Carrying the FecB (Booroola) mutation is associated with lower birth weight and slower post-weaning growth rate for lambs, as well as a lighter mature bodyweight for ewes

The present study was conducted in an Assaf flock in which the FecB ( Booroola) mutation was segregated to determine whether the FecB mutation affects birthweight and the pre- and post-weaning growth rate of ewe lambs, as well as the mature bodyweight of ewes. Significant differences ( P = 0.01) in birthweight ( mean +/- s. e. m.) were found between BB ewe lambs (4.03 +/- 0.08 kg) and B+ and ++ ewe lambs (4.16 +/- 0.04 and 4.32 +/- 0.07 kg, respectively), which themselves did not differ significantly ( P > 0.05). An FecB-associated maternal effect on the birthweight of ewe lambs was also detected, with the birthweight of lambs born to BB mothers (3.93 +/- 0.08 kg) being significantly ( P < 0.0001) different from the birthweight of lambs born to B+ and ++ mothers (4.26 +/- 0.04 and 4.33 +/- 0.07 kg, respectively), which did not differ significantly. The genotypes of the lambs did not affect their preweaning growth rate. However, the post-weaning growth rate of ewe BB lambs ( 274 +/- 5 g day(-1)) was significantly ( P = 0.05) different from the similar ( P > 0.05) post-weaning growth rates of B+ and ++ lambs ( 284 +/- 3 and 290 +/- 4 g day(-1), respectively). The genotype at the FecB locus also affected the mature bodyweight of ewes, with that of BB ewes ( 67.3 +/- 1.4 kg) being significantly ( P < 0.001) different from the similar mature bodyweight of B+ and ++ ewes (70.8 +/- 1.1 and 70.1 +/- 1.7 kg, respectively).