REPRODUCTIVE WASTAGE IN THE ANDROSTENEDIONE-IMMUNE EWE

An experiment was carried out using 320 adult Merino ewes to examine t he effects of immunization against an androstenedione human serum albu min conjugate (Fecundin) on ovulation rate, fertilization rate and emb ryo viability at days 2, 9 and 13-14 after fertilization. The ovulatio n rate of immunized ewes (2.19 +/- 0.06) was greater (P < 0.001) than that of control ewes (1.43 +/- 0.04). The recovery rate of embryos or of unfertilized oocytes on day 2 was reduced in immunized ewes, but fe rtilization rate of recovered oocytes was unaffected by immunization. The mean number of normal embryos per ewe pregnant (prolificacy) was h igher and the proportion of ewes pregnant (fertility) was lower in imm unized than in the control ewes. The distribution of the number of cel ls per embryo showed no differences in developmental age over the peri od of sampling, the majority of embryos at this time being at the two- to four-cell stage of development. At day 9 of pregnancy, blastocyst recovery rates were lower in immunized than in control ewes. About 90% of blastocysts recovered were developing normally in control ewes com pared with 64% in immunized ewes. The majority of blastocysts recovere d on day 9 had hatched from the zona pellucida prior to recovery (mean values were 94.2% and 87.8% for control and immunized groups, respect ively). In control ewes single blastocysts were larger than twin blast ocysts, but for the immunized ewes this difference was not significant . Both single blastocysts (P < 0.01) and twin blastocysts (P < 0.05) f rom immunized ewes were smaller than those from control ewes. By day 1 3-14 of pregnancy the blastocyst recovery rate, the percentage of blas tocysts developing normally and the number of blastocysts per 100 corp ora lutea were all significantly depressed in immunized compared with control ewes, but there were no differences between single and twin bl astocysts in the size of the trophoblast or of the embryonic disc for either group. Blastocysts from immunized ewes were smaller than blasto cysts of comparable ages from control ewes. The longest diameter of th e trophoblast (P < 0.001), the diameter of the trophoblast at 90-degre es to the longest axis (P < 0.05) and the longest diameter of the embr yonic disc (P < 0.001) were all reduced in embryos recovered from immu nized compared with control ewes.