Yes you can feed ryegrass to horses and livestock....most meadow hay is made up largely of ryegrass and clover....
if you are really concerned and using large amounts of hay i woud as the person growing the hay to have it tested. They will need to test for Bacteria and seed gall nematodes you could also contact the ag dept and ask if there have been cases of ARGT in the area where they grow hay
Annual ryegrass toxicity [ARGT] is the poisoning of livestock by toxins contained in bacterially infected annual ryegrass. The toxins are produced by bacteria, which is carried into the ryegrass by a seed gall nematode.
the majority of infected seed heads show no visible signs
but some signs of infection include
* Moist yellow slime at seed-head emergence
* Dried slime is translucent, crystalline and a darker yellow
* Affected spikets often glued to stalk
* Some normal spikets can occur in affected heads
* Occassional head distortion
* Affected tillers sometimes stunted
Hope that some help
We grow our our meadow hay - mostly ryegrass and clover and have never had a problem