Seventy-three Friesian dairy cows culled as repeat breeders were slaughtered three to six, 16 to 19 or 40 to 49 days after insemination to establish fertilisation and embryo survival rates. Fertilisation rate following a single insemination was 72 per cent. The estimated embryo survival rates for days 16 to inverted question mark19 and 40 to 49 were 67 per cent and 76 per cent, respectively. The previous breeding history of the cows showed that only eight (11 per cent) had consistently regular returns (18 to 24 days) to service. Fifty-three (75 per cent) had a combination of both long and short returns to service. Before service on experiment, 64 (89 per cent) cows had regular cycles and the six cows which repeated from the 40 to 49 days group, five (83 per cent) had regular return intervals. It is suggested that errors in oestrus detection contribute substantially to the problem of repeated returns to service of dairy cows in Ireland.
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