If the grass was lush and green, your cattle probably died from fog fever. Fog fever can occur on any vegetation that is green and lush due to overeating by the animals and a buildup of the amino acid tryptophan in the rumen. This then causes edema in the lungs of the animal and causes them to suffocate. You do not want to stress or overexcite the animals if you see them with their necks stuck straight out, labored breathing, tongue sticking out, etc. These are classic signs of suffocation. Move the animals slowly out of the area where the grass is and keep them off it for two to three days. Then gradually allow them to graze the field, only letting them in for two to three hours at a time each day, and taking them off. After two to three weeks of doing this, you can just turn them in and not worry, because their rumen has adjusted to the change in diet. Animals that are exhibiting problems breathing can recover using this method.

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