Representation of a mathematical model to predict methane output in dairy goats

Ruminants may contribute to global warming through the release of methane (CH4) gas by enteric fermentation. Most CH4 emissions from ruminants are estimated using simple regression equations. Thus a mechanistic dynamic model to predict CH4 output by goats was developed by using a computer-aided simulation device via object-oriented modeling. The model was structured into seven stocks; body weight, feed, metabolism, milk, methane and reserves (with two stocks). The goat model was set up to simulate indoor facilities in which the goat was fed a mixed ration. Then, 24 goats were used to evaluate the model during 150 days of lactation. A calorimetry system based on an open circuit respiration mask was used for quantification of respiratory CH4 production, as a way to validate the CH4 simulated. The mathematical simulation model estimated an average CH4 conversion factor (Ym) value of 5.3%, and an average daily CH4 production of 1.55 MJ/d. The average daily CH4 production for the validation group of goats was 1.51 MJ/d. Based on our simulation over 5 months of lactation for a mixed diet, use of the Intergovernmental Panel for Climate Change values (Ym = 6.5) could result in an overestimation of enteric CH4 for dairy goats fed concentrate diets.

► We represent a mathematical lactation goat model from system dynamics perspective: stocks and flows. ► We model lactation curve and methane conversion factor (Ym) in goats from dietary energy balance. ► We examinant changes in methane emission during lactation. ► We validate the methane emission with an open circuit respiration calorimetry.