A simple model for the effect of thermal stress on the productivity of small ruminants

Abstract

Projected climatic changes are expected to change temperature and precipitation patterns and to increase the frequency of extreme events in many regions of the world. This will affect livestock systems through direct effects on animal performance as a result of thermal stress. The purpose of this work is to develop a model that is able to estimate the potential impact of thermal stress on the productivity of small ruminants. To do so, a semi-mechanistic model is proposed, based on an energy balance perspective and the application of the temperature-humidity index (THI) as an indicator of the heat stress severity level. The effect of thermal stress on animal's energy balance is captured by two main mechanisms: i) an increase in energy maintenance requirements and ii) a modification on feed intake. As a result of energy imbalance, the decline on animal productivity is estimated (i.e. milk yield, tissue growth). The different components of the model have been tested against available experimental data, showing that it is able to capture non-linear productivity losses across a range of heat stress conditions and systems. Finally, the applicability of the model is tested with dfifferent examples, and limitations and strengths are discussed. Despite some constraints, we highlight its relative simplicity and flexibility, so it would be feasible to be integrated into whole farm modelling approaches and/or feed requirement systems for small ruminants. This will help to predict the potential consequences of climate change on productivity, and to explore appropriate adaptation strategies.