Choline contributes to vital biological functions of body, as for example for the synthesis of the phospholipids, which are structural cell components, as precursors for the intracellular messenger molecules, and for acetylcholine. Choline is the major source of methyl groups.
The molecular formula of choline chloride is C5H14NO.Cl and its molecular weight is 139.63. It has a melting point of 247 °C, shows a bulk density of 1.1 g/cm3 and is soluble in water (800 g/L at 25 °C) and ethanol, insoluble in ether and benzene. Choline chloride is the active substance under application and is a white crystalline powder. Specifications set by producers allow a minimum of 99 % purity (anhydrous basis).
Requirements for choline (NRC, see McDowell, 2000) are in the range of 300–2000 mg/kg feed for pigs and poultry, 400–1500 mg/kg feed for fish and 1250–2400 mg/kg feed for pets.
The requirement for adult ruminants is not known. Typical poultry diets provide already 70–80 % of the requirements for choline from feed materials. Different factors make it difficult to characterise the requirements for supplemental choline in farm animals: (i) the range of choline content in plant feed materials (e.g., maize ~ 500 mg/kg, rapeseed ~ 6800 mg/kg), (ii) the differences in bioavailability of choline from feed materials (25–70 %), (iii) the dietary supply with other substances involved in transmethylation reactions (methionine, betaine, homocysteine, cobalamine and folic acid), (iv) the absence of data on the amount of endogenously synthesised choline and of the supply with other transmethylating substances, and (v) the remarkable increase in performance of poultry and pigs and nutritional quality of complete feed in the period from the time when the studies cited were conducted and today.
Vitamin supplementation of commercial compound feed is mostly oriented towards recommendations for supplemental choline, which are in the range of 200–800 mg/kg feed for pigs and poultry (1200 mg/kg for turkeys), 600–1000 mg/kg feed for fish and 1200–1400 mg/kg feed for pets (AWT, 2001).