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 treatment groups (n = 9).All yaks were allowed to graze naturally during the daytime and received supplemental feed at 1% of body weight (BW), consisting: (1) supplementary feed (Control), (2) supplementary feed plus 7.5 g NCG/head/day (NCG1), (3) supplementary feed plus 15 g NCG/head/day (NCG2).Following 7-day adaptation period, the 60-day experimental trial was conducted.Twenty-seven late-lactation Niangya yaks (2.33±0.68parity; 164.85±9.58days in milk; 239.50±36.37kg 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 did not affect yak body weight (BW) but 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.