WEST LAFAYETTE, Ind. – Overeating doesn’t do a dairy cow any more good than it does a human. In fact, the negative consequences could be greater when a bovine makes a pig of itself, said Tim Johnson, Purdue University Extension dairy nutrition specialist.
Dairy producers need to carefully monitor how much supplemental protein they feed their animals in order to avoid possible environmental and herd health problems, as well as higher operating costs.
Too good. Bovines are good at processing protein – almost too good, Johnson said. Therein lies the trouble with overfeeding protein supplements such as soybean meal.
“The cow is an incredibly efficient animal in utilizing nitrogen and amino acids to make milk protein,” he said.
The overflow, which we might call the excess protein that a cow could consume, is excreted in two ways. One is in the urine and the other is in the milk. By monitoring milk urea nitrogen, you can determine whether you are overfeeding protein by a greater amount than is actually required for the cow to manufacture the milk protein.
Urea. Urea is an organic molecule formed from ammonia in the liver and then packaged for reabsorption from the blood into the cow’s rumen or transported to the kidney for excretion. Urea resides in blood and other body fluids and is a normal component of milk.
The conversion of ammonia to urea prevents ammonia toxicity in the dairy cow, which processes huge amounts of nitrogen into milk protein each day.
Producers have known that feeding supplemental protein carries both rewards and risks. With the growth of the biofuels industry, they will have to be even more aware of the proper feeding rates, Johnson said.
“With the influx of ethanol distilleries all over the state, the ethanol byproduct – dried distillers grains with solubles – is coming as a very economically efficient energy and protein source,” he said. “And yet, there can be problems that are related to overfeeding dried distillers grains.”
Problems. One potential problem with feeding too much distillers grains with solubles is that the unsaturated fat – corn oil – in the solubles can inhibit some fiber digesting bacteria normally found in the rumen. This can lead to depressed milk fat, a valuable component used to make butter.
There’s also the environmental consequence of feeding too much protein through the possible contamination of waterways.
The other possibly negative side effect of overfeeding protein relates to the reproduction of the dairy cow. There is some indication that there can be more loss of pregnancies in beef cattle. And in dairy cattle, the conception rate after breeding can be lower in dairy cows that have been way overfed protein.
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