Genotype by Birth or Rearing Type Interaction in the Growth Trajectory of Merino Lamb

Abstract

Genotype by Birth or Rearing Type Interaction in the Growth Trajectory of Merino Lamb This study explores genotype by birth or rearing type interaction for body weight across the growth trajectory of Merino lambs by estimating the contribution of sire by birth type or rearing type interaction (SxBT/RT) to the phenotypic variance and by estimating the genetic correlation between body weights (BW) expressed in single versus twin birth type (BT) or rearing type (RT) at different ages. Results from univariate random regression analysis showed that from 75 to 200 days of age the heritability for body weight increased gradually from 0·43 to 0·65 and decreased afterwards to 0.55 at 300 days of age. A sire by birth type and sire by rearing type interaction contributed around 2-6% to variation in body weight at 200 until 300 days of age, while before 200 days of age this contribution was almost zero. Results from bivariate random regression analysis showed that genetic correlation between weights in single BT and RT and twin BT and RT classes of lambs (single born/single reared (SS) vs twin born/twin reared (TT)) was consistently high (0.84-0.97) along the trajectory, while the genetic correlation between weights in different BT but the same RT (SS vs TS) increased gradually from 0.75 to 0.95 until 250 days and decreased afterwards (to 0.84). Genetic correlation between weights in different RT but the same BT (TS vs TT) increased from 75 to 175 days of age (from 0.86 to 0.94) and flattened until 250 days and decreased thereafter to 0.87. Result indicated that genotype expression differed in different BT and RT across the growth trajectory with BT having a larger effect than RT in earlier growth and with RT having a larger effect than BT in later growth of lambs. Keywords: genotype by birth or rearing type interaction, body weight, Merino lamb, random regression model