The effect of oils fed to sheep on methane production and digestion of ryegrass pasture

Abstract

Selecting ryegrass for higher concentrations of lipid to increase dietary energy density may increase the productivity of pasture-fed animals and reduce rumen methane emissions. A proof-of-concept study was undertaken to identify responses of sheep to increasing dietary lipid intake. Sheep housed in metabolism crates were fed fresh ryegrass at 120% of ad libitum intake for two 17-day periods with dry matter intake (DMI) and energy balance measured over the final 7 days and methane over five consecutive days at the end of each period. A blend of linseed and sunflower oils (3 : 1) were infused directly into the rumen of 8-month-old wether sheep (37 ± 1.7 kg [mean ± s.d.]; n = 2 per level) to provide 0% (control), 1.2%, 2.5%, 3.7%, 5.0% and 6.2% of DMI. Sheep were re-randomised among treatments for the second measurement period. Oils were infused over 2 h during each of the morning and afternoon feeding period at rates calculated to achieve the target addition. Measurements included DMI, energy intake and digestibility, enteric methane production and rumen volatile fatty acid (VFA) profiles. Sheep tolerated additional oil up to 5% of DMI, but when 6.2% was given, intakes declined and this treatment was discontinued. Up to 5% oil infusion did not affect methane production, DMI, energy digestibility or rumen VFA concentrations or proportions. The results suggest plant breeding to increase fatty acid content may benefit production provided total lipid did not exceed 9% of the DM, but methane production during digestion would be unaffected.