Egg production curve of Rhode Island Red chickens
Data on the monthly egg production of a strain of Rhode Island chickens (500 breeder hens) were used to test the goodness of fit of six mathematical models, viz; Exponential, Parabolic exponential, Wood's Gamma type and modified Gamma type by McNally, Inverse polynomial and Linear regression. Egg production was summarized for each hen into 28-d periods, starting from the day of first egg. The hens were classified into different production cycle length based on the number of 28-d periods. The models were fitted to the mean results obtained for periods within groups of hens. The effect of cycle length on goodness of fit was also examined separately for the 'best' three models with highest R2 values. The egg production cycle (i.e. number of 28-d periods) varied from 9 to 15 periods. Similarly, the coefficients of determination (R2) varied from 0.16 to 0.95 from fitting the models to mean egg production data for groups of hens. The results suggest that the ‘best’ three models that were chosen fitted 52 week laying records quite well, judging from their respective R2 values, which were higher for McNally (0.95) and Parabolic exponential (0.93) than for Wood (0.75). Based on the goodness of fit to 52-week production record, the McNally model gave the best results. However, its suitability in predicting full year production from part year record needs to be further investigated.
Keywords: Egg production, model, Rhode Island Red layers.