Some broodmares might struggle to conceive or maintain pregnancy due to age, disease, or infection; however, veterinarians can intervene to help improve their chances of becoming pregnant and delivering healthy foals. Ryan Ferris, DVM, MS, Dipl. ACT, of Summit Equine, in Newberg, Oregon, and Karen Von Dollen, DVM, MS, Dipl. ACT, of Equine Medical Services Inc., in Columbia, Missouri, answered common questions about treating problem broodmares during their presentation at the 2023 American Association of Equine Practitioners Convention, held Nov. 29-Dec. 3 in San Diego, California. They covered topics ranging from kerosene administration to using prednisolone to treat inflammation in broodmares. 

1. When do veterinarians recommend using kerosene for broodmares? 

Kerosene strips the endometrium (uterine lining) and serves as a chemical curettage, or removal of uterine tissue. It can be highly effective for previously barren mares. “I’ve never found anything to work as good as kerosene,” said Ferris. However, due to some potentially severe, yet rare, breeding-career-ending side effects and risks to the person administering it, Von Dollen suggests using it primarily for mares near the ends of their breeding careers. 

2. When in the mare’s cycle and how should veterinarians administer kerosene? 

Von Dollen suggested administering 200 ml of kerosene after Day 5 of ovulation. She uses plastic disposable tubing (because kerosene can melt the rubber on a syringe) and lets gravity do the work for her. Applying Vaseline to the mare’s hindquarters can prevent scalding if she gets splashed by the kerosene. Later in the day the mare receives a dose of dinoprostone (a naturally occurring prostaglandin E2 administered to dilate and clear the uterus). Then, the following day, her veterinarian performs a uterine lavage.  

Ferris said his approach is similar, noting he avoids performing this procedure during peak estrus because the cervix is “wide open,” and he doesn’t want the kerosene to leak out. He noted that veterinarians should always use clear K1 kerosene from the hardware store and should not use pink or blue kerosene. After Ferris administers kerosene the mare goes in a round pen afterward and gets lavaged the next day at a nonspecific time and for two or three days afterward. Von Dollen added that she cultures the lavage fluid to check for bacteria and treats accordingly. 

3. Should veterinarians breed mares on the same cycle as when the kerosene is used? 

“I personally would not choose to breed on the same cycle as the kerosene,” Von Dollen said. “I would give them at least a cycle in between and then plan to breed on the next cycle.” The lavage culture often shows pathogens, which is another reason to wait to breed treated mares, she added.  

For Ferris, it depends on the goals for that mare. “Usually the mares I’m doing it in, they have a long list of potential embryos they want recovered, and so they don’t want to wait.” 

4. What do veterinarians know about how kerosene affects future foals after mares are treated with it? 

Ferris said he hasn’t seen anything in the literature to indicate this. “I think it’s going to be a complicated question, just because of the fact that a lot of the mares are going to be older mares, which are already going to have a history of problems, and have a higher risk of complications,” he said. 

5. What do veterinarians think about mycotoxins, feeder hay (hay for feeder cattle), and embryonic loss? 

Mycotoxins (toxic metabolites produced by fungi) are not a top concern among practitioners, but the literature seems to be mixed, said Van Dollen. Ferris agreed with Von Dollen’s assessment and was also skeptical of the equine community’s capacity to investigate because, while there’s some evidence of mycotoxins in hay being a problem for cattle, horses are not bred on a large enough scale to observe any significant impact on pregnancy rates. 

6. Where does prednisolone fit in for early embryonic loss treatment plans? 

Prednisolone is a potent anti-inflammatory. In mares with inflammation, Von Dollen gives 200 mg of prednisolone daily beginning Day 5 post-ovulation and then tapers over three weeks starting at Day 30 or Day 60. Von Dollen and Ferris agreed it can be challenging to rule out infections in mares with bacterial endometriosis. Von Dollen said she has higher confidence a mare is not “dirty” after she infuses a mucolytic (a mucus-thinning agent) such as acetylcysteine, the mare has cultured clean afterward, has no visible signs of endometritis—inflammation of the uterine lining—on a scan, has normal edema patterns, and isn’t carrying excessive fluid. 

Take-Home Message 

Managing broodmares with fertility issues might require incorporating advanced veterinary techniques and the cautious use of treatments such as kerosene and prednisolone. However, under the right circumstances, they can potentially offer a lifeline for broodmares struggling with conception and maintaining pregnancy.