EFFECTS OF BOOROOLA MERINO BREEDING AND THE FEC(B) GENE ON PERFORMANCE OF CROSSES WITH LONGWOOL BREEDS .1. EFFECTS ON GROWTH, ONSET OF PUBERTY, WOOL PRODUCTION AND WOOL TRAITS

Booroola strain Merino rams which were homozygous, heterozygous or non -carriers of the Fec(B) (''F'') gene were mated to Romney and Perendal e ewes to produce heterozygous (F+) and non-carrier (++) crossbred pro geny. The crosses were compared to contemporary Romneys and Perendales to assess independently the effects of the F gene and Merino backgrou nd on lamb and hogget performance. Crossbreds were slightly lighter in body weight at birth and this difference increased to 1 kg (5%) at we aning and 5 kg (10%) at 16 mo of age; however, a higher proportion of crossbreds reached puberty during their first autumn. Relative to wool from purebreds, wool from crosses had smaller fibre diameter and shor ter staple length but was both whiter and brighter. Crossing Merino wi th Romneys reduced hogget fleece weight and yield but increased loose wool bulk. Perendale crosses were similar to Perendale purebreds in fl eece weight, yield and loose wool bulk. The F gene had no significant effects on either growth or wool traits, but relative to ++ hoggets a higher proportion of F+ hoggets reached puberty in their first autumn and F+ hoggets reaching puberty showed a greater number of oestrus cyc les. Heritability estimates derived from Booroola crosses were similar to estimates from the two purebreds for body and fleece weights, inci dence of hogget oestrus and all wool traits except fibre diameter. Her itability of fibre diameter was lower in the crossbreds than in purebr eds.