Pregnancy rate in dairy cows treated with human chorionic gonadotropin five days after insemination

Abstract

This study tested whether the administration of hCG five days after insemination increased progesterone concentration
and pregnancy rate (PR) in dairy cows. A total of 989 lactating Holstein cows with different parity and number of prior services were
used. Cows were inseminated after overt estrus or at a fixed-time. Five days post-insemination, cows were randomly assigned to two
treatment groups: hCG (n=482), which received 3500 IU of hCG by intramuscular injection; and the control group (n=507), which
did not receive any treatment. Pregnancy was diagnosed by ultrasound on day 30 post-insemination, and gestation was confirmed
on day 60 post-insemination by rectal palpation. In 15 cows from each treatment group, plasma progesterone concentration was
determined on days 5, 11, and 15 post-insemination. Pregnancy rate was analysed using logistic regression. Variations in progesterone
concentration between treatments were tested by ANOVA for repeated measurements. Progesterone concentration was higher on days
11 and 15 in cows treated with hCG, compared to the control group (P<0.05). Treatment with hCG increased pregnancy rate (47.5 vs.
37.4%. Odds ratio 1.3; P<0.05). No interaction was observed between treatment and body condition, prior services, milk production,
parity, or insemination type (overt estrus or fixed time). Treatment with hCG did not reduce pregnancy losses between day 30 and 60
post-insemination (P>0.1). We conclude that injection of hCG five days after insemination increased progesterone concentration and
pregnancy rate in dairy cows.