Microalgae (<i>Chlorella vulgaris</i> and <i>Spirulina platensis</i>) as a Protein Alternative and Their Effects on Productive Performances, Blood Parameters, Protein Digestibility, and Nutritional Value of Laying Hens’ Egg

Protein is an essential nutrient for laying hens, playing a crucial role in egg production and supporting their overall health. An 8-week feeding trial was conducted on 120 Lohmann Brown laying hens (aged 38 weeks). The layers were assigned randomly to three groups and housed in cages (twenty replicates × two birds/cage). All groups were fed a corn–soybean meal basal diet (2750 kcal/kg metabolizable energy (ME) with 17.8% crude protein (CP)). In contrast to conventional diet (CON), the experimental groups were supplemented primarily at the expense of soybean meal with 2.0% <i>Chlorella vulgaris</i> (CV2%) and 2.0% <i>Spirulina platensis</i> (SP2%). Their high concentrations of chlorophyll <i>a</i> (5.56; 9.06 mg/g), chlorophyll <i>b</i> (0.88; 1.34 mg/g), and antioxidant activity expressed as 2,2-diphenyl-1-picrylhydrazyl (73.29; 81.27 DPPH% inhibition) improved egg yolk quality. At the end of the trial, eighteen eggs/group (six yolk samples/group, three eggs/sample) were collected to determine the egg quality and nutritional parameters (fatty acids profile, cholesterol, β-carotene, yolk color, and antioxidant capacity). To determine the activity of antioxidant enzymes, including superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GSH), and total antioxidant capacity (TAC), blood samples were collected at the end of the period. Microalgae inclusion increased (<i>p</i> < 0.05) the fatty acid content, ß-carotene concentration (<i>p</i> < 0.001), antioxidant capacity (<i>p</i> < 0.0001), and yolk color intensity (<i>p</i> < 0.001) significantly, especially the yolk redness a* color parameter, but without any significant results concerning cholesterol concentration. Boiling the eggs for 10 min significantly (<i>p</i> < 0.001) increased the b* color parameter on microalgae treatments. The supplementation of laying hens’ diet with microalgae positively influenced egg quality and nutritional properties.