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Your Pasture Pharmacy: Part 1

July 2017 by Dr Mariette van den Berg, BAppSc (Hons), MSc, PhD (Equine Nutrition), RAnNutr, Certified Permaculture Design Consultant,

In this new and exclusive series, Dr Mariette van den Berg will take you on a journey of discovery of the grazing life of horses, exploring how herbivores and plants have adapted to not just co-exist, but benefit each other and thrive. 

You will learn that both plants and horses constantly respond to their environment and have a well-developed ability to make wise-decisions to protect themselves and avoid costly mistakes.  (Yes, we will show you that just like horses and other animals, plants make decisions and even learn!).   

Learning abour the behaviour and  interaction between plants and horses provides an opportunity for your pastures to become more than a dining room - a pharmacy - that provides your horses the nutrients and supplements they need to be happy and healthy.

So, whether you are intrigued or you find the concept of ‘thinking plants’ far-fetched, you have to read on... 

Adapting in a world of change

Have you ever wondered how horses decide what to eat at pasture? Why they prefer certain plants and avoid others, and why this may differ between horses or ponies? Maybe you’ve noticed that some horses can get sick from some plants, while other horses don’t. 

It turns out that, just like other animals, horses learn what to eat and what to avoid, and they do so in many different ways. For example: 

  • They learn from following their mothers after they are born,
  • They learn from other horses, and 
  • They learn through trial and error, by using their senses, and feedback from their digestive system and metabolism to determine what they prefer or need to avoid. 

The topic of foraging behaviour, and how grazing animals learn about their diet and habitat inspired a group of specialised researchers to create BEHAVE (Behavioural Education for Humans, Animals, Vegetation and Ecosystem Management) - a research and outreach program that explores the principles behind diet and habitat selection of grazing livestock. 

BEHAVE’s main focus is to increase our understanding of how animals learn about foods and their environments, in order to enable us - their carers - to make more refined decisions when managing both pasture and animals. 

Applying these grazing principles can make a difference to our animal’s wellbeing and performance, our natural resource conditions and farm profitability. 

As an example, grazing can become a tool that reduces the use of expensive machinery, fossil fuels and toxic herbicides. That is, by understanding how grazing animals learn, we can use their natural grazing behaviours to manage weeds, enhance biodiversity, improve feeding systems, minimise use of fragile riparian areas and much more.

Although BEHAVE’s primary research focus has been livestock, they have also worked in wildlife and even conducted a couple of studies in horses. It was the limited information available on horses that inspired me to use their principles as the basis of my own PhD thesis, which was entitled “Behavioural mechanisms of diet selection in horses” with various chapters of this thesis being published in scientific journals. 

My own PhD project was just the beginning. I hope that other equine researchers will follow in my footsteps and conduct more research in this area as it will enlarge our understanding of our horses’ behavioural needs, and how we can best manage them and our pastures. 

In order to translate some of these principles and answer some of the earlier questions about how horses detect nutrients and toxins in pasture plants, this new series will reveal some interesting facts about: 

  • Plant behaviour: Plants’ defence mechanisms and toxins, 
  • Food palatability and preferences: detecting flavours, nutrients and toxins in plants, and 
  • Self-supplementation and/or medication, and how all the above relates to the importance of managing our pastures to promote biodiversity. 

In particular, I will delve into the current understanding that pasture is more than a horse’s dining room, that it is also a pharmacy “where horses can be taught to select their own medicine”. 

Increasing our knowledge on how plants use toxins will help us improve our understanding of grazing behaviour, pasture management and what supplementary feeds we should provide to our horses.

An ever-changing landscape

We are all aware of the foraging and grazing nature of our horses, but have you ever considered how horses survive in an ever-changing landscape, such as their own pastures? 

Horses are continuously faced with fluctuations in flavours, nutrients and toxins because climate, soils and plants are interrelated facets of systems that change constantly. Change requires that each component of the system continually adapt. Understanding the challenges grazing herbivores, such as horses, face and how they cope can reduce stress and improve the animal’s wellbeing and performance. 

Sensing nutrients

Whether your horses are confined to a stable or foraging on pasture, they have to cope with changes in themselves and the environment. 

An animal’s nutritional needs vary with age and physical activity. For example, they increase when animals are working, breeding or growing. These changes may transpire gradually during pregnancy or they may occur quickly with shifts in physical activity or an abrupt change in the weather. 

Compared to us humans who acquire nutritious foods from grocery stores, restaurants and veggie gardens, horses in natural systems or pastures must sift through an ever-changing landscape full with biochemical complexity. 

Nature constantly alters the quantity of energy, protein and minerals in the foods herbivores require. Individuals must manoeuver through these challenges, recognising nutritional deficiencies in themselves and in the plants they eat. 

In a domesticated system, we usually supplement horses with roughage, concentrates, minerals and vitamins and yet horses, no matter what, will still continue exploring their pastures for edible items, weighing off the nutritional components. So, how do they detect nutrients, and why is over-eating induced obesity such a big problem in ponies and horses, compared to other livestock? 

These are some of the questions we will answer in Part 3 where we will discuss the origin of preference and food palatability (flavours, nutrients and toxins), and how this relates to post-ingestive feedback (how information flows from the gut to the brain).  

Reducing intake of plant toxins

While plants provide primary nutrients, such as protein and carbohydrates, they also pose a toxic challenge. Most plants on pastures, as well as forbs, shrubs and trees, produce toxins - often in significant concentrations. These toxins serve as chemical defenses against herbivores. This may seem surprising to some horse owners, but even our garden vegetables, such as corn, tomatoes, potatoes, broccoli and spinach contain toxins, but they do so in low concentrations we can tolerate thanks to our efforts to select for lower-toxin varieties of crops. 

There are tens of thousands of plant toxins, and they all vary in biochemical structures and activities. In animals, they interfere with metabolic processes or reduce digestibility of foods. 

While most of the time herbivores seem to balance on this tightrope of nutrients versus toxins, at times toxins can cause severe illness or even death. Throughout this series, we will look at how herbivores use plants that contain toxins and whether horses do this in different ways, compared to ruminant herbivores.  

Changes in pasture plants

Perhaps the trickiest challenge herbivores, such as horses, face are the fluctuation in nutrients, toxins and physical characteristics of foods, as well as the changes in environments. 

Just think of the times you moved your horses to a new paddock or travelled interstate to a completely different climate or terrain. While the biochemical composition of our foods at the grocery store is relatively constant, the nutrient and toxin concentrations of plants on pastures vary from morning to night, from day to day, from season to season, and from place to place. 

As plants mature, physical attributes (for example, lignin or silica) that makes foraging difficult increase, while nutrient concentrations decline. An animal’s challenge is to track these biochemical changes as they occur. 

Can herbivores figure out where and when to eat to meet their needs for nutrients, and avoid ingesting toxins, and, if so, what are the implications for managing our pastures? These questions will also be reviewed in this series.  

Your pasture pharmacy

While most people seem to think that plant toxins are bad news, we must also be aware that some plant toxins can be beneficial in small quantities and can work therapeutically. 

Just think of all the beneficial herbs and human medications that are based on plant chemistry. 

Take, for example, aspirin’s main ingredient - salicylic acid - a compound that has been isolated from the bark of the willow tree. 

In livestock and horses, condensed tannins are being investigated for their anti-parasitic properties (see our previous report on a new equine study at 

This is why we should view pasture as more than a horse’s dining room, it’s a pharmacy too; “where horses can be taught to select their own medicine”. 

This self-supplementation, known scientifically as zoopharmacognosy, happens all the time in natural systems, but is not widely acknowledged in domestic management. In Part 4 of this series, we will revisit this topic in much more detail, how it works with horses, and how you can promote it in your own property and pasture. 

Biodiversity - the spice of life

Variety is the spice of life, not only for people, but also for herbivores, such as horses - whether they are confined in stables or grazing on pasture.  

Just like us, horses periodically satiate on familiar and thrive on variety. The science behind this mechanism may be related to the fact that eating a variety of foods (specifically if you are dealing with plants) reduces the chances of over-ingesting plant toxins. At the same time, no one plant species provides all the nutrition an animal needs. 

Thus, selection for nutrients may also be the reason why grazing animals, such as horses, need to be able to select from an array of plant species. 

At the same time and, even when toxins are of no concern and the animals’ nutrition needs are being met, animals will tend to eat an assortment of different foods. Researchers think that flavours may also play a role, just as it does with us humans!

In our final part of our series, we will tie the changes in palatability and preferences, together with the need for biodiversity in our pasture systems. We will discuss strategies on how to increase biodiversity in your pastures and how additional feeding strategies may contribute to this. In addition, we should not forget that each horse is an individual and may have different needs. Thus, creating pastures with more options allows each animal to select their own foods to meet their nutritional needs. 

Don’t miss next month’s article, which will delve further into plant behaviour and begin looking at the types of toxins that plants use to defend themselves, and how they can affect your horse.