The evaluation of selection in a crossing ram breed to improve litter size in sheep.

Abstract

Five genotypes were compared as sires of crossbred ewes from Scottish Blackface dams. These included Border Leicester (BL), New Zealand Romney (R) (from two group breeding schemes where selection had emphasized litter size), and three lines from the composite A.B.R.O. Damline (DL). Selection of the male and female lambs in the purebred DL flock was: a)for an average of 5.5 years on a Ewe Index of eight week litter weight (Martin and Smith, 1980).b)for an average of 3.5 years on a Testis index, combining testis size (adjusted for body weight) and Ewe Index of eight week litter weight both components receiving approximately equal weight andc)a random bred control.These five genotypes (two rams per genotype per year for five years) were group mated (sires of individual ewes were not known) with Scottish Blackface ewes on an upland farm in Ayrshire.