PERFORMANCE OF CROSSBRED PROGENY OF TRANGIE FERTILITY MERINO AND BOOROOLA MERINO RAMS AND POLL DORSET EWES .3. REPRODUCTION, LIVEWEIGHT ANDWOOL PRODUCTION OF ADULT EWES

Reproduction, liveweight and wool production are reported for 4 cohort s of 377 Trangie Fertility x Dorset (TD) and 261 Booroola x Dorset (BD ) ewes over 6 years. The ED ewes were 3-4 kg lighter (P<0.001) and had a higher ovulation rate prior to joining in February-March (2.37 +/- 0.03 v. 1.65 +/- 0.03) than TD ewes. This resulted in a higher litter size (2.07 +/- 0.03 v. 1.66 +/- 0.04) and number of lambs born per ewe joined (1.92 +/- 0.04 v. 1.56 +/- 0.04) for the BD ewes. Lamb surviva l was lower from BD than TD ewes (0.71 +/- 0.02 v. 0.85 +/- 0.02), so that the 2 ewe strains weaned the same number of lambs. The growth rat e of lambs was lower from the BD ewes and overall they weaned 3.8 kg l ess (P<0.001) weight of lamb than TD ewes. Chill (index of environment al conditions at lambing), litter size and average birth weight of lam bs in the litter (linear and quadratic) affected (P<0.001) lamb surviv al. At moderate levels of chill there was little difference in surviva l of single and twin lambs from BD and TD dams when birth weight was 4 -5 kg, but survival declined more rapidly for progeny of BD ewes at lo wer birth weight. Under severe lambing conditions survival was depress ed more for lambs born from BD ewes than TD ewes. Almost all ewes expr essed oestrus over the 3, 6-week periods, December-January, January-Fe bruary and March (joining). There was significant variation (P<0.001) in incidence of oestrus due to year and age (linear and non-linear), b ut not liveweight at joining, and there was little difference between ewe strains. Similarly, for post-lambing oestrus (to fit 8-monthly joi ning) and post-lambing anoestrous interval, there was little differenc e between strains, but year and age were highly significant (P<0.001). BD ewes had a lower (P<0.001) greasy fleece weight (3.76 v. 3.86 kg), than TD ewes. BD ewes were classified as either carriers (F+) or non- carriers (++) of the Fec(B) gene, which was significant (P<0.001) for ovulation rate (+1.14 ovulations), litter size (+0.8 lambs), lamb surv ival (-18%), lambs born per ewe joined (+0.64 lambs) and total weight of lamb born per ewe joined (0.5 kg, P<0.01). The effect of the Fec(B) gene was nonsignificant for lamb survival when litter size and lamb b irth weight (P<0.001) were included in the model. Repeatability estima tes based on over 3 records per ewe were about 0.2 for lambs born, wei ght of lamb born, lambs weaned and weight of lamb weaned per ewe joine d. Component traits ranged from 0.27 for litter size to 0.10 for lamb survival, with fertility intermediate (0.15). Creasy fleece weight (0. 72) and ovulation rate (0.41) had high repeatabilities with post-lambi ng anoestrous interval being low (0.11). Repeatability for ovulation r ate was reduced to 0.34 when F+ ewes were excluded.