Question

I have a nine-year-old pregnant mare. Last year she had her first foal, and he is a great-looking, healthy colt. About the the third week of March last year, she got a dry cough and started breathing heavily, and it got worse until she had lost a ton of weight. It took her about three months to rebound and gain the weight back. She has just started the same cough and is showing the same breathing signs again. My vet cannot come up with a possible cause for the cough. She is in a drylot during the day and stabled at night. She doesn’t eat grass, only high-quality hay, a fortified textured feed, and a vitamin/mineral supplement.

Answer

The description of the problem fits well with heaves, especially if the improvement coincided with her being turned out full time in the spring. Horses with heaves often work so hard to breathe that they do not want to eat, as they cannot do both at the same time.

It is possible too that the growing fetus puts more pressure on her diaphragm, and if she is mildly affected with heaves already, the increased work to breathe with the larger fetus compounds the problem. No owner wants to hear it, but even good-quality hay is loaded with mold spores and dust.  Other barn-related situations that incite heaves include bedding on straw and storing straw or hay in a loft.

In an ideal world, this mare would live outside at all times. If that won’t work, there are some management tips that will help her:  (1) clean and bed her stall only when she is outside; (2) bed on shavings; (3) try hay cubes or pellets to reduce hay exposure; (4) feed hay on the ground; and (5) remove straw and hay from the loft.

It is not unusual for heaves to be seasonal, and she could be treated with steroids to get her over the hump. Some owners worry that administration of steroids will trigger premature foaling, but this is only true for ruminants, not horses.

Cold weather could figure into the cough, but it should not be causing enough respiratory problems for weight loss.

It is important to note that I’m basing my opinion only on how you’ve described the mare’s symptoms. Without seeing her in the flesh, I can’t truly diagnose the problem.  You’ll need to work with your local vet, who can physically examine the mare and observe her symptoms, before a final diagnosis can be made.  With that caveat, your vet might consider a steroid such as dexamethasone or prednisolone to speed your mare’s recovery.  Either can be given by mouth, but a vet will have to prescribe any medication (and perhaps administer the first dose). Finally, steroids alone will not make the mare better without environmental changes.