Neutrophils are the most vital part of the first line of immune defense against invading mastitis pathogens in the mammary gland of high yielding dairy cows. Their quality and quantity in the gland is important. Vitamin C is one of the most important water-soluble protective agents in mammalian cells. Although cows can synthesize vitamin C, substantial evidence suggests a link between vitamin C and immunity. We hypothesized that feeding vitamin C in dairy cows would improve milk neutrophil function via its antioxidant properties. This study was, therefore, aimed to determine whether supplemental dietary vitamin C affects on milk neutrophil quality and quantity immediately after calving. We fed Holstein cows supplemental vitamin C during the peri-partum period; at 10 d before anticipated calving, the cows were fed diets that provided 0 (n = 7) or 50 (n = 7) gm/d of supplemental vitamin C (phosphorylated ascorbic acid). Treatments continued until approximately 15 days in milk. The viability of milk neutrophils and somatic cells were examined after calving. Compared with non-vitamin C supplemented group, feeding vitamin C during periparturient period resulted in significant-increased neutrophils viability and decreased somatic cells in the mammary gland after calving. The reduced somatic cells in the gland from vitamin C treated cows suggests that it may reduce damage to the gland, milk and neutrophils caused by parturition-and-lactation-related stress. In our previous experiments we observed that the unnecessarily high number of neutrophils and excessive somatic cells in the milk may relate to udder and milk damage as free radicals and proteases released by neutrophils appear to be actively involved in the damage. Therefore, in the current study limited, but fairly enough, SCC with high quality of neutrophils observed in cows receiving vitamin C supplementation implies a more efficient neutrophil response compared with the response in non-supplemented cows. Overall, supplemental dietary vitamin C during the peri-partum period improves neutrophil function; this potentially results in faster elimination of pathogens in the gland during mastitis. Though still remains inconclusive, the application of vitamin C would be further examined in dairy cows for prevention and treatment of clinical mastitis; because it boosts milk neutrophil viability.

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