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Vitamins C and E have been supplemented separately to improve fertility in cattle. The objective of this study was to evaluate the effect of combined injections of increased doses of vitamins C and E on reproductive parameters in dairy cattle. Lactating Holstein cows (n= 44) were randomly assigned to one of three treatments: 1) Control: n= 15, cows were not injected with vitamins; 2) VCE3: n= 15, cows received a single intramuscular injection of 3,000 IU of vitamin E before estrus and multiple subcutaneous injections of vitamin C with a total dose of 3,000 mg before and after estrus; 3) VCE6: n= 14, cows were treated as in VCE3, but doses of vitamins C and E were increased to 6,000 mg and 6,000 IU. The reproductive indicators measured were diameter of the preovulatory follicle, time to estrus, area of the corpus luteum, pregnancy rate 35 and 45 d after AI and plasma concentrations of estradiol and progesterone. There was no effect of treatment on any of the evaluated reproductive parameters (P˃0.05), except that the lowest dose of vitamins sustained similar pregnancy rates among treatments, even though they had lower progesterone concentrations (P≤0.05) (19.4 ± 2.66 vs 10.1 ± 2.55 vs 19.2 ± 0.44 ng mL-1 for Control, VCE3 and VCE6, respectively). In conclusion, the supplementation with the highest amount of vitamin C and E (6,000 mg and 6,000 IU versus 3,000 mg and 3,000 IU) does not significantly increase the reproductive parameters measured.

Ascorbic acid (vitamin C: VC) is an antioxidant that participates in the regulatory processes involved in the development of ovarian structures and fertility. However, supplementation of VC to dairy cattle to improve fertility has received little attention. However, reduced fertility in dairy cattle associated with high genetic merit for milk production and heat stress, which also diminish blood VC concentrations, suggest a potentially beneficial role for VC supplementation. The objectives of this review are to contribute to the current knowledge regarding the relationship between VC and fertility and to share many experiences that support the relevance of VC supplementation to improve dairy cattle reproductive performance.