Case Study
What is a weed in a regenerative grazing system?
The presence of ‘weeds’ in pastures is always a talking point for farmers that visit the FAI farm, and for landowners and communities who are used to ‘tidy’ looking farms. But what is a weed? And what can they tell us?
Last year, the AMP project and farm team engaged in training on ‘Weeds as Red Flags’ with regenerative agriculture coach Caroline Grindrod and conservation ecologist Rob Dixon. In the training we were encouraged to think of plants that are traditionally seen as weeds as ‘Red Flags’ or indicators that the system is out of balance. System imbalance can be caused by a variety of factors such as overgrazing, or a low or high fertility environment.
When animals are left in paddocks for extended periods of time, they tend to overgraze certain species and as these species start to regrow after a grazing episode they are grazed again by the livestock. This over-grazing of the most preferred species impacts their ability to grow and proliferate and allows less preferred ‘weed’ species to start to dominate swards. Nettles and thistles can be a sign of overgrazing in environments where cattle graze; they become dominant as the more palatable species are over-grazed and competition is removed.
In permanent grassland, weed control generally entails a mix of herbicide use (usually via a weed wiper) or topping. Although more selective than spraying, any herbicide use can impact non-target species broad-leaved plants, and enter water courses. There are also important concerns around the economic costs and potential health implications of the improper use or application. In organic systems like ours, topping is the main method of weeds control, requiring the use of a tractor and fuel. The possibility of using grazing cattle to control weed species is therefore of great interest.
A study in Canada in 2006 experimentally tested three cattle grazing systems, including (1) continuous or season-long grazing (SL), (2) short duration (SD) (or low intensity-high frequency) rotational grazing and (3) high intensity-low frequency (HILF) rotational grazing (similar to an AMP grazing system), for their ability to reduce creeping thistle (De Bruijn & Bork 2006). They found that while SL grazing maintained or increased severe creeping thistle infestations and reduced forage yield, HILF rotational grazing of cattle reduced the shoot density, biomass and flowering of creeping thistle (to a greater extent than the SD system). Two intense defoliations annually over 2–3 years nearly eliminated creeping thistle stems. Remaining shoots were also primarily vegetative and greater in forage quality under HILF grazing. The authors concluded that high intensity low frequency grazing may be an important weed biological control.
At the FAI Farm, we have noticed that the AMP grazing cattle are eating both thistles and nettles (Fig. 1). Because in AMP grazing systems, cattle are mobbed together creating competition, they tend to graze all of the edible plants rather than just their preferred species. Furthermore, there is some evidence in the literature that nettles and thistles could have beneficial nutritional properties.
Figure 1: Thistles after being grazed by the AMP grazing cattle group
Nutritional properties of two common ‘weed’ species
Creeping thistle
A 2022 systematic literature review investigated the potential uses of creeping thistle (Cirsium arvense) as a food and medicinal plant for humans. In academic publications, human consumption of creeping thistle was evidenced from India, Italy, Kazakhstan, Pakistan, Romania, Russia, Slovakia, Spain, Turkey, the UK and Ireland, and North America. A multitude of medicinal uses were found, the most reported being: anti-inflammatory, antioxidant, hemostatic and diuretic effects (Ebel 2022).
A small study in the US found that the average protein value of creeping thistle throughout the growing season was 12.8%; but protein quality varied from 8% (mature plants) all the way up to 27% (young regrowth) (n=11 samples). Total digestible nutrients (TDN) were 65.5%, which was similar to mixed pasture in late vegetation or alfalfa pasture (Vickers et al., 2017). Creeping thistle has significantly more Calcium, Sulphur, Zinc, Copper and Cobalt than either perennial ryegrass or white clover (Harrington et al. 2006).
Stinging nettle
Stinging nettle (Urtica dioica) has been used by people as a natural remedy for its healing properties for over 2000 years (Bhusal et al., 2022). Its uses include anti-proliferative, anti-inflammatory, antioxidant, analgesic, immune stimulatory, anti-infectious, anti-ulcer activities, and cardiovascular disease prevention (Ait Haj Said et al., 2015). Nettle has a balanced protein composition and a relatively high mineral and vitamin content, containing a lot of vitamin C and provitamin A (Guil-Guerrero et al., 2003; Bhusal et al., 2022). In terms of minerals, zinc, iron, cobalt, potassium, nickel, and molybdenum are all abundant (Ait Haj Said et al., 2015).
Stinging nettle (both raw material and infusion) has been administered as a herbal remedy to animals, including cattle, goats, pigs and donkeys in Switzerland, Spain, Italy and Austria to enhance general strength, to treat skin afflictions and sores and to help with gastrointestinal disorders and metabolic dysfunctions (Disler et al., 2014). In dairy cattle, on-farm data have shown that nettle supplementation can boost productive performance and improve milk quality (Khanal et al. 2017). Nettles are used in traditional veterinary medicine in Canada, where it is fed to ruminants as a tonic and to provide trace minerals, as a treatment for diarrhoea and internal parasites and to pregnant and lactating animals (Lans et al., 2007). In vitro studies in the rumen fluid of dairy cattle have found that stinging nettle haylage increased the pH of rumen fluid by 30% for a period of a week in place of ryegrass silage (Lolium perenne). Diets containing more nettles reduced the time rumen pH was at 5.5, the critical level for rumen acidosis (Humphries & Reynolds, 2014).
Conclusions
Encouraging as well as training cattle to eat ‘weed’ species, for example by using AMP grazing, could have benefits for both the environment (via reduction in herbicide and fuel use for topping) and cattle health and welfare, due to nutritional and healing properties. Weed consumption by cattle is something we will further monitor in the AMP grazing project this year.
References
Ait Haj Said, Amal & Otmani, I.S.E. & Derfoufi, Sanae & Benmoussa, Adnane. (2015). Highlights on nutritional and therapeutic value of stinging nettle (Urtica Dioica). International Journal of Pharmacy and Pharmaceutical Sciences. 7. 8-14.
Bhusal, KK, Magar SK, Thapa R, Lamsal A, Bhandari S, Maharjan R, Shrestha S, Shrestha J. Nutritional and pharmacological importance of stinging nettle (Urtica dioica): A review. Heliyon. 2022 Jun 22;8(6):e09717.
De Bruijn, S. L., & Bork, E. W. (2006). Biological control of Canada thistle in temperate pastures using high density rotational cattle grazing. Biological Control, 36(3), 305-315.
Disler, M., Ivemeyer, S., Hamburger, M., Vogl, C. R., Tesic, A., Klarer, F., ... & Walkenhorst, M. (2014). Ethnoveterinary herbal remedies used by farmers in four north-eastern Swiss cantons (St. Gallen, Thurgau, Appenzell Innerrhoden and Appenzell Ausserrhoden). Journal of Ethnobiology and Ethnomedicine, 10(1), 1-23.
Ebel, R. (2022). Eating instead of managing it?–a systematic literature review on potential uses of creeping thistle as food and medicinal plant. Journal of Crop Improvement, 1-31.
Guil-Guerrero, J. L., Rebolloso-Fuentes, M. M., & Isasa, M. T. (2003). Fatty acids and carotenoids from Stinging Nettle (Urtica dioica L.). Journal of Food Composition and Analysis, 16(2), 111-119.
Harrington, K. C., Thatcher, A., & Kemp, P. D. (2006). Mineral composition and nutritive value of some common pasture weeds. New Zealand Plant Protection, 59, 261-265.
Humphries, D. J. and Reynolds, C. K. (2014) The effect of adding stinging nettle (Urtica dioica) haylage to a total mixed ration on performance and rumen function of lactating dairy cows. Animal Feed Science and Technology, 189. pp. 72-81.
Lans, C., Turner, N., Khan, T., Brauer, G., & Boepple, W. (2007). Ethnoveterinary medicines used for ruminants in British Columbia, Canada. Journal of Ethnobiology and Ethnomedicine, 3(1), 1-22.
Vickers, L, Bondaroff, K. & Burton, S. (2017). Nutritional Value of Thistle. Peace River Agriculture Development Fund. Available at: https://peaceforage.bc.ca/wp-content/uploads/2021/06/FF_104_Grazing_Weeds_Nutritional_Value.pdf
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