Effects of By-Product Inclusion and Linseed Oil Supplementation to a Pasture Based Diet on Methane Production, Diet Utilisation and Ruminal Fermentation Parameters in the Rumen Simulation Technique (Rusitec)

The objective of this study was to investigate the effects of by-product (BP) inclusion and linseed oil (LO) on diet digestibility, fermentation pattern and methane production using the rumen simulation technique (Rusitec), with perennial ryegrass pasture as the main forage source. Dietary treatment consisted of a supplementary concentrate (factor I) containing either 35% BP (BP35) or 95% BP (BP95) with and without 6% LO inclusion (factor II), thereby culminating in a 2 (concentrate; BP 35 or BP95) x 2 (LO; + or-) factorial arrangement. Dietary in vitro treatments consisted of a 50:50 perennial ryegrass based pasture (PRG) and one the four supplementary concentrates. Treatments were randomly allocated to sixteen fermentation vessels. The in vitro incubation trial involved of a single incubation period lasting 14 d consisting of 10 d adaption and 4 d sampling period. The DM digestibility of the concentrate treatments were: BP35 (68.9%); BP35+oil (68.7%); BP95 (57.4%) and BP 95+oil (54.4%). In general, concentrate that contained lower levels of BP had a higher digestibility parameters (DM, OM, CP, NDF and ADF) than the concentrates that contained a higher BP inclusion (P <0.0001). No significant difference was recorded in pH or NH₃-N production for any treatments examined (P>0.10). Production of volatile fatty acids (VFA) was highest for the low BP diets (BP35; P<0.05) relative to the BP95. Acetic acid proportion (P<0.05) and acetate:proprionate ratio (P<0.05) was greatest in the BP95 concentrate compared to the BP35 diet. Methane production (when expressed as production per day or in terms of production per organic matter digested) was affected (P<0.05) by BP concentrate type and LO supplementation. Addition, of LO reduced methane (CH₄) for both BP concentrate types with BP95+LO having the lowest CH₄ production, BP35+LO and BP95 intermediate and BP35 having the highest CH₄ production, respectively. Under in vitro conditions, the inclusion of BP and addition of supplementary LO to a concentrate supplemented grass based diet of ruminants can effectively reduce CH₄ production.