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 (NH 3 -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.