I ran across an NDSU article that I am sharing here. Their contact for more information is at the bottom.
(I made a few highlights/suggestions.)
Plagiarized text below …
Cattle increase body temperature for the next 4-6 hours after feeding ... because of the digestion process.
Nitrate poisioning from balling up failed crops can be an issue. ACV has an enzyme, nitrate reductaze (the whole apple ACV from Idaho has MORE nitrate reductaze, because it is never pasteurized)) that can help if you find yourself with wheat, barley, oats, brassicas, millet, sorghum and sudan grass, corn, and either standing wheat or harvested for hay.
Heat stress this year has hampered photosynthesis which could cause nitrates to accumulate in these stressed plants.
Cloudy conditions, frost and hail can also cause this condition. If nitrogen fertilizer has been applied, the condition is magnified.
This nitrate converts to nitrite in the rumen which gets absorbed into the bloodstream and lessens the bloods ability to carry oxygen. This can cause ABORTIONS (I added the emphasis).
(A good thing to keep in mind when putting up hay), Nitrate levels are highest in the AM.
Cut hay when the sun shines in the afternoon. Cut higher to avoid the highest concentration of nitrate in the plant. Nitrate levels are highest in young plants..
ENERGY supplementation helps the rumen convert nitrate to protein. (Heavy apple juice at 6% alcohol is pure energy).
There is a Nitrate QuickTest to determine if it is present in a field you intend to graze or bale. If present, retest in a week or so to find a lower-nitrate time to harvest/graze.
Photosynthesis is requited to reduce nitrates in the plant. If cut for dry hay at the wrong time ... you are stuck with it. The ensiling fermentation process reduces the nitrate somewhat.
For more info, get the NDSU extension publication "Nitrate poisoning of livestock"
Can be found at ...
www.ag.ndsu.edu/publications/livestock/nitrate-poisioning-of-livestock