Effects of Different Levels of Dietary Curcumin Nano-Micelles on Nutrient Digestibility, Skeletal Growth Indices, and Faecal Consistency of Suckling Simmental Calves Under Heat Stress Conditions.

This study evaluated the effects of dietary curcumin nano-micelles (CNM) on growth performance, nutrient digestibility, skeletal development, and faecal consistency in heat-stressed suckling Simmental calves. Thirty-two male calves (10 days old; 43.7 ± 2.5 kg) were randomly assigned to one of four dietary treatments: CTRL (control), T20, T40, and T80, corresponding to 0, 20, 40, and 80 mg of CNM per calf per day, with eight replicates per group. The trial lasted 45 days, including a 7-day adaptation period. CNM supplementation significantly improved growth performance, with average daily gain (ADG) increasing in T40 and T80 groups (0.31 kg/day) compared to CTRL (0.29 kg/day; p = 0.029). Dry matter intake (DMI) was higher in T80 (1.58 kg/day) than CTRL (1.47 kg/day; p = 0.003), while feed conversion ratio was unaffected. Nutrient digestibility was generally unchanged, except for neutral detergent fibre (NDF) digestibility, which showed a quadratic response (p = 0.010), with the lowest value observed in T40 (22.33%). CNM significantly enhanced skeletal growth: body length (p = 0.041), hip height (p < 0.001), heart girth (p = 0.005), abdominal girth (p = 0.025), ankle circumference (p = 0.006), pin bone width (p < 0.001), hip width (p = 0.031), and body depth (p = 0.012) increased notably in T40 and T80 groups over time. Faecal consistency remained stable (p = 0.964), indicating no negative effects on intestinal health over time. These findings demonstrate that CNM supplementation can improve feed intake and promote skeletal development in heat-stressed calves, potentially enhancing resilience under thermal stress. Further research is warranted to optimise CNM dosing for sustainable ruminant production.