Q.When is it too hot for my horse to wear a fly sheet? My friend and I both use fly sheets on our horses, but she leaves hers off if the weather gets really hot and humid. Should I do the same? I don’t want to hurt my horse.

—Christine, Tampa, Florida

A.This is a multi-factor question which you must take into account the fly sheet, the breed and color of horse you have, whether there is shade available, your horse’s body condition score (BCS), the air temperature, and the humidity. So let’s break this down.

Fly sheets are made of different material and weight. Those with larger mesh and loose straps will breathe much better compared to those that fit closer to the hair coat and are a finer mesh.

The breed of horse and the body condition should always be taken into consideration when it comes to “overheating” a horse. For example, a draft horse with a BCS of 8 will have more difficulty in an environment with a heat index of 90 degrees or more compared to a light horse with a BCS of a 5, with or without a fly sheet.

Owners should take in consideration the amount of shade they have for their equine companions, whether they are located in an area that has a natural breeze or not, or if they will be stalled with fans on them.

Finally, you can check the heat index outside by going to your preferred weather website or app and looking over the chart of temperature and humidity because the humidity can make the heat index increase significantly.

I would recommend anything under 90 degrees heat index would be tolerated in a normal weight, sweating horse in the shade with a breeze or fan on them. Over 90 degrees I would recommend providing a cool environment in order for them to tolerate the blanket and heat well.