Booroola strain Merino rams which were homozygous, heterzygous or non-carriers of the FecB("F") gene were mated to Romney and Perendale ewes to produce heterozygous (F+) and non-carrier (++) crossbred progeny. The crosses were compared to contemporary Romneys and Perendales to assess independently the effects of the F gene and Merino background on lamb and hogget performance. Crossbreds were slightly lighter in body weight at birth and this difference increased to 1 kg (5%) at weaning 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 shorter staple length but was both whiter and brighter. Crossing Merino with Romneys reduced hogget fleece weight and yield but increased loose wool bulk. Perendale crosses were similar to Perendale purebreds in fleece 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 cycles. Heritability estimates derived from Booroola crosses were similar to estimates from the two purebreds for body and fleece weights, incidence of hogget oestrus and all wool traits except fibre diameter. Heritability of fibre diameter was lower in the crossbreds than in purebreds. © 1994.
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