In vitro rumen fermentation and gas production: influence of yellow grease, tallow, corn oil and their potassium soaps

The effect of addition of fat on in vitro gas production, volatile fatty ac id (VFA) production, in vitro true digestibility (IVTD), and ammonia-N conc entration was assessed by incubation of a simulated total mixed ration in b uffered rumen fluid using an in vitro gas technique. Fat sources were com o il (CO), tallow (TL), yellow grease (YG), and potassium soaps (K-soaps) of CO., YG, and TL. Addition of YG increased (P<0.001) in vitro gas production while TL had no effect. Neither YG nor TL affected IVTD and total VFA prod uction. Addition of either YG or TL decreased acetate production and increa sed propionate production. Addition of CO increased in vitro gas production , but had no effect on IVTD and total VFA production. However, CO decreased acetate and increased propionate production with a concomitant decrease in the acetate to propionate ratio. Addition of K-soaps of CO. TL and YG depr essed in vitro gas production, IVTD, VFA and ammonia-N concentrations. K-so aps also caused a marked decrease in acetate and increase in propionate pro duction. The absence of negative effects on rumen fermentation parameters i n response to the inclusion of fat in the form of triglycerides to an in vi tro system at up to 25% DM suggests that triglycerides have much less effec t on rumen fermentation parameters than corresponding free fatty acids. In contrast, the K-soaps of each respective fat had detrimental effects on in vitro rumen fermentations. (C) 2001 Elsevier Science B.V. All rights reserv ed.