EFFECT OF HEMOGLOBIN AND IMMUNIZATION STATUS ON ENERGY-METABOLISM OF WEANLING PIGS

We investigated the effect of (Hb) and immunization status on energy m etabolism of newly weaned pigs. An additional focus of the study was t o determine the development of circadian rhythms as evidenced by heat production patterns. Twenty-four 4-wk-old crossbred weanling barrows w ere placed into groups of three based on weight and litter origin, and the groups were allotted to one of four treatments. Treatments were a rranged as a 2 x 2 factorial. The factors included 1) Hb status (low v s high) and 2) immunization status (antigen vs placebo). Hemoglobin st atus was obtained by injecting 3-d-old barrows with 100 (low) or 200 m g (high) of Fe. At 4 wk, initial blood Hb concentrations were 6.0 mM f or the low group and 7.8 mM for the high group. Energy metabolism,was measured using two weekly total energy and nitrogen balance collection s. Energy intake and retention were higher (P < .05) in pigs with a hi gh Hb level. Energy metabolism was not affected (P > .10) by immunizat ion status, and heat production was not affected (P > .10) by either H b or immunization status. Total heat production (H-TOT) increased (P < .001) daily and reflected a daily increase (P < .001) in activity (H- ACT) and activity-free (H-COR) heat production. An increase (P < .001) in H-TOT and H-ACT was detected for the light period compared with th e dark period over the total experimental period but a decrease (P < . 001) in H-COR was detected; however, H-ACT for the dark period was app roximately half of that measured during the light period. In conclusio n, Hb status affected energy metabolism; pigs having a high Hb status had a higher energy retention. Immunization status had minimal effects on energy metabolism and heat production. Additionally, the diurnal c ircadian rhythm seen in older pigs had not been established by 2 wk af ter weaning.