Using intelligent behavioral monitoring to assess the impact of dietary energy and protein on growth, digestion, metabolism, and behavior of young female yaks.

This study investigated the effects of graded dietary energy and protein levels on growth, nutrient utilization, and behavior in housed young female yaks, integrating automated behavior monitoring via a YOLO-based computer vision system. Twenty-four 17-month-old Maiwa yaks (160.43 ± 14.54 kg) were randomly assigned to three dietary treatments (n = 8 per treatment): low energy and protein (LELP: net energy for gain [NEg] = 3.3 MJ/kg, crude protein [CP] = 10.50%, medium energy and protein (MEMP: NEg = 3.9 MJ/kg, CP = 12.51%), and high energy and protein (HEHP: NEg = 4.5 MJ/kg, CP = 14.50%). A 120-d feeding trial was conducted, followed by a 4-d digestion and metabolism trial. Growth performance was enhanced in the MEMP group relative to the LELP group, as indicated by significantly greater average daily gain (ADG) and a reduced feed-to-gain ratio (F/G) (P < 0.05). Nutrient metabolism was enhanced at higher dietary levels, as indicated by elevated serum urea nitrogen (BUN) and ruminal ammonia nitrogen (NH3-N) contents in the MEMP and HEHP groups (P < 0.05). Automated behavioral analysis revealed that the MEMP group spent less time standing and more time lying than the HEHP group (P < 0.05), suggesting improved welfare and rumination opportunity. Furthermore, the moderate diet (MEMP) optimized the utilization and deposition rates of both energy and nitrogen. In conclusion, a moderate energy and protein diet (NEg = 3.9 MJ/kg, CP = 12.51%) optimally supports the growth and metabolism of young female yaks under housed conditions. This study provides a scientific basis for the precise nutritional management and intelligent monitoring of yaks in intensive production systems.