Hill's Pet Nutrition recalled eight more varieties of canned dog food today due to vitamin D concerns, bringing to 33 the total number of varieties pulled from the market since late January.

The company announced the widened recall this morning in a letter to veterinarians after making a "detailed review" of its canned dog foods. The internal tests were spurred by findings that 25 varieties of Hill's Prescription Diet and Hill's Science Diet canned dog foods contained excessive levels of vitamin D, prompting a recall on Jan. 31. In February, Hill's withdrew more products that failed to meet its formula specifications. Those products had not yet been distributed for sale.

Hill's has not said how much vitamin D the recalled diets contained, nor whether all contained excessive amounts of it. Company officials blame the irregularities on a vitamin premix obtained from a supplier and used in specific lots of canned dog foods. They have not publicly identified the supplier.

Hill's posted a public announcement on its website late today about the recall expansion.

In the letter to veterinarians, Hill's Vice President and General Manager Jesper Nordengaard explained: "[O]ur review did determine that there were additional products affected by that vitamin premix, and it is for that reason that we are expanding the recall."

He underscored that dry foods, cat foods and treats are not affected.

Hill's alerted veterinarians ahead of consumers in response to criticism that it was slow to communicate with practitioners about the initial recall in January. Unlike most other pet foods, Hill's diets are recommended by veterinarians to treat medical conditions and often sold through their practices.

Hill's is "working to make this right," Nordengaard said in the letter.

"We understand that this recall has caused pet parents considerable anxiety and that the well-being of their pets may have been affected," he wrote. "We are also aware of the disruption and difficulty that this has caused you and your staff. ... We're informing you ahead of the public announcement so that you can respond effectively to consumers."

Nordengaard said Hill's will pay to screen affected pets for hypervitaminosis D, a rare, potentially deadly condition in which the body stores too much vitamin D. For pets with elevated vitamin D levels, Hill's promised to pay for continued tests until they return to normal. "We will reimburse pet parents for medical treatment for an affected pet eating impacted food," Nordengaard promised.

Vitamin D overdoses can lead to a range of signs in dogs, from drooling, constipation and/or vomiting, to seizing. Increased urination and thirst also are commonly reported. Vitamin D poisoning can raise levels of calcium in the blood, a condition known as hypercalcemia. Left untreated, too much calcium in the blood can induce bone loss and may result in kidney stones and calcification of organs including the heart and kidneys.

Veterinarians have reported suspected adverse reactions in dogs that ate affected Hill's diets. Thousands of pet owners have posted on social media platforms and other online forums about illnesses and deaths they believe were caused by Hill's diets. A dozen class action lawsuits against Hill's are pending related to the vitamin D problem.

To handle questions about the recall, Nordengaard said, Hill's is operating its Veterinary Consultation Service and consumer call center seven days a week.

The contact information for consumers is: 800-445-5777 and contactus@hillspet.com. 

Editor's note: This story has been changed from the original to remove Hill's contact information for veterinarians from the public domain. The information also has been blurred in the letter from Hill's, linked in the article. The changes were made per the company's request.