Overview

As veterinary professionals continue to navigate an evolving landscape of pet nutrition and ingredient science, new studies are bringing attention to the role of specific nutrients in companion animal health. This article reviews recent findings related to choline bitartrate and the identification of calcium tartrate tetrahydrate (CTT) uroliths in dogs. It examines the biological role of choline, differences between supplemental forms, and what this emerging information means for veterinary nutrition recommendations and formulation decisions.

Choline is an essential nutrient for dogs and cats that, until recently, had received relatively limited attention in veterinary nutrition. That changed in April 2025, when Dr. Jodi Lulich and colleagues at the Minnesota Urolith Center published a case series identifying a new calcium-based urinary stone type in dogs: calcium tartrate tetrahydrate (CTT).

The study found that affected dogs were consuming diets or supplements containing choline bitartrate, a common form of choline used in both human and pet nutrition. This discovery has prompted new discussions around the ingredient’s role in urinary stone formation and how different forms of choline supplementation may influence canine health.

What is the role of choline, and why is it important?

Choline is neither a true vitamin nor a mineral, but it is water-soluble and often grouped with the B vitamin complex. It plays multiple essential roles in the body:

Metabolic function: Serves as a methyl group donor, necessary for the synthesis of S-adenosylmethionine, which supports antioxidant production (e.g., glutathione) and DNA synthesis.

Cell structure: Forms the backbone of phosphatidylcholine, the most abundant phospholipid in cell membranes.

Neurotransmission: Serves as a precursor for acetylcholine, critical for muscle function and neurological signaling.

While dogs and cats can synthesize small amounts of choline in the liver, endogenous production is insufficient to meet total body needs, making choline an essential dietary nutrient.

Clinical signs of deficiency are nonspecific and may include weight loss, vomiting, and hepatic fat accumulation (Best and Huntsman, 1935).

According to the AAFCO 2025 Official Publication, commercial dog foods must contain ≥340 mg choline per 1,000 kcal (or 1,360 mg/kg on a dry matter basis).

Natural food sources such as eggs and salmon contribute dietary choline, but concentrations vary widely and supplementation with either choline chloride or choline bitartrate is standard in most commercial and home-prepared diets.

Why use one form of choline supplement over another?

Freshpet uses choline chloride instead of choline bitartrate because it is the more established, well-studied, and biologically reliable form of this essential nutrient.

Choline Chloride

Choline chloride is the supplemental form included in all Freshpet diets. It is hygroscopic, meaning it readily absorbs moisture from the air, which can create manufacturing challenges. However, this characteristic does not affect the nutrient’s stability or bioavailability. Freshpet’s production processes are designed to manage this ingredient effectively while maintaining nutrient integrity.

Choline Bitartrate

Choline bitartrate does not absorb moisture, making it easier and less costly to use during pet food or supplement production. For this reason, it is more commonly found in both human dietary supplements and some pet foods. Recent findings have identified an association between consumption of diets containing choline bitartrate and an emerging pattern of calcium tartrate tetrahydrate (CTT) urinary stones in dogs, which has led to increased scientific scrutiny of this ingredient.

What are calcium tartrate tetrahydrate uroliths?

The first calcium tartrate tetrahydrate (CTT) stones analyzed by the Minnesota Urolith Center were not from dogs but from rodents in a research colony at Kansas State University in 2000. Between 2001 and 2015, the Center identified only two canine cases of CTT among tens of thousands of submissions each year.

After 2015, an increase in detections prompted Dr. Jodi Lulich and colleagues to conduct a retrospective review to better understand potential risk factors and any association with diet or supplementation.

Study Findings (2020–2024)

• Total cases: 63 dogs out of 318,147 total stone submissions, representing 0.02% of all stones analyzed.
• Demographics: 53 of 63 were male dogs, consistent with anatomical predisposition to urinary obstruction with all urolith types.
• Breeds: While 15 of the 63 were mixed breeds, the remaining dogs were comprised of 15 small breeds also predisposed to calcium oxalate urolithiasis, including Shih Tzus, Bichon Frises, Yorkshire Terriers, and Miniature Schnauzers.
• Dietary data: Survey responses were obtained from 33 caregivers. Of those, 29 provided detailed medical and dietary histories. Among these, 25 dogs were eating diets that contained choline bitartrate, including 20 commercial diets and 6 home-prepared diets formulated by Board-Certified Veterinary Nutritionists.
• Management outcomes: In most cases, changing the diet prevented recurrence. However, three dogs experienced recurrent CTT stones when they continued eating the same diet associated with their initial episode.

Interpretation and Clinical Implications

Despite the observed correlation between choline bitartrate supplementation and CTT stone formation, it is critical to interpret these findings within their context.

This was a descriptive case series, not a controlled interventional study. The low incidence rate (0.02%) among all submissions highlights that while a relationship may exist, it does not establish causation.

Further research is warranted to elucidate the biochemical mechanisms that may link choline bitartrate metabolism with tartrate stone formation and to assess any breed-specific metabolic predispositions.

Freshpet Takeaways:

1. Choline is an essential but under-studied nutrient in companion animal health that supports hepatic, neurological, and cellular function.
2. Patient factors such as sex and breed may influence the risk for calcium tartrate tetrahydrate urolith formation.
3. Correlation does not imply causation. Additional controlled research is needed to clarify the role of choline bitartrate in urolithiasis.
4. Freshpet exclusively uses choline chloride to ensure alignment with established nutritional science and to help safeguard pet health.