Response to dietary supplementation of choline is dependent on age of animals, protein and sulfur amino acid intake, and levels of dietary choline and other choline-sparing nutrients. Unlike most vitamins, choline can be synthesized by dogs and cats when labile methyl compounds such as betaine and methionine are present in adequate amounts in the diet. Thus, protein-rich diets can actually reduce choline requirements. Generous use of animal by-products rich in methionine and choline for pet foods should preclude a choline deficiency. In view of the sparing effect of methionine and the widespread distribution of choline in plant and animal materials, it is most unlikely that a dog or cat will become choline deficient under normal circumstances.
Methionine furnishes methyl groups for choline synthesis for most species, including dogs and cats. Choline, however, is effective only in sparing methionine, which otherwise would be used to make up for a choline shortage. Methionine is not used up for choline synthesis if there is an adequate level of dietary choline. In formulating pet diets that are high in grains and low in animal products, methionine is frequently one of the most limiting amino acids. Therefore, it would be impractical for marginal quantities of methionine to be wasted for synthesis of the vitamin when supplemental choline can be provided more economically.
Choline chloride is stable in multivitamin premixes but is highly destructive of various other vitamins in the premix (Frye, 1978; Gadient, 1986). Choline is stable during processing and storage in pressure-pelleted and extruded feeds. Since the material is hygroscopic, containers supplying choline should be kept closed when not in use.