THE RELATIONSHIP OF NUTRITIONAL IMMUNITY TO IRON SUPPLEMENTATION IN THE YOUNG PIG

CHRISTOPHER DENNIS KNIGHT, Purdue University

Abstract

Evidence in the literature has suggested that iron injection can increase host susceptibility to infection by providing growth-essential iron to invading microorganisms. Several experiments were performed to evaluate the possibility that injected of iron dextran may be detrimental to the health of the young pig. In the first experiment, pigs were injected with 400 mg (HiFe) or 100 mg (LoFe) of iron as iron dextran and enteropathogenic E. coli (strain 263) or sterile tryptic soy broth was injected into 40 cm. segments of ligated intestine to determine the influence of enteric infection on systemic iron-limiting mechanisms. All pigs exhibited a 70% depression of serum iron (SFe) within 6 hours after installation of intestinal segments that was probably due to the surgery. Greater iron availability was observed in HiFe than LoFe pigs as indicated by greater SFe, lower total iron-binding capacity (TIBC) and greater transferrin saturation. Intestinal E. coli was associated with an increase in TIBC in LoFe (but not HiFe) pigs that was probably due to fluid secretion into the intestine and subsequent hemoconcentration. Liver iron content was significantly increased in the presence of intestinal E. coli in HiFe pigs. That a systemic infection caused the increase in liver iron cannot be ruled out, however. Experiments were performed to determine the ability of serum from iron-injected pigs to support the growth of 2 strains of E. coli (263 and 026:B6). In the first of these experiments, E. coli growth in serum collected 1, 3 and 5 days or 7, 9 and 11 days following injection of 0, 100 or 200 mg of iron as iron dextran was not associated with SFe concentration. The dilution of serum 1:10 with saline may have reduced SFe below the level necessary to influence E. coli growth in the in vitro assay. A similar experiment was performed that included 5 treatments: 100 or 200 mg of iron as iron dextran; 215 or 430 mg of dextran, (the amount of dextran in a 100 and 200 mg iron dextran injection respectively); and uninjected controls. The growth of E. coli was determined in serum drawn 1, 3 and 5 days post-injection and diluted 1:5 with saline. Serum E. coli growth for uninjected controls was not different from iron-injected pigs. This may have been due to a growth depressant effect of dextran associated with the iron dextran injection or that pigs not receiving iron were severely anemic. Serum growth of both strains of E. coli was greater in 200 than 100 mg iron-injected pigs and was also greater in iron-injected than dextran injected pigs. Thus, although iron supplementation was necessary to prevent anemia, large doses of iron could be detrimental to the pigs' health by stimulating bacterial growth. Fasting serum glucose was monitored in all experiments and found to be negatively associated with iron dextran injection. Oral glucose tolerance tests performed in the second serum E. coli growth study indicated that iron-injected pigs were less glucose tolerant and exhibited lower immunoreactive insulin values than dextran-injected and uninjected control pigs. As erythrocytes have membrane bound insulin receptors, the increased number of erythrocytes in iron-injected pigs may have reduced circulating insulin concentrations causing the observed effects. The depression of fasting serum glucose did not affect serum E. coli growth and did not appear to have any detrimental effect on the iron-injected pigs.

Degree

Ph.D.

Subject Area

Livestock

COinS