Abstract: Data corresponding of 276 local kids` periodic control, harvested during 4 years (2001-2005) under pastoral mode in Tunisian arid region, was used to study some factors effects upon body parts evolution after birth. Morphostructural variables were; body length, height-at-withers and heart girth. The linear measurement periodically registered at every control day from birth and till 5 months age. For each kid, performances were standardized at typical ages; birth, 30, 60, 90, 120 and 150 days. Statistical analysis were achieved by GLM procedure and SNK (α = 5%) means comparison test to identify factors effects upon studied variables and the homogeneous classes. The kid`s body parts seem affected (p<0.05) by several environmental factors, sex, type of birth and age of dam. The type of birth and the age of dam exerts a high effect (p<0.01) on all characters after the birth. However, the factors statistical effects depend to the kid`s age. The sex acts differently on the morphometric characters before and afterwards of two month age. Thus, phenotypic individual differences can be elapsed by environmental factors of arid harsh conditions. Such conclusion underlines the necessity to study the particularities of the genetic expression of adapted populations towards restrictive resources.