Most lawns in Wyoming are some combination of Kentucky bluegrass and fescue. We spend a lot of resources fertilizing, watering, and mowing our lawns. Is there any value in all of that grass?
Horses should never be fed grass clippings! Because of the short fiber length, most lawn grass clippings will pass through the digestive system very quickly. A pile of fresh grass clippings is too tempting to resist, and most horses would gorge themselves given the opportunity. Both of these factors can lead to excess fermentation in the hind gut, and colic. Horses are also susceptible to botulism which can develop in anaerobic conditions (i.e. a pile of grass clippings).
Cattle and sheep have a different digestive system and are not at risk of colic or botulism. However, that does not mean throwing grass clippings into the feed bunk is always a good idea.
Nitrate toxicity is a risk with many forages, including grass clippings. Bacteria in the guts of ruminants convert the nitrate in forage into ammonia which is used to make protein for bacterial growth and reproduction. Nitrite is produced as an intermediate compound created in this process, and can inhibit the ability of the blood to transport oxygen. Toxicity depends on the nitrate concentration of the forage and rate of consumption. For example, an animal that consumes high nitrate forage quickly is more at risk of poisoning than an animal that consumes this same forage over a longer period of time.
Stressful conditions include drought or cold weather, herbicides, and disease. While levels of nitrogen in the soil are also a factor in nitrate accumulation, it is not as important as plant stress. Allowing fresh grass (i.e. green chop or grass clippings) to heat up before feeding greatly increases the levels of toxic nitrite (due to bacterial activity in the pile) and can turn an otherwise safe feed deadly.
Considering this, the highest risk of nitrate toxicity from grass clippings would come from a heavily fertilized lawn under stress, that was stored in a pile and allowed to heat up before feeding, and then was consumed quickly by livestock and not mixed with other forages.
If you are concerned about the nitrate concentration of your lawn grass, or any other forages, send a sample into a lab for analysis. It will cost you less than $20. If the grass is high in nitrates, you may still be able to feed it as long as it is mixed thoroughly with other feeds.
Ensiling forages can reduce nitrate levels by 40 to 60%. However, it is still a good idea to test the silage for nitrates before feeding.
Ensiling is a way of storing forages in anaerobic conditions (no oxygen) that preserves their nutritional value. Bacteria ferment the sugars and starches in the grass and produce lactic and acetic acids. Successful ensiling requires grass that has a moisture content of 60-70% and a sealed environment that excludes oxygen. After several weeks of fermenting, silage should have a pH below 4.5, a slight vinegar odor, and be light green to yellow in color.
If the area where you are collecting clippings has been sprayed with any pesticides be sure and thoroughly read the label to determine if the grass is safe to feed to livestock. Some herbicides will pass through the gut without harming the animals and still be active when excreted in manure.
There are many plants that are poisonous to livestock. If you mow an area with heavy weeds, tree leaves, or pine needles it would be wise to put that load in the compost pile instead of the feed bunk.
- Plants Poisonous to Livestock - Cornell University
- Plants Poisonous to Livestock in the Western States - USDA-ARS (120 pages)