Assessment of algae meal as a ruminant feedstuff: Nutrient digestibility in sheep as a model species

Heterotrophic microalgae combined with soyhulls forms an algae meal (ALG), which contains partially deoiled microalgae (PDM; 57% DM basis) and soyhulls (43%). Two experiments were conducted to evaluate the effects of PDM and ALG on lamb digestibility. In Exp. 1, 8 wethers (23.02 ± 0.54 kg) were used in a 4 × 4 Latin square design to determine the effect of the PDM portion of ALG on total tract nutrient digestibility. Diets included a soyhull-based control (CON; 53% soyhulls), 10% PDM from ALG, 20% PDM from ALG (PDM20), and 30% PDM from ALG. Dry matter and OM intake and fecal DM and OM output were similar ( ≥ 0.11) between CON- and ALG-fed lambs. Urine output linearly increased ( = 0.02) as PDM increased in diets. Dry matter, OM, NDF, and ADF digestibility linearly decreased ( < 0.01) as PDM increased in diets. Ether extract digestibility did not differ ( = 0.24) between CON- and PDM-fed lambs. Nitrogen digestibility and N retention linearly decreased ( ≤ 0.05) as PDM increased in the diet. In Exp. 2, to determine the effects of ALG on diet and nutrient digestibility and N retention, 10 whiteface cross wethers (33.71 ± 0.55 kg) were used in a replicated 5 × 5 Latin square. Diets included a cracked corn-based control (CORN), 15% ALG, 30% ALG, 45% ALG (ALG45), and 60% ALG (ALG60). Dry matter and OM digestibility linearly ( < 0.001) decreased as ALG inclusion increased. Digestibility of NDF and ADF were lesser ( ≤ 0.03) for CORN-fed sheep than for ALG-fed sheep and linearly ( ≤ 0.03) increased as ALG increased in the diet. Ether extract digestibility was lesser ( = 0.002) for CORN than ALG, with a linear ( = 0.002) increase as ALG inclusion increased. There was a cubic ( = 0.03) effect for N digestibility with ALG45 and ALG60 being lesser and CORN being greater than all other treatments. Retention of N and plasma urea N concentration did not differ ( ≥ 0.22) between CORN and ALG. Nonfibrous carbohydrate digestibility linearly ( < 0.001) decreased as ALG increased in the diet. These results suggest that the PDM portion of ALG may be less digestible than soyhulls in ruminants, and differences in N retention in Exp. 1 may suggest an effect on growth in lambs. Furthermore, changes in digestibility of specific nutrients suggest that ALG is more characteristic of a concentrate rather than a fibrous feedstuff. However, lambs will readily consume ALG and this novel feedstuff could potentially serve as a viable component of ruminant diets.