Fertilizing ability of semen from rams of high- and low-prolificacy flocks

The difference between fresh undiluted ram semen from high (H) and low (L) prolificacy Romney selection lines in success in fertilizing artificially inseminated Romney, half-Romney and Cheviot ewes (unrelated and randomly allocated) was examined in 3 experiments. For ewes producing natural multiple ovulations, the fertilization rate was 71% (40/56) and 40% (20/50) for semen from H rams and L rams respectively (P < 0.01). Fertilization rates for PMSG-induced multiple-ovulating ewes were 61% (11/18) for H semen and 22% (4/18) for L semen (P > 0.05). Values for single-ovulating ewes were 52% (35/67) for H semen and 50% (28/56) for L semen (P > 0.05).