Effects of vitamin A injection on antioxidant status, ovarian function, and reproduction performance in repeat breeder Holstein cows

The objective of this study was to investigate the effect of vitamin A injection on reproductive performance in repeat breeder cows. One hundred and sixty-two multiparous Holstein cows with at least three consecutive unsuccessful inseminations were randomly assigned to experimental treatments. Treatments included (1) control: twice intramuscular injection 10 ml placebo30 days apart: 0.9% sodium chloride (n=87) and (2) vitamin A:  twice intramuscular injection 10 ml retinol palmitate 30 days apart (n=75). Animals submitted to double-ovsynch protocol and received their experimental treatments on the tenth day of the protocol (the day of the second injection of GnRH). The injection of retinol palmitate significantly increased the number of ovarian follicles larger than 10 mm compared to the control (P <0.05). Plasma concentration of superoxide dismutase enzyme tended to increase (P = 0.09) and malondialdehyde concentration tended to decrease (P = 0.08) under the influence of vitamin A injection. The conception rate at first artificial insemination was 25.29% and 34.66% for control and vitamin A treatments respectively, this difference was not significant (P = 0.19). The odds ratio of conception in the first service for vitamin A treatment was 1.57 times higher than the control treatment but was not statistically significant (P = 0.19). In conclusion, vitamin A injection improved antioxidant function and ovarian function. The reproductive performance improved, although not statistically significant.