Choosy grazers: Influence of plant traits on forage selection by three cattle breeds

Forage selection by herbivores is a major driver of plant diversity in pasture vegetation. Yet, we know relatively little about how plant traits influence decisions of different herbivore species and breeds to select or avoid a certain plant species on semi-natural pastures. We quantified the influence of the traits leaf N and P content, leaf dry matter content (LDMC), specific leaf area (SLA) and physical defence mechanisms on plant species selection for three cattle breeds: high-yielding Angus x Holstein crossbreed, dual-purpose Original Braunvieh and undemanding Highland Cattle. The cattle grazed a series of adjacent paddocks in different alpine pastures. Plant species selection was quantified by assessing the difference in biomass proportions of all plant species in 66 vegetation subplots per breed before and after grazing. Plant traits and indicator values were extracted from the TRY database. Data on 152 plant species were analysed using a local mixed-effects model and a global multivariate hierarchical regression model. Plant traits had a clear impact on forage behaviour. Plants with high SLA, leaf N and P contents were significantly selected, whereas plants with high LDMC (e.g. woody plants) and defence mechanisms (e.g. thistles) were generally avoided. Species with high forage quality indicator values as defined by Briemle et al. (2002) were significantly preferred. More importantly, significant differences between forage behaviour of cattle breeds were detected. Selection by less-productive Highland Cattle was much less influenced by plant traits than the selection by the two higher-yielding breeds. Results indicate a clear impact of plant traits on forage selection and demonstrate breed-specific influences. Highland Cattle (and possibly other robust breeds) graze less selectively and impose less selective exclusion on plants. Thereby, they likely influence plant species composition of pastures in a different way than high-yielding breeds, thereby creating a distinct habitat. A free Plain Language Summary can be found within the Supporting Information of this article.