Standing oestrus, ovarian function and early pregnancy in virgin and repeat breeder heifers.

Seventeen virgin heifers (VH) and 14 repeat breeder heifers (RBH) were inseminated in spontaneous oestrus during a total of 86 oestrous cycles. Pregnancy was checked either by non-surgical embryo collections 14 or 17 days after ovulation or by real time ultrasonography 20-26 days after ovulation. The two categories of heifers were compared with respect to duration of standing oestrus, ovarian function and plasma progesterone levels after insemination and during early pregnancy. The results indicate that the duration of standing oestrus was longer in RBHs than in VHs. Ovulation disturbances occurred and were more common among the RBHs than among the VHs. Disturbances in the development of the corpus luteum were noted in both categories of heifers, the RBHs having less luteal tissue volume than the VHs. In general, plasma progesterone levels did not differ significantly between the two categories of heifers. Despite the strict control of oestrus and ovulation as well as additional AI when necessary in this study, a poorer pregnancy result for the RBHs than for the VHs was seen.