If your hay is wet, it is best not to tarp it tightly because it can sometimes spontaneously combust.
When you store your alfalfa hay, it is best to avoid getting it wet in the first place, you can stick tarps up against the hay to provide a barrier against the rain coming into your storage area. Wet hay is often more combustible than dry hay simply because of the science behind it. Storage, plus wet hay, plus tarps = moisture. Simply put, moisture causes gasses to be released, which are combustible.
Often times people have tried weird things like putting salt on hay or dry ice, but that won't prevent the combustion from occurring. You can put it out to dry, but chances are it might mold anyway so it is best to separate it and air it out if you can and monitor it before you try to feed it to any animal. The best way to handle it is to spread it out and lay it out so that air can get to both sides of the hay.
I heard of a person recently who had hay stored in their horse trailer and it rained and the wind blew the rain inside the trailer causing a lot of rain to fall on they hay. They were able to manage to move the hay out of the trailer, spread it out in the barn and separate it out in various places to air dry. In this case, the person opened the bales and put some flakes turned on their side and then rotated them so that they would dry on both sides and minimal damage was done. They also fed the wettest bales first right away to the horses, a little water on your hay shortly after it rains won't hurt, many people wet down their hay before feeding to reduce dust and this is similar to that. However, hay sitting around wet for long periods of time will mold and moldy hay is not something you want to feed to your beloved horse. So you need to be really careful!
In addition to the mold problem, rain can damage the hay by leaching out the nutrients in the hay. Tests can be run on your hay to determine if is a total loss or not. Bottom line is you should try to prevent your hay from getting wet in the first place by following proper hay storage practices. If you know your hay has been exposed to the rain, you should really check it out and make sure the hay is not starting to mold, if it is, you need to check it all and decide if it is something you can feed or not.
When you store your alfalfa hay, it is best to avoid getting it wet in the first place, you can stick tarps up against the hay to provide a barrier against the rain coming into your storage area. Wet hay is often more combustible than dry hay simply because of the science behind it. Storage, plus wet hay, plus tarps = moisture. Simply put, moisture causes gasses to be released, which are combustible.
Often times people have tried weird things like putting salt on hay or dry ice, but that won't prevent the combustion from occurring. You can put it out to dry, but chances are it might mold anyway so it is best to separate it and air it out if you can and monitor it before you try to feed it to any animal. The best way to handle it is to spread it out and lay it out so that air can get to both sides of the hay.
I heard of a person recently who had hay stored in their horse trailer and it rained and the wind blew the rain inside the trailer causing a lot of rain to fall on they hay. They were able to manage to move the hay out of the trailer, spread it out in the barn and separate it out in various places to air dry. In this case, the person opened the bales and put some flakes turned on their side and then rotated them so that they would dry on both sides and minimal damage was done. They also fed the wettest bales first right away to the horses, a little water on your hay shortly after it rains won't hurt, many people wet down their hay before feeding to reduce dust and this is similar to that. However, hay sitting around wet for long periods of time will mold and moldy hay is not something you want to feed to your beloved horse. So you need to be really careful!
In addition to the mold problem, rain can damage the hay by leaching out the nutrients in the hay. Tests can be run on your hay to determine if is a total loss or not. Bottom line is you should try to prevent your hay from getting wet in the first place by following proper hay storage practices. If you know your hay has been exposed to the rain, you should really check it out and make sure the hay is not starting to mold, if it is, you need to check it all and decide if it is something you can feed or not.