Effects of exogenous α-amylases glucoamylases and proteases on ruminal invitro dry matter and starch digestibility gas production and volatile fatty acids ofmature dent corn grain

摘要

Two separate experiments were carried out to evaluate the effects of incremental doses of10 exogenous endo-acting α-amylase and exo-acting glucoamylase; 1LAT (bacterialα-amylase), 2AK, 3AC, 4Cs4, 5Trga, 6Afuga, 7Fvga, and 10Tg (fungal α-amylases,glucoamylases, and α-glucosidase), 8Star and 9Syn (fungal amylase-mixtures; experiment 1)and three exogenous proteases; 11P14L, 12P7L, and 13P30L (bacterial proteases; experiment2) on in vitro dry matter digestibility (IVDMD) and in vitro starch digestibility (IVSD)of mature dent corn grain using a batch culture system. Incremental doses of the exogenousenzymes (0, 0.25, 0.50, 0.75, and 1.00 mg/g of dried substrate) were applied directly tothe substrate (0.5 g of ground corn, 4 mm) in sextuplicate (experiment 1) or quadruplicate(experiment 2) within F57 filter bags, which were incubated at 39 °C in buffered rumenfluid for 7 h. Rumen fluid was collected 2–3 h after the morning feeding from threelactating dairy cows and pooled. Cows were consuming a midlactation total mixed ration(TMR; 1.60 Mcal/kg DM and 15.4%; net energy of lactation and crude protein, respectively).Three independent runs were carried out for each experiment. Data were analyzed as arandomized complete block design using run as the blocking factor. Dose was used as afixed factor while run was considered a random factor. Linear, quadratic, and cubicorthogonal contrasts were also tested. In experiment 1, enzymes 2AK, 3AC, and 10Tg did notincrease (P > 0.10) IVDMD and IVSD, whereas 0.25 mg of enzymes 1LAT,5Trga, and 8Star increased (P < 0.01) IVDMD by 23%, 47%, and 62% andIVSD by 35%, 41%, and 58%, respectively, compared with the control. Enzymes 4Cs4, 6Afuga,7Fvga, and 9Syn linearly increased IVDMD and IVSD (P < 0.01). Greatestincreases in IVDMD (82.9%) and IVSD (85.9%) resulted with 1 mg of 6Afuga compared tocontrol. In experiment 2, the lowest dose of exogenous proteases 11P14L and 12P7Lincreased (P < 0.01) IVDMD by 98% and 87% and IVSD by 57% and 64%,respectively, whereas the highest dose of 13P30L increased (P = 0.02)IVDMD by 44.8% and IVSD by 30%, relative to the control. In conclusion, IVSD and IVDMDwere increased by one α-amylase, certain glucoamylases, and all proteases tested, with theglucoamylase 6Afuga in experiment 1 and the neutral protease 12P7L in experiment 2,increasing IVDMD and IVSD to the greater extents. Future in vivo studies are required tovalidate these findings before these enzyme additives can be recommended for improving thedigestibility of mature dent corn grain.