate of the calf is increased without wasting feed dollars and sans the extra nitrogen in the manure.

The key may be balancing the proportions of the 21 amino acids that make up proteins. "In current accelerated calf growth programs, amounts of all 21 amino acids are increased," Lambert said. "But it may only be necessary to increase two or three amino acids."

Until the last few years, most dairy producers would limit the milk intake of calves in order to quickly wean them onto solid feed. Early weaned calves would typically be ready to breed by about 15 months, becoming a productive milk producer soon after their first calf.

More recently however, the idea has been maximize calf feed intake to take advantage of the young animal’s ability to efficiency utilize protein and grow fast. The idea is to reduce the 24 months to the first calving by one or two months, and thus have the cow become a productive member of the milking herd sooner.

These feeding programs, called "accelerated calf growth" programs, use milk replacers – not all that different from formulas fed to human babies. The milk replacers have very high crude protein content, some up to 26 percent. Such high-protein diets have been shown to increase feed use efficiency by more than 50 percent, Lambert said.

All proteins are composed of chemically linked amino acids. All creatures require proteins for growth and good health. Some of these amino acids can be synthesized by an animals metabloism; others cannot.

The ones that cannot be synthesized are called "essential" amino acids. For humans and other non-ruminants – swine, for example – the required amino acids are known with certainty. In humans, for example, nine amino acids are considered essential. Two of these nine, lysine and tryptophan, are either not present or found only in small amounts in plant protein. This is why strict vegetarians must pay careful attention that their diet contains these two amino acids.

For multi-stomach animals such as dairy cows, the situation is more complicated. The first two stomachs host bacterial that can synthesize protein from plant fiber. There is a limit, however, to how much protein these rumen-based bacteria can supply. Also, it is not clearly known by dairy nutritionists which of the amino acids are "limiting" factors: which ones need to be increased by what amount to provide complete protein for the growing dairy calf, Lambert said. "There are no current National Research Council recommendations for the essential amino acid requirements of young growing dairy calves," he said.

So the current formulas take the "shotgun approach"– increasing all 21 essential amino acids, Lambert said. The result is as planned: increased calf growth and feed efficiency but there’s also more waste in terms of unused protein. Moreover, nitrogen is a component of protein. When fed more protein than they can metabolize, calves excrete the unused nitrogen as urine and feces. The "shotgun" method therefore, Lambert said, tends not only to waste feed dollars but complicates environmental protection measures as well.

Lambert plans to use a method that’s never been used to measure ruminant amino acid requirements, a laboratory process called "indicator amino acid oxidation."

Usually, ruminant nutritionists use something called "nitrogren balance" calculations. Simplified, this means the amount of nitrogen (in the form of protein) going into the animal is measured; then the amount of nitrogen excreted in the urine and feces is calculated. The more nitrogen retained in the body, the greater the amount of protein synthesized. The method has been compared to a ledger sheet.

But nitrogen balance measurements have a time lag, too slow to accurately determine a young calf’s metabolic development, Lambert said. "As a consequence of their rapid growth rate, the underlying physiology and hence, nutrient needs, of young dairy calves change on almost a weekly basis," Lambert said.

The indicator amino acid oxidation process is much quicker and more accurate, but also more expensive to set up and conduct. Lambert has heretofore been conducting preliminary studies with limited funding. He has applied for a U.S. Department of Agriculture grant in order to scale up the study. "Our ultimate goal is to allow producers to maintain current rates and efficiencies of calf growth, while continuing to place emphasis on environmental stewardship" Lambert said.

Robert Burns | EurekAlert!
Further information:
http://www.tamu.edu

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