Automated feeding of sheep. 2. Feeding behaviour influences the methane emissions of sheep offered restricted diets

Context: During the non-growing season of pastures and during droughts, the dry-matter intake (DMI) of sheep is often constrained due to low pasture availability and the need to feed for weight loss or maintenance. Below-maintenance feeding may have consequences for methane (CH4) production and yield in farm systems. Aims: The effect of six restricted feeding levels on CH4 emissions measured using portable accumulation chambers (PACs) was examined in relation to DMI, oxygen consumption (O-2) and carbon dioxide (CO2) emissions and observed changes in feeding behaviour in sheep fed with automated feeders.Methods: An automated feeding system was used to apply daily feeding levels to Maternal Composite ewes (n = 126). Sheep were adapted to the automated feeding system over 19 days, with unlimited access to feed. Following adaptation, sheep were allocated to restricted daily feed levels at 40%, 80%, 100%, 140% and 180% of estimated maintenance requirements (MR) for 41 days. Methane, CO2 and O-2 emissions from ewes were measured using PACs on Days 30 and 31 of the restricted feeding period. Key results: Methane production (g/day) increased (P < 0.001) with the level of feeding. However, time since the last meal decreased with the level of feeding and was associated with CH4 production. Sheep on lower levels of feeding tended to consume meals earlier in the day and had longer times since their last meal at PAC measurement and lower CH4 production. These two factors explained 58.7% of the variance in CH4 production in an additive linear model. Methane yield (g CH4/kg DMI) decreased as the level of feeding was increased. Conclusions: Methane emissions were affected not only by daily DMI, but also time since the last meal. An understanding of the effect of feeding behaviour and time since the last meal should be incorporated into feeding protocols prior to CH4 measurements when PACs are being used to measure CH4 emissions from sheep fed restricted diets. Implications: Utilising automated feeders may improve the accuracy of PAC measurements of sheep CH4 emissions fed both ad libitum and restricted feed amounts, by increasing understanding of DMI and feeding behaviour.