Marine microalgae meal (Schizochytrium sp.) influence on intake, in vivo fermentation parameters and in vitro gas production and digestibility in sheep diets is dose-dependent

The objective of this study was to evaluate the dry matter intake (DMI), intake of nutrients and in vivo ruminal fermentation in wethers fed diets without or with 2 or 4% of marine microalgae meal ( Schizochytrium sp. ) as a source of docosahexaenoic polyunsaturated fatty acid (DHA; C22:6 n-3), as well as the total gas production and digestibility of the experimental diets using in vitro techniques. Six Santa Inês wethers with a body weight of 55.6 ± 5.20 kg and 18 months of age fitted with a ruminal cannula, were used and housed in individual stalls. The experimental design consisted of a double 3 ×3 Latin square (three treatments and three periods) with each experimental period lasting 21 days (14 days for adaptation to diets, 5 days for sample collection and 2 days of blank time between periods), for a total of 63 days. Animals fed 4% microalgae meal showed lower DMI (P<0.05; 1,14 vs. 0,86 kg/d) and lower intake of nutrients (P<0.05), except for ether extract (EE; P=0.967), compared to animals not fed microalgae. Wethers that were not fed marine microalgae had lower ruminal pH just two hours after feeding (P=0.042) and lower concentrations of ammoniacal nitrogen (NH 3 -N) in the ruminal fluid at all sampling times (P=0.011) compared to wethers fed diets with 2 and 4% level inclusion. The addition of marine microalgae meal did not have an effect on heat production and in vitro gas production (P>0.05). The in vitro digestibility of non-fibrous carbohydrates (NFC) increased (P=0.033) with the inclusion of marine microalgae in the diet, being higher in the 4% treatment compared to the others. Additionally, marine microalgae meal significantly reduced (P=0.002; 0.55 to 0.47 g/g of DM) the in vitro digestibility of neutral detergent fiber corrected for ash and protein (NDF). The inclusion of marine microalgae meal Schizochytrium sp . as a DHA source did not negatively affect ruminal fermentation. However, it compromised dry matter and nutrients intake, as well as NDF digestibility in animals fed 4% microalgae while a reduction on DMI as well as intake of nutrients at 2% inclusion was not significant. Therefore, it is recommended to use marine microalgae meal in the feeding of wethers under tropical conditions at a concentration of 2% of the diet. • Animals fed 4% of microalgae meal had lower DM and nutrients intake • Sheep fed with marine microalgae had higher pH and NH 3 -N in the ruminal fluid after feeding • Inclusion of microalgae in diets for ruminants does not interfere with digestibility, short-chain fatty acids and methane production.