Effect of Spirulina Dietary Supplementation in Modifying the Rumen Microbiota of Ewes

SIMPLE SUMMARY: The supplementation of microalgae as additives in animal diets has gathered the scientific community’s attention over recent years due to their beneficial properties. A better understanding of the effect of such additives on the rumen physiology could unravel their mode of action and overall functionality. Therefore, this study investigated the effect of Spirulina supplementation on modifying the rumen microbiota of ewes. Our results suggested that supplementing Spirulina, in the highest studied level (15 g/ewe/day), resulted in significant alterations in the relative abundance of the rumen microorganisms, with those reported regarding the cellulolytic bacterial species being considered the most interesting. ABSTRACT: Supplementing ruminant diets with microalgae, may prove an effective nutritional strategy to manipulate rumen microbiota. Forty-eight ewes were divided into four homogenous groups (n = 12) according to their fat-corrected milk yield (6%), body weight, age, and days in milk, and were fed individually with concentrate, alfalfa hay, and wheat straw. The concentrate of the control group (CON) had no Spirulina supplementation, while in the treated groups 5 (SP5), 10 (SP10), and 15 g (SP15) of Spirulina were supplemented as an additive in the concentrate. An initial screening using metagenomic next-generation sequencing technology was followed by RT-qPCR analysis for the targeting of specific microbes, which unveiled the main alterations of the rumen microbiota under the Spirulina supplementation levels. The relative abundance of Eubacterium ruminantium and Fibrobacter succinogenes in rumen fluid, as well as Ruminococcus albus in rumen solid fraction, were significantly increased in the SP15 group. Furthermore, the relative abundance of Prevotella brevis was significantly increased in the rumen fluid of the SP5 and SP10 groups. In contrast, the relative abundance of Ruminobacter amylophilus was significantly decreased in the rumen fluid of the SP10 compared to the CON group, while in the solid fraction it was significantly decreased in the SP groups. Moreover, the relative abundance of Selenomonas ruminantium was significantly decreased in the SP5 and SP15 groups, while the relative abundance of Streptococcus bovis was significantly decreased in the SP groups. Consequently, supplementing 15 g Spirulina/ewe/day increased the relative abundance of key cellulolytic species in the rumen, while amylolytic species were reduced only in the solid fraction.