Response of early weaned piglets to graded levels of dietary cobalamin

The water-soluble vitamin cobalamin plays a central role as a co-factor in key pathways of energy and protein metabolism. The dietary requirement of this vitamin for the young pig (5-10 kg) has been estimated at 17.5 (mu)g kg^-1 but it is derived from estimates made over 40 yr ago. In light of changes in swine production, including the selection for high lean potential genotypes and the move to earlier weaning times, a reassessment of the adequacy of current cobalamin estimates is warranted. To this end, two trials were conducted to test the following alternate hypothesis: The current National Research Council (NRC 1998) estimated cobalamin requirement for the 5- to 10-kg early-weaned piglet is inadequate to maintain optimal cobalamin status, as reflected by growth, feed conversion efficiency, plasma cobalamin and plasma homocysteine concentrations. In trial 1, 60 Cotswold pigs (17± 1 d, equal males and females) were randomly assigned to receive diets, formulated with ingredients essentially devoid of cobalamin, and containing either 0, 35, 70, 105, or 140 g crystalline cobalamin kg^-1 After 15 d, growth, feed intake and feed conversion efficiency were not significantly different (P > 0.05) between the dietary cobalamin levels. However, plasma cobalamin was significantly lower (49.9 vs 186.7, 168.0, 164.7, and 178.7 pg mL^-1; SEM 17.3; P < 0.05) and homocysteine was significantly higher (34.5 vs. 22.5, 26.0, 24.7, and 23.4 (mu)mol L^-1; SEM 2.9; P < 0.05) in piglets consuming diets containing 0 vs. 35, 70, 105 and 140 (mu)g crystalline cobalamin kg^-1, respectively. Trial 2 retained the same study design as trial I, but added dietary cobalamin concentrations were equivalent to 0, 10, 20, 30, and 40 g kg^-1. The observed pattern of responses in plasma cobalamin and homocysteine support a requirement of added cobalamin in excess of 30 (mu)g kg^-1 of diet. Taken together, the data support a requirement for the addition of 35 (mu)g crystalline cobalamin kg of a diet formulated with ingredients essentially devoid of natural cobalamin for the early-weaned piglet between 5 and 10 kg, a value that is double the current NRC requirement. In addition, the current study uses changes in the plasma concentration of the metabolite homocysteine as a novel approach for the estimation of the dietary requirement for cobalamin in animals.