Cattle are naturally foragers, but not everything they consume is naturally good for them.
A comprehensive guide listing dangerous forages by species, created by forage seed supplier LaCrosse Seed, notes two forages inappropriate for dairy animals:
Sweet clover – It has a precious name, but sweet clover is anything but adorable when it comes to dairy rations. Sweet clover contains coumarin, which, under certain spoilage circumstances when it is made into hay or silage, can convert to dicoumarol. Similar to the drug warfarin, dicoumarol is a powerful anti-coagulant and can prevent animals’ blood from clotting properly.
Cattle that consume sweet clover may have hematomas beneath the skin, hemorrhaging/internal bleeding, and respiratory problems. They also may experience nosebleeds, blood in milk or feces, and/or increased risk of bruising or bleeding during calving. This makes the forage especially dangerous for close-up dry cows.
Hairy vetch – Grazing hairy vetch can cause dermatitis, which is most likely to occur when seeds are consumed or when hairy vetch makes up the majority of a pasture mix. Affected animals also may show weight loss, intense itching, hair loss, diarrhea, swelling of the head and neck and/or difficulty breathing.
In some cases, animals can have a sudden, severe allergic reaction, even if they have consumed hairy vetch for several weeks. While impairments from hairy vetch are more likely to occur when it is fed as pasture versus hay or haylage, it is advisable to not feed it to dairy cattle at all.
The caution against feeding these forages applies to lactating, dry, and pre-lactating dairy animals.
And if you happen to be producing hay for horses, the “not safe” list is even longer. In addition to sweet clover and hairy vetch, the LaCrosse experts noted horses should not be fed milo/forage sorghum, sudangrass, or brassicas. You can access the full guide here.
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