In the present study, the data on 1649 Bharat Merino (BM) lambs; progeny of 144 sires over the year from 2000 to 2014 available at Southern Regional Research Centre (SRRC), Central Sheep and Wool Research Institute, Mannavanur were considered for the analysis. The different economic growth traits used for the analysis were birth weight (BWT), weaning weight (3MWT), 6 month weight (6MWT), 12 month weight (12MWT) and greasy fleece yield (GFY). The overall least square means for weights (in kg) were 3.28 +/- 0.02, 19.08 +/- 0.23, 25.00 +/- 0.35, 34.79 +/- 0.59 and 2.13 +/- 0.07 for BWT, 3MWT, 6MWT, 12MWT and GFY respectively. Different non genetic factors such as year, sex, type of birth and dam's age had significant (P<0.01) influence on BWT and 3MWT. Season influenced the BWT (P<0.05) while it had no significant effect on 3MWT. Six month weight was also significantly (P<0.05) influenced by all non-genetic factors taken under present study. Twelve month weight was significantly affected by year (P<0.01), sex and season (P<0.05). Similarly, analysis of variance showed that the year, sex of the lambs (P<0.01) and season (P<0.05) were important sources of variation on GFY of Bharat Merino sheep. Lambs born single had higher values of BWT and 3MWT than that of the lambs born as twins. The trend of the increase in BWT and 3MWT of the lambs is being observed up to the period when the age of their corresponding dams is 4-5 years. The findings of the present study showed that non - genetic factors play an important role in the expression of genetic potential in the lambs as well as growth performance of Bharat Merino sheep under sub temperate conditions of Kodai hills of Tamil Nadu, India. The genetic parameters estimated of 6MWT indicate that it is most suitable for use as selection criterion. Improvement of body weight of BM sheep seems feasible in selection programs, as some of the related traits are moderately heritable and those traits specially are well correlated, which could suggest that these traits are useful in selection programs.
