Avian coccidiosis is caused by the intestinal protozoa Eimeria. The parasite"s site of infection in the intestine is site specific. Eimeria acervulina infects the duodenum, E. maxima the jejunum, and E. tenella the ceca. Lesions in the intestinal mucosa cause reduced feed efficiency and body weight gain in Eimeria-challenged chickens. The growth reduction may be due to changes in expression of digestive enzymes and nutrient transporters in the intestine. The objective of this thesis was to examine the expression of digestive enzymes: APN and SI, peptide and amino acid transporters: Pept1, ASCT1, bo,+AT/rBAT, B0AT, CAT1/2, EAAT3, LAT1 and y+LAT1/2, sugar transporters: GLUT1, GLUT2, GLUT5 and SGLT1, mineral transporter: ZNT1 and an immune factor: LEAP2 in the duodenum, jejunum, ileum and ceca of Eimeria-challenged layers and broilers. Comparisons were made between E. acervulina-challenged layers and broilers and E. acervulina, E. maxima and E. tenella-challenged broilers to examine the effect of chicken breeds and Eimeria species, respectively, on digestive enzymes and nutrient transporter expression. E. acervulina-challenged layers and broilers showed downregulation of APN, bo,+AT/rBAT, B0AT, CAT2, EAAT3, GLUT2, SI, ZNT1 and LEAP2 in the duodenum, but not in the jejunum and ileum. E. acervulina-challenged duodenum, E. maxima-challenged jejunum and E. tenella-challenged ceca samples showed common downregulation of APN, GLUT5 and ZNT1. These results demonstrate that there are common changes in intestinal gene expression in response to E. acervulina in broilers and layers, and common changes in response to challenge by different Eimeria species in broilers. / Master of Science