Effects of differential ewe condition at mating and early postmating nutrition on embryo survival.

Ewes in two trials were given either a high (H) or a low (L) level of premating nutrition for 19 wk followed by 6 wk of either H or L postmating nutrition to examine effects on reproductive performance. Trial 1 ewes were 5- to 8-yr-old Polypays and Trial 2 ewes were 3-yr-old Polypay and Coopworth x Polypay crosses. Ewes given L nutrition premating were either immunized with androstenedione-7-carboxyethylthioether:human serum albumin (also known as ovandrotone or Fecundin) in (diethylamino)ethyl-dextran adjuvant (Trial 1) or flushed for 3 wk premating (Trials 1 and 2) to enhance ovulation rates. All ewes were synchronized for mating in both trials. Trial 1 premating treatments created a difference of 10 kg in BW and 1.1 in condition score units between H and L ewes preflushing; flushing halved the BW difference. Ovulation rates averaged 2.58 and were similar for H, L-flushed, and L-immunized (LI) ewes; however, both conception rate and litter size were lowest for immunized ewes. Among both twin and triple-ovulating ewes, highest mean litter size was produced by H ewes, followed in order by L and LI ewes. High postmating nutrition increased BW by 6 kg vs slight weight loss in L ewes, but postmating treatments did not affect litter size of either twin or triple ovulators. The H and L premating groups of Trial 2 differed by 18 kg and 2.2 condition score units preflushing. The H ewes exhibited higher ovulation rates (overall mean = 2.63) but lower conception than the L ewes to synchronized estrus. Litter size averaged 2.15 for H ewes vs 1.82 for L ewes. Among both twin and triple ovulators, L ewes produced fewer lambs than H ewes.(ABSTRACT TRUNCATED AT 250 WORDS)