Contraceptive efficacy of an intra-uterine device in Brahman cattle.

The contraceptive efficacy of an intra-uterine device was evaluated using 218 heifers and 212 cows on three north Australian cattle stations. The heifers were aged approximately 2 years and weighed 250-378 kg; the cows were aged 3-16 years and weighed 256-540 kg. All cattle were non-pregnant, non-lactating Brahmans. At the end of the monsoon (wet) season (April-June 1997), the cattle were allocated by stratified randomisation to the three treatments which were untreated controls (n=59), surgical ovariectomy (n=105), or implantation with a bovine intra-uterine device (BIUD; n=266). All cattle grazed and were managed as one group within each station. They were exposed to bulls (4 per 100 females) from soon after treatment until slaughter approximately 12 months later. The BIUD could not be implanted in 25% of heifers and 8% of cows due to narrow or twisted cervices. Correct placement of the BIUDs appeared to be achieved in 57% of heifers and 72% of cows. At slaughter, the devices were incorrectly positioned in 73% of heifers and 49% of cows into which BIUDs had been inserted and that remained non-pregnant. Uterine perforations by the BIUD were observed in 35 and 45% of these heifers and cows, respectively; most perforations appeared to occur during implantation. Low-grade endometritis was observed at slaughter in most BIUD-implanted animals; 2% had pyometra.BIUD animals did not have significantly different growth to that of control or ovariectomised animals, other than when ovariectomy suppressed growth following surgery. Most animals implanted with BIUDs appeared to have normal ovarian function and animals were observed mating. All ovariectomised animals remained non-pregnant. Over 80% of controls were pregnant within 8 months of exposure to bulls, except heifers at one station where pregnancy rate was restricted to 25% as a result of severe nutritional conditions. Pregnancy was diagnosed in 21% of heifers and 33% of cows with implanted BIUDs. The device remained correctly positioned and with no pregnancy diagnosed in the year following implantation in only 2% of heifers and 14% of cows originally allocated. Because of the difficulties of implanting BIUDs, the high frequency of associated uterine injury, the high pregnancy rate in implanted animals, and that growth was unaffected by the presence of a BIUD, it was concluded that the device had poor contraception efficacy and no growth-promotant effect in Brahman cattle.