Response to dietary supplementation of choline depends on 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. 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% of the diet. Hongtrakul et al. (1997) have suggested that supplemental choline is not required in the diets of weanling pigs, since in their study growth performance was not affected by the addition of 150 g of choline per ton. Hongtrakul et al. (1977) emphasized that supplemental choline is still required for gestating and lactating sows.
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 a choline shortage. Methionine is not used for choline synthesis if there is an adequate level of dietary choline. In formulating typical swine 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 by Ruiz et al. (1983). Lovett et al. (1986) found that when inorganic sulfate (Na2SO4) plus methionine or Na2SO4 plus choline was added to weanling swine diets, daily gains and feed efficiency were increased. Sulfur is present in a number of body metabolites (i.e., mucopolysaccharides), and if it is not adequately supplied in the diet, sulfur amino acids are likely to be degraded. Data suggest that sulfate must be present for choline to spare a maximum amount of methionine (Miles et al., 1983). The practical implication is that sulfate and choline must 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.
Most choline supplementation studies emphasize production benefits of providing the vitamin to young animals. However, research and observations with adult swine demonstrate improved litter size at weaning and indicate that supplementation may keep sows in the producing herd longer (Cunha, 1977). The exact level of choline needed for sow diets is unknown. Until more research data are available, Cunha (1972) suggested use of the following levels when spraddled hindlegs are likely to occur: (1) during the first part of gestation, 3,000 mg per sow daily and (2) for the last month of gestation, 4,200 to 4,500 mg daily.
Choline chloride is stable in multivitamin premixes but may decrease the stability of 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 containing choline should be kept closed when not in use.
