Modelling reproduction in farm animals: a review

During the last few decades, our knowledge of the biology of the reproductive system has improved significantly and also become more quantitative. In parallel, there has been an increase in the development of mathematical models, as both research tools and management tools, that can integrate our knowledge of reproductive events and then attempt to predict reproductive efficiency. This review considers these modelling approaches according to the level of organization that they address, from representation of the dynamic functions of the reproductive axis to the prediction of reproductive performance of a flock or herd. We emphasize the contribution of modelling to the exploration and understanding of a complex system-a system that responds to a host of internal regulatory mechanisms as well as to an array of external factors such as nutrition, photoperiod and sociosexual signals. To date, models have proven useful for depicting the kinetics of some of the endocrine signals that are implicated in perturbations of the reproductive axis and they have also been successful in the exploration of ovarian dynamics during the oestrous cycle. However, two areas are still largely unexplored by biomathematical models: the dynamic links between the different stages of the reproductive life of an animal, and mechanistic influences of environmental factors on the reproductive axis.