Short communication: Effect of oilseed supplementation of an herbage diet on ruminal fermentation in continuous culture

A 4-unit continuous culture fermentor system was used to evaluate the effects of oilseed supplementation of an herbage-based diet on nutrient digestibility, fermentation profile, and bacterial nitrogen (N) synthesis. Treatments were randomly assigned to fermentors in a 4 × 4 Latin square design with 7 d for diet adaptation and 3 d for data and sample collection. Dietary treatments were an herbage-only diet (HERB), or the following ground oilseeds supplemented to an herbage-based diet at 10% of total dry matter (DM) fed: flaxseed (FLAX), canola (CAN), or sunflower (SUN). Apparent DM, organic matter, and neutral detergent fiber digestibility were not affected by diet, averaging 62, 68, and 78%, respectively. True DM and organic matter digestibility were not affected by diet, averaging 78 and 82%, respectively. Fermentor pH and total volatile fatty acids were not affected by diet. Branched-chain volatile fatty acids tended to be lower for HERB compared with the 3 oilseed diets. Ammonia N concentrations were lowest for the HERB diet. Crude protein digestibility was not affected by diet. Flow of NH3-N was lowest for the HERB diet reflecting the lowest culture concentration of NH3-N. Bacterial N flows were lowest for HERB and SUN diets, intermediate for FLAX, and greatest for CAN. Flows of total N, non-NH3-N, and dietary N were not affected by diet. Likewise, efficiency of bacterial N synthesis was not affected by diet. Supplementation with FLAX, CAN, or SUN at 10% of total DM fed did not affect nutrient digestibility or ruminal fermentation compared with an all-herbage diet. The oilseeds tested herein may be considered as alternative energy supplements for grazing dairy cows, particularly during times of low availability of corn. However, in vivo studies are needed to further evaluate the effects of oilseeds supplementation of an herbage-based diet on milk production and composition (specifically human-beneficial fatty acids).