Genomic Analysis of the Influence of Selenium Sources in Broiler Chickens Challenged with an Enteric Avian Reovirus

Abstract

Technological advances in animal nutrition have shown that organic selenium in yeast protein is superior to inorganic selenium as a feed supplement. Reasons for improved performance of farm animals fed organic selenium remain unresolved. The objective of this research was to examine the differences between inorganic selenium (sodium selenite) and organic selenium (Sel-Plex) and their influences on genomic responses in control and enteric avian reovirus (ARV-CU98)-challenged chickens. Sel-Plex-feeding induced an apparent faster recovery from ARV challenge as indicated by intestinal histomorphology in three weeks old broilers. The small intestine villi were taller, more narrow and had greater villus height/crypt dept ratios indicating a healthier intestinal tract. Body weights of Sel-Plex-fed chickens, although not significantly different among the ARV-challenged birds, had greater two to three week weight gains. To determine whether dietary organic selenium, provided via Sel-Plex, had influenced faster recovery after ARV challenge, investigations were conducted to ascertain if there were differences among control and ARV-challenged chickens in selenoprotein P (sepp1; a selenium-dependent protein) expression, expression of polymeric immunoglobulin receptor (pIgR), which transposes secretory IgA through the intestinal enterocytes for release into the intestinal lumen, and examine with microarray experiments whether there were groups of genes differentially affected by ARV, selenium sources and/or aging. Five tissues (brain, liver, pancreas, bursa of Fabricius, and thymus) were selected for investigation of sepp1 expression. Sepp1 expression was found to decrease with age. Dietary selenium supplementation, generally up-regulated sepp1 expression, and Sel-Plex tended to induce the greatest expression of sepp1. In brain, liver, thymus, and bursa of Fabricius, sepp1 expression was down-regulated after ARV challenge. Sepp1 expression in brain and liver was greatest in 7 days old chickens, but aging to 14 and 21 days of age down-regulated sepp1 expression in all tissues. In Sel-Plex-fed birds, sepp1 was up-regulated in brain, liver and thymus. Another experiment, using qRT-PCR, examined the influence of dietary selenium on pIgR expression in specific tissues of ARV-challenged broilers. Sel-Plex increased pIgR expression in the liver of ARV-infected chickens, and ARV increased pIgR expression in pancreas and bursa of Fabricius. PIgR expression increased with aging in bursa, liver and pancreas, but not in the thymus. Two microarray experiments were conducted in which dietary selenium supplementation was examined using the liver of 14 days old broilers, and ARV influences were examined in liver of selenium-deficient, torula yeast-fed broilers at 7, 14, and 21 days of age. In experiment 1, Sel-Plex up-regulated more genes then did the control or sodium selenite diets. Sel-Plex up-regulated genes involved with metabolism, protein synthesis, and immune functions and this was somewhat different from the effects due to control and sodium selenite diets. The ARV-infected birds up-regulated more genes than controls. ARV infection seemed to elevate the intensity patterns for all of the genes noted as up-regulated by Sel-Plex and Control diets. Genes up-regulated by sodium selenite were not as intense as those up-regulated by Sel-Plex and control diets. In experiment 2, gene expression appeared to decrease as the bird aged. The control birds up-regulated a few more genes then did the ARV-infected chickens. Decreased gene expression due to aging alone was more apparent than treatment effects. It was concluded that selenium sources and ARV infection exert differential influences on the genome of young broilers. Organic selenium has a greater influence on gene expression than inorganic selenium.