Abstract

The trial reported in this paper was undertaken at the Rotomahana Research Station to compare the performance of sheep of different genetic background and breeding history. Border Leicester, Coopworth and Romney rams from different sources were mated to Romney ewes representing a wide range of genetic sources between 1979 and 1983. Rams from 6 Romney strains were sampled including a commercial industry sample, the Ruakura High Fertility (RHF) flock, a Romney stud and 3 group breeding schemes. The Coopworth ram source was also a large group breeding scheme. Data collected on the first cross females born between 1979 and 1983 and lambing between 1981 and 1985 are summarised in this paper. Analyses of ewe hogget performance (growth, wool production and oestrous activity) revealed relatively minor variation among the 6 Romney strains, with the exception of greater oestrous activity in RHF-sired hoggets. Coopworth and Border Leicester crosses were heavier, had higher fleece weights and showed more oestrous activity than straightbred Romneys. Highest reproductive performance was obtained from Coopworth and Border Leicester crosses reflecting breed differences, positive heterosis and heavier ewe body weights. Among the 6 Romney strains greatest variation in reproductive performance was seen for litter size with the RHF-sired ewes excelling and also having the best performance for lambs weaned per ewe joined and lambs weaned per ewe joined as a ratio of ewe body weight. Similarly, the litter size advantage for ewes sired by rams from the 3 Romney group breeding schemes demonstrated that selection for reproductive performance over a period of 10 to 15 years has been successful.

SC, Hathaway, and AI McKenzie

Proceedings of the New Zealand Society of Animal Production, Volume 47, , 85-87, 1987