The effects of defaunation on the metabolism of lactic acid in the rumen

Abstract

AbstractTwo experiments examined the effects of defaunation on the ruminal metabolism of lactate. Three rumen‐cannulated sheep given a diet of molassed sugar beet pulp and barley (80:20) were used to study the effects of defaunation (with manoxol‐OT) on the metabolism of lactic acid produced endogenously from rumen fermentation. Defaunation increased mean ruminal concentrations of lactate from 3.4 mmol litre−1 to 8.9 mmol litre−1 but other rumen measurements remained virtually unchanged: pH, 6.3 and 6.3; molar proportions of acetic acid, 645 and 645 mmol mol−1; propionic acid, 189 and 197 mmol mol−1 and butyric acid 142 and 115 mmol mol−1 for the faunated and defaunated states respectively. In a second experiment, two groups each of four rumen‐cannulated sheep were used to study the effect of defaunation on the ruminal metabolism of added Na‐D, L lactate. One group of four was defaunated using a rumen‐washing technique whilst the other group of four remained faunated. The animals were given a diet of rolled barley and hay (60:40) and were given a series of intraruminal doses of Na‐D, L lactate from 0 to 100 g day−1, increasing by 20 g day−1 every third day. Disappearance of added lactate was much more rapid in faunated animals: at the 100 g day−1 dose rate, L‐lactate concentrations had fallen from a peak of 6 g litre−1 to >1 g litre−1 after 3 h whereas in defaunated sheep the peak of 6.5 g litre−1 was reduced to >1 g litre−1 only after 7 h. In faunated animals lactate addition caused an increase in the ruminal concentration of total volatile fatty acids (VFA) from 147 to 217 mmol litre−1 between the zero and 100 g day−1 dose rates, accompanied by an increase in the molar proportion of propionic acid from 190 to 320 mmol mol−1. However, in defaunated animals there was only a small increase in total VFA concentrations from 94 to 106 mmol ml−1 with no change in the molar proportion of propionic acid and a small increase in butryric acid from 140 to 180 mmol mol−1.