Swiss Federal Veterinary Office, Centre for Proper Housing of Ruminants and Pigs, Agroscope, 8356, Ettenhausen, Switzerland.
Graduate School for Cellular and Biomedical Sciences, University of Bern, 3012, Bern, Switzerland.
Sci Rep. 2020 Dec 21;10(1):22336. doi: 10.1038/s41598-020-78931-w.
Contrafreeloading (CFL) is the phenomenon when animals work for a resource although an identical resource is available for free. Possible explanations for CFL are that animals seek context for species-specific behaviours or to control their environments. We investigated whether goats show CFL and whether breeding for productivity traits has altered its occurrence. In a manipulation task, we compared two selection lines: 27 Nigerian dwarf goats, not bred for productivity traits, and 30 dairy goats, bred for high milk yield. Over 10 trials, each goat could perform one of three behaviours: not participating in the trial, feeding for free from an open door, or opening a sliding door for a feed of similar value. The results were analysed using an Item Response Tree (IRTree) generalized linear mixed model (GLMM). The fitted probabilities to participate were > 0.87 over all trials in both selection lines. For dwarf goats, the probability of choosing the closed door, and thereby demonstrating CFL, increased from 0.30 in Trial 1 to 0.53 in Trial 10. For dairy goats, this probability was constant at approximately 0.43. Unlike dwarf goats, dairy goats were faster to approach the closed compared to the open door. Overall, our results suggest that both selection lines were similarly interested in CFL.
对免费资源的对抗性获取（CFL）是指动物在有相同免费资源的情况下，仍为获取某一资源而工作的现象。对于 CFL，可能的解释是动物寻求特定物种行为的背景或控制其环境。我们研究了山羊是否表现出 CFL，以及生产力特征的选育是否改变了其发生的频率。在一项操作任务中，我们比较了两个选育系：27 只未选育生产力特征的尼日利亚矮山羊和 30 只高牛奶产量选育的奶山羊。在 10 次试验中，每只山羊可以执行三种行为之一：不参与试验、从打开的门中免费进食，或打开滑动门获取同等价值的饲料。使用项目反应树（IRTree）广义线性混合模型（GLMM）分析结果。在两个选育系中，所有试验的参与概率均超过 0.87。对于矮山羊，选择关闭门以表现出 CFL 的概率从试验 1 的 0.30 增加到试验 10 的 0.53。对于奶山羊，该概率约为 0.43，保持不变。与矮山羊不同，奶山羊更倾向于接近关闭的门，而不是打开的门。总体而言，我们的结果表明，两个选育系对 CFL 的兴趣相似。
