Food selection and preference in grazing cattle

放牧是最自然和福利友好的方式来喂养奶牛，是有机乳制品的要求。贴有“草饲”标签的产品正出现在杂货店里，这反映出消费者对牧场牛奶的健康益处或对动物福利的关注日益增长的需求。在大多数以牧场为基础的牛奶生产系统中，实现高水平的动物生产性能和健康是一个关键目标。在过去的五年里，在我的NSERC发现基金的支持下，我研究了牧场生产系统中的奶牛和小母牛，目的是通过更好的生产力和健康来提高它们的福利和效率。我们调查了小母牛的放牧行为是如何发展的，观察了被引入牧场的年龄的影响，并研究了它们的社会环境的作用。我们还研究了胃肠道寄生虫对动物对富含有益单宁的某些类型的饲料偏好的影响。这项研究计划的长期目标是促进我们对以牧场为基础的生产系统中小母牛和奶牛的喂养偏好和放牧行为的理解。这一长期目标将通过一系列短期目标来实现，这些短期目标旨在确定饲养偏好和放牧行为(1)与动物健康和生产力的关系；2)受牧草特性的影响；3)可以通过早期的经验和学习加以修正。在第一个实验中，我们将把放牧行为和牧草摄入量的个体差异与健康和生产力联系起来。在第二个实验中，我们将研究高单宁饲料对胃肠道线虫感染的偏好是先天的，还是在摄取后阳性结果后获得的。在第三个实验中，我们将探索奶牛对具有潜在营养价值的不同浓缩单宁含量的饲料的自愿摄入量和偏好。在第四个实验中，我们将研究饲料浓缩单宁水平对奶牛偏好的影响，而不考虑其他特征和化学成分（如纤维），这些特征和化学成分已被证明会对偏好产生负面影响。第五项实验将旨在证实存在一个敏感期，对小母牛的放牧行为和效率的发展。我们的最后一个实验将幼小动物暴露在不同发育阶段的新鲜植物物种中，试图发现学习植物特征的敏感期。为奶牛提供牧场是改善动物福利和乳制品行业形象的一种特权方式。然而，在更广泛的以牧场为基础的系统中保持奶牛的生产力和健康需要通过改进喂养行为和饮食选择的知识以及开发有效的解决方案来有效利用饲料资源。

Pasturing is the most natural and welfare friendly way to feed dairy animals, and is a requirement in organic dairying. Products labelled as "grass-fed" are making an appearance in grocery stores, reflecting a growing demand from consumers conscious about the health benefits of milk from pastured cows, or concerned about animal welfare. Achieving high levels of animal performance and health from grazed forage is a key objective within most pasture-based, milk production systems. Over the last five years, supported by my NSERC Discovery Grant, I studied dairy cows and heifers in pasture-based production systems, with the intent of improving their welfare and efficiency, through better productivity and health. We investigated how grazing behaviour developed in young heifers, looking at the effect of age of introduction to pasture and studying the role of their social environment. We also investigated the effect of gastrointestinal parasites on animal preference for certain types of forages rich in beneficial tannins. The long-term objective of this research program is to advance our understanding of feeding preference and grazing behaviour of heifers and cows in a pasture-based production system. This long-term objective will be achieved through a series of short-term objectives, which aim to determine how feeding preferences and grazing behaviour 1) are related to animal health and productivity; 2) are influenced by forage characteristics; 3) can be modified by early experience and learning. In a first experiment, we will relate individual differences in grazing behaviour and herbage intake with health and productivity. In a second experiment, we will investigate whether the preference for high-tannin forages in response to infection with gastrointestinal nematodes is innate, or acquired following positive post-ingestive consequence. In a third experiment, we will explore voluntary intake and preference of dairy heifers for forages with potential nutraceutical properties, varying in their condensed tannin content. In a fourth experiment, we will investigate the effects of forage condensed tannin levels on cow preference, independently of other characteristics and chemical components, such as fibre, which has been shown to negatively affect preference. A fifth experiment will aim to confirm the existence of a sensitive period for the development of grazing behaviour and efficiency in heifers. Our last experiment will expose young animals to fresh plant species at various stages of development in an attempt to detect a sensitive period for learning plant characteristics. Providing cows with access to pasture is a privileged way to improve animal welfare and the image of the dairy industry. However, maintaining cow productivity and health in a more extensive pasture-based system necessitates an efficient use of forage resources, through an improved knowledge of feeding behaviour and dietary choices, and the development of effective solutions.