LAUSR

This study was conducted on a cattle farm in Yucatan, Mexico. The objective was to assess the effect of energy supplementation on milk yield and composition, and on the efficiency of use of dietary N in cows fed Leucaena leucocephala foliage (30% of total diet) and grass Pennisetum purpureum. Four multiparous crossbred Bos indicus × B. taurus cows in the first third of lactation were used in a 4 × 4 Latin square design. Treatments consisted of two energy sources: sugar cane molasses and rice polishing, offered individually or mixed, and a control group (Ctrl) without energy supplementation. The supplements were iso-proteic and iso-energetic and were formulated to provide 25% of the daily energy requirement. Supplementation increased dry matter intake (3 kg/cow/d). Milk yield was 13% higher (P = 0.048) in the supplemented treatments (7.86 kg/cow/d) than in the Ctrl group (6.97 kg/cow/d). Milk yield did not differ (P > 0.05) among supplemented treatments. Milk fat was higher for the Ctrl treatment compared with molasses and rice polishing. Concentrations of protein, lactose and solids non-fat in milk were not significantly affected by energy supplementation. The lower concentrations of blood urea nitrogen (BUN) found in the treatments with supplementation (9.77 mg/dl) compared with Ctrl (15.61 mg/dl) indicates greater efficiency in capturing N by rumen microorganisms. No differences in BUN were found among supplemented groups. It is concluded that energy supplementation with rice polishing alone or in combination with molasses, can improve the efficiency of use of dietary N, and milk yield, in cows fed 30% L. leucocephala foliage.