Although both lawns and pastures contain predominantly grasses, the feeding of lawn grass ‘clippings’ specifically to horses can create a perfect storm of harm for the horse that is easily overlooked.
When a horse grazes it goes through a series of motions, selecting, ripping, and thoroughly chewing the grasses. This process creates a slow and steady trickle of feedstuffs to the digestive system. If, however, the horse is presented with a pile of lawn grass clippings it can quickly consume a very large amount of grass. This is because the rotary mower produces a dense concentration of grasses with a small particle size.
The sudden influx of highly digestible feedstuffs into the horse’s gastrointestinal tract can upset the delicate microbial balance in the hindgut, potentially leading to colic or laminitis (founder). Lawn clippings, like grains, are high in sugars and carbohydrates and their fermentation in the hindgut creates an acidic environment. The acidic environment causes microbes to die and release endotoxins into the bloodstream which in turn can trigger laminitis.
Individual horses vary in their sensitivity to ingestion of grass clippings and the amount consumed. For some horses, it may be of little consequence while for others it can trigger a major metabolic crisis.
Another matter of concern with fresh lawn clippings is the manner in which some horses tend to gulp or bolt down the small, wet, compacted clumps of finely cut grass. The bolus of clippings can become lodged in the esophagus and a condition called ‘choke’ may result. The resolution of choke generally requires the intervention of a veterinarian.
Whenever lawn clippings are piled, the high moisture content of the lawn grass coupled with warm temperatures leads to rapid production of moulds and bacteria in the decaying pile. Horses that consume the contaminated grass clippings may experience colic or diarrhea. The dust and moulds contained within these piles can also trigger respiratory distress in horses sensitive to airborne insults. Therefore, it is prudent to dispose of lawn clippings where horses will not have access to them.
A major consideration often overlooked when feeding lawn grasses to horses is the nature of lawn grass itself. Many lawns are treated with lawn-care products which can contain chemicals, such as herbicides and fertilizers. These chemicals can be detrimental to the horse and the residuals of these chemicals can persist in the grasses for a long time after application.
A final concern of note when lawn grasses are fed to horses is the possibility of inadvertently including small pieces of common ornamental plants such as oleander or Japanese yew and/or noxious weeds such as horsetail which contain toxic substances.
Field horsetail (Equisetum arvense) is a native plant growing across Canada. This plant contains thiaminase which causes thiamine deficiency in horses. Horses normally avoid these plants. However, when finely chopped into small pieces alongside the grass clippings the horse will be unable to sort them out and can accidentally ingest them with detrimental consequences.
In general it is advisable to avoid feeding lawn grass clippings to horses as the nature of the clippings carries a number of risks for potential harm.