<i>Spirulina platensis</i> supplementation in fish-oil diets improves yolk fatty acid profile, follicle development, and egg shelf life in aged laying hens

The present study was conducted to investigate the effect of Spirulina Platensis (SP) supplementation in diets containing different levels of fish oil (FO) on performance, blood parameters, ovarian follicle growth, yolk fatty acids profile, and egg shelf life during storage in aged laying hens. For this purpose, 288 laying hens (Hy-line-W36, 70 weeks of age) were used in a completely randomised design with a 2 × 3 factorial arrangement with 6 replications and 8 birds per each for 8 weeks. The experimental treatments included diets containing 3 levels of FO (0, 1.5, and 3% w/w of the diet) and 2 levels of SP (0 and 5 g/kg of diet). Performance parameters were recorded daily, while blood parameters, ovarian follicle characteristics, egg quality traits, and yolk fatty acid composition were measured at the end of the trial (day 56). The results showed that hens fed 1.5 and 3% FO with 5 g/kg SP of diet had the highest egg mass, which was significantly higher than the control treatment (p < 0.01). The ovarian large yellow follicles weight and number increased in birds fed 1.5 and 3% FO compared to the control birds (p = 0.006). The use of 5 g/kg of SP prevented the decrease in Haugh unit, yolk index, and yolk colour, and the increase in albumen and yolk pH after 30 days of storage at 4 °C temperature (p < 0.05). The inclusion of 5 g/kg SP in diets containing 3% FO significantly increased α-linolenic acid (ALA), eicosapentaenoic acid (EPA), and docosahexaenoic acid (DHA) in egg yolks. Spirulina platensis supplementation led to a moderate but significant increase in yolk ALA and total polyunsaturated fatty acids (PUFA), accompanied by an improved PUFA/saturated fatty acids ratio relative to the non-supplemented groups (p < 0.05). Both FO and SP markedly enhanced yolk ω-3 fatty acid deposition and consequently reduced the n-6/n-3 and linoleic acid/ALA ratios, with the lowest values observed in the 3% FO + 5 g/kg SP treatment (p < 0.05). In conclusion, SP supplementation in diets containing FO improved production performance, follicle development, and yolk fatty acid profile, while maintaining egg quality during storage in aged laying hens.