Effects and mechanism of action of a fungal amylase preparation on performance characteristics of finishing beef cattle

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Title: Effects and mechanism of action of a fungal amylase preparation on performance characteristics of finishing beef cattle
Author: Abney, Michael Dustin
Abstract: Six experiments were conducted to examine the effects of a supplemental amylase on the performance of finishing beef cattle and to determine its possible modes of action . In Exp . 1 , 120 steers (average BW = 363 kg ; SD = 33 kg ) were blocked by body weight (BW ) into six blocks (five pens per block and five steers per pen ) and assigned to four dietary treatments in a 2 x 2 factorial experimental design with roughage source (RS ) and supplemental amylase (AMA ) as the factors . An AMA x RS interaction was detected for average daily gain (ADG ) from d 0 to 28 (P < 0 .02 ) , 0 to 56 (P < 0 .10 ) , and 0 to 112 (P < 0 .04 ) . Interactions were detected for DM intake (DMI ) ; AMA x RS on d 0 to 56 (P < 0 .09 ) and 0 to 112 (P < 0 .05 ) . The greatest improvements in ADG and DMI were observed for those steers receiving cottonseed hulls (CSH ) as their RS plus supplemental amylase , and AMA increased longissimus muscle area (P < 0 .05 ) . Experiment 2 was used the same CSH diets with and without AMA that were used in Exp 1 . Ninety -six cross bred heifers (average BW = 436 kg ; SD = 33 kg ) were blocked by BW into four blocks and randomly assigned to the two dietary treatments within each block . No cattle performance differences were detected for either RS or AMA in Exp . 2 . Experiment 3 examined the role of DMI in the responses observed in Exp . 1 . Fifty -six crossbred steers (average initial BW = 365 kg ; SD = 31 .4 kg ) in a randomized complete block design were fed the same diets used in Exp . 2 . These steers were fed a limited quantity of feed to produce a shrunk ADG of 1 .52 kg /d were provided . When DMI was restricted in this manner , no effects of AMA or RS were detected , indicating that responses to AMA in Exp . 1 were likely a function of increased DMI . Experiment 4 was determined how the activity of AMA would respond to changes in pH and Ca concentration . Using a laboratory assay , the ability of AMA to hydrolyze starch was examined using a 3 x 4 factorial design (Ca =1 .11 , 2 .22 , and 4 .44 g of Ca /L ; pH = 4 .8 , 5 .2 , 5 .6 , and 6 .0 ) . An interaction between Ca and pH (P < 0 .001 ) was observed for the activity of AMA , but practical effects of this iteraction would likely be small . Post -ruminal digestion was simulated in Exp . 5 using acid only (HCl ) , acid -pepsin (AP ) , and trypsin -chymotrypsin (TC ) solutions . When AMA was subjected to HCl , AP , TC , or any combination of those solutions , activity was lost . However when the amylase was subjected to only TC , the activity did not differ (P > 0 .10 ) from that of an undigested sample . These results suggested that AMA would have little activity in the small intestine . A continuous culture system was used to determine the effects of com processing method and AMA supplementation on minimal fermentation . Four dietary treatments were used in a 2 x 2 factorial design (dry -rolled com [DRC] , steam -flaked com [SFC] , with [+] and without [ -] AMA ) . When the diets contained SFC instead of DRC , decreases in microbial N synthesis (g /d ; P < 0 .04 ) , microbial OM synthesis (P < 0 .10 ) , and N digestibility (P < 0 .05 ) were observed . Diets with SFC had a decreased molar proportion of acetate (P < 0 .01 ) , increased molar proportions of propionate (P < 0 .02 ) , and isovalerate (P < 0 .08 ) , and a tendency for an increased molar proportion of butyrate (P < 0 .14 ) compared with DRC . Supplementing AMA increased microbial N synthesis (g /d ; P < 0 .03 ) , and tended to increase in microbial efficiency (g /kg of OM truly fermented ; F < 0 .19 ) and N digestibility (P < 0 .15 ) . Results suggest that AMA may improve performance of finishing beef cattle , but a better understanding of the mechanism of action of this enzyme is needed .
URI: http : / /hdl .handle .net /2346 /12351
Date: 2004-12

Citation

Abney, Michael Dustin Effects and mechanism of action of a fungal amylase preparation on performance characteristics of finishing beef cattle. Doctoral dissertation, Texas Tech University. Available electronically from http : / /hdl .handle .net /2346 /12351 .

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