Comparison of oestrus synchronisation programmes in dairy cattle using oestradiol benzoate, short-acting progesterone and cloprostenol, or buserelin and cloprostenol

AIM: To evaluate the efficacy of a programme using oestradiol benzoate, pro gesterone and the prostaglandin-F-2 alpha (PG) analogue, cloprostenol, to s ynchronise oestrus and ovulation in dairy cows, compared with a programme u sing a gonadotropin-releasing hormone (GnRH) agonist, buserelin, and clopro stenol. METHODS: Twenty non-lactating dairy cows, at random stages of the oestrus c ycle, were randomly assigned to 1 of 2 treatments. In Treatment 1 ( OPPG; n = 10), cows were injected with 2 mg oestradiol benzoate intramuscularly (IM ) plus 200 mg progesterone subcutaneously (SC) on Day 0, followed by 500 mu g cloprostenol IM on Day 9 and 1 mg oestradiol benzoate on Day 10. In Treat ment 2 (GPG; n= 10), cows were injected with 10 pg buserelin IM on Day 0, 5 00 pg cloprostenol IM on Day 7 and 10 mug buserelin on Day 9. The ovaries o f all cows were examined by ultrasonography, using an 8 MHz probe, from 5 d ays before the initial treatment until ovulation. Cows were observed for oe strus 3 times daily for 7 days after cloprostenol treatment. Blood samples were collected daily for determination of progesterone, and 6-hourly for 36 h after the second oestradiol or buserelin injection for the determination of follicle stimulating hormone (FSH) and luteinising hormone (LH) concent rations. RESULTS: The percentage of cows observed in oestrus was higher in the OPPG group than in the GPG group (100% vs 55.6%, p=0.018). Treatment with either short-acting progesterone plus oestradiol benzoate or buserelin was follow ed by atresia or ovulation of the dominant follicle. Emergence of a new fol licular wave occurred earlier (p<0.001) in the GPG group (2.2 +/- 0.2 days) than in the OPPG group (3.6 0.2 days). There was no significant difference between treatment groups in the variation of time of follicular wave emerg ence or size of the largest follicles at either the time of initial treatme nt (10.8 +/- 1.4 mm vs 11.1 +/- 0.8 mm), cloprostenol treatment (13.8 +/- 0 . 7 mm vs 14.0 +/- 1.3 mm) or of ovulation (15.4 +/- 0.7 mm vs 17.6 +/- 1.1 mm; p=0.10). The LH surge occurred sooner after the second injection of bu serelin (4.0 +/- 1.0 h) than after the second injection of oestradiol benzo ate (22.8 +/- 1.2 h; p<0.001). The interval between the second injection of oestradiol benzoate or buserelin and ovulation did not differ significantl y between treatment groups (1.7 +/- 0.3 days vs 1.6 +/- 0.2 days; p=0.69). CONCLUSIONS: The use of short-term progesterone treatment, combined with oe stradiol benzoate for follicular wave synchronisation, and cloprostenol to cause lysis of residual luteal tissue, is a promising alternative to establ ished methods of oestrus synchronisation in cows.