The influence of odour and taste on the food preferences and food intake of sheep

Abstract

The responses of sheep to the odour and/or taste of a range of naturally occurring chemical compounds were examined in five experiments. Thirty-two odours were tested as contaminants of a chaffed hay ration. Only six odours significantly influenced feeding behaviour over 72 h. There was evidence of adaptation to odour because the sheep lost an initial dislike for four odours (cedarwood oil, tannic acid, propionic acid and amyl alcohol), and developed a liking for butyric acid. The odours of five substances were disliked throughout the 72 h test period (glycine, wintergreen oil, peppermint oil, aniseed oil, 5-hexene-1-ol). The voluntary food intake of hay by normal sheep was significantly increased by the odour of butyric acid and amyl acetate, and depressed by the odour of coumarin and glycine, whilst that of anosmic sheep was unaffected. The responses to the taste of different concentrations of 13 compounds in solution was studied in two test systems. The overall ranking of substances was similar for both systems. Water was preferred to solutions of acetic, citric, quinic, malonic, succinic and aconitic acids at concentrations above 0.5% and of tannic acid above 0.05 %. Sheep appeared to show a marked liking for citric, malonic and quinic acids at certain concentrations. Odour of solutions influenced the preferences of three substances. Anosmic sheep generally had much higher solute intakes than normal or agustatory sheep. Small quantities (1.5 to 5.0 % of the dry matter) of eight chemical constituents of herbage plants were added separately to a cocksfoot hay. None of them increased food intake, and significant depressions in intake were obtained with 1 .5 % coumarin, 1.0 % gramine and 5.0 % tannic acid, 1.5 % malonic acid and 2% glycine. Sheep that were both anosmic and agustatory were affected in the same way as normal sheep, which showed that sensory stimuli were not involved. In vitvo digestibility was drastically depressed by tannic acid and gramine, slightly by coumarin, but was unaffected by the other contaminants. The possible effects of these compounds on the rumen and general tissue metabolism of sheep are discussed. The five substances that reduced intakes in the above experiment were fed to normal, anosmic, agustatory, and asensory (both anosmic and agustatory) sheep at four concentrations. The intake of anosmic sheep was higher for all compounds but only tannic acid and gramine reduced intake in all types of sheep, increasingly so with increasing concentration.