Efficacy of double injection of buserelin in improving pregnancy rates in prolonged oestrus repeat breeding crossbred cattle

Abstract

The present study was aimed at investigating the efficacy of twice administration (at AI and mid luteal) of GnRH analog buserelin over a single injection (at AI) in improving the pregnancy rates in prolonged oestrus repeat breeding crossbred cows. For this, 75 prolonged oestrus repeat breeding and 13 normal cycling cattle were subjected to rectal palpation of genitalia and blood sampling for assessing the ovarian structures and progesterone concentration for one oestrus cycle between 3 and 4 days intervals. In the next oestrus, group 1 has normal cycling CO\VS (13: untreated~ normal cycling control). The repeat breeding cattle were randon11y distributed amongst 3 groups viz. group 2 (18: repeat breeding control)-in which no treatment was given~ group 3 (29: single injection)-Inj. buserelin 20 mg (receptal, 5 ml) was given intramuscularly 6 h before the AI~ and group 4 (25: double injection) - first injection of buserelin 20 mg (receptal, 5 ml) was given intramuscularly 6 h before the AI and second injection on day 12 after last insen1ination. In all the animals AI was done twice (12 h apart) according to the AM-PM rule and pregnancy "vas confirmed by rectal palpation between 12 and 18 weeks after the last AI. There was a significant delay in the rise of peripheral progesterone after the expected ovulation i.e. around day 4 to 5 in repeat breeding cows as compared to normal CO\VS, during the oestrous cycle \vhen no AI was done. The first service pregnancy rate in the group 1, 2, 3 and 4 \vere 54, 17, 34 and 52%, respectively. In brief, the double injection ofbuserelin (first 6 h before AI and second at day 12 post-insemination) proved to be more successful than single buserelin injection (at AI), in increasing the pregnancy rates in prolonged oestrus repeat breeding crossbred cows.