ABSTRACT In vitro gas production (GP) method was used to investigate associative effects on ruminal digestion when grains (corn or barley) were supplemented to spring pasture and autumn pasture. Pasture (75%) was incubated with 25% corn
or barley and gas production was monitored up to 96 h. After incubation, the residues were used to determine dry matter and organic matter digestibility (DMD and OMD). Gas production parameters were analyzed by applying a single exponential equation. Organic matter effective degradability
(OMED) was determined from GP parameters and OMD. The positive associative effects on the rate of GP, DMD, OMD and OMED were observed when spring pasture was incubated with corn. However, similar effects were not observed in a barley mixture. However, for autumn pasture, both corn and barley
mixtures showed positive associative effects on rate of GP, OMD and OMED. The results of this study indicated that supplementation of corn would be better than barley for spring pasture with high water‐soluble carbohydrate contents, whereas both grain supplementations were effective
to obtain positive associative effects on the rate of GP and OMED for autumn pasture with high cell wall content.