Response of lactating cows to supplemental rumen protected methionine and Niacin

Eight Chinese Holstein cows were used in a 4 × 4 Latin square design to determine the effects of rumen protected methionine (RPMet) and Niacin on milk yield and milk composition of lactating cows with 14 d adaptation and 6-d sampling periods. The cows were fed the control diet or the control diet plus RPMet (25 g·⁻¹), niacin (6 g·⁻¹), or RPMet (25 g·⁻¹) + niacin (6 g·⁻¹). The results showed that RPMet supplementation in the diet increased 4% fat corrected milk (FCM) yield (P < 0.05) and milk fat percentage (P < 0.05). However, supplemental RPMet had no effect on the solid non fat (SNF) (P > 0.05) and lactose percentage (P > 0.05). Dietary niacin supplementation increased milk yield (P < 0.05), milk protein percentage (P < 0.05) and lactose percentage (P < 0.05), but had no effect on milk fat percentage (P > 0.05) and SNF (P > 0.05). RPMet supplementation in the diet of lactating cows significantly decreased serum urea nitrogen (P < 0.01) and glucose contents (P < 0.05), but had no effects on nonesterified fatty acids (NEFA), total cholesterol and triglyceride (P > 0.05). Niacin supplementation influenced the contents of glucose and NEFA in serum, but had no effects on the urea nitrogen, total cholesterol and triglyceride (P > 0.05).