Investigating age-related changes in variability of body weight in sheep

'Variance compounding' and 'compensatory growth' in growth curve of Zandi sheep were investigated through monitoring ontogenetic changes in causal components of phenotypic variability of body mass from birth until one year of age. To do this, phenotypic variance and its casual components were estimated for body weight taken at different ages in male and female lambs separately by REML procedure fitting a multi-trait animal model. Estimates of standardized variance components showed greater genetic and environmental differences among animals for traits related to early growth. In addition, results indicated that sexual puberty can act to growth compensation as phenotypic, additive genetics and residual coefficient of variations minimized at about sexual puberty. Latter result provided evidence that body weight measured around sexual puberty is not a suitable selection criterion for improving body weight as it experienced low additive genetic variation. In most studied growth phases, compensatory growth was predominant and only in the period between 9 and 12 months of age, in which an accelerated growth occurred, variance compounding process was observed.