Effect of palatability on voluntary feed intake by sheep. I. Identification of chemicals that alter the palatability of a forage

The effect of chemical compounds on the palatability of a wheaten hay was investigated in short-term preference tests in which sheep were offered simultaneously treated and untreated hay. The palatability of wheaten hay chopped to 17 mm lengths was increased by treating it with aqueous solutions of either butyric acid (range 1.3-10 g/kg air-dry hay) or monosodium glutamate (2.4-44 g/kg hay). Hay chopped to 17 mm lengths was chosen because its potential intake rate was sufficiently low to allow the best quantitative measure of the increase in palatability to be established. The palatability of the same hay chopped to 6 mm lengths was decreased by applying MgO powder (1.6-60 g/kg hay) to hay pretreated with a solution of (1% w/w) sodium caseinate to adhere the MgO. The palatability of 6 mm hay was also decreased by treating it with aqueous solutions of acetic acid (0.02-10 g/kg hay), aconitic acid (0.2-19 g/kg hay) or malonic acid (1-20 g/kg hay). Hay of 6 mm lengths was chosen because its potential intake rate was sufficiently high to allow the best quantitative measure of the decrease in palatability to be determined. From the dose response curves, it was possible to identify a single concentration of selected chemical compounds that was suitable for altering the palatability of hay. A combination of butyric acid (2.5 g/kg hay) and monosodium glutamate (10 g/kg hay) were identified as the most suitable for increasing the palatability of 17 mm hay, and MgO (41 g/kg hay) or acetic acid (5 g/kg hay) for decreasing the palatability of 6 mm hay. A quantitative measure of the effect of these chemicals on the change in the palatability of either 17 or 6 mm hay was obtained. The sheep demonstrated a strong preference for 17 mm hay treated with a combination of butyric acid plus monosodium glutamate and conversely, a strong aversion to 6 mm hay treated with MgO. The specific concentration of the compounds selected would be suitable for investigating the effect of a change in palatability on the voluntary intake of wheaten hay.