Effects of Dietary N-Carbamylglutamate in Supplemental Feed on Lactation Performance of Grazing Yak Cows.

OBJECTIVE: Yak milk serves as crucial source of dairy products for pastoralists on the Qinghai-Tibetan Plateau. This study investigated the effects of dietary N-carbamylglutamate (NCG) in supplemental feed on lactation performance, milk composition, serum biochemical parameters, and free amino acid profiles in grazing yaks. METHODS: Twenty-seven late-lactation Niangya yaks (2.33±0.68 parity; 164.85±9.58 days in milk; 239.50±36.37 kg BW) were randomly assigned to three groups (n=9). Yaks grazed naturally by day and were penned individually at night to receive a 1% BW supplement: Control, NCG1 (7.5 g/d), or NCG2 (15 g/d). Following a 7-day adaptation, the experimental trial lasted 60 days. RESULTS: Results showed that NCG supplementation significantly increased (P < 0.05) milk yield compared with the control group. On day 60, the NCG1 group had a significantly higher (P < 0.05) milk fat percentage than both the control and NCG2 groups. On day 30, the NCG1 group exhibited significantly elevated (P < 0.05) serum concentrations of arginine, alanine, and valine relative to the control group, along with higher (P < 0.05) valine, isoleucine, and leucine levels compared to the NCG2 group. Both the NCG1 and NCG2 groups had increased (P < 0.05) levels of serum alanine compared with the control group. CONCLUSION: Collectively, milk yield increased linearly with NCG dosage and was highest at 15 g/d, whereas milk fat percentage exhibited a quadratic response, peaking at 7.5 g/d. This suggests that moderate NCG supplementation (7.5 g/d) optimally promotes milk fat synthesis, while a higher dose (15 g/d) further enhances milk volume without conferring additional benefits on fat content. The dose‑specific responses point to a potential dissociation between pathways regulating mammary lipogenesis and amino acid‑driven lactogenic signaling; nevertheless, these mechanistic hypotheses require direct experimental confirmation.