Mechanisms of adaptation in sheep to overcome silage intake depression induced by biogenic amines

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Abstract
Effects of biogenic amines on silage intake and rumen fermentation during dietary changes were studied in sheep. Two direct-cut grass silages were prepared from a single grass sward, one untreated (WAS) and one treated with 4·0 litres formic acid (850 ml/1) per tonne (FAS). Diets of FAS, and FAS supplemented with 7·2 g biogenic amined/kg DM (FAS +A), were offered ad libitum, once daily to four rumen-cannulated, and four intact wethers in a repeated crossover design experiment. During a pre-period before each crossover, the animals were offered either the silage low in biogenic amines (FAS), or that containing moderate concentrations (WAS). During the first 4 d of the FAS+A treatment, the added biogenic amins tended to lower daily DM intake (DMI) and lowered significantly the DMI during the principal meal after feeding. This acute effect on DMI tended to be reduced when the sheep were previously preconditioned to amines by feeding WAS, and the acute DMI depression during the principal meal was significantly reduced. At the end of the 14 d FAS+A feeding period daily DMI was similar to that of the FAS treatment, but the daily pattern of intake remained different, with lower intake of FAS+A during the first 5 h after feeding, this being compensated for by the end of the day. Rumen fermentation tended to be less during the first 4 d that FAS+A was offered, due to the lower DMI and not due to the acute effect of amines. However, in the sheep unadapted to FAS+A, amine content in the rumen was higher than when the sheep were adapted for 14 d to FAS+A or WAS. Adaptation to FAS+A and feeding WAS during the pre-periods, increased the amine-degrading capacity of rumen fluid. In conclusion, in sheep unadapted to dietary amines, feeding amines will acutely lower DMI through reduced palatibility and most probably by stressing intermediary metabolism. Being preconditioned to amines slightly reduces the acute effect on daily DMI. Although the sheep adapted within 14 d to biogenic amines in the diet and increased daily DMI, there was clear evidence that amines have a negative effect on palatability.