Hyfer is a new composite breed suited to specialized lamb production and developed from Dorset (+), Booroola Merino (+)and Trangie Fertility Merino (+) genotypes. Genetic parameters estimated by restricted maximum likelihood methods are reported for liveweight, wool production and a range of reproduction and lamb production traits. Estimates of heritability were 0 44 � 0.10, 0.222 � 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 fat depth. Estimates of heritability for ewe liveweight 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). Heritabilities 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.

Reproductive performance of ewes in a large Dorset stud flock is reported. The data included 2488 ewes with 10016 joining records over 25 years. Average performance for reproductive traits were: fertility 92%, litter size 1.31, neonatal lamb survival 91%, lamb survival to weaning 85%, with overall lambs born 1.20 and lambs weaned 1.02 per ewe joined. Differences between breeds (Poll Dorset and Dorset Horn), season of birth (spring and autumn) and season of joining (spring and autumn) were significant for most reproduction traits. Linear and quadratic regressions for age of ewe at joining were highly significant for all traits (P < 0.001) with maximum performance between three and six years of age.Estimates of heritability for ewe reproductive traits were: 0.062~ 0-02 for number of lambs born and 0.04f0.01 for number of lambs weaned per ewe joined, and component traits, 0 . 0 2 f 0 -01 for fertility, 0 0 8 f 0 -02 for litter size and 0 -0Of 0.01 for lamb survival. Estimates of repeatability were less than 0.14 for all the reproduction traits, which resulted in substantially higher predicted heritabilities when repeated records were used. Heritability estimates for average ewe lifetime performance, with approximately four records, were 0.O8f 0 06 for lambs born, 0 . 1 2 f 0.05 for lambs weaned, O.O8f 0 -04 for fertility, O . l 9 f 0 -04 for litter size and zero for lamb survival. The genetic correlations between litter size and lambs born and weaned were close to unity, whereas those for fertility were lower and declined from lambs born ( 0 . 6 l f 0.22) to lambs weaned (0 -4 5 f 0.30). The estimated heritability for ewe longevity, defined as the number of years the ewe remained in the breeding flock, was 0-OGf 0-03.The potential for genetic improvement in reproductive rate is discussed in relation to other reports in the literature and in the context of the roles of the Dorset breed in the Australian lamb industry. Increased reproductive rate in Dorset flocks impacts on stud profitability and the rate of genetic improvement from selection for other traits such as liveweight. The parameter estimates derived will be used in compiling breed-specific parameter sets for genetic evaluation in LAMBPLAN,

Commercial application of multiple ovulation and embryo transfer (MOET) technology will be subject to practical constraints and economic rationalism. This study examines use ofMOET in its most profitable arena: to breed stud rams which will disseminate genetic improvement widely through multiplier studs to commercial flocks. A deterministic prediction is used to evaluate schemes based on an open nucleus MOET group within a Merino parent stud, taking account of genetic merit and inbreeding. Selection is based on clean fleece weight with an assumed heritability of 0-4. Embryos are collected at a rate equivalent to 3-45 live lambs per donor. Benefits of MOET were calculated from the discounted expressions of rams sold, and compared with the costs incurred. As the proportion of the flock born from MOET increases, the rate of genetic gain increases rapidly at first, but diminishing returns are observed. The costs ofMOET increase linearly with the number of lambs produced, so the optimum proportion ofMOET lambs is for practical purposes always less than 100%. Some use of MOET was profitable provided the stud sells sufficient stud rams each year. Sensitivity tests found that other parameters had only a small impact on the optimum level ofMOET. In general however, changes which increased the rate of genetic gain (heritability, flock size) or increased its value (wool price, lower discount rate) increased the optimum number ofMOET lambs. The results should provide guidelines to optimum investment in MOET for the wool industry. An across flock genetic evaluation scheme is probably necessary to motivate this investment.

The genetic and phenotypic variances and covariances for liveweight at 5 to 19 months of age and ultrasonic subcutaneous fat depth were estimated using REML procedures for the Border Leicester, Suffolk, Corriedale, Coopworth and Gromark breeds. The data comprised 12 923 progeny from 46 flocks, representing 590 sires, and were collected by the New South Wales Meatsheep Testing Service between 1981 and 1990. Fixed effects included in the model were management group, birth type, rearing type, age of dam and age of lamb. Each breed was analysed separately, and the larger breed data sets (Border Leicester and Suffolk) were split on age at measurement. The estimates of heritability for the various data sets ranged from 0.09 � 0.09 to 0.40 � 0- 10 for liveweight and 0.07 � 0.08 to 0.40 � 0 -07 for fat depth. There was a moderate positive genetic correlation (0 - 14 to 0.77) between liveweight and fat depth. Adjustment of fat depth for liveweight reduced this genetic correlation (-0.34 to 0.24) and had little effect on the heritability of fat depth, which then ranged from 0-06 � 0-08 to 0.44 � 0.07. Variation in estimates between the breeds is discussed. The results will be used to provide breed-specific parameters to improve the accuracy of Estimated Breeding Values produced by LAMBPLAN, Australia's national performance testing scheme for meatsheep. The mean age of sires at the birth of progeny varied from 3-2 to 3-5 years amongst the breeds, with 14% to 30% of animals sired by rams 5 years of age or older. Sire-use patterns in some breeds indicated high levels of inbreeding.

Performance of sheep from a large Corriedale stud flock was assessed. Weaning and yearling liveweights, greasy and clean fleece weights, clean fleece yield and average fibre diameter records on approximately 3000 animals representing 64 sires were analysed. Also scrotal circumference of 1009 rams representing 27 sires were analysed. Some 3740 reproduction records over 11 years, for 980 ewes representing 114 sires, were also analysed. Heritability estimates were 0 34 �0.07 for weaning liveweight, 0.132 � 0.04 for yearling liveweight, 0.32 � 0.07 for greasy and 0.29 � 0.07 for clean fleece weights, 0.534 � 0 10 for clean fleece yield, 0-56 � 0 10 for yearling and 0 62 � 0 - 14 for hogget fibre diameters and 0.l5 � 0.11 for scrotal circumference. The genetic correlations between liveweight and fleece weight ranged from 0.13 to 0.34, and those for liveweight and fibre diameter were close to zero. The genetic correlations of scrotal circumference with liveweight and wool traits were positive and moderate. Reproductive performance in the flock was high, with fertility 92% and litter size 1.62, resulting in 148% lambs born and 130% lambs tagged alive of ewes joined. Estimated heritabilities for reproduction traits were 0-03 � 0.02 for lambs born and for lambs tagged, and the component traits, fertility 0 01 � 0 -02, litter size 0.04 � 0.03 and neonatal lamb survival was zero. Lambing date had a heritability of 0.06 � 0.03. Estimates of repeatability ranged from 0-04 � 0-01 for fertility to 0.07% 0.02 for lambs tagged and lambing date. Predicted heritabilities for the average of 3.8 records per ewe generally agreed with those estimated for average ewe lifetime performance, which ranged from 0.02 � 0.08 for fertility to 0.12 � 0.09 for lambs tagged and 0.l3 � 0.09 for lambing date.