Reproductive wastage in the androstenedione-immune ewe

An experiment was carried out using 320 adult Merino ewes to examine the effects of immunization against an androstenedione human serum albumin conjugate (Fecundin) on ovulation rate, fertilization rate and embryo viability at days 2, 9 and 13-14 after fertilization. The ovulation 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 fertilization rate of recovered oocytes was unaffected by immunization. The mean number of normal embryos per ewe pregnant (prolificacy) was higher and the proportion of ewes pregnant (fertility) was lower in immunized than in the control ewes. The distribution of the number of cells per embryo showed no differences in developmental age over the period 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 compared with 64% in immunized ewes. The majority of blastocysts recovered 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, respectively). In control ewes single blastocysts were larger than twin blastocysts, but for the immunized ewes this difference was not significant. Both single blastocysts (P < 0.01) and twin blastocysts (P < 0.05) from immunized ewes were smaller than those from control ewes.(ABSTRACT TRUNCATED AT 250 WORDS)