A mechanistic model in sheep incorporating energy allocation trade-offs between the ewe and her lambs

Being able to predict the animal’s multiple traits responses to its environment is of high interest to study livestock adaptation to future conditions. In particular, trade-offs between traits are assumed to be a key determinant of animal robustness. Mechanistic models of energy allocation have been developed to predict potential trade-offs due to the competitive use of energy between biological functions, both within an individual’s life and among individuals. However, previous models have not explicitly integrated potential trade-offs between the mother and her offspring as well as among siblings. Yet those features are essential, particularly in suckling systems. Here we present an energy allocation model in sheep that incorporates the energy transfers between the mother and her offspring. The model simulates the trajectories of responses to feeding and herd management during the sheep’s lifetime. We first provide a detailed description of the model following a standard protocol. We then show that simulation results are in a realistic range in general. We finally illustrate how the model can represent individual variation in ewe-lamb trade-offs by varying the value of five input parameters controlling energy acquisition and allocation. Such parameterization allows to define different individual “types” of energy allocation strategies that are characterized by repeatable patterns of ewe and lamb output traits. This new sheep model provides the basis for future individual-based studies.