Zootechnical and genetic aspects of a Prolific Merino program

In a Prolific Merino nucleus herd of 200 ewes the ovulation rate (OR) test results obtained in 169 animals between 1988 and 1993 were compared with th ose of 113 ewes from the same herd in 1996. Whereas earlier the ratio of in dividuals showing an OR greater than or equal to 4 was only 32%, that of th e group checked in 1996 was 59%. This increase could be attributed to 40 ew es, both of whose parents had proven to be homozygous carriers of the proli fic gene. To develop the Prolific Merino breed, 21 Booroola Merino rams wer e imported from New Zealand, and mostly their frozen semen was used. Of the se rams, one was not a prolific gene carrier, 8 were homozygous carriers, 1 0 were heterozygous carriers and two had not been identified yet. Of the 36 home-bred rams, 9 proved to be homozygous by parents, 11 heterozygous, 8 h omozygous, one proved to be a non-carrier, and 7 rams and their frozen seme n were to be progeny tested. Six thousand doses of frozen semen from a tota l of 33 animals (16 imported rams and their 17 home-bred offspring) are sto red in plastic straws. Sixty-three % of this is semen reserve from rams of the Fec(B)Fec(B) genotype, belonging to 10 ram lines. The remaining 37% is gene reserve intended for creating homozygous ram lines. Only one ram (no. 3244) was bought for the nucleus herd, the other ram lines were introduced into the herd by assortative mating, using intrauterine insemination. The a verage conception rate found after 472 intrauterine inseminations was 53% w ith large (occasionally 10-100%) individual ram differences.