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A group of 97 spring-calving beef cows were initially oestrus synchronised with controlled internal drug release (CIDR) intravaginal progesterone implants inserted for nine days and a prostaglandin injection on day 7. Approximately half the cows were given 10 microg buserelin when the implants were inserted, and they all received a single fixed-time artificial insemination (AI) 56 hours after the withdrawal of the implants. The overall pregnancy rate to the first synchronised AI was 55 per cent, the buserelin-treated cows having a pregnancy rate of 63 per cent compared with 47 per cent in the untreated cows (P>0.05). Sixteen days after the first synchronised AI all the cows were re-implanted with used CIDR implants which were removed five days later, and the cows received a second synchronised AI on days 23 to 24. Cows which received the second AI were implanted with new CIDR devices 16 days later and these were removed after five days and the non-pregnant cows received a third synchronised AI. The pregnancy rates to the second and third synchronised services were 74 per cent and 75 per cent, respectively.

The potential value of milk progesterone profiles in conjunction with rectal examination in the diagnosis of subfertility in beef suckler cows was investigated. Ten of 20 cows suckled their calves three times per day and the other 10 suckled their calves continuously. Milk samples were collected twice weekly during the 21 days prior to first service and up to day 50 post mating in cows confirmed pregnant. The uterine and ovarian states of the cows were examined per rectum weekly between calving and first service. Progesterone profiles of cows conceiving to first service showed a typical smooth curve, while those of cows failing to conceive were irregular and indicated disturbances in the normal functioning of the corpus luteum.

The time to resumption of ovarian cycles was determined in 27 post partum beef suckler cows by twice weekly milk progesterone analysis and was 24.5 +/ 1.6 (SEM) days. Treatment of 87 cows with a double injection of 500 micrograms cloprostenol at an interval of 11 days resulted in 55 cows (63.2 per cent) responding by a fall in progesterone levels and ovulation. Thirty-eight of these cows (43.7 per cent of total) subsequently conceived to a timed double insemination. Eight (9.2 per cent) had high progesterone levels at the second injection had failed to respond; three (3.4 per cent) had a prolonged period of low progesterone levels after the first injection which were still low when the second was given. A further 21 cows (24.1 per cent) had low progesterone levels at the time of the second injection but could not be categorised further with certainty because of lack of previous samples. These cows were treated at a significantly earlier stage post partum than the rest and in fact were treated earlier than the recommended day 42. However, four of the 21 cows conceived to the timed insemination resulting in a total conception rate of 48.3 per cent.