Dynamic modelling for nutritional management of ruminants in the face of climate change

Abstract

Livestock producers are being asked to become more efficient and more sustainable, while facing higher environmental risk due to climate change. Producers are paid on quality as well as yield, increasing pressure to optimise their systems. However, to optimally manage and feed livestock under increasing risk, producers need tools to assist them in achieving economic and environmental sustainability. Many current nutrition systems attribute variation in performance to feed characteristics and predict energetic requirements additively, first predicting maintenance, then gain, with some adjustment of maintenance as energy intake increases. However, the underlying biology is dynamic and nonlinear-animals may be gaining protein and losing fat, or vice versa, which current systems cannot account for. Rather than predicting energy change and partitioning it into fat and protein, we have developed a model that accounts for whole body gain or loss of fat and protein. Efficiencies are not fixed or defined by feed, as they are in other models, but arise from the interaction of animal, feed, and the animal's nutritional history. This dynamic approach calculates heat production as a function of feed intake and internal pools of protein and fat, and their changes as the animal's nutritional and physiologic states change. This model is dynamic and can reflect both the animal's current state as well as the effects of its previous nutritional state, and therefore is able to capture the variation in body composition due to past and present nutrition. Because of the relatively small number of parameters in this model it is easy to parameterise and to adapt to different situations. By using a dynamic, nonlinear model that reflects not only what the animal is now but what it has been in the past, the effects of previous nutritional circumstances, such as feed restriction from prior management or environmental stressors, may be accounted for in their effects on current body composition and future gain.