Effects of Forage-to-Concentrate Ratio During Cold-Season Supplementation on Growth Performance, Serum Biochemistry, Hormones, and Antioxidant Capacity in Yak Calves on the Qinghai–Tibet Plateau

This study investigated the effects of different forage-to-concentrate (F:C) ratios during cold-season supplementation on growth performance, serum biochemical parameters, hormone levels, and antioxidant capacity in yak calves on the Qinghai-Tibet Plateau. Eighteen 8-months-old male yaks with similar body weights (110.01 ± 2.08 kg) were randomly assigned to two groups receiving diets with high (F:C = 7:3) or low (F:C = 3:7) forage. The trial lasted 60 days, including early (days 0-30) and late (days 31-60) experimental stages. Body weight was measured, and serum samples were collected on days 30 and 60 for biochemical and hormonal analyses. Yaks in the low-forage group showed significantly greater average daily gain during both stages and the entire experiment (<i>p</i> < 0.05), with a 7.92% increase in final body weight. Serum total protein and globulin levels were significantly higher in the low-forage group throughout the trial (<i>p</i> < 0.05 or <i>p</i> < 0.01), while other biochemical parameters remained unaffected. Growth hormone concentrations were significantly elevated in the low-forage group at both stages (<i>p</i> < 0.05). Additionally, malondialdehyde levels tended to decrease in the early stage (<i>p</i> = 0.056), and total antioxidant capacity was significantly lower in the late experimental stage (<i>p</i> = 0.040) in the low-forage group. A higher net economic benefit was observed in the group fed an F:C ratio of 3:7 than in the 7:3 group. These findings suggest that cold-season supplementation with a low-forage diet improves growth performance and protein utilization in yak calves but may negatively impact antioxidant status. An optimal F:C balance should therefore be considered to support both performance and health in yak husbandry under harsh environmental conditions.