Search

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.

This paper reviews the biology of wool, mohair and cashmere growth and the options available to sheep and goat farmers to manipulate the quantity and characteristics of fibre produced to meet processors' requirements. The annual pattern of fibre growth in sheep and fibre producing goats is photodependent and regulated by hormone action. In sheep and Angora goats, fibre growth rate is greater in summer than winter with the amplitude varying between breeds. Cashmere-producing goats grow fibre between the longest and shortest day after which it is shed. The large diversity in fleece and fibre characteristics between genotypes of sheep and goats can be used to change characteristics by selection. Fibre characteristics of greatest importance to processors are all of medium to high heritability. Negative genetic correlations between some important characteristics limit overall genetic progress achievable through selection. The principal non-genetic factors affecting fleece and fibre characteristics in both sheep and goats are age, nutrition, physiological status, disease and shearing regime. Further work is required to gain a greater understanding of biological changes occurring within the follicle and fibre during growth to facilitate the production of fibre of specific characteristics through breeding or altering animal management.

Data were obtained at Whatawhata on the growth of goats to the yearling stage and on their cashmere production as hoggets. There were 884 animals recorded from the 1985 to 1989 birth years, comprising the progeny of 60 sires. Records from kid shearings were also obtained in the last two years. Mixed-model restricted maximum likelihood (REML) models were fitted. Heritabilities from yearling fleece records were 0.42±0.13 for fleece weight, 0.57±0.15 for yield, 0.62±0.15 for down weight, 0.35±0.12 for guard hair weight, 0.99±0.19 for down fibre diameter and 0.57±0.15 for mean down length; corresponding values from kid fleeces (23 sires only) were smaller in most cases than from yearlings, being respectively 0.14±0.06, 0.19±0.07, 0.20±0.07, 0.04±0.04, 0.19±0.07 and 0.87±0.29. The phenotypic and genotypic correlations between down weight and fibre diameter in yearlings were 0.50±0.03 and 0.81±0.08 respectively, representing an unfavourable relationship when selecting for heavier but finer down. The genetic correlations of yearling weight with down weight and down fibre diameter were slightly negative (−0.34 and −0.25), but the estimates were non-significant.