Recent studies relating to early embryonic death in the mare

Summary Early pregnancy loss was studied by sequential ultrasound examinations of 404 pregnancies in commercial brood mares. Overall, the rate of early pregnancy loss was 11.1 per cent. More pregnancies were lost at two to four weeks post ovulation than at four to six or six to eight weeks post ovulation (23 of 45 versus nine of 45 or 10 of 45). The mean (±se) number of days from detection of pregnancy loss until the subsequent ovulation was higher for mares in which pregnancy loss was detected at six to eight weeks post ovulation than at the earlier stages (21.1 ± 3.90 versus 12.0 ± 1.59 or 9.5 ± 1.05, respectively). Thirty‐one of 45 mares that lost pregnancies were subsequently mated; 20 (60 per cent) became pregnant but eight of these pregnancies (40 per cent) were again lost. In a second study a total of 84 embryo collection attempts were made from 14 maiden and 14 subfertile mares. More uterine flushes from maiden mares yielded embryos than from subfertile mares (29 of 42 versus 17 of 42). There were more flushes in which one or more normal embryos were recovered from maiden mares than from subfertile mares (28 of 42 versus eight of 42). There were fewer flushes in which only abnormal embryos were recovered from maiden mares than from sub‐fertile mares (one of 42 versus nine of 42).