Betaine has three chemically reactive methyl groups attached to the nitrogen atom of the glycine molecule. Therefore, it can be used as a methyl group donor partially to replace methionine in poultry and pig diets. Recent work also suggests that betaine has an energy sparing role by reducing maintenance requirement of the pig (Schrama and Gerrits, 2000). Betaine has improved performance and carcass leanness in some studies but the results are variable and seem to depend on age and sex of the animal, feeding level and diet composition.
Choline can also be used as methyl donor in animal feeds. In poultry, methyl groups are available after the conversion to betaine in the liver. However, dietary betaine is twice as efficient as the equi-molar dietary choline for increasing liver betaine levels in broiler chick (Saarinen et al., 2000). The aim of this study was to compare the response of pigs fed equi-molar betaine and choline in terms of pig performance and carcass characteristics.