Effect of palatability on voluntary feed intake by sheep. II. The effect of altering the palatability of a wheaten hay on long-term intake and preference

The effect of either an increase or a decrease in palatability on both long-term intake and preference for a wheaten hay was studied using two groups of sheep. Quantitative assessments of palatability confirmed that it was possible either to increase the palatability of 17 mm length hay by treating it with a combination of butyric acid plus monosodium glutamate or to decrease the palatability of 6 mm length hay by treating it with MgO. The voluntary intake of hay treated with butyric acid plus monosodium glutamate was 10% higher than that of the untreated hay when offered singly to sheep over 25 days. The increase in intake of the treated hay was associated with an increase in the apparent fractional rate of digestion in the rumen. There was no difference in voluntary intake between hay treated with MgO and untreated hay, even though there was a reduction in the apparent digestibility of the treated hay. The addition of MgO resulted in a decrease in the apparent fractional rate of digestion in the rumen which was compensated for by an increase in rumen digesta load. The palatability of a forage did affect its long-term preference, as determined by offering treated and untreated forages together in separate containers for 25 days. The sheep demonstrated a preference for hay treated with butyric acid plus monosodium glutamate (77 cf. 23%) and an aversion to hay treated with MgO (23 cf. 77%). The results indicated that palatability had little effect on the voluntary intake of a wheaten hay when it was offered as the sole forage to sheep. However, when offered a choice between forages, animals consumed significantly more of the more palatable forage.