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Utilization of Nitrogen in [¹⁵Nitrogen] Ammonia Treated Corn Silage Fed to Lactating Cow¹

Department of Animal Science, University of California, Davis 95616

ABSTRACT

Three lactating, rumen fistulated cows (two Jerseys and one Holstein) were fed mixed diets containing (dry matter) 40% corn silage, 45% concentrate, and 15% coarse ground alfalfa hay. The corn silage was treated prior to ensiling with 1.4% ammonia (dry matter) to which ¹⁵nitrogen was added. Total fecal and urine collections and rumen sampling at 0, 2, and 4 h after feeding were conducted for all three cows during the 3rd wk on the diet and again during the 6th wk on the diet for one of the cows. Average daily intake of dry matter and milk yield ranged from 7.4 to 7.2 kg for the smallest Jersey to 18.3 and 33.0 kg for the Holstein. Apparent digestibilities of total dietary dry matter, energy, and nitrogen were 65.6, 65.1, and 66.9%. Percent ¹⁵nitrogen excess in rumen ammonia was slightly greater than that in rumen bacteria prior to feeding. Concentrations of ¹⁵nitrogen in ammonia and bacteria increased during the first 2 h after feeding, with the increase greatest for ammonia, and then plateaued to 4 h after feeding. Ratios of ¹⁵nitrogen excess indicated that up to 70% of bacterial nitrogen was derived from rumen ammonia. All cows were at equilibrium or in positive nitrogen and ¹⁵nitrogen balance during collection periods. Proportion of ¹⁵nitrogen retained was much greater than that for nitrogen at 3 wk but was similar during the 6th wk on the diet, indicating that body ¹⁵nitrogen was essentially in equilibrium with diet or absorbed ¹⁵nitrogen at that time. Ratios of total nitrogen to ¹⁵nitrogen excretion in milk suggest that the [¹⁵nitrogen] ammonia added to corn prior to ensiling was utilized about 80% as efficiently for milk nitrogen as was total feed nitrogen and that the soluble and insoluble nitrogen compounds from the added ammonia were utilized with the same efficiencies as other nitrogen compounds in the diet with similar solubilities.

¹ Research was supported partially by Calor American, Okemos, MI 48864

² Department of Animal Science, Michigan State University, East Lansing 48824.