A Jonker1, S Hickey2, S MacLean1, C Woyimo Woju1, M Garcia Rendon Calzada1, W Yu1, J McEwan3, S Rowe3
1Grasslands Research Centre, Agresearch Ltd; 2Ruakura Research Centre, AgResearch Ltd; 3Invermay Agricultural Centre, AgResearch Ltd
Total ruminal volatile fatty acids (VFA) or acetate concentrations (mM) were previously found to be moderate correlated proxies to select sheep that are genetically low methane (CH4) emitters. This was, however, based on trials with sheep fed lucerne pellets at a fixed feeding level, which is different to pastoral farming conditions in New Zealand, where the correlated proxy would be applied. The objective of the current study was to determine individual level correlation (ri) of rumen VFAs and CH4 emissions in sheep (37 low and 35 high CH4 yield selection line progeny) fed ad libitum cut pasture in four repeated seasons. Methane emissions were measured in respiration chambers and rumen samples were collected via oral stomach tubing before morning feeding. Methane (g/d) production and yield (g/kg dry matter intake; DMI) were low to moderately repeatable traits across seasons (0.46±0.05 and 0.32±0.05, respectively). Repeatability across seasons was generally twice or more for VFA proportions (0.13 to 0.30) than for VFA concentrations (0.02 to 0.14). Rumen caproate and propionate proportions (% of VFA) had strong negative ri (-0.87±0.13 and -0.99±0.30) and acetate/propionate ratio (A/P) a strong positive ri (0.78±0.13) with CH4 yield in sheep fed cut pasture, while the ri of ruminal VFA and acetate concentrations (mM) with CH4 yield were only moderate and non-significant (ri = 0.43±0.26 and 0.45±0.23). In conclusion, some VFAs (caproate %, propionate % and A/P) were strong correlated proxies to select sheep with a low CH4 yield, however, these were different VFAs than previously identified when sheep were fed lucerne pellets.
Dr Jonker is a senior scientist in the animal nutrition and physiology team at AgResearch in Palmerston North.