Enzyme activities of rumen solid‐adherent microorganisms in chronically underfed ewes

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Abstract
Four ruminally cannulated ewes were used in a series of two crossover designs to investigate the effects of underfeeding and of supplementation with slowly degradable protein on polysaccharide and glycoside‐degrading enzyme activities in rumen solid‐adherent microorganisms. The ewes were fed twice daily on a hay based diet to satisfy either 1.2 or 0.5 maintenance energy requirements, with or without 125 and 65 g fish meal supplement for the high and the low intakes, respectively. Enzyme preparations were isolated from rumen solid contents 2, 6, and 12 h after feeding. Protein supplementation had no significant effect on the activity of any of the enzymes measured. The effects of feeding level on carboxymethycellulase and xylanase activities were small, the specific activity (expressed per mg microbial protein) being slightly increased at low intake (P < 0.10). However, β‐D‐galactosidase, β‐D‐glucosidase, β‐D‐xylosidase, and β‐D‐cellobiosidase activities were considerably increased with low feeding level ( + 56 to +70% for specific activities; +31 to + 50% when expressed per g dry matter). The activities of all enzymes tested increased significantly with time after feeding. The extent of specific activity response to variation of feeding level was greater for late sampling times than 2 h post‐feeding. Ruminal degradation of the dietary bay was not affected by fishmeal supplementation, but increased with reduction of feeding level (+ 59.7 g kg−1 for neutral detergent fibre during the first 12 h of rumen incubation; P < 0.001). The higher microbial efficiency associated with greater retention time of feed particles in the rumen may account for the increase in cell wall degradation usually observed when feeding level declines.

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