Growth Traits In Sheep Research Articles

The impact of data structure on genetic (co)variance components of early growth in sheep, estimated using an animal model with maternal effects.

Several studies have noted high negative correlations between maternal genetic and direct additive effects and their influence on additive and maternal heritability of early growth traits in sheep. Multigeneration data from the Suffolk Sire Reference Scheme (SSRS) were used to investigate the effect of data structure on estimates of direct and maternal (co)variances for lamb 8-wk weight. In all analyses the additive, maternal genetic, maternal environmental, and residual effects were fitted along with the covariance between direct and maternal additive effects. The contributions of particular genetic relationships to the estimates were studied by analyzing subsets of the SSRS data. A further eight subsets were formed having 10% or 50% of the dams with their own records and having one or two, three or four, five or six, and more than six offspring per dam. Analysis of data having only 10% of the dams with their own record and one or two offspring records yielded a high negative correlation (-0.99) between direct and maternal genetic effects. However, the seven other data sets with more records per dam or a higher proportion of dams with their own records produced values of -0.35 to -0.51. Data structure and the number of dams and granddams with records are important determinants of estimated direct and maternal effects in early growth traits.

Adjustment factors for growth traits of Chios sheep

Data on 3741 purebred Chios lambs, collected at Athalassa and Orites, were used to determine the effects of year, month and type of birth, sex of lamb and dam lactation number on pre-weaning and post-weaning growth traits of sheep. Least-squares analyses revealed that most of the factors studied had a significant effect ( P < 0.01) on lamb live weights. Flock effects were important for weaning weight only, but year and month of birth were significant for all live weights ( P < 0.01). Dam lactation number effects were small and insignificant for post-weaning growth rate alone. Although year-by-month interactions were in all cases significant, no changes in rank were detected. Type of birth-by-sex interaction was not significant for any of the traits studied. Adjustment factors were computed across year of birth for the effects of month of birth, type of birth, sex of lamb and dam lactation number. Since flock effects were insignificant, these multiplicative adjustment factors could be used in performance testing programs for the improvement of growth traits in Chios sheep.