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Abstract
AIM: To evaluate the efficacy of a programme using oestradiol benzoate, progesterone and the prostaglandin-F2α (PG) analogue, cloprostenol, to synchronise oestrus and ovulation in dairy cows, compared with a programme using a gonadotropin-releasing hormone (GnRH) agonist, buserelin, and cloprostenol.
METHODS: Twenty non-lactating dairy cows, at random stages of the oestrus cycle, 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 𝛍g cloprostenol IM on Day 9 and 1 mg oestradiol benzoate on Day 10. In Treatment 2 (GPG; n=10), cows were injected with 10 𝛍g buserelin IM on Day 0, 500 𝛍g cloprostenol IM on Day 7 and 10 𝛍g buserelin on Day 9. The ovaries of all cows were examined by ultrasonography, using an 8 MHz probe, from 5 days before the initial treatment until ovulation. Cows were observed for oestrus 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) concentrations.
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 followed by atresia or ovulation of the dominant follicle. Emergence of a new follicular 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 emergence or size of the largest follicles at either the time of initial treatment (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 buserelin (4.0 ± 1.0 h) than after the second injection of oestradiol benzoate (22.8 ±1.2 h; p<0.001). The interval between the second injection of oestradiol benzoate or buserelin and ovulation did not differ significantly 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 oestradiol benzoate for follicular wave synchronisation, and cloprostenol to cause lysis of residual luteal tissue, is a promising alternative to established methods of oestrus synchronisation in cows.