Caren Pauler is currently a Ph.D. student at Agroscope in Zürich and the Centre for Organismal Studies, University of Heidelberg. Caren will be defending her PhD this July. In this insight, Caren discusses with us her article “Choosy grazers: Influence of plant traits on forage selection by three cattle breeds” and how her interest in ecology was shaped.
About the paper
The starting point for my article was the well-known facts that grazing animals select the plants they eat and that selectivity between herbivore species differs considerably. However, I was astonished how little is known about selection differences between livestock breeds; for example different breeds of cattle. This is surprising because breeding by humans created plenty of breeds that not only differ in colour, but particularly in productivity and size. There are undemanding, traditional breeds with low meat or milk yields, and high-productive breeds, which are heavier, grow faster and produce much more milk or meat. I wondered if these differences in productivity between breeds influence forage selection and – that’s the ecological part of the question – ultimately the composition of pasture vegetation.
Presumably, forage selection by grazing livestock is rather unimportant in intensively managed pastures in the lowlands in which mowing, fertilisation and/or herbicides regulate plant species composition. On species-rich, upland pastures in alpine regions, however, forage selection may play a much more important role for vegetation. These low-productive and vulnerable habitats of impressive biodiversity were formed by centuries of grazing livestock and are, thereby, highly influenced by animals’ forage selection and potentially by the dramatic modification of these animals by modern breeding.
In summer 2018, I had the opportunity to conduct a field experiment in the Swiss Alps at 2000 m a.s.l., comparing three cattle breeds with different levels of productivity: (1) undemanding, low-productive Highland cattle, (2) the local mountain breed Original Braunvieh with intermediate productivity, and (3) the high-yielding Angus × Holstein crossbreed. The biggest challenge was to assess cattle plant species selection on pasture, especially in such a heterogeneous, diverse environment where I found more than 150 plant species. Together with my co-authors, I therefore developed a new approach to estimate consumption of individual plant species by comparing vegetation before and after grazing.
Applying this approach, I found that Highland cattle selected their forage less strictly than the more productive breeds. The less productive a breed was, the less selectively it foraged – with regards to numerous plant traits, such as leaf N and P content, C:N ratio, leaf dry matter content, specific leaf area, woodiness and defence mechanisms. Plants commonly known as poor forage plants were less avoided by Highland cattle, that also preferred plants with high forage quality less than the other two breeds. My biggest surprise was observing a Highland cow foraging a whole plant of aconite – one of the most toxic plants in Europe, a few grams of which can kill a man.
About the research
Over recent decades, a tremendous structural change in agriculture took place in industrialized countries. Fertile land is managed intensively, leading to an alarming reduction of biodiversity. There is less focus on an antipodal trend on low-productive land. Many marginal sites are abandoned, because it is not profitable to manage them. In grasslands for example, high-productive modern livestock breeds are hardly able to deal with the poor nutritional quality and hard physical conditions of alpine rangeland. The consequence of abandonment is not unlike intensification: often, the rich biodiversity of infertile grassland is lost. The species-rich habitats, created by centuries or even millennia of low-intensity grazing, are encroached by shrubs and many grassland-adapted species vanish.
We therefore suggest a site-adapted pasture management: Low-productive breeds are better able to handle the conditions of low-productive pastures and thereby preserve their biodiversity. Furthermore, from a previous study (Pauler, Isselstein, Braunbeck, & Schneider, 2019) we know, that low-productive pastures grazed by low-productive Highland cattle are significantly more species-rich than comparable pastures managed with production-oriented cattle breeds. Foraging behaviour can at least partly explain this difference.
The question yet to answer is whether there is a compromise between agricultural production and nature conservation: Is it possible to create higher-yielding breeds that forage like Highland cattle? Would Highland cattle keep their forage behaviour if they were bred towards higher productivity? Moreover, I would really like to investigate whether the differences in foraging behaviour are genetically determined or acquired by learning. It would be a fascinating project to exchange calves of cows from low- and high-yielding breeds and check their adult foraging behaviour.
About The Author
My path to agroecology was not a direct one. I studied theology and biology in Heidelberg, heartland of the humanities and laboratory science. Reading old Greek and pipetting cell cultures, I realized that the questions that really matter to me are answered outdoors in nature. Hence, I wrote my final thesis about biodiversity implications of grazing in the Alps, even if I was the only agroecologist at Heidelberg University. Based on the hypotheses of this thesis, I worked out a PhD-project, searched for supervisors and funding, and will finally defend in a few months. Thereby, I have learned to focus on questions first and then look for answers.
I have never regretted giving up my original fields of study and becoming an ecologist. It is not only the fieldwork, which I enjoy in all aspects, but the wish to contribute relevantly to nature conservation, with the means at my disposal. In ecology, I especially love the holistic approach rather than focusing on encapsulated details. It is great to work not only with one model organism, but with a plethora of plants, animals and, of course, humans. In fact, the contact with local farmers was one of the most interesting and important parts of my field work. When listening carefully to each other and taking concerns and experiences seriously, practitioners are able to improve research questions and give fresh impetus. As a scientist, first listen, then investigate and only then give advice. I consider it essential for agroecology to develop ways of nature conservation jointly with, not against, farmers.