Effects of infusing the rumen with acetic acid and nitrogenous constituents in maize silage extracts on food intake, ruminal osmolality and blood acid–base balance in sheep

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Abstract
SUMMARY: Four experiments were conducted to determine whether the products of fermentation in maize silage could limit food intake by lambs. In all experiments the lambs were fed ad libitum adietoi dried and pelleted lucerne, but were deprived of food for 4 h on the morning of intraruminal infusion. The infusions were made according to latin-square designs and commenced after 1 h of food deprivation. In Expt 1, the infusion of 3·5 I acetic acid solutions to provide 15, 30 and 60 g acetic acid had no effect (P > 0·05) on cumulative food intake compared with water. In Expt 2 infusion of three maize silage extracts differing in their composition of nitrogenous constituents suppressed (P < 0·05) food intake relative to acetic acid alone, but there were no significant (P < 0·05) differences among the extracts. When 2·71 of an extract from a low dry matter (D.M.) maize silage were infused in Expt 3 cumulative food intake was significantly (P > 0·05) decreased compared with acetic acid, but ruminal osmolality was increased to 430 mosmol/kg and ruminal pH declined to less than 5·5. In Expt 4, 1·5 1 of the low D.M. maize silage extract, an amount actually consumed by lambs during 4 h, decreased voluntary intake by 25% compared with the control but the effect was not statistically significant. Estimates of ruminal osmolality and pH ranged between 250 and 360 mosmol/kg and between 68 and 6·2 respectively. Measures of acid-base status were not affected (P < 0·05) by the infusion of acetic acid or maize silage extract. Whether specific soluble constituents of maize silage fermentation could limit food intake by ruminants was not proven.