During 1993 outbreaks of diarrhoea in adult dairy cows in three geographically unrelated herds were found to be caused by bovine viral diarrhoea virus (BVDV). The affected animals showed signs of acute watery diarrhoea, agalactia and pyrexia (39.4 to 42 degrees C). Ulceration of the buccal mucosa, a mucoid nasal discharge and stiffness were inconsistent signs. The disease spread rapidly in each case. The diagnosis was confirmed by the isolation of non-cytopathic BVDV from blood and tissues and by the demonstration of significantly rising titres to BVDV by an ELISA. The highest morbidity recorded was 40 per cent with one herd experiencing a 10 per cent mortality. There was no increased incidence of abortion in any of the herds, either at the time of or subsequent to the outbreaks of diarrhoea. In one herd the purchase of a persistently viraemic heifer 14 days before the outbreak was thought to be the source of infection, but in the other two herds the source was not established.

To investigate whether there was a subpopulation of repeat breeders (cows or heifers that returned to oestrus after three inseminations) that were less fertile after a fourth artificial insemination (AI) with or without additional embryo transfer, and to estimate the efficacy of AI plus embryo transfer to overcome repeat breeding problems, a two-part investigation was carried out. Part 1 involved 85 repeat breeders and 85 controls subjected to AI alone. In part 2, 128 repeat breeders received AI on day 0 plus an embryo transfer seven days later, while controls received embryo transfer alone on day 7. In repeat breeders, the interval between calving and pregnancy was 80 days longer than in the controls (P=0.01), irrespective of previous fertility treatment which had mainly focused on the ovaries. The incidence of dystocia was similar in repeat breeders and in controls, but repeat breeders had a higher previous incidence of moderate uterine infection compared with controls (P=0.04). In repeat breeder cows, pregnancy rates for AI alone were 30 per cent after the fourth AI (controls: 45 to 64 per cent after one to three inseminations) compared with 52.6 per cent after a fourth AI with embryo transfer (controls with embryo transfer alone: 49 per cent). Successful pregnancies after a fourth AI plus embryo transfer produced a 6.25 per cent incidence of twins.

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