Interaction between the sequence of feeding of hay and concentrate, and boiling of barley on feed intake, the activity of hydrolytic enzymes and fermentation in the hindgut of Arabian mares

The interaction between the sequence of feeding of hay and concentrate and the hydrothermal processing of barley in alleviating concentrate effects on intake, and hindgut fermentation in horses was tested. Six Arabian mares (4-10 years of age, 410 ± 35 kg body weight) were used to evaluate the effects of feeding sequence (FS) and type of barley (TB) on intake, and faecal volatile fatty acids (VFA), activities of α-amylase (AA: EC 3.2.1.1), carboxymethyl cellulase (CMCase: EC 3.2.1.4), microcrystalline cellulase (MCCase: EC 3.2.1.91) and general filter paper degrading activity (FPD). Mares were offered a ration of air-dried alfalfa and concentrate (70:30 as-fed) in four subsequent periods of 14 days including 8 days of adaptation and 6 days of sampling. In each period and each meal, mares received concentrate either 30 min after (HC) or 30 min before (CH) alfalfa hay. Barley was either milled or boiled in water. Rectal samples were grabbed directly from rectum once per period. Mares subjected to CH had higher dry matter intakes than mares under HC regime. The acetate:propionate ratio (A:P ratio) in rectal content was higher with CH than HC. The AA activity was higher under CH than under HC. Mares fed boiled barley had lower rectal concentrations of VFA and propionate and a higher A:P ratio than mares fed milled barley. Furthermore, the rectal content showed a higher MCCase activity but a lower AA activity when mares were fed boiled compared with milled barley. Interactions between FS and TB were observed with respect to CMCase activity, and concentrations of propionate and valerate. In conclusion, the present results suggest that both, feeding concentrate before hay and boiling the barley, might improve the hindgut environment in Arabian mares, and that the two measures were mostly additive and sometimes even synergistic.

The crystal structure of the endoglucanase Cel10, a family 8 glycosyl hydrolase from Klebsiella pneumoniae

Cellulases are produced by microorganisms that grow on cellulose biomass. Here, a cellulase, Cel10, was identified in a strain of Klebsiella pneumoniae isolated from Chinese bamboo rat gut. Analysis of substrate specificity showed that Cel10 is able to hydrolyze amorphous carboxymethyl cellulose (CMC) and crystalline forms of cellulose (Avicel and xylan) but is unable to hydrolyze p-nitrophenol β-D-glucopyranoside (p-NPG), proving that Cel10 is an endoglucanase. A phylogenetic tree analysis indicates that Cel10 belongs to the glycoside hydrolase 8 (GH8) subfamily. In order to further understanding of its substrate specificity, the structure of Cel10 was solved by molecular replacement and refined to 1.76 Å resolution. The overall fold is distinct from those of most other enzymes belonging to the GH8 subfamily. Although it forms the typical (α/α)₆-barrel motif fold, like Acetobacterxylinum CMCax, one helix is missing. Structural comparisons with Clostridium thermocellum CelA (CtCelA), the best characterized GH8 endoglucanase, revealed that sugar-recognition subsite -3 is completely missing in Cel10. The absence of this subsite correlates to a more open substrate-binding cleft on the cellooligosaccharide reducing-end side.