The Marin Humane Society is monitoring the health of several horses whisked away from a Chileno Valley ranch in the last two weeks as it continues to investigate whether to file charges of animal abuse against the breeder.

Four horses, which were removed from a pasture on Chileno Valley Road run by Petaluma-based Gray Fox Farm, are receiving treatment for injuries and malnourishment. They include an injured stallion and three mares, at least one of which appeared “very thin,” shelter spokeswoman Carrie Harrington said, adding that the conditions of the horses were “enough to warrant 24-hour veterinary observation.”

Breeder Jill Burnell has denied allegations of neglect and abuse and has hired an attorney to petition the Marin Superior Court to allow her to recover her horses, Ms. Harrington said. Attorney Maggie Weems, whose office is in Fairfax, did not return calls for comment.

Ms. Weems told reporters that the stallion sustained injuries from a fight with another stallion on December 26. That was one day before shelter officials, responding to complaints of mistreatment, were led to the ranch, from which they seized two horses.

Officials removed two more mares on January 4 after uncovering more signs of “serious neglect, injuries, unsafe and inhumane living conditions,” according to the humane society’s website.

In an anonymous posting in the late summer on an equestrian website, the Chronicle of the Horse, Ms. Burnell was criticized for leaving her horses to “stand in the rain and frost and heavy winds with no protection whatsoever.”

The shelter receives “hundreds” of complaints each year about animal abuse, Ms. Harrington said, typically involving domestic animals. But, she added “we have not seen something of this nature in quite some time.”

Officers with the humane society, which is seeking donations to cover treatment costs, are monitoring the welfare of more than three dozen horses, including varying ages of Hanoverians and thoroughbreds, remaining on the ranch. “We anticipate that his is going to be ongoing for a while,” Ms. Harrington said.