Analysis of poultry fertility data. 2. Comparison of long- and short-term fertility trials

The purpose of the present study was to determine the effect of egg collection interval on interpretation of fertility trial results. Low-fertility (LF) and randombred (RB) Delaware hens were inseminated with spermatozoa from LF or RB Delaware roosters. Three replicate trials were performed for each cross. Eggs were collected for 21 days following insemination. Fertility was analyzed with a log odds model following logit transformation. Separate analyses were performed on data collected throughout the first 7 days and the entire egg collection interval. Duration of fertility over the 21-day interval was analyzed by iterative least squares. Whereas the 21-day egg collection interval afforded detection of differences between males and between females, no differences were observed following analysis of data from the 7-day interval. Differences in reproductive efficiency also were detected when data were analyzed by iterative least squares. Thus, the value of a fertility trial is, in part, determined by the length of the egg collection interval.