The influence of ammonia, biogenic amines and γ-aminobutyric acid on grass silage intake in sheep

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Abstract
We investigated whether biogenic amines alone, or a combination of NH3, amines and γ-aminobutyric acid (GABA) influenced grass-silage intake, intake behaviour and rumen liquid content in sheep. Three diets were studied: a grass silage preserved with formic acid (4 litres/tonne) (FAS), FAS with 4·9 g amines/kg DM added (FAS+A), and FAS supplemented with a combination of N-components at the following concentrations: 2·7 g amines, 3·0 g NH3and 5·0 g GABA/kg DM (FAS+C). The diets were offered ad libitum, once daily to six rumen-cannulated Texel wethers in a crossover design. Daily DM intake (DMI; g DM/d) tended to be influenced by diet (P = 0·08). The DMI of FAS+A was similar to that of FAS alone, whereas that of FAS+C tended to be higher. The mean rate of ingestion (g DM/min) over all feeding bouts tended to be the lowest for FAS+A (P = 0·06). No differences were found among the diets concerning intake behaviour during the principal meal. Average intake rate of the small meals tended to be the lowest for FAS+A (P = 0·06). Although rumen NH3 concentration was higher (P<0·05) after the principal meal, rumen pH, osmolality, rumen pool size and liquid content were not significantly altered by adding amines or the mixture of N-components to FAS. We conclude that biogenic amines or N-containing products of protein fermentation in concentrations normally found in poor-quality silages do not reduce the intake of well-preserved formic acid-treated silage. A direct effect on chemostatic regulation of intake was not observed, but a slight negative effect on silage palatability cannot be excluded.