Abstract
Two industrial exogenous enzymes, alpha-amylase from Bacillus licheniformis and glucoamylase from Aspergillus niger, were evaluated in vivo and in lambs fed 700 g/kg (dry matter (DM)) sorghum grain diets. Six Suffolk lambs (30 ± 2.5 kg body weight (BW)) fitted with ruminal and duodenal cannulas were randomly allotted to two 3 × 3 Latin square experiments, to evaluate effects of alpha-amylase and glucoamylase on intake, digestibility and ruminal fermentation. The same level of protein from the two enzyme sources (0.0, 1.45 or 2.90 g enzyme/kg DM sorghum) was applied to sorghum. The enzymes were sprinkled on the sorghum 24 h before mixing the diet. The highest level of each enzyme was also fed (45 days) to 15 individually housed lambs (Suffolk crossbred, 22.5 ± 1.4 kg BW) in a completely randomized design (i.e., control, alpha-amylase or glucoamylase) to evaluate lamb performance. The highest activity units/mg protein ( P < 0.01) was for the alpha-amylase (4.190) followed by glucoamylase (1.952) and ruminal fluid (0.062). Dry matter, organic matter (OM) and starch intake decreased as level of dietary alpha-amylase increased (linear: P < 0.05), but ruminal starch digestion and total tract digestibility of DM, OM and starch increased quadratically ( P < 0.05). Total volatile fatty acids VFA and protozoa numbers decreased linearly ( P < 0.01), whereas lactate was quadratically ( P < 0.01) increased with alpha-amylase. Ruminal pH, protozoa and lactate increased ( P < 0.01) with glucoamylase. Propionate molar proportion responded quadratically ( P < 0.01) with both enzymes. The intermediate level of glucoamylase increased intake of DM, OM and starch (quadratic: P < 0.09), but total tract starch digestibility decreased (linear: P = 0.08) as level of glucoamylase increased. Feed intake, gain and feed conversion were not affected by enzymes, but alpha-amylase improved ( P < 0.05) partial feed efficiency. Results indicate that amylase from B. licheniformis increases ruminal starch digestion and could be used to improve ruminal starch digestion in ruminants fed diets high in grains with low digestion rates.
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