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

Abstract

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.

Food sensory characteristics: their unconsidered roles in the feeding behaviour of domestic ruminants

“…It was supposed that browsers have evolved to be less sensitive to bitter taste because they commonly encounter toxic plants that have a bitter taste (Glendinning, 1994). The umami taste, induced by monosodium glutamate, is perceived by sheep since (i) it increased intake of sham-fed animals (Colucci and Grovum, 1993) and (ii) it induced preferences when added to hay compared with the same untreated hay (Gherardi and Black, 1991). Recent studies, using either a non-caloric flavour or monosodium glutamate to induce the umami taste, showed that lambs are able to perceive umami taste in a feed, as they increased their preference for this feed (Favreau et al, 2010a;Villalba et al, 2011;Bach et al, 2012).…”

“…a calorie-free sweetener such as saccharin; Hellekant et al, 1994), (iii) by offering the different food items simultaneously since it increases the difficulty for the animal to identify which food item is responsible for which consequence (Duncan and Young, 2002;Favreau et al, 2010b), and/or (iv) by checking, with a conditioning procedure, that the intake of the added sensory modifier does not cause any post-ingestive consequence at the dose rate involved in the study (Gherardi and Black, 1991;Favreau et al, 2010a).…”

“…Sensory characteristics were indeed able to induce food preferences by their own, that is, without any immediate positive postingestive reinforcement as it is the case with umami taste (Grovum and Chapman, 1988;Gherardi and Black, 1991). The umami taste, induced by monosodium glutamate, seems to have a positive hedonic value in sheep, as it induced strong and constant preferences for the treated food over the same untreated food, regardless of the doses (Gherardi and Black, 1991;Favreau et al, 2010a). In cattle, umami induced such a preference in young animals (e.g.…”

“…umami taste; Gherardi and Black, 1991), and ruminants show difficulties to learn in complex experimental feeding situation where the food sensory characteristics are just used as discriminating tools. It thus seems that the role of sensory characteristics in ruminants' feeding behaviour have been underestimated and is more important than previously described in the literature.…”

The influence of odour, taste and nutrients on feeding behaviour and food preferences in horses

“…Typically nutritional consequences influence food preferences and sensory characteristics regulate the discrimination between various food items as demonstrated in humans (Stubbs and Whybrow, 2004), rats (Sclafani and Ackroff, 2004), and ruminants (Provenza and Villalba, 2006). However, pre-ingestive stimuli have been shown to override post-ingestive signals in some cases and sensory characteristics can induce preferences in the absence of any immediate post-ingestive feedback (Gherardi and Black, 1991;Berthoud, 2004).…”