EFFECTS OF BREED, RAPID INBREEDING, CROSSBREEDING AND ENVIRONMENTAL-FACTORS ON FLEECE WEIGHT AND FLEECE SHEDDING IN SHEEP

Fleece weight and shedding score, a measure of premature fleece loss, were examined at first shearing and in older female sheep of three hil l breeds and their reciprocal crosses. Starting from a non-inbred base , the sheep were mated, mostly by younger-parent X offspring, for four generations, to produce inbreeding coefficients from 0.25 to 0.59. Cr osses of inbred lines were also produced within breed type. The experi mental design allowed the effects of inbreeding of the individual to b e separated from the effects of maternal inbreeding. Inbreeding of the individual significantly and linearly reduced fleece weight. This eff ect was still apparent after adjustment for body weight. Maternal inbr eeding significantly reduced only the weight of first fleeces, but the trends were similar at the later ages, especially among the purebreds . There was no significant interaction of purebred/crossbred status wi th level of inbreeding. Inbreeding did not significantly affect sheddi ng score. The pure breeds and the crosses did not differ, on average, in fleece weights or shedding scores, but within the purebred and with in the crossbred classes breed variation was significant. Fleece weigh t declined and the incidence of shedding increased with increasing age . The larger the number of lambs born in the year of shearing the lowe r the fleece weight and the greater the extent of fleece shedding. The effects of inbreeding could not be fully explained, statistically, in terms of dominance alone. Therefore, it seems probable that epistasis also plays a role in producing the observed changes with inbreeding i n these traits.