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Urea-Treated Corn Silage in Low Protein Rations for Lactating Cows¹

Dairy Department, Michigan State University East Lansing 48823

ABSTRACT

Corn silages (34 to 37% dry matter) ensiled with 1) no additive; 2) 0.5% urea; 3) 0.75% urea; and 4) 0.75% urea + 0.17% CaSO₄ were fed as the only forage to lactating cows averaging 29.3 kg milk per day when treatment began. Concentrates containing 8, 12 or 18% crude protein also were fed at 1 kg per 3 kg milk. Treatments (six groups of 10 cows each), designated by silage number and per cent crude protein in the concentrate were: A) 1, 8;B) 2,8; C) 3, 8; D) 4, 8; E) 2, 12 and F) 1, 18. Experimental rations were fed for 70 days. Nitrogen balances were determined on five cows per group at the end of the feeding period. Intakes of total and silage dry matter (kg per 100 kg body weight) averaged, respectively, 2.4, 1.2; 2.7, 1.4; 2.7, 1.5; 2.8, 1.5; 3.1, 1.6; and 2.8, 1.6. Silage intake of A was lower (P < 0.05) than of E and F. Milk yields (kg per day) and persistencies (%) were significantly affected by dietary nitrogen and, for the respective treatments, averaged 19.2, 67; 23.7, 81; 23.8, 82; 23.9, 84; 26.4, 91; and 25.7, 88. Added sulfate did not affect milk yields. Crude protein and dry matter digestibilities were directly related to ration protein. Negative controls (A) excreted equivalent to 143% of their digested nitrogen as milk and urine while averages for other groups ranged from 89 to 109%.

¹ Published with the approval of the Director of the Agricultural Experiment Station as Journal Article 5124.