The feasibility of replacing natural service in the suckler herd with artificial breeding (artificial insemination or embryo transfer), following synchronisation of oestrus in breeding animals, was investigated. In 1991 a herd of 143 spring-calving beef cows, matched for date and ease of calving, sex of calf, parity, body condition score and liveweight, were assigned to one of five controlled breeding programmes: natural service (group 1); single oestrus synchronisation using a norgestomet implant and fixed time insemination followed by natural service (group 2); double synchronisation with two consecutive norgestomet implants each with fixed-time insemination followed by natural service (group 3); synchronised as for group 2, but subjected to a movement stress two days after insemination (group 4); and cows synchronised by intravaginal progesterone/prostaglandin regimen with non-surgically transferred in vitro fertilised embryos followed by natural service (group 5). The percentage pregnancy rates to the first and second heats and overall were, respectively: group I, 55.5, 66.7 and 92.6; group 2, 44.4, 71.4 and 89.9; group 3, 52.0, 78.0 and 96.0; group 4, 55.0, 58.3 and 81.5, and group 5, 40.0, 68.2 and 85.7 per cent. In groups 2, 3, 4 and 5 the costs per pregnancy for artificial insemination or embryo transfer were 40.50 pounds, 56.62 pounds, 32.40 pounds and 149.98 pounds, respectively, and the calf weaning weights for groups 1, 2, 3, 4 and 5, adjusted for date of calving, were 250 kg, 255 kg, 252 kg, 261 kg and 259 kg, respectively.
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