By learning from older more experienced adults, younger members of our mixed age groups hone their senses to navigate and be selective of the diverse flora they graze across Kent’s stunning nature reserves.
Poisonous plants & grazing animals' natural instincts
In Kent, our grazing animals roam the reserves using their instincts and experience to guide them towards delicious nutritious vegetation and away from potentially toxic plants. This deep-rooted wisdom is a product of evolution and survival instincts passed down from generation to generation but particularly prevalent in the old-fashioned breeds that we use.
©️ Jessica Allam
Ragwort
With is bright yellow flowers, ragwort is a common sight and easily identifiable at that (see picture). The plant itself contains pyrrolizidine alkaloids – a toxic substance that, if ingested in large quantities by some animals, can cause loss of condition, liver damage, and can even be fatal.
While ragwort is a concern in the equestrian industry, animals will generally avoid it due to its bitter taste – if given the choice. Our reserves are large and offer a variety of food, many of which are more palatable than the bitter leaves of ragwort. If alternative food sources are scarce, leading to nutrient deficiencies, or the animals are under pressure from hunger, they may ingest the plant and become ill.
Another issue is that ragwort loses its bitter smell and taste when cut, leading to accidental ingestion. This is particularly problematic in hay bales, when sufficient ragwort removal has not taken place before the hay is cut and baled.
Whilst ragwort can pose a danger to cattle and ponies, it serves as an excellent nectar source for insects, and is the only food plant of the cinnabar moth caterpillar. Sheep demonstrate a unique ability to graze and control ragwort in the early spring while at rosette stage, showcasing the benefits of implementing mixed grazing strategies. Striking the right balance of grazing pressure is key to controlling ragwort. It is an opportunist that likes bare and disturbed ground. Overgrazing can increase disruption of the seed bank through poaching of the soil potentially causing a surge in ragwort numbers. Up to approximately 5% ground cover of ragwort is considered manageable and contributes to a healthy ecosystem.
©️ Zsuzsanna Bird
Acorns
Many might not suspect acorns to be harmful, but these small nuts contain high level of tannins. Tannins are a natural compounds found within various plants, acting as a defence mechanism causing gastrointestinal distress, as well as kidney and liver damage. Acorns are also considered anti-nutrients, as the tannins bind with proteins, reducing the body’s ability to absorb nutrients from food.
Similar to ragwort, acorns have an unpleasant bitter taste, deterring many animals from consuming large quantities of them. Tannin levels vary depending on the oak type – white oak species such as the native English and Sessile oak have lower levels of tannins, making them slightly more palatable than red oak species which have very high levels of this bitter compound. It is worth noting that the UK does not have any red oak species as they are a native oak to North America.
Whilst they can be toxic in large amounts, they, like many types of nut, play a crucial role in an animal’s diet acting as an important source of fats and carbohydrates. This makes them quite calorific, which is essential for maintaining condition in the colder months. In the past, wild boar - who are immune to the effects of the tannins - would have played a significant role in keeping levels of acorns low and preventing other animals from gorging on too many of them and becoming ill. The practise is still used in the New Forest with domestic pigs to protect the ponies that live in the National Park.
Squirrels and jays contribute significantly to the dispersal of plant seeds. Squirrels, known for burying acorns in various locations, play a key role in moving seeds away from the parent plant, reducing competition of resources. Similarly, jays have established a symbiotic relationship with oak trees by caching acorns away from the parent tree. These acorns, even when uprooted and replanted by the birds, contribute to the survival of young saplings. The actions of both squirrels and jays contribute to the successful dispersal and germination of oak seeds.
©️ Amy Lewis
Yew and foxglove
Yew trees contain toxic alkaloids known as taxines, the most potent being taxine A and B. These compounds have a detrimental effect on heart function by inhibiting the normal sodium and calcium exchange across the heart muscle, leading to abnormal heart rhythm. Ingesting enough yew leaves can result in symptoms such as muscle tremors, loss of coordination, difficulty breathing and ultimately death. Interestingly, wild deer are able to browse yew trees in the winter without being affected by the toxic chemical and our cattle have been seen to take the occasional leaf with no ill affects as part of their balanced diet.
Foxgloves, on the other hand, contain toxic cardiac glycosides that also profoundly affect heart function. Livestock generally avoid foxglove due to its bitter taste, however if ingestion occurs, early signs may include drowsiness, staggering, fitting, collapse, and diarrhoea. Many of our livestock have learnt what to eat and what to avoid. In many instances, if an older, more experienced herd member avoids a plant, others tend to follow suit. However, goats, being curious browsers, can be an exception to this behaviour pattern.
©️ Jessica Allam
Bracken
In comparison to the other plant species mentioned, bracken can be ingested by animals for several weeks before bracken poisoning develops. This type of poisoning is more likely to happen in the spring and summer months when the younger shoots emerge, proving more palatable compared to the older, woodier bracken stems in the autumn and winter and when animals do not have access to alternative food. Affected animals typically exhibit weakness, rapidly weight loss, and lethargy. Prolonged exposure to the plant can lead to excessive bleeding, even from minor wounds such as bug bites and scratches.
Despite its potential toxicity, bracken plays a crucial role in ecological succession and restoration. It often thrives in areas of disturbed ground, with the dense canopy providing shelter and microhabitats for various insects, spiders, and small mammals to exploit.