Genetic enhancement in livestock can be realized through selection and breeding systems in which the influence of genetic and non-genetic factors on productive traits is the utmost imperative feature for obtaining accurate estimates of breeding values. This study was carried out to analyze the genetic and non-genetic factors influencing the growth performance in sheep breeds. The data on the body weight of Kilakarsal, Vembur, Chevaadu, Ramnad White, and Mecheri sheep breeds at different ages were collected for a period of 10 years. The mean daily gains from birth to the weaning period (90 days) and from weaning to one year were estimated. Statistical analysis was performed using R software. The least-square means of birth weight of Kilakarsal, Vembur, Chevaadu, Ramnad White, and Mecheri were 2.4±0.01, 2.62±0.01, 2.37±0.10, 2.57±0.12 and 2.39±0.16 kg, respectively. The least-square means of one-year body weight of Kilakarsal, Vembur, Chevaadu, Ramnad White, and Mecheri were 19±0.16, 19.9±0.16, 21.6±1.62, 24.9±1.62 and 22.9±2.28 kg, respectively. The phenotypic correlations among birth weight and body weights at successive ages showed positive values and varied from low to high. This directed that selection for body weight at birth and or earlier ages would result in genetic improvement in successive ages. At birth, there is no significant difference among breeds. But as age advances breed differences occur. Ramnad White and Chevaadu are heavier than Kilakarsal and Vembur breeds. The effect sex of sheep on body weight was significant. In the selection and breeding programs, the consequences of environmental factors should be included.