Energy metabolism of immunized weanling piglets is not affected by dietaryyeast

Additional dietary nucleotides may benefit the energy metabolism of weanlin g piglets by saving the costs of de novo biosynthesis of nucleotides. This hypothesis was examined in early weaned barrows in which the nucleotides de mand was enhanced by an antigenic challenge. Thirty-two, 4-week-old crossbr ed barrows were allocated into groups of four, and assigned to a 2 x 2 fact orial arrangement of treatments. The factors included: (1) basal feed versu s basal feed supplemented with 0.04% of nucleotides,(2) immunization status (T-cell-dependent antigen versus nonimmunization). Energy metabolism was m easured using two weekly total energy and nitrogen balance collections. Sup plementing the diet with nucleotides did not affect the energy intake, heat production, and energy retention of the barrows. Furthermore, no interacti on was found between dietary treatment and immunization status. Immunizatio n of the barrows was associated with increased gross energy intake (p < 0.0 5), metabolizable energy intake (p < 0.10), nonactivity related heat produc tion (p < 0.10), total energy retention (p < 0.10), and energy retention fo r fat (p < 0.05). Conversely, the energy required for maintenance was decre ased in the immunized group (p < 0.10). In conclusion, supplemented dietary nucleotides did not benefit energy metabolism, in both immunized and nonim munized barrows. A humoral immune response towards T-cell-dependent antigen s induced an increased energy retention, resulting from both an increased f eed intake, and a reduced maintenance requirement. The reduction in energy for maintenance was due to a decline in energy expenditure on physical acti vity by the immunized pigs.