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Microalgae might be considered as an alternative source of fat and/or protein for ruminant's diets. However, changes in populations of ruminal micro-organisms associated with biohydrogenation process, methane and ammonia production in response to microalgae dietary supplementation have not been well characterized. Thus, 16 cross-bred goats were divided into two groups. Each goat of both groups was fed individually with alfalfa hay and concentrates separately. The concentrates of the control group had no microalgae while those of the treated group were supplemented with 10 g lyophilized Chlorella vulgaris/kg concentrate (chlor). On the 30th experimental day, samples of rumen fluid were collected for microbial DNA extraction, fatty acid profile and enzyme activity analyses. The results showed that the chlor diet compared with the control increased significantly the populations of Methanosphaera stadtmanae, Methanobrevibacter ruminantium and Methanogens bacteria and protozoa in the rumen of goats. A significant reduction in the cellulase activity and in the abundance of Ruminococcus albus, and a significant increase in the protease activity and in the abundance of Clostridium sticklandii in the rumen liquid of goats fed with the chlor diet, compared with the control, were found. Chlorella vulgaris supplementation promoted the formation of trans C18:1, trans-11 C18:1 and monounsaturated fatty acids (MUFA), while the proportions of C18:0 and long-chain fatty acids (LCFA) reduced significantly in the rumen liquid of goats. This shift in ruminal biohydrogenation pathway was accompanied by a significant increase in Butyrivibrio fibrisolvens trans C18:1-producing bacteria. In conclusion, the supplementation of diets with microalgae needs further investigation because it enhances the populations of methane-producing bacteria and protozoa.

The effect of dietary inclusion of microalgae on goat's milk chemical composition, fatty acids (FA) profile and enzymes activities related to antioxidant mechanism has not been adequately investigated so far. Thus, the present study aimed to investigate the effects of dietary inclusion of Chlorella pyrenoidosa on: a) milk yield, chemical composition and FA profile, b) on the activities of superoxide dismutase (SOD), catalase (CAT), glutathione reductase (GR), glutathione transferase (GST) and glutathione peroxidase (GSH-Px) in blood plasma, and c) on the activities of SOD, GR and lactoperoxidase (LPO) in milk of goats. Additionally, the oxidative stress indicators for measuring total antioxidant and free radical scavenging activity [Ferric Reducing Ability of Plasma (FRAP) and 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) assays] and oxidative stress biomarkers [malondialdehyde (MDA) and protein carbonyls (PC)] in goats blood plasma and milk were also determined. Thus, sixteen crossbred goats were divided into two homogenous groups. All the goats were fed individually alfalfa hay and concentrates separately. The concentrates of the control group (Control) had no microalgae while that of the treated group supplemented with 10 g lyophilized Chlorella pyrenoidosa/ kg concentrate (Chlor). The results showed that the Chlor diet compared with the control had not noticeable impact on goats milk yield, chemical composition and fatty acids profile. Furthermore, the Chlor diet had no effect on the antioxidant enzymes activities, antioxidant capacity and oxidative stress indicators in both blood plasma and milk of goats. In conclusion, the daily dietary inclusion of Chlorella pyrenoidosa at 11 g per goat for 28 days did not improves the milk quality and/or the antioxidant status of both animals and milk.

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