A controlled internal drug release device, containing progesterone (CIDR-B), was evaluated as an aid to reproductive management in beef cattle in 2 trials. In Trial 1, 223 animals, comprising 64 early calving cows, 61 late calving cows, 59 maiden cows and 39 15-month heifers (yearling heifers), were treated intravaginally with CIDR-B for either 12d (plus 10mg oestradiol benzoate; 12d CIDR-B + ODB) or for 15d (15d CIDR-B). CIDRs were reused for 5d in half the animals from 16d after initial use. In Trial 2, 145 animals, comprising 53 early calving cows, 43 late calving cows and 49 15 month heifers, were treated intravaginally with CIDR-B for either 14d (14d CIDR-B) or 21d (21d CIDR-B). At CIDR-B withdrawal, half of the animals received an intra-muscular injection of 400IU PMSG. In Trial 1, within 48h of CIDR-B withdrawal, 58% and 54% of the animals were mated in the 15d CIDR-B and 12d CIDR-B + ODB groups respectively. Within 96h, the incidence of mating was 87% and 76% respectively with the difference between treatments being more pronounced in cows (88% v 74%; P<0.05) than in yearling heifers (86% v 84%). In cows, pregnancy rate to mating over the first 4 days was 50% in the 15d CIDR-B group and 67% in the 12d CIDR-B + ODB group (P<0.05). In yearlings, there was an opposite tendency (71% v 44%; P>0.1). Final pregnancy rate was 92% with no treatment group differences. CIDR-B ruse did not alter conception rates to first or second service but did synchronise returns. In Trial 2, within 4d of CIDR-B removal, 88% and 97% of the 14d CIDR-B and 21d CIDR-B groups had mated. In the 0 and 400 IU PMSG groups, 90% and 95% had mated. Pregnancy rate in treated animals to mating over the first 4 days following CIDR-B withdrawal were similar in the 14d CIDR-B and 21 CIDR-B groups (54% v 57%) and 0. and 400 IU PMSG groups (55% v 56%). However, pregnancy rate tended to be lower in yearling heifers compared to cows (46% v 57%; P>0.1). Final pregnancy rate tended to be higher in the 21d CIDR-B group than in the 14d CIDR-B group (89% v 82%; P>0.1). Fewer heifers were finally pregnant compared to early and late calving cows (74% v 85% v 95%). In both trials, longer CIDR-B treatment intervals were associated with earlier and more synchronised matings. Acceptable pregnancy rates were achieved with CIDR-B treatment intervals of between 12d and 21d. These results indicate that CIDR-B treatment without supplementary hormones can produce acceptable synchrony and fertility in naturally mated suckling beef cows and yearling heifers.

AJ, Pearson, MG Ashby, and LD Staples

Proceedings of the New Zealand Society of Animal Production, Volume 49, , 47-52, 1989
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