Multiphasic mixed growth models for turkeys

Not all turkeys grow the same. Find out how divergent selection changed the way they grow. Growth models are important for optimization of feed formulation and breeding programs in turkeys. The objectives of this study were 1) to compare sex and line differences in turkeys in parameter estimates of mono- and di-phasic Gompertz growth models, and 2) to evaluate mono and diphasic mixed Gompertz growth models to determine the variation in parameter estimates in a group of female line turkey toms. A total of 1,056 manually recorded weekly average body weight (BW) observations from male and female turkeys of a male and female line from weeks 1 to 20 were used for objective 1. Daily median values of automatically collected individual BW of female line turkey toms were used for objective 2 and random components associated with individual subject animals related to mature weight and/or timing of maximum gain during each phase were introduced in the Gompertz model. Growth curve shapes were different between male line toms, male line hens, female line toms, and female line hens (P < 0.001). However, inflection points were similar between male and female line toms and between male and female line hens (14.06 vs. 13.72 wk and 11.22 and 10.71 wk, respectively), while mature BW differed between lines by 6.49 and 3.81 kg for toms and hens, respectively. The normalized growth rate constant (growth rate constant corrected for mature weight) was around the same magnitude between male and female line toms (0.0031 vs. 0.0038, respectively), but slightly lower in male line hens compared to female line hens (0.0072 vs. 0.0091, respectively). Diphasic Gompertz models described growth better in all line x sex combinations compared to the monophasic models (P < 0.001) and mixed diphasic Gompertz models showed improved fit over mixed monophasic Gompertz models. The correlation structure of the random components identified that individuals with a higher mature weight had a later inflection point and lower growth rate coefficients. These results provide tools for improved breeding practices and a structure to evaluate the effects of dietary or environmental factors on growth trajectories. Lay Summary Turkeys have been bred for several purposes over the past decades. We studied growth patterns of turkeys of two genetic lines bred for either meat production or egg production. Mathematical equations were designed and fitted to describe the average bodyweight of several consecutively grown groups of turkeys. Similarly, individual body weight was measured and studied in one group of male turkeys, to detect differences in growth patterns between individual turkeys. It showed that there were differences between both sexes as well as between both lines in the shape of the growth curve. The age at which males and females grew fastest was similar between meat production and egg production type turkeys, for males around 13 to 14 wk and for females around 10 to 11 wk. Males of the meat production line grew 6.5 kg heavier than males of the egg production line, whereas females of the meat production line grew 3.8 kg heavier than females of the egg production line. Individual turkeys that have a heavier mature weight grow at a slower pace and delay the growth spurt associated with sexual maturation. With these outcomes, turkey feed producers and genetic companies can better study and steer the desired growth of turkeys.

Automated summary

This study compared the parameter estimates of growth models in different genders and lines of turkeys and evaluated the variation in parameter estimates of female turkeys using mono- and diphasic Gompertz growth models. The results showed that growth curve shapes were different between different genders and lines of turkeys, but inflection points were similar. The diphasic Gompertz models described growth better than monophasic models. These findings provide important tools for improved breeding practices and studying the effects of dietary or environmental factors on turkey growth trajectories.