Effect of Dietary <i>Chlorella vulgaris</i> or <i>Tetradesmus obliquus</i> on Laying Performance and Intestinal Immune Cell Parameters

A feeding trial was conducted to investigate the effect of dietary supplementation of <i>Chlorella vulgaris</i> (CV) or <i>Tetradesmus obliquus</i> (TO) on laying performance, egg quality, and gut health indicators of laying hens. A total of 144 Hy-Line Brown laying hens aged 21 weeks were randomly assigned to one of three dietary treatments with eight replicates of six hens. Dietary treatments were as follows: CON, basal diet; CV, basal diet + 5 g <i>C. vulgaris</i>/kg of diet; TO, basal diet + 5 g <i>T. obliquus</i>/kg of diet. The results showed that diets supplemented with CV or TO had insignificant effects on laying performance, egg quality (i.e., Haugh unit and eggshell strength and thickness), jejunal histology, cecal short-chain fatty acids, and antioxidant/immune markers in ileal mucosa samples of laying hens. Compared with the control group, the egg yolk color score was higher (<i>p</i> < 0.05) in laying hens fed on diets containing CV and TO, although the former was a more intense yellow than the latter. Small intestinal lamina propria cells were isolated using flow cytometry to examine the percentages of immune cell subpopulations. Dietary microalgae did not affect B cells or monocytes/macrophages but altered the percentage of CD4+ T cells and CD8− TCR γδ T cells. Collectively, diets supplemented with <i>C. vulgaris</i> or <i>T. obliquus</i> can improve egg yolk color and would modulate host immune development and competence in laying hens.