Genetic effects in GrowBulk sheep.
GrowBulk sheep are a strain of long-wool type sheep that have been developed in New Zealand by introgressing high-bulk genes from Texel and Dorset rams into Romney ewes. Between 1992 and 1997, fleece weight and bulk records were collected for 3171 hoggets from the nucleus and 4 multiplier flocks, shorn at 3 and 12 months of age. Genetic effects were evaluated using a Restricted Maximum Likelihood animal model. Heritability estimates were 0.46±0.05 for bulk and 0.30±0.05 for clean fleece weight, with a genetic correlation of -0.48±0.09. The crossbred genotypes represented in the nucleus flock showed a range in average breeding merit for bulk of 27-31 cm3/g, their weighted mean genetic superiority over contemporary Romneys being 5.3 cm3/g. The first crop of commercial progeny by rams from this flock showed an average genetic superiority in bulk over their dams of approximately 4 cm3/g.