Effects of Rumen-Protected Chromium-Nicotinic Acid on Lactation Performance, Nutrient Digestion, Ruminal Fermentation, Serum Biochemical Parameters, and Antioxidant in Lactating Water Buffaloes

This study evaluated the effects of rumen-protected chromium-nicotinic acid (RPCNA) supplementation on lactation performance, nutrient digestion, ruminal fermentation, serum biochemical parameters and antioxidant in lactating water buffaloes under conditions of a critical thermal comfort index (TCI). Healthy lactating water buffaloes (milk yield = 5.96 ± 0.21 kg; parity = 2.96 ± 0.15, mean ± SD) were randomly assigned to four groups, which were the control (without RPCNA), and three treatment groups designated as RPCNA2, RPCNA4, and RPCNA6, with 0, 2, 4, and 6 mg/(d·head) of RPCNA, respectively. During a 56-day experimental period, the average temperature was 29 °C with an average TCI of 40.60, indicating a critical state of environmental stress. The results showed that the addition of RPCNA to the diet had no significant effect on the apparent digestibility of nutrients, lactation performance, and dry matter intake in lactating water buffaloes. However, RPCNA supplementation positively influenced rumen fermentation, reducing ammonia nitrogen (NH₃-N) concentrations and promoting microbial protein synthesis. Supplementation with RPCNA4 and RPCNA6 decreased rumen NH₃-N levels by 48.3% and 36.4%, respectively, while RPCNA4 increased isobutyrate concentrations. This demonstrates that the coating technology does not provide 100% rumen protection. Serum analysis revealed that RPCNA significantly increases total antioxidant capacity (T-AOC). Additionally, the supplementation of 4 mg/(d·head) of RPCNA, improved serum glutathione peroxidase (GSH-Px) activity and reduced malondialdehyde (MDA) levels. These findings suggest that moderate doses of RPCNA supplementation can improve antioxidant status and rumen nitrogen metabolism in lactating water buffaloes under critical state, without significantly altering milk production or composition.