REINSERTION OF A PROGESTERONE-CONTAINING INTRAVAGINAL DEVICE TO SYNCHRONIZE RETURNS TO ESTRUS IN DAIRY HEIFERS

Recommendations for oestrus synchronisation of dairy heifers using pro gesterone-containing intravaginal devices suggest reinsertion of used devices 16 days after first insemination for a period of 5 days to all ow a second opportunity for artificial insemination. Controlled studie s on the effectiveness of re-using intravaginal devices to synchronise returns to oestrus in nonpregnant dairy heifers are lacking. A clinic al trial was conducted involving 750 Friesian heifers in 13 herds. Aft er an initial synchronisation programme, the used intravaginal devices were re-inserted 14 or 16 days after first insemination into half of the heifers in each herd for a period of 5 days. After the first synch ronisation programme, 47.5% of heifers remained non-pregnant. Re-inser tion of used intravaginal devices for 5 days significantly increased t he number of non-pregnant heifers detected in oestrus and inseminated by 48 hours after device removal compared to heifers in which devices were not re-inserted (45.2% v. 27.3% p < 0.05, in herds where intravag inal devices were re-inserted on day 14; 48.8% v. 13.6%, p < 0.05, in herds where intravaginal devices were re-inserted on day 16). Re-inser tion at 14 or 16 days after first insemination was equally effective i n increasing visible returns to service. However, the number of non-pr egnant heifers synchronised for a second round of artificial inseminat ion was less than expected. Conception rate to the re-synchronised oes trus was unaffected by the treatment. It is concluded that the additio nal procedures of CIDR re-insertion, removal, tailpainting and insemin ation involved in the re-synchrony programme, and the relatively low i n-calf rate to the re-synchronised round of insemination, reduced the potential benefits of re-synchronisation.