Day 7 eggs (oestrus = Day 0) were surgically transferred singly to the uterine horn contralateral to the CL and heifers were either slaughtered on Day 24-26 (Group 1) or palpated per rectum on Day 42 (Group 2) to determine the presence of a developing conceptus and a maintained corpus luteum. There was a fall in pregnancy rate of the control heifers in Groups 1a (6/10) and 2a (2/10) (P = 0.085). Pregnancy rate was unaffected by progesterone treatments from Day 13 to the day before slaughter in Group 1b (8/10), or to Day 23 in Group 2b (2/10). Two of the conceptuses recovered in Group 1b were developing in the presence of regressed corpora lutea. There was, however, an increase in pregnancy rate in Group 2d (6/10) compared with Group 2a (2/10) when heifers were treated with hCG from Days 13 to 35 (P = 0.085). The results indicated that embryonic death is occurring after Day 24 and suggest that a change in the nature of the embryonic signal may be occurring at this time.

Summary. The

No abstract

Placental lactogen has been detected by radioreceptor assay in bovine conceptuses colletected between 17 and 25 days post coitum, at or shortly after the time of appearance of binucleate cells in the bovine trophectoderm, but before attachment or implantation.

The non-surgical recovery of bovine embryos was examined using a three-lumen PVC catheter passed to the tip of each uterine horn. The recovery of eggs placed in Dulbecco's phosphate buffered saline, with protein was very efficient whether in boiling tubes or funnels. In the absence of protein egg recovery was considerably lower. In a group of 42 heifers, superovulated on two occasions, embryos were recovered non-surgically on day 7 after the first superovulation (Day 0 = oestrus) and surgically after the second. Laparotomy was performed on each occasion and the number of corpora lutea counted. Ovulation rate was lower at the second superovulation and a correspondingly greater recovery of embryos was obtained surgically (P less than 0.02). Non-surgical recovery rates from anaesthetised cows and heifers and from standing sedated heifers were found to be similar. The distance of the catheter tip from the utero-tubal junction (UTJ) significantly affected recovery rate (P less than 0.001). Best results were obtained when the catheter tip was within 5 cm of the UTJ. Most embryos were recovered in the first 100 ml of recovered medium. The method compares favourably with other reported methods.