Abstract
Three matched groups of calves (five Holsteins and one Brown Swiss) were fed from age 8 to 18 wk on complete-feed diets. Protein-to-energy ratios were 1:17.4, 1:36.0, and 1:41.1 (grams digestible protein per kilocalories of digestible energy) for Rations 1, 2, and 3. The ratios were established by varying the amounts of soybean oil meal and corn in the diets. Growth and feed efficiency were similar on Rations 1 and 2 and superior to that on Ration 3. Based on digestibilities and nitrogen balances, nitrogen utilization was higher on Ration 1 than that on the two other diets. Blood serum protein groups and total free amino acids in blood were similar for calves on all three rations. Blood valine and isoleucine were similar on Rations 1 and 2 but greater than on Ration 3. Protein:energy ratio should be more narrow than 1:41.1 for adequate growth of calves from 8 to 18 wk of age.
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