23 RELATIONSHIP BETWEEN CONCENTRATION OF SUPEROXIDE DISMUTASE WITH TIME AND TIMED ARTIFICIAL INSEMINATION PREGNANCY RATE IN COWS WITH HIGH MILK PRODUCTION

Abstract

Disorders related to oxidative metabolism, which occur in the production cycle of high-producing dairy cows (HPC) are more frequent during the transition period and early lactation. Blood concentrations of the enzyme superoxide dismutase (SD) are closely related to the activity of stabilizing conditions of oxidative stress (OS). It is very important to know the main mechanisms involved in regulation of metabolic events, to develop new strategies to increase the productive and reproductive performance of HPC. The objective of this study was to evaluate differences in pregnancy rates and pregnancy losses of HPC with different concentrations of SD with fixed-time AI (FTAI). The experiment was conducted on a commercial farm with 140 HPC (multiparous pregnant Holsteins). The evaluations of concentrations of SD were done from 21 days before birth to the day of the first-service FTAI (75 days in milk), with intervals of 14 days. The animals were retrospectively divided into 2 groups (G1 and G2) in accordance with the average output from all cows in peak lactation (4–8 weeks). Data were analyzed using logistic regression to determine the pregnancy rates between groups. There was a time effect and group effect for the concentrations of SD (P < 0.05) only on the first day of FTAI (3054.4^a ± 37.4 and 3662.4 ± 42.1^b) for G1 and G2, respectively. But this was not reflected in differences in pregnancy rates between the experimental groups (G1 and G2) and 30 (26.7 v. 31.4) and 60 (20 v. 19.6) days. Although the dismutation activity was high, it seems that the plasma concentration of this enzyme alone does not explain the effects of oxidative stress on fertility in HPC.