Abstract. The effect of transferrin (TF) polymorphism and the levels of some blood serum indices, functionally linked to this protein, were studied. The following determinations were made in the blood serum of 311 hybrid suckling piglets - TF polymorphism, TIBC (total iron binding capacity), TF iron saturation percentage and levels of iron ceruloplasmin (CP) and copper.

Clinically healthy piglets and piglets with diarrhoea caused by E. coli were divided into younger (aged 10 to 14 days) and older (aged 15 to 28 days). The piglets showed two genotypes, TF AB and TF BB. The TF BB genotype dominated among clinically healthy piglets, and the TF AB genotype in those suffering from diarrhoea. TF polymorphism differentiated the levels of CP and copper in clinically healthy piglets, and modified iron concentration and TF iron saturation percentage in piglets with diarrhoea. Regardless of health status, age had an almost identical effect on the levels of blood serum indices in piglets of both genotypes.

The differences in the levels of CP, iron, and TF iron saturation percentage in healthy piglets and piglets with diarrhoea were modified by the presence of the TF^A allele, but in older piglets only.