A general method to relate feed intake and body mass across individuals and species
We propose a simple two-parameter allometric relationship between body weight gain (Y) and cumulative voluntary feed intake (X) during a given growth period: Y = A Xb. The relationship was supported by fitting datasets on individuals and groups across livestock species, including pig, rabbit, chicken, turkey, sheep and cattle. The datasets span over ~100 years of selection, different breeds, diets and sexes. Comparison was made with existing alternative relationships. Differences among species, breeds or diets were reflected in the parameters ‘b’ and ‘A’ and associated with efficiency of utilisation of feed for growth (and feed conversion ratio) and with history of selective breeding. (1) Variation in ‘b’ related to efficiency but not to animal size; b=0.8-0.95 and 0.75-0.8 in the more- and lessintensively- selected animals, respectively; and ‘b’ was lower in ruminant species than in monogastric species. (2) Wider variation in ‘A’, A=0.08-2.2, related both to efficiency and to animal size; e.g. ‘A’ was largest in cattle breeds and smallest in rabbits. The model is easily fitted to empirical data offering a flexible way of predicting feed intake from weight gain, and vice-versa, during any period prior to the slowdown of growth towards maturity. Changes in daily feed intake and feed efficiency during growth and their variation among individuals and groups are estimated more accurately via this model than using the raw data. The approach to maturity is accounted for through a third parameter in the relationship, but is not required in many livestock applications. We suggest this approach has a range of potential applications in selective breeding and livestock management. This study received funding from the European Union’s H2020 program through grant agreement no. 633531.