Effects of a laminarin-rich algal extract on caecal microbiota composition, leukocyte counts, parasite specific immune responses and growth rate during Eimeria tenella infection of broiler chickens

Coccidiosis, infection with protozoan parasites of genus Eimeria, is a major problem in poultry husbandry worldwide. The disease is currently managed by coccidiostats and live vaccines, but these approaches are not sustainable. Hence, it is important to identify new means to control the infection and/or ameliorate its detrimental effects on gut health. Laminarin, a (3-glucan found in marine brown algae, has prebiotic and bioactive properties that could be beneficial in coccidiosis control. The present study aimed to examine the potential of laminarin as an immunostimulatory and microbiota-regulatory compound in broiler chickens infected with E. tenella. Chickens were continuously fed a diet supplemented with a laminarin-rich algal extract (AE) from first feed and subsequently infected with E. tenella at 19 days old. The outcome of infection including caecal microbiota and some immune parameters were monitored during the experiment. Results showed that AE supplementation affected some lymphocyte subpopulations, with increased numbers of TCR gamma/delta+CD8-, B-cells and CD4-CD8 alpha(3+ cells and lower numbers of CD4+CD8 alpha alpha+ cells in blood and increased proportions of CD4-CD8 alpha(3+ spleen cells compared to those in control chickens. The AE diet did not affect parasite excretion, lesion scores or E. tenella specific T-cell responses. However, reductions of E. tenella induced contraction of Bifidobacteriaceae and expansion of Clostridiaceae in caecal microbiota were observed for AE fed chickens compared to chickens fed the control diet. Thus, AE feed supplementation induced some immunostimulatory activity in chickens and affected some of the alterations in caecal microbiota evoked by E. tenella infection.