Use of GnRH and PGF(2)alpha for synchronisation of oestrus in confined dairy herds

The combination of GNRH and prostaglandin F(2)alpha allows the control of t he luteal phase and the follicular dynamic that coexist in the ovary, facil itating precise oestrus synchronisation schemes. The study was intended to characterise the reproductive response to the use of this combination for a n oestrus detection program. The study considered 423 clinically sound dairy cows, from two herds, 1 to 7 calvings and adjusted production levels from 7.500 to 12.500 Kg. Cows wer e confined under a free-stall system and both herds were under a sanitary a nd nutritional control program. Since 50 days after calving, cows received 10 mu g of buserelin and those having a corpus luteum, based on ultrasound assessment 7 days later, received 0.75 mg of tiaprost, At the moment of tia prost administration and 72 h later, milk was collected for progesterone by RIA, The results showed that 90.7% (206/227) cows had a functional corpus luteum at the moment of prostaglandin administration, 93.7% (193/206) responded w ith luteolysis, and that 85.0% (164/193) showed oestrus behaviour. The inte rval to the oestrus was 66 +/- 15.2 h with 93.9% of cows presenting oestrus between days 2 and 4, with a high percentage(54.9%) presenting oestrus on day 3 after tiaprost administration. Finally, the conception rate was simil ar to the untreated controls (55.4% (144/269) vs. 50.3% (82/163) for treate d vs. unteatred respectively. No differences were found between herds in an y parameter considered in the study. Based on the results, it can be conclu ded that the combination of GnRH and PGF(2)alpha can be an effective altern ative to approach the problem of estrus detection in confined dairy herds.