Favreau A, Ginane C, Baumont R
INRA, UR1213 Herbivores, Site de Theix, F-63122 Saint-Genès-Champanelle, France.
Animal. 2010 Aug;4(8):1368-77. doi: 10.1017/S1751731110000443.
Understanding what determines feeding behaviour in herbivores is essential to optimise the use of forages in breeding systems. Herbivores can evaluate foods by associative learning of their pre-ingestive characteristics (taste, odour, etc.) and their post-ingestive consequences. Post-ingestive consequences are acknowledged as influencing intake and food choices, but the role of pre-ingestive characteristics is still being debated. Our experiment was designed to test their separate effects on daily dry matter intake (DMI), intake patterns and short-term choices in sheep by crossing the nature of the hay orally consumed (o) ad libitum, lucerne (L) or grass (G), with the nature of the hay introduced into the rumen (r), L or G, at a rate of half the total amount of hay received the day before. We applied four treatments, Go/Gr, Go/Lr, Lo/Gr and Lo/Lr, to test the effects of (i) post-ingestive consequences with similar pre-ingestive characteristics (Go/Gr v. Go/Lr; Lo/Gr v. Lo/Lr) and (ii) pre-ingestive characteristics with similar post-ingestive consequences at the end of the feeding period (Go/Lr v. Lo/Gr). Six rumen-fistulated sheep underwent all the treatments over 11-day periods in a latin square design. Eating time was restricted to 6 h/day, intraruminal introductions were performed just before food offer and choice tests were conducted after food removal. For similar pre-ingestive characteristics, DMI increased when L hay was introduced into the rumen rather than G (P < 0.05), possibly owing to a lower fill effect of L due to its lower NDF content and higher rumen degradability. The increased DMI resulted from longer eating time when G was orally consumed (149 v. 192 min, P < 0.05), whereas it resulted from higher intake rate with L (4.8 v. 6.1 g/min, P < 0.05). For similar post-ingestive consequences at the end of the feeding period (Go/Lr and Lo/Gr), DMI were similar (P > 0.05). Pre-ingestive characteristics or palatability per se did not therefore influence daily intake, although they influenced eating patterns. Pre-ingestive characteristics also greatly influenced short-term choices in favour of the hay that was not previously consumed, independently of any post-ingestive influence. This study confirms the effects of post-ingestive consequences on daily intake, but demonstrates that these variations are obtained by different behavioural adjustments under the influence of pre-ingestive characteristics. Preference for novelty, regardless of post-ingestive consequences, thus suggests that sheep may seek a diverse diet more for pleasure than for functional purposes, with implications for animal welfare.
了解决定食草动物采食行为的因素对于优化育种系统中草料的利用至关重要。食草动物可以通过对其采食前特征（味道、气味等）及其采食后后果的联想学习来评估食物。采食后后果被认为会影响采食量和食物选择，但采食前特征的作用仍在争论中。我们的实验旨在通过将随意口服的干草（o）的性质（苜蓿（L）或草（G））与以前一天所采食干草总量一半的速率引入瘤胃（r）的干草性质（L或G）进行交叉，来测试它们对绵羊日干物质摄入量（DMI）、采食模式和短期选择的单独影响。我们应用了四种处理方式，即Go/Gr、Go/Lr、Lo/Gr和Lo/Lr，以测试（i）具有相似采食前特征的采食后后果的影响（Go/Gr与Go/Lr；Lo/Gr与Lo/Lr）以及（ii）在采食期结束时具有相似采食后后果的采食前特征的影响（Go/Lr与Lo/Gr）。六只装有瘤胃瘘管的绵羊按照拉丁方设计在11天的时间段内接受了所有处理。采食时间限制为每天6小时，在提供食物前进行瘤胃内引入，在移除食物后进行选择测试。对于相似的采食前特征，当将苜蓿干草引入瘤胃而非禾本科干草时，DMI增加（P<0.05），这可能是由于苜蓿较低的中性洗涤纤维含量和较高的瘤胃降解性导致其填充效应较低。DMI的增加是因为口服禾本科干草时采食时间更长（149对192分钟，P<0.05），而口服苜蓿干草时则是由于采食速率更高（4.8对6.1克/分钟，P<0.05）。对于采食期结束时具有相似采食后后果的情况（Go/Lr和Lo/Gr），DMI相似（P>0.05）。因此，采食前特征或适口性本身并不影响日摄入量，尽管它们会影响采食模式。采食前特征也极大地影响短期选择，使其倾向于之前未采食的干草，而不受任何采食后影响。这项研究证实了采食后后果对日摄入量的影响，但表明这些变化是在采食前特征的影响下通过不同的行为调整获得的。对新奇事物的偏好，无论采食后后果如何，因此表明绵羊可能更多地是为了愉悦而非功能目的寻求多样化的饮食，这对动物福利有影响。
