GENETIC-PARAMETERS FOR REPRODUCTION AND LAMB PRODUCTION AND THEIR COMPONENTS AND LIVEWEIGHT, FAT DEPTH AND WOOL PRODUCTION IN HYFER SHEEP

Hyfer is a new composite breed suited to specialized lamb production and developed from Dorset (1/2), BoorooLa merino (1/4) and Trangie Fertility Merino (1/4) genotypes. Genetic parameters estimated by restricted maximum likelihood methods are reported for live-weight, wool production and a range of reproduction and lamb production traits. Estimates of heritability were 0.44+/-0.10, 0.22+/-0.08 and 0.28+/-0.08 for liveweight, ultrasonic fat depth (C site) and fat depth adjusted for liveweight respectively, for 1454 rams averaging 14 months of age, which were the progeny of 130 sires. The genetic correlation for ram liveweight and fat depth was 0.06+/-0.17 and -0.30+/-0.16 with adjusted Eat depth. Estimates of heritability for ewe live weight at 12-18 months of age and greasy fleece weight at 11-19 months of age were 0.61+/-0.10 and 0.38+/-0.08 respectively, with a genetic correlation of 0.35+/-0.13, based on 1619 ewes, which were the progeny of 135 sires. A maternal effect was significant for ewe liveweight and its inclusion in the model reduced the estimate of heritability to 0.44+/-0.09. Young ewes were joined three times in two years in an accelerated 8-monthly lambing system, and joinings commenced in mid-February, late October and mid-June. The estimates of heritability for overall ewe performance were for lambs born 0.09+/-0.03, lambs weaned 0.04+/-0.02 and weight of lamb weaned 0.06+/-0.02 (all per ewe joined). Heritabilties for the component traits were: fertility 0.03+/-0.02, litter size 0.19+/-0.04 and lamb survival 0.07+/-0.03. Estimates of repeatability for the corresponding traits ranged from 0.11 to 0.15, except for litter size (0.26+/-0.02). Estimates of heritability for lambs born, lambs weaned and weight weaned were higher for the first joining than when estimates were based on three joining records. This was associated with higher heritability for fertility from first joining (0.10+/-0.06) than for all three records and the reverse for lamb survival. Estimates of heritability for mean ewe performance were considerably higher and in agreement with the values predicted from the repeatability analyses and number of records, illustrating the value of using repeated ewe records for selection. The genetic correlations between the component traits and overall measures of lamb production were not high enough to consider using component traits as indirect selection criteria. The genetic correlations of liveweight with reproduction traits were positive, but generally not significant, and ranged from 0.01 to 0.63, except for litter size (-0.19+/-0.17). The genetic correlations of greasy fleece weight with reproduction traits were generally smaller than those for liveweight, were not significant and ranged from -0.12 to 0.32. These results, together with others, will be used to compile parameter sets for use in LAMBPLAN to provide meatsheep breeders with comprehensive breeding objectives incorporating growth, leanness, wool and reproduciton.