Preference for flavored wheat straw by lambs conditioned with intraruminalinfusions of starch administered at different times after straw ingestion

We hypothesized that the development and extinction of preferences for flav ored foods paired with infusions of starch depends on the delay between foo d ingestion and starch administration and on the frequency of starch admini stration. To test this hypothesis, we divided 24 lambs into three groups of 8 lambs/group. On even days, half of the lambs were offered chopped wheat straw flavored with a distinctive flavor, whereas the other half received s traw with a different flavor. Starch (12% of the daily DE required by the l ambs) was infused into the rumen immediately after lambs began to eat straw in Group 1 (150 g starch), immediately after lambs began to eat straw (75 g) and 30 min later (75 g) in Group 2, and when straw refusals were collect ed Ih after lambs began to eat straw in Group 3 (150 g). On odd days, the f lavors were switched and infusions of starch were replaced with water. Afte r 8 d of conditioning, starch infusions were suspended, and lambs were offe red a choice of wheat straw with the two distinctive flavors. All lambs acq uired strong preferences for flavored straw paired with starch (P < .001), but the delay between straw ingestion and starch infusion affected preferen ces (P < .05). Lambs that received starch 1 h after beginning to eat straw (Group 3) had lower preferences than lambs that received starch immediately after beginning to eat straw (Groups 1 and 2). Lambs that received two sta rch infusions (Group 2) did not show higher preferences for flavored straw than lambs that received only one starch infusion immediately after beginni ng to eat (Group 1). Lambs in our study retained preferences for at least 1 7 d when eating straw was no longer reinforced with starch (P < .001). Howe ver, preferences were less persistent for lambs that received starch immedi ately after beginning to eat straw (Group 1) than for lambs that received s tarch in two pulses (Group 2) or lambs that received starch 1 h after begin ning to eat straw (Group 3). Collectively, our results support the hypothes is that the delay between food ingestion and starch administration affects food preferences of lambs. These findings suggest that manipulating the che mical characteristics of foods, which affects the kinetics of forage degrad ation in the rumen, can increase food preferences in ruminants.