Growth is a key characteristic of animals and can be defined as any change in body size per time unit, and is influenced by genotype and environment. Mathematical functions called ‘growth models’ have been used to explain the growth patterns of poultry species. These semi-mechanistic growth models have a non-linear structure, sigmoid shape, and certain biologically meaningful parameters. In poultry science, Gompertz, Logistic, Richards and von Bertalanffy functions have been commonly used to model the growth patterns of birds. In this review, the studies concerned have been summarised under the titles ‘determination of the best-fitting growth model’, ‘a comparison of the growth of poultry species or various experimental groups’, and ‘genetic parameter estimates for growth curve parameters’. This review discusses existing and new approaches to growth modelling.

Poultry industries face various decisions in the production cycle that affect the profitability of an operation. Predictions of growth when the birds are ready for sale are important factors that contribute to the economy of poultry operations. Mathematical functions called ‘growth functions’ have been used to relate body weight (W) to age or cumulative feed intake. These can also be used as response functions to predict daily energy and protein dietary requirements for maintenance and growth (France et al., 1989). When describing growth versus age in poultry, a fixed point of inflexion can be a limitation with equations such as the Gompertz and logistic. Inflexion points vary depending on age, sex, breed and type of animal, so equations such as the Richards and López are generally recommended. For describing retention rate against daily intake, which generally does not exhibit an inflexion point, the monomolecular would appear the function of choice.