The aggressive behavior of horses with rabies is quite remarkable and dangerous. It appears as an "intentional" rather than accidental form of aggression, that latter which can be seen in any horse in distress or severe pain as in colic. Horses attack mangers, buckets, and bars on the stall, and will certainly bite you! Later, there can be further paralysis of any area of the body, severe depression, a "flat out unresponsive" appearance, or seizures, coma, and sudden death. Presumably, the horse is scared and stressed, and this explains the high heart rate and respiratory rate seen. In other cases, when the horse is flat out, the heart and respiratory rate can be oddly slow and even.
It is essential that the diagnosis is confirmed, but this can only be done at autopsy. Your veterinarian is skilled at removing the brain carefully, for proper submission to the state public health laboratory. All tissues are considered a human health hazard, so stay away.