The effects of the 3 main variants of alphaS1 casein fed three levels of crude protein on milk production and composition, and on metabolic responses after infusion of alanine were studied in early or mid lactation dairy goats. Milk production and composition were not affected by level of CP in diet. Milk yield and fat content were not affected by type of variant; CP content in milk was significantly higher in variant AA than in variant EE and FF. Increases in plasma glucose, non esterified fatty acids (NEFA), or insulin after infusion of alanine were not affected by the type of variant or CP content of the diet. The continuous increase in plasma urea after the beginning of infusion was higher for the low CP diet than for the other diets. The continuous decreases in plasma BHB was significantly higher in variant AA than in the other variant.