A mouse only consumes a very small amount of BlueMax Mini Blocks Rodenticide or other baits at a time and passes it very quickly, only keeping a smaller amount in their liver until they succumb to the effects of the bait. A cat would have to actually eat 20-30 mice that have consumed the bait for it to have any effect. In most cases, well fed, domesticated animals will not actually eat a mouse or a rat that they come across. Instead, they will play with it, chew it and then leave it behind.
Each is BlueMax Mini Block is about .71 ounces. There are 363 blocks per 16 pound pail.
The BlueMax Mini Blocks and any rodenticide you use would need to be placed in bait stations and should not be used loose in the feed. You would not want the bait to be available to the horses at all as it would be toxic. Protecta Sidekick Bait Stations would be ideal for rats and mice to feed within and securely store the bait so that only the rodents can access it, and its protected from the elements.