This study details the production performance of ewes and lambs that originated from a terminal crossbreeding experiment that involved five Merino type dam lines and two terminal crossbreeding sire lines from 1999 to 2002. Ewe lines were SA Mutton Merino (SAMM), SAMM rams crossed to Merino ewes (SAMM cross), Dohne Merino, as well as specialist Merino lines selected for clean fleece weight (FW+) and for an increased reproduction rate (Rep+). Dormer and Suffolk rams were used as sire breeds on these ewes. Data include 777 birth and 605 weaning records of lambs and 562 production year records of ewes. At birth the progeny of SAMM ewes were heavier than those of the other ewe lines, while FW+ ewes produced smaller lambs at birth than SAMM cross and Rep+ ewes. Lamb survival was not significantly affected by ewe line or sire breed. The progeny of the dual-purpose ewe lines (SAMM, SAMM cross and Dohne Merino) were heavier than those of Merino ewes (FW+ and Rep+) at weaning. No sire breed difference was found for birth or weaning weight. The joining weights of dual-purpose ewe lines were higher than those of Merinos. Although considerable variation was found between ewe lines in terms of lamb output (number or weight of lamb weaned per ewe joined), the only significant difference was for weight of lamb weaned between SAMM cross and FW+ Merino ewes. Means for weight of lamb weaned per joining (in kg) were 37.3 for SAMM ewes, 39.6 for SAMM cross ewes, 35.5 for Dohne Merino ewes, 28.9 for FW+ ewes and 34.6 for Rep+ ewes. No differences in ewe reproduction were found between ewes joined to Dormer or Suffolk rams. The clean wool production of SAMM ewes amounted to 46% of that recorded in FW+ ewes. Corresponding percentages were 68% for SAMM cross ewes, 74% for Dohne Merino ewes and 90% for Rep+ ewes. The wool of SAMM ewes was slightly coarser in diameter than those of SAMM cross and FW+ ewes, which in turn was coarser than those of Rep+ and Dohne Merino ewes. The economic viability of crossbreeding programs involving the respective ewe lines would depend on the ratio between the prices of wool and lamb. No conclusive advantage could be demonstrated in favour of any of the sire breeds. ________________________________________________________________________________________________

A total of 497 Merino ewes were allocated to one of four experimental groups for the period 1996 to 1998. The treatments were designed to provide data on the effect of shade during an autumn lambing season and the effect of shearing prior to joining in September or prior to lambing in February. Dietary intake in shaded and control paddocks was similar, but animals in shaded paddocks consumed less water than those in control paddocks. Lambs born in shaded paddocks tended to be heavier at birth than those born in control paddocks. Survival of lambs was unaffected by the provision of shade, but lambs born in shaded paddocks were 3.8 % heavier at weaning than contemporaries born in control paddocks. Lambs born to ewes that were shorn prior to lambing tended to be lighter than those from ewes shorn prior to joining. Lamb survival prior to weaning tended to be higher in lambs born to ewes shorn prior to lambing than in those shorn prior to joining. Shearing of ewes prior to lambing had a beneficial effect on lamb survival during 1997, when the survival of progeny of ewes shorn prior to joining was low. Annual lamb survival data obtained in the present experiment were combined with that from two previous experiments conducted at the same site. The response in lamb survival of the progeny of ewes shorn prior to lambing depended on the average lamb survival observed in the control group. Multiple-born progeny of ewes shorn prior to lambing grew faster to lamb marking than contemporaries born to ewes shorn prior to joining. No difference was detected in single lambs. The clean fleece weight of ewes shorn prior to lambing was heavier than that of contemporaries shorn prior to joining. Similar benefits were found for staple strength and the frequency of mid-staple breaks. It was concluded that the shearing of ewes prior to lambing might be advantageous under certain conditions, particularly when lamb survival is likely to be low.

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Commercial Merino ewes were randomly allocated to 1 of 2 groups, which were joined either to commercial Merino or South African Meat Merino rams during October 1996 and 1997. Merino rams were involved in 161 joinings, and South African Meat Merino rams in 157 joinings. The proportions of ewes that lambed were independent of the breed of the sire when expressed relative to the number of ewes joined (0.809 and 0.801 in ewes joined to South African Meat Merino and Merino rams, respectively). The proportion of multiple lambs was similarly not affected by the breed of the service sire. Lambs sired by South African Meat Merino rams were on average ( s.e.) heavier (4.17 0.07 v. 3.86 0.07 kg; P<0.01) at birth. They also tended to have a better (0.69 v. 0.59; P<0.10) survival to weaning, and were heavier (26.9 0.6 v. 22.8 0.6 kg; P<0.01) at weaning than purebred Merino contemporaries. The combined effect of the tendency towards an improved survival rate as well as the increased lamb weaning weight resulted in a 36% increase (P<0.01) in lamb output in Merino ewes joined to South African Meat Merino ewes compared with ewes joined to Merino rams. Higher (P<0.01) proportions of ram lambs sired by South African Meat Merino rams reached slaughter weight (about 40 kg) before the onset of the dry Mediterranean summer than purebred Merinos. Two-tooth ewes sired by South African Meat Merino rams were heavier (P<0.01) at 2-tooth age (53.0 0.6 v. 52.0 0.6 kg) than purebred Merinos. The 2-tooth greasy fleece weight of South African Meat Merino sired 2-tooth ewes were lower (3.85 0.08 v. 4.66 0.09 kg; P<0.01), with a lower (66.8 0.6 v. 70.5 0.7 %; P<0.01) clean yield than that of purebred Merinos. This resulted in a marked difference in clean fleece weight between the 2 types (2.56 0.06 v. 3.28 0.06 kg, respectively). Wool produced by South African Meat Merino sired 2-tooth ewes was generally broader (21.8 0.3 v. 20.3 0.3 m; P<0.01) and shorter (87.3 1.3 v. 96.4 1.4 mm; P<0.01) than that of their purebred Merino contemporaries. The coefficient of variation of fibre diameter as well as staple strength was independent of the breed of the sire. Liveweight of adult ewes and wool traits were independent of the breed of the service sire.