Effects of vitamin C on production performance, rumen fermentation, and blood antioxidant indices in heat-stressed Holstein dairy cows.

Abstract

Heat stress exerts severe detrimental effects on lactation performance, rumen health, and antioxidant status in dairy cows, inflicting substantial economic losses on the global dairy industry. This study investigated the effects of dietary Vitamin C-2-phosphate supplementation on lactation performance, rumen fermentation, and serum antioxidant parameters in heat-stressed Holstein cows. Thirty multiparous Holstein cows (659.6 &#xb1; 18.4 kg body weight, 2.83 &#xb1; 0.65 parity, 93.3 &#xb1; 9.3 days in milk, 44 &#xb1; 4.3 kg/d milk yield) were randomly allocated to three groups (= 10) using a randomized complete block design: control (CON, basal diet), low-dose Vitamin C-2-phosphate (LVC, basal diet + 20 g/head/d Vitamin C-2-phosphate), and high- dose Vitamin C-2-phosphate (HVC, basal diet + 40 g/head/d Vitamin C-2-phosphate). The 42-day trial consisted of a 7-day adaptation period and a 35-day experimental period, with an average temperature-humidity index (THI) of 77.86. Results showed that Vitamin C-2-phosphate supplementation significantly increased ruminal total volatile fatty acid (TVFA) and acetate concentrations, energy-corrected milk (ECM) yield, milk protein concentration, and milk protein yield (< 0.05), while decreasing ruminal ammonia nitrogen (NH-N) concentration and milk somatic cell count (SCC) (< 0.05). Additionally, Vitamin C-2-phosphate supplementation reduced serum malondialdehyde (MDA) and heat shock protein 70 (HSP70) levels and enhanced total antioxidant capacity (T- AOC) (< 0.05). In conclusion, dietary Vitamin C-2-phosphate effectively improves rumen fermentation, alleviates oxidative stress, enhances lactation performance, and promotes mammary gland health in heat-stressed Holstein cows. The 40 g/head/d dosage yielded the most favorable effects among the tested levels. Future studies should determine the optimal Vitamin C-2-phosphate inclusion levels under different heat stress intensities and physiological stages of production, and explore its synergistic effects with other functional additives.