If you're wondering why your cattle appear sick, check your hay supply. Hay that has been stored with excessive moisture and heat can become moldy, less palatable and less nutritious than properly stored hay. As one study by South Dakota State University showed, the nutritional value of moldy hay was reduced by 25 to 30 percent.

Moldy hay also creates the potential for the ingestion of mycotoxins. Mycotoxin contamination is something that has largely been overlooked compared to other areas of potential feed-related mycotoxicoses. While not all moldy hay is toxic, the risk remains because the specific toxic compound in moldy hays has not been isolated. What's dangerous about mycotoxins is that ingestion at high levels can lead to liver damage.

If you think your cattle may have ingested mycotoxins and are suffering from liver problems, look for sunburn in light colored areas of the skin or where there is little hair, such as the muzzle, ears, teats and udder, since liver problems lead to light sensitivity.

You still can use moldy hay, as long as it is diluted with higher-quality hay and grain or a commercial supplement to compensate for the reduced nutritional value of moldy hay and the mycotoxicosis risk. Hay severely damaged by mold and heat should be diluted to no more than 30 percent of the ration. Less damaged hay should be diluted to 40 to 60 percent of the ration.