Kronberg S L, Walker J W, Fitzgerald J A
USDA-ARS, U.S. Sheep Experimental Station, Dubois, ID 84323.
Physiol Behav. 1993 Dec;54(6):1191-4. doi: 10.1016/0031-9384(93)90347-i.
The mechanisms underlying diet selection of ruminants are less studied than those for monogastrics. However, recent studies have shown that these mechanisms may be more similar in ruminants and monogastrics than previously believed. Food aversion learning is observed in both monogastrics and ruminants, and the hypothalamic-pituitary-adrenal axis appears to be involved in avoidance learning. Using leafy spurge (Euphorbia esula), an introduced weed whose expansion has costly ecological and economic implications in western North America, as a model for underconsumed plant species, we hypothesized that sheep experience increased cortisol levels when they first consume leafy spurge and that this may be related to their reluctance to graze it. We also hypothesized that preexposure to leafy spurge would attenuate the development of a spurge-based aversion. Correspondingly, we hypothesized that preexposed sheep would not experience increased blood cortisol levels with leafy spurge gavage during an aversion trial. None of our hypotheses were disproved by the experiments. Our results lend support to the hypothesis that stress is required for the development of conditioned taste aversions and extend it to ruminants. We suggest that activity of the hypothalamic-pituitary-adrenal axis is integral to food aversion learning in ruminants.
与单胃动物相比，反刍动物饮食选择的潜在机制研究较少。然而，最近的研究表明，这些机制在反刍动物和单胃动物中可能比以前认为的更为相似。在单胃动物和反刍动物中都观察到食物厌恶学习，并且下丘脑 - 垂体 - 肾上腺轴似乎参与了回避学习。使用北美西部一种外来杂草——乳浆大戟（Euphorbia esula）作为未被充分采食的植物物种的模型，其扩张具有高昂的生态和经济影响，我们假设绵羊首次食用乳浆大戟时皮质醇水平会升高，并且这可能与它们不愿采食它有关。我们还假设预先接触乳浆大戟会减弱基于大戟的厌恶反应的形成。相应地，我们假设预先接触过的绵羊在厌恶试验期间通过乳浆大戟灌胃不会出现血液皮质醇水平升高。我们的假设均未被实验否定。我们的结果支持了条件性味觉厌恶形成需要应激这一假设，并将其扩展到反刍动物。我们认为下丘脑 - 垂体 - 肾上腺轴的活动对于反刍动物的食物厌恶学习至关重要。
