No. Cattle are much more susceptible to nitrate problems than horses. This is due to the fact that nitrates which are broken down by bacteria are found at the upper end of the digestive tract (the rumen) in cattle and at the lower end (cecum and colon) in the horse. Nitrates cause the conversion of hemoglobin into methemoglobin, which is incapable of carrying oxygen. The toxic level of nitrates for horses has not been determined. If you have hay analyzing between 6,000 ppm and less than 10,000 ppm, you should be cautious when feeding it to horses. Any hay or feed analyzing more than 10,000 ppm nitrates probably should not be fed to horses unless you are supplementing the hay so that the total feed eaten has a concentration of less than 10,000 ppm.