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

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.