Response to dietary supplementation of choline will be most dependent on species, age of animals, protein and sulfur amino acid intake, dietary choline and other choline sparing nutrients. Unlike most vitamins, choline can be synthesized by various animals, although often in insufficient amounts. It appears that choline deficiency in the young of some species (e.g., chicks) is perhaps not due to lack of ability to synthesize choline but more likely to lack of ability to synthesize it at a rate sufficient for the animal’s needs. Age is an important consideration as, for example, it is difficult to produce a choline deficiency in growing chicks over eight weeks of age.
The young of many species (e.g., pig and rat) do not require supplementary choline if dietary methionine level is sufficiently high. On a synthetic milk diet containing 1.6% methionine, young pigs were found not to require supplemental choline (Firth et al., 1953). Neumann et al. (1949) reported that the young pig requires 0.1% dietary choline when methionine is present at 0.8% to 1.0% of the diet.
Methionine can furnish methyl groups for choline synthesis for most species. Choline, however, is effective only in sparing methionine which otherwise would be used to make up for the choline shortage. Methionine is not used up for choline synthesis if there is an adequate level of dietary choline. In formulating typical poultry diets, 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. In providing supplements of methionine and (or) choline, a third nutrient, sulfur, must be considered. Significance of a three-way interrelationship among methionine, choline and sulfate has been reviewed (Ruiz et al., 1983; Miles et al., 1986; Miles and Butcher, 1997).
Sulfur is present in a number of body metabolites (e.g., mucopolysaccharides) and if not adequately supplied in the diet, sulfur amino acids would likely be degraded. In feeding broilers, supplemental sulfate accompanied by choline or methionine achieved a greater growth response than when either was fed alone (Miles et al., 1983). Data suggest that sulfate must be present for choline to spare a maximum amount of methionine. The practical implication is that sulfate and choline need to be adequately provided in diets so that the more expensive and often marginally deficient nutrient methionine is not used to provide either of these nutrients.
Schutte et al. (1997) reported an experiment investigating the interrelationship of betaine and methionine for broiler chicks. The addition of methionine significantly increased body weight; the addition of betaine resulted in only a small numerical response when compared with the appropriate level of methionine. It is concluded that in diets deficient in choline, betaine may spare methionine from methyl donor functions and result in an improvement in growth rate. While betaine is an efficient methyl donor, choline is significantly cheaper and would be the methyl donor of choice for use in practical broiler feeds. Neither betaine nor choline can produce a significant net increase in available methionine for use in protein synthesis or other metabolic activities, unless quantities of homocystine are present, which is not usually the case.
Betaine may have beneficial effects in alleviating coccidiosis infections in chicks (Augustine et al., 1997; Matthews et al., 1997). Coccidiosis is associated with osmotic and ionic disorders, which are probably caused by dehydration and diarrhea that are characteristic of coccidial infection. Remus and Virtanen (1996) reported that betaine and methionine were equally efficacious in diets for coccidiosis-infected chicks. Zimmerman et al. (1996) reported similar results for chicks fed 0.05 mg per kg (0.023 mg per lb) of betaine, but not in chicks fed 0.1 mg per kg (0.045 mg per lb) of betaine. In both of these studies, all chicks were infected with coccidiosis, and in the report by Zimmerman et al. (1996), all chicks received an anticoccidial medication. Virtanen et al. (1996) reported that betaine in combination with salinomycin was more effective in preventing the signs of coccidiosis (lesion scores and decreased feed efficiency) than salinomycin alone. As in the aforementioned research, all chicks were infected with coccidiosis.
The most widely used supplemental form of choline is choline chloride. Choline is available for feed use as the 70% or 75% liquid or 25% to 60% dry powder. Choline chloride can be available on a cereal carrier; the product is obtained by spraying and thoroughly mixing aqueous choline chloride on a suitable cereal carrier and then drying to a low moisture content. The 70% to 75% liquid is very corrosive and requires special storage and handling equipment. It also is not suitable for inclusion in concentrated vitamin premixes, but rather is most generally added singly to concentrate mixtures.
Currently, a variety of lecithin products that are derived from soybeans are available for use in feeds. The products range from crude fluid lecithin to 50% lecithin co-dried with corn syrup solids to a newly developed dry de-oiled soy lecithin (Meyers, 1990). A number of studies suggest that choline from soybean meal is close to 100% available (Menten et al., 1997). The advantage of a de-oiled soybean lecithin is that it can be handled as a dry feed ingredient. The dry de-oiled lecithin product also possesses those advantageous properties of soybean lecithin in general that impart important dietary formulation features, including vitamin stabilization (thus protecting vitamins from oxidation); improvement of fat and vitamin utilization; and providing a source of choline, inositol, and growth-stimulating compounds.
Choline chloride is stable in multivitamin premixes but is highly destructive to various other vitamins in the premix (Frye, 1978). Choline is stable during processing and storage in pressure-pelleted and extruded feeds. Since the material is hygroscopic, containers of choline should be kept closed when not in use. Some research has shown that supplemental betaine, a product of choline oxidation, is beneficial to swine and poultry production (Lowry et al., 1987; Odle, 1996). Supplemental betaine is available as betaine hydrochloride (98.0% betaine on an anhydrous basis).
