Samples of rumen and abomasal contents were obtained at approximately 1000 and 1400 hr on days 12 and 14 of each period. Rumen samples were taken by suction pump at 55 min postfeeding and the two daily samples were composited on an equal volume basis. The pH of the whole rumen contents was taken immediately and the samples were filtered through two layers of cheesecloth and stored at -4 C. One milliliter of 20% sulfuric acid was added per 50 ml strained rumen fluid to stop bacterial action.