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

Abstract

Liveweight, wool production, oestrous expression and ovulation rates of 260 Trangie Fertility Merino x Dorset (TD) and 278 Booroola Merino x Dorset (BD) ewes born in late winter-spring over 4 different years were analysed from post-weaning to first joining at about 19 months of age. 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 prior to first joining. The proportion of ewes ovulating followed a similar pattern. The proportion of ewes expressing oestrus in March, May and June increased (P<0.001) substantially with increasing age and liveweight, which accounted to some extent for the large differences in oestrous activity between years. There was little difference between the strains in proportion of ewes expressing oestrus or ovulating throughout the year. TD ewes were heavier (P<0.001) than BD ewes, the difference increasing from 2 to 4 kg at 7 and 19 months. They also produced 0.3 kg more clean wool which had 1.2 pm 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. BD ewes had a higher ovulation rate than TD ewes on all occasions, and the difference averaged +0.4 ovulations. The mean ovulation rate in February (19 months) for ewes born over 3 years was 2.1 ova for BD and 1.4 ova for TD ewes (P<0.001). Based on subsequent ovulation rate and litter size records, 42% of the BD ewes were identified as carriers of the FecB gene. Ages at first oestrus and ovulation varied considerably between years (P<0.001). There was no difference between the strains in age at first oestrus, although BD ewes first ovulated at a younger age (P<0.05) than TD ewes. The stud of origin of the dam, dam age, dam parity and birth type were not significant for any reproduction trait. There was significant (P<0.001) variation in liveweight due to the origin of the dam. Half-sib estimates 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 for sire.