A MODEL TO DESCRIBE AND PREDICT POSTPEAK CHANGES IN BROILER HATCHABILITY

A model to accurately describe and predict hatchability is critical to management. Hatch records of 68 broiler breeder flocks, collected ove r 4 yr, were analyzed. The data were classified by grower, strain of c hicken, ratio of males to females, season, and age. Flock hatchability met commercial expectations and statistically significant differences were attributed solely to age. Neither a strain x age interaction nor strain effect was detected. Hatchability increased rapidly until it r eached a peak, and the post-peak decline was not uniform. Post-peak ha tchability was best described by a seven-parameter segmented regressio n model. The three segments of the model consisted of the ascending sl ope (alpha), the gradually descending slope (beta), and the rapidly de scending slope (gamma). The other parameters of the model were peak ha tchability (H-p), age at peak (A(p)), age at breakpoint (A(b)) when th e decline in post-peak hatchability abruptly shifted, and hatchability at breakpoint (H-b). The model may be used to evaluate the effect of diet and management, to predict hatchability, to assess economic longe vity of a broiler breeder flock, and to plan replacement flocks.