PERFORMANCE OF CROSSBRED PROGENY OF TRANGIE FERTILITY MERINO AND BOOROOLA MERINO RAMS AND POLL DORSET EWES .2. REPRODUCTIVE ACTIVITY, LIVEWEIGHT AND WOOL PRODUCTION OF EWE LAMBS

Liveweight, wool production, oestrous expression and ovulation rates o f 260 Trangie Fertility Merino x Dorset (TD) and 278 Booroola Merino x Dorset (ED) ewes born in late winter-spring over 4 different years we re analysed from post-weaning to first joining at about 19 months of a ge. The percentage of ewes expressing oestrus reached a peak of 68% in May-June, declined to 7% in September and rose to 93% in January prio r to first joining. The proportion of ewes ovulating followed a simila r pattern. The proportion of ewes expressing oestrus in March, May and June increased (P<0.001) substantially with increasing age and livewe ight, which accounted to some extent for the large differences in oest rous activity between years. There was little difference between the s trains in proportion of ewes expressing oestrus or ovulating throughou t the year. TD ewes were heavier (P<0.001) than ED ewes, the differenc e increasing from 2 to 4 kg at 7 and 19 months. They also produced 0.3 kg more clean wool which had 1.2 mu m higher fibre diameter (P<0.001) . Ovulation rate, measured in each of 2 years at 2-monthly intervals, increased from 7 to 19 months of age. ED ewes had a higher ovulation r ate than TD ewes on all occasions, and the difference averaged +0.4 ov ulations. The mean ovulation rate in February (19 months) for ewes bor n over 3 years was 2.1 ova for ED and 1.4 ova for TD ewes (P<0.001). B ased on subsequent ovulation rate and litter size records, 42% of the ED ewes were identified as carriers of the Fec(B) gene. Ages at first oestrus and ovulation varied considerably between years (P<0.001). The re was no difference between the strains in age at first oestrus, alth ough ED ewes first ovulated at a younger age (P<0.05) than TD ewes. Th e stud of origin of the dam, dam age, dam parity and birth type were n ot significant for any reproduction trait. There was significant (P<0. 001) variation in liveweight due to the origin of the dam. Half-sib es timates of heritability for ewe liveweight, ovulation rate at various seasons and wool production traits were generally high with relatively high standard errors as they were based on 23-40 degrees of freedom f or sire.