EDUCATION AND PRODUCTION A Model for Individual Egg Production in Chickens1

ABSTRACT Our primary objective was to improve on an existing model for the individual weekly egg produc-tion curve by modeling the curve as a sum of logistic functions: one for the increasing phase of production and a sum for the decreasing phases. To illustrate the model, we used four data sets from two pairs of individuals. For these data, the model consisted of an increasing phase and a single decreasing phase of production: yt = m k1 1 − e−t 1 + e−t − m(k1 − k2) 1 − e−t 1 + e−(t −c2) where yt is egg production at week t, m is maximum production during a specific time interval, k1 is propor-tion of maximum production for the increasing phase, k2 is proportion of maximum production for the decreasing phase, and c2 is point of inflection from the upper level of the increasing phase to the lower level of the decreasing phase; thus, c2 is a measure of persistency of egg pro-duction. For one pair of individuals, production was about 88% of maximum (k1) for the increasing phase and about 76% of maximum (k2) for the decreasing phase. For the other pair, production was about 91 % of maximum (k1) for the increasing phase and about 75 % of maximum (k2) for the decreasing phase. Persistency (c2) was about 25 wk for one pair and about 28 wk for the other. Predicted total 52-wk production was within one or two eggs of actual production. The secondary objective was to improve estimation of model parameters by summarizing egg production dat