Abstract
Voluntary fluid intake studies utilizing phenylthiocarbamide (PTC) have demonstrated variation in willingness to consume bitter compounds among sheep. Bitter sensitivity has been linked to dietary preferences in other species, leading researchers to inquire whether this ability impacts foraging decisions. The objective of this study was to determine whether bitter tasting ability could be identified by measuring feed intake and behavioral responses of sheep to alfalfa pellets topically sprayed with a PTC-solution. A pilot study was conducted to determine if group-housed lambs (n = 6) would exhibit an aversive response to topical applications of PTC-treated (LOW: 20 mM; HIGH: 30 mM) feed and the maximum duration of feed consumption (981.4 ± 70.6 sec; P ≤ 0.011). Lambs exhibited a greater (P ≤ 0.002) number of feeding events, positional changes around the feed bunk, and increased (P = 0.002) reliance on olfaction when offered PTC. Based on these results, ram lambs (n = 56) were divided into two groups (n = 28; Polypay: n = 10; Rambouillet: n = 10; Targhee: n = 8) and tested sequentially for bitter sensitivity. Rams were offered alfalfa pellets sprayed with either LOW or HIGH PTC solutions followed by control pellets for 15 min each. Feed intake was not affected by PTC treatment (P = 0.18). Control pellet intake was greatest (P ≤ 0.001) after consuming HIGH PTC pellets and was directly correlated (P < 0.001, r = 0.45) to intake of PTC-treated feed. Lambs displayed more (P ≤ 0.001) behavioral reactions and exhibited a more discontinuous feeding pattern when presented with PTC-treated pellets (P ≤ 0.005). Classifications were devised based on the range of behaviors observed over both concentrations of PTC (low: 0-3, n = 14; moderate: 4-6, n = 30; high: 7-10, n = 11). Highly and moderately reactive lambs consumed the greatest amount of PTC and control pellets (P ≤ 0.006). Differences were observed between the classes (P ≤ 0.035) for the sniffing, head shaking and butting, biting, pawing, and fenceline behaviors which may aid in the identification of bitter sensitivity. However, further research is needed to determine the effects of bitter tasting ability on feeding behavior and the willingness of sheep to consume bitter feeds.