## 4 Discussion
These findings are similar to those of other studies which studied different microalgae sources and inclusion levels and noticed an improved production parameter when including microalgae in poultry diets due to the high protein content, essential amino acids, vitamins, and minerals present in spirulina and chlorella. Additionally, the presence of certain bioactive compounds and antioxidants in microalgae may have positive effects on production performance. [PERSON] et al. [43] included four levels of spirulina powder (0, 0.10, 0.15, or 0.20%) in laying hens' diet and registered an improved egg production rate, daily egg mass, and feed conversion ratio compared to those of the control group. [PERSON] and [PERSON] [44] tested spirulina on broilers and found a significant increase in body weight. Other studies have [45] supplemented the basal diet of laying hens raised under a chronic hot ambient temperature with spirulina powder (0.15 mg/kg diet) and seleno-methionine (0.10 mg/kg diet). The obtained results indicated that dietary spirulina and organic selenium showed improved productive performance under heat stress. In contrast, the chlorella supplementation at varying dosages of 2.5 g, 5.0 g, or 7.5 g per kg feed, in both spray-dried and bullet-milled/spray-dried forms, did not result in any impact on laying intensity, egg weight, daily egg mass production, or feed conversion. However, it was observed that the treatment groups exhibited an increase in yolk weight and an improvement in egg quality [46]. In a study conducted by [PERSON] et al. [47], laying hens at 44 weeks of age were fed with diets containing 1.5% and 2.5% spirulina for a period of 6 weeks. The results indicated that the inclusion of 2.5% spirulina in the diet significantly increased egg weight. However, no significant effects were observed on other productive parameters, including dietary treatment, duration of the diet, or their interaction. Concerning the antioxidant enzyme activity, the results obtained in our study showed that chlorella and spirulina dietary addition exhibited significant improvements in blood antioxidant enzyme activities (SOD, CAT, GSH) and total antioxidant capacity (TAC). Moreover, the increased serum levels of GSH and TAC in both experimental diets demonstrate and support the idea that the microalgae-supplemented diets positively influenced the hens' antioxidant status compared to the control group. The main antioxidant enzymes, such as SOD, CAT, and GSH, protect the organism against oxidative stress [48], improving the poultry immune system [49]. CAT is one of the most important antioxidant enzymes which mitigates oxidative stress via the catalysis of hydrogen peroxide [50]. [PERSON] et al. [51] obtained the same linearly increased GPx and SOD enzymes in broilers fed with spirulina and explained that this was due to the fact that spirulina contains antioxidants such a \(\beta\)-carotene, locopherol, selenium, polypeptide pigment, or phenolic acids. [PERSON] et al. [52] suggested that spirulina has stronger antioxidant capabilities than chlorella, which is probably due to the higher content of phenolic compounds. Utilization of microalgae in laying hens' diet had no effect concerning the apparent digestibility coefficients. Our results are similar to those of [53], who reported that the incorporation of green seaweed (_Illumina spp._) meal between 20 and 35 g/kg in Boschveld hens' diets did not alter apparent nutrient digestibility. Additional research [19] indicated that the inclusion of brown seaweed meal derived from (_Ecklonia maxima_) into the diet of Boschveld cockerels did not have a significant impact on the digestibility of dry matter, organic matter, crude protein, and fiber. This result was observed despite the seaweed inclusion rate ranging from 2 to 8 g/kg. In our experiment, we obtained a high \(\beta\)-carotene content and increased antioxidant capacity of the yolk, which represents indicators of an improved egg quality, with potential health-promoting effects for consumers. [PERSON] et al.