The data were collected from 1992 to 2009 in Burri, White Boni and Black Boni sheep maintained at the Regional Research Station in the Central Highlands of Yemen. Data were analyzed to study the effects of environmental and genetic factors on body weight and growth rate from birth to weaning. The least square means for body weights (BW) were 2.54, 2.18 and 2.26 kg for birth; 12.49, 10.58 and 11.14 kg for weaning weight (WW) and 114.91, 98.68 and 106.04 g for growth rate in Barri, Black Boni and White Boni sheep, respectively. Year of birth effects were significant (P<0.05) on BW, WW and growth rate in all the breeds. Also, analysis of variance showed that the sex of the lambs and the type of birth were important sources of variation (P<0.05) in the three breeds for all traits. The size of the ewe during lambing had also significant effect (P<0.01) on birth in all the breeds. The results show direct heritability for all traits, it was varied between 0.36 and 0.38 for BW, 0.30 and 0.35 for WW, 0.26 and 0.36 for growth rate in all breeds. HHHHvgigher estimates of heritability for growth performance traits are refers to the presence of more additive genetic variance. Manuscript profile