Effect of the addition of malate onin vitrorumen fermentation of cereal grains

Abstract

Batch cultures of mixed rumen micro-organisms were used to study the effects of different concentrations of malate (Rumalato®; Norel & Nature S.A., Barcelona, Spain; composed of disodium malate–calcium malate (0·16:0·84, w/w)) on the fermentation of four cereal grains (maize, barley, wheat and sorghum). Rumen contents were collected from four Merino sheep fed lucerne hayad libitumand supplemented with 300 g concentrate/d. Rumalato® was added to the incubation bottles to achieve final concentrations of 0, 4, 7 and 10 mM-MALATE. Gas production was measured at regular intervals up to 120 h. Malate increased (P<0·01) the average fermentation rate of all substrates, and the lag time decreased (P<0·05) linearly with increasing concentrations of malate for all substrates, with the exception of sorghum. in 17 h incubations, the final pH and total volatile fatty acid production increased (P<0·001) linearly for all substrates as malate concentration increased from 0 TO 10 mM. Propionate and butyrate production increased (P<0·05), while the value of the acetate: propionate ratio and L-lactate concentrations decreased (P<0·05) linearly with increasing doses of malate. Malate treatment increased (P<0·05) the CO2production and decreased the production of CH4, although this effect was not significant (P>0·05) for maize. Malate at 4 and 7 mm increased (P<0·05) optical density of the cultures measured at 600 nm for maize, with no differences for the other substrates. The results indicate that malate may be used as a feed additive for ruminant animals fed high proportions of cereal grains, because it increased pH and propionate production and decreased CH4production and L-lactate concentrations; however, in general, no beneficial effects of 10 compared with 7 mM-malate were observed.