Varying Levels of Urea for Dairy Cows Fed Corn Silage as the Only Forage

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Abstract
The effect of dietary urea mixed with the concentrate on milk yields, voluntary consumption of corn silage and nutrient balances was studied with 91 lactating cows. The percent of the ration N as urea ranged from 0 to 48%. Milk yields were significantly depressed when urea furnished 22% of the ration N, but no effect on production was detected at 11%. Voluntary intake of corn silage was not affected by urea. Rumen valerate and isovalerate tended to be lower for urea rations, but acetate and propionate were not affected. Significant depressions in dry matter, crude fiber and NFE [nitrogen free extract] digestibilities resulted from urea additions. The percent of the ingested N recovered in milk was lower, and that in urine higher when urea provided 22% of the dietary N compared to 0 and 11%.
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