title: Re-insertion of a progesterone-containing intravaginal device to synchronise returns to oestrus in dairy heifers.
abstract: Recommendations for oestrus synchronisation of dairy heifers using progesterone-containing intravaginal devices suggest re-insertion of used devices 16 days after first insemination for a period of 5 days to allow a second opportunity for artificial insemination. Controlled studies on the effectiveness of re-using intravaginal devices to synchronise returns to oestrus in non-pregnant dairy heifers are lacking. A clinical trial was conducted involving 750 Friesian heifers in 13 herds. After 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 synchronisation programme, 47.5% of heifers remained non-pregnant. Re-insertion of used intravaginal devices for 5 days significantly increased the 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 intravaginal 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-insertion at 14 or 16 days after first insemination was equally effective in increasing visible returns to service. However, the number of non-pregnant heifers synchronised for a second round of artificial insemination was less than expected. Conception rate to the re-synchronised oestrus was unaffected by the treatment. It is concluded that the additional procedures of CIDR re-insertion, removal, tailpainting and insemination involved in there-synchrony programme, and the relatively low in-calf rate to the re-synchronised round of insemination, reduced the potential benefits of re-synchronisation.
authors: Department of Veterinary Clinical Sciences, Massey University, Palmerston North, New Zealand.
authors: D W
authors: DW
authors: Hanlon
authors: N B
authors: NB
authors: Williamson
authors: I J
authors: IJ
authors: Steffert
authors: J J
authors: JJ
authors: Wichtel
authors: D U
authors: DU
authors: Pfeiffer