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The feasibility of breeding spring-calving, single-suckled beef cows without the use of natural service was investigated over two breeding seasons by using repeated oestrus synchrony and fixed-time artificial insemination (AI). Initially, cows were oestrus-synchronised with subcutaneous norgestomet implants inserted for 10 days, with an injection of prostaglandin before the implants were removed. The cows were inseminated once 56 hours after the implants were removed, and 12 days later they were re-treated with norgestomet implants to allow a second synchronised service. Twenty-one days after the first synchronised AI, milk samples were taken for progesterone assay and the norgestomet implants were removed. The cows received a second service 56 hours later if the 21-day milk progesterone assay suggested that they were not pregnant. All the cows receiving a second service were retreated with norgestomet implants to allow a third synchronised service as necessary. Pregnancy was later confirmed by rectal palpation. In the first year, 48 cows entered the programme and the pregnancy rates to the first, second and third synchronised services were 56, 69 and 40 per cent, respectively, with 17 per cent of cows barren at the end of the breeding period. In the second year, 69 cows entered the programme and the pregnancy rates were 58, 48 and 33 per cent to the successive services with 20 per cent of cows barren at the end of the breeding period. The accuracy of milk progesterone assay for pregnancy diagnosis was 84 per cent and 87 per cent in the first and second years, respectively.

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.

The influence of time of feeding pregnant beef cows on the timing of parturition was investigated. The results suggest that the distribution of calvings between 'day' and 'night' can be altered by time of feeding. The calculations, based on a small quantity of data, suggest that feeding at 22.00 would result in 79 per cent of cows calving between 06.00 and 22.00. On the same basis of calculation the traditional 09.00 time of feeding would result in 57 per cent of cows calving during the 'day' period. There appears to be some evidence that by feeding pregnant beef cows in the evening better supervision of calving with a smaller proportion of cows calving at night can be achieved.

The epidemiology of Nematodirus battus infection under a husbandry system based on an annual alternation of sheep and cattle was studied from 1983 to 1985. Pasture larval levels and sheep and cattle worm egg outputs were monitored from April to September each year. The level of N battus contamination on the sheep pasture and the number of clinically affected lambs increased over the three years despite grazing with cattle in the intervening year. Examination of cattle faeces demonstrated that six-month-old calves excreted moderate numbers of N battus eggs in June and July, thus contaminating next season's sheep grazing.

Profitable suckled calf production, like any other business, depends on the balance between costs and output (Fig 1). The major costs incurred in suckled calf production are feed costs to the cow. Output is simply the weight of weaned calf sold per cow put to the bull, coupled with planned marketing of good quality, cull cows. To maintain this balance at an optimum level requires correct herd management. This can only be achieved with all cows in the herd being at a similar stage of production--a compact two-month calving period. In the long term, a compact two month calving period can only be maintained with correct management of bulling and first-calved heifers. Day-to-day management decisions must be based on the current condition of the cows in relation to the target condition scores set for the system. Understanding this model allows a simple management system to be implemented and achieve the high levels of fertility and suckled calf output required for a profitable enterprise in today's economic climate.