Growth and lay modelling in a population of Castellana Negra native Spanish hens

1. This study shows the results of (a) fitting growth data to a Gompertz-Laird model and (b) fitting egg production per housed bird to a Grossman model, in a population of Castellana Negra hens. 2. The maximum growth point for males and females, respectively, occurred at 10.6 and 9.3 weeks and the estimated weights at maturity were 2852 and 1878 g. Growth curve parameters were lower than those of commercial lines and similar to reports of other unselected breeds. 3. The start of lay was at 23 weeks. Total egg production reached 163 at 52 weeks, with a persistency (length of constant production) of 3.4 weeks and a production maximum of 69%. The maximum rate of change segment of the laying curve started at 24.3 weeks of age, and the production maximum started at 5.8 weeks into lay. The rate of decline was 1.4% weekly. 4. The Castellana Negra breed belongs to the class of slow-growing light lines and egg production was 163 eggs per calendar year.