INRA, UR1213 Herbivores, Site de Theix, F-63122 Saint-Genès-Champanelle, France.
J Anim Sci. 2010 Apr;88(4):1535-44. doi: 10.2527/jas.2009-2455. Epub 2009 Dec 4.
Previous work has shown that herbivores successfully learn to associate food sensory characteristics with postingestive consequences when the conditioning procedure is simple, whereas this ability breaks down when the learning task is made more complex. We hypothesized that sensory characteristics could act as indicators of postingestive consequences and that the presence of preingestive cues would improve the food learning of sheep in situations varying in complexity. Sixteen sheep were subjected to a first conditioning phase to associate 2 flavors added to alfalfa hay with either a positive or a negative consequence, induced by intraruminal administration of starch (330 mg/g of DMI) or LiCl (5 mg/g of DMI). Sheep progressively decreased their choice of the flavored hay associated with the negative consequence (P < 0.05). This procedure provided sheep with experience with postingestive consequences associated with the different flavors. In a second conditioning phase, the experienced sheep and 16 naïve sheep were divided into groups of 8 and subjected to either a simple or a complex conditioning procedure [i.e., the 2 flavors were offered on separate days (simple conditioning) or simultaneously within a day (complex conditioning)]. The 2 flavors applied to grass hay were associated with either positive (starch, 330 mg/g of DMI) or negative (LiCl, 10 mg/g of DMI) consequences. As hypothesized, sheep in the simple conditioning group expressed a greater aversion to the flavored hay associated with the negative consequence than did those in the complex conditioning group (0.303 +/- 0.035 vs. 0.474 +/- 0.035 respectively; P < 0.01). Experienced sheep rejected the flavor associated with the negative consequence more strongly than did naïve sheep, regardless of the conditioning procedure (0.304 +/- 0.029 vs. 0.470 +/- 0.041 respectively; P < 0.05). The initial increased preference for aniseed (0.80 +/- 0.04), however, greatly influenced food learning because sheep negatively conditioned on this flavor expressed less avoidance than those negatively conditioned on orange (0.53 +/- 0.04 vs. 0.25 +/- 0.03 respectively; P < 0.01). In conclusion, the simultaneous scenario was actually perceived as complex by all sheep, and experienced sheep were more efficient in food learning than naïve sheep in both the simple and complex learning contexts. The sheep were thus able to generalize the association between sensory cues and postingestive consequences, especially in a complex environment, and then to use these sensory cues as indicators of postingestive consequences.
先前的研究表明，当条件作用过程简单时，食草动物能够成功地将食物的感官特征与消化后的结果联系起来，而当学习任务变得更加复杂时，这种能力就会瓦解。我们假设感官特征可以作为消化后结果的指示物，并且在存在预消化线索的情况下，绵羊在不同复杂程度的情况下的食物学习能力会得到提高。16 只绵羊被置于第一条件作用阶段，通过瘤胃内给予淀粉（330mg/g DMI）或 LiCl（5mg/g DMI），将添加到紫花苜蓿干草中的 2 种味道与积极或消极的结果联系起来。绵羊逐渐减少了对与负面结果相关的风味干草的选择（P < 0.05）。这个程序为绵羊提供了与不同味道相关的消化后结果的经验。在第二条件作用阶段，有经验的绵羊和 16 只新的绵羊被分为 8 组，并进行简单或复杂的条件作用程序[即，2 种味道在不同的日子提供（简单条件作用）或在一天内同时提供（复杂条件作用）]。应用于草干草的 2 种味道与积极（淀粉，330mg/g DMI）或消极（LiCl，10mg/g DMI）的结果相关联。正如假设的那样，在简单条件作用组中的绵羊对与负面结果相关的风味干草表现出更大的厌恶，而在复杂条件作用组中的绵羊则没有（分别为 0.303 +/- 0.035 和 0.474 +/- 0.035；P < 0.01）。有经验的绵羊比新的绵羊更强烈地拒绝与负面结果相关的味道，而不管条件作用程序如何（分别为 0.304 +/- 0.029 和 0.470 +/- 0.041；P < 0.05）。然而，初始时对茴芹的偏好增加（0.80 +/- 0.04）极大地影响了食物学习，因为对这种味道进行负面条件作用的绵羊比对橙色进行负面条件作用的绵羊表现出的回避行为更少（分别为 0.53 +/- 0.04 和 0.25 +/- 0.03；P < 0.01）。总之，所有的绵羊都认为同时出现的情况实际上很复杂，而有经验的绵羊在简单和复杂的学习环境中都比新的绵羊更有效地学习食物。因此，绵羊能够将感官线索与消化后结果之间的联系概括起来，特别是在复杂的环境中，然后将这些感官线索用作消化后结果的指示物。
