Dealing with choline chloride
It's an "Intel inside" type of molecule -- but also a problem child
Dogs and cats, like many other species, require choline. It's the "Intel inside" kind of molecule that allows others to function to their full potential. Almost all commercial petfoods contain supplemental choline, predominantly from choline chloride. However, putting choline chloride into the formula can have profound effects on the way the ingredients are combined and processed during production due to the molecule's hygroscopic (water-loving) nature.
Studies with dogs in the 1930s first led researchers to identify choline as a necessary nutrient. Since that time it has been recognized as a:
Key component of cell membrane phospholipids;
Vital part of the neurotransmitter molecule acetylcholine;
Lipotropic agent in fat utilization and lipid signaling; and
Methyl group donor in reactions involving methionine, folic acid, vitamin B12, glycine and serine.
The choline oxidation product betaine also acts as an osmolyte in the kidney. In its absence, choline deficiency can result and cause weight loss, vomiting, fatty liver and even death in dogs and cats.
While often grouped with theB-vitamins, choline is actually a closer fit, structurally and functionally, with the amino acids and fatty acids. Its similarity to B-vitamins is associated with the way it moves through the body. Specifically, choline is soluble in polar solvents like water and alcohol, has no bodily storage depots and is metabolized and excreted in proportion to the amount consumed. Thus, it must be replenished daily. Because of this constant efflux and the fact that dogs and cats are unable to produce adequate quantities themselves, dietary sources are required.
Meeting the needs naturally
Much of the required choline can be found in common petfood ingredients. Choline occurs naturally in plant and animal tissues. In ingredients, free choline is found only in small amounts with the greatest proportions appearing as the phospholipids phosphatidylcholine (lecithin), phosphatidylethanolamine and sphingomyelin.
The richest natural source of choline in the ingredient market is the emulsifier lecithin, which contains approximately 2 to 3.5% choline; most is derived from soybeans. Eggs (especially the yolk), liver, fish, meats, rendered protein meals, soybeans, soybean meal, peas and wheat germ are rich sources with levels ranging from 1,500 to as high as 3,000 mg/kg. Grains, fruits, vegetables, fats and oils contain only marginal levels of choline with concentrations of 500 to 1,000 mg/kg.
Considering that the requirements for dogs and cats on a bioavailability adjusted, 4,000-kcal diet basis are 1,700 and 2,550 mg/kg, respectively, there can be a gap in the amount provided by the diet and that needed by the animal. There are provisions for methionine as a methyl group substitute for choline in feline diets (3.75 parts methionine for one choline when methionine exceeds 0.62%). Betaine (hydrochloride or anhydrous) can also be used to replace supplemental choline.
However, the more common approach for petfood manufacturers is to make up the shortfall and provide some insurance to cover the variability of the base diet ingredients by supplementing with synthetic choline sources. Several choices are allowed in feed and petfood, such as choline chloride, choline bitartrate, choline pantothenate and choline xanthate. The most common in petfood is choline chloride; it's found in almost every petfood product labeled as complete and balanced. Its popularity is due to a combination of cost, choline content and availability.
The problem child
The pencil and paper exercise of putting choline chloride in a petfood formula is pretty straightforward, but using it in production can be a real headache. Choline is chemically synthesized from trimethylamine and ethylene chlorohydrin or ethylene oxide. In free form, 2-hydroxy-N,N,N-trimethylethanaminium (also known as 2-hydroxyethyl trimethylammonium) is a very hygroscopic organic base (alkaline). The chloride salt popular in the livestock and petfood market is more hygroscopic than the bitartrate salt used more commonly in the human foods and supplements market.
Because of its hygroscopic nature and solubility in water, an aqueous solution (approximately 75% choline) causes the least number of plant sanitation issues. However, it requires capital investment in liquid holding tanks and plumbing. Further, because the application rate is relatively small, with supplemental levels at 0.05 to 0.25% of the diet, sophisticated systems are required for uniform dispersion and mixing. Not every petfood company is willing or able to take such measures.
An alternative is choline chloride enrobed onto a dry carriermost commonly ground corn cobs. The resulting powder can be handled in bulk or in bags and is more consistent in form and handling to other dry ingredients. However, using corn cobs as a carrier dilutes the amount of choline delivered per pound to levels of 50% and 60%.
The cost-benefit to the liquid form is often enough to justify the capital improvement, with a payback in one to three years, especially when the cost of plant cleanup is taken into account. The choline powder is very hygroscopic. It pulls moisture from the surrounding air and quickly becomes a sticky mess that clings to equipment and personnel and creates zones of cross-contamination. Its challenge is compounded in facilities lacking humidity controls.
A logical approach is to use the vitamin premix to carry choline into the formula. However, because of its affinity for moisture, choline chloride is also the culprit in vitamin losses in premixes. As it draws water into a vitamin premix, the increase in water activity creates an environment more conducive to oxidation.
For this reason, vitamin suppliers vehemently discourage customers from including choline chloride as part of their premix because of the reduced vitamin retention during storage. Most affected are vitamins A, K3 (menadione sodium bisulfite complex), thiamine mononitrate and niacinamide. Inclusion can result in spotting and discoloration in the premix. This can extend into product appearance, especially for wet foods. However, once in the product, choline chloride itself is very stable through extrusion, drying and enrobing.
Addressing the issue
There are options for meeting the choline needs in dog and cat formulas but no quick and inexpensive ways around the use of choline chloride. Regardless of form used, there will be complications and cost due to its hygroscopic nature. The most prudent management approach is to fortify to meet choline needs with the route that causes the least pain and overall cost.