Question
I recently shipped several broodmares to the Midwest (Illinois, United States). Seven of the eight mares have begun chewing on the fence, usually preferring to chew wood than eat hay. They all eat the same diet: about 12 pounds of fortified grain a day and free-choice mixed-grass hay. My veterinarian suggested adding dicalcium phosphate to their rations. Could there be something missing from their diet? Should I give the mares access to cedar posts to chew on?
Answer
Without having a detailed description of the feed and hay the mares receive, it is impossible to determine if your mares are being properly nourished. If the mares are consuming a properly fortified feed for their stage of life and production and are being offered good-quality hay to maintain body condition, I would say nutrient inadequacy is likely not the issue. Therefore, adding dicalcium phosphate would not be advised.
Because your mares just traveled a long distance and are now in unfamiliar surroundings, stress might have played a part in the development of gastric ulcers. Some horses will begin engaging in vices such as wood chewing or cribbing when the stomach is irritated and painful. Limited access to forage will decrease saliva production and therefore reduce its buffering capacity in the stomach, possibly leading to ulcer formation.
Stress might also be the case if the mares were integrated into a well-established herd. Rearrangement of the social hierarchy might take some time, and certain mares might not handle this stress as well as others. Dominant mares may also be driving away more passive herdmates from forage sources. Observing the mares as they interact might go a long way in determining if there is a behavioral cause. Separation of certain mares may be necessary so that each mare consumes sufficient feed and hay to maintain body condition and mental well-being.
Wood chewing is quite possibly more related to the type of forage provided. Perhaps the mares are not receiving sufficient fiber or the right type of fiber.
Nothing should be done to encourage wood chewing, so avoid setting out cedar posts. Instead, providing an alfalfa-mix hay might encourage them to eat more forage (it is very tasty to most horses), and researchers believe that alfalfa hay has buffering properties that other forages do not provide, which will help with any gastric irritation that is present.
