A model for persistency of egg production.

The objectives of our study were to propose a new definition for persistency of egg production and to develop a mathematical model to describe the egg production curve, one that includes a new measure for persistency, based on the proposed definition, for use as a selection criterion to improve total egg production. Persistency of egg production is an important determining factor for total egg production. Hens with the same total production, however, can exhibit different egg production curves because of differences in persistency. We propose a new definition for persistency of egg production: the number of weeks during which a level of constant production is maintained. No egg production model exists that includes a measure of persistency in terms of duration of time or that allows this measure of persistency to be derived from model parameters. It was necessary, therefore, to develop a new model to describe an egg production curve for a flock: equation [see text] and for an individual: equation [see text] where y(t) = egg production at time t, t1 and t2 = times at transition, r = duration of transition, y(p) = level of constant production, b4 = rate of decline in production, and P = persistency of constant production. These parameters measure directly the important biological characteristics of an egg production curve. To illustrate the model, six data sets were used: two from flocks (one pullet flock and one hen flock) and four from two pairs of individuals. The proposed definition of persistency should be important for genetic selection because it might be desirable to select for increased persistency. The novel approach to the definition and measure of persistency presented here should provide a better understanding of the relationship between the new measure of persistency and other characteristics of egg production.