Incremental changes in and distribution of chick weight with hen age in four poultry species.

1. It is proposed that a general biological pattern exists for chick weight increase with hen age for the various commercial species of poultry and that one general equation can be used for the estimation of chick weight increment. 2. The parameters estimated for this equation are based on (a) chick weights as a percentage of annual mean chick weight, and (b) age, from onset of lay, as a percentage of maximum age of the hen; both serving as common denominators. Hence, if the annual mean chick weight is known for any species, breed or strain, then the increase in chick weight can be predicted for the whole season, or for any particular hen age. 3. For early prediction, first-month chick weight can be used to estimate the annual mean weight and consequently the chick weight curve for the full season. Although such prediction will be somewhat less accurate, it still can be used for general planning. 4. Results indicate that chick weights of various avian species are normally distributed. Therefore, at each point of hen age, the chick weight distribution can be estimated by employing the computerised Burr's (1967) equation. This may be useful for segregating chicks by size, thus improving uniformity and reducing competition within the flock. 5. Computation results show that coefficient of variation (CV) of chick weights, originating from 22 and 62 week dam ages, is increased by up to about 75%. The CV may thus be used as a quality indicator.