Feed accounts for 60 to 70% of total costs in most livestock enterprises, with energy as the major constituent of feed. Reducing feed cost is the primary driver for utilizing exogenous fibrolytic enzymes in livestock production. The high concentration of fiber, but low lignin, allows dried distillers grains with solubles (DDGS) to partially replace grain in finishing diets. Although DDGS contains high proportions of digestible fiber, recent studies reported that ruminal digestion of neutral detergent fiber declined as dietary inclusion of DDGS level increased in corn DDGS-fed cattle or in wheat DDGS-fed cattle.
Batch culture technique was used to screen and identify enzyme additives with potential of increasing fiber digestibility of corn DDGS and silage. The enzymes were then evaluated using in situ technique to measure effects on ruminal digestibility of DM using three ruminally cannulated steers. A backgrounding and finishing study were further conducted to evaluate the potential of exogenous enzymes to increase fiber digestibility of corn silage and DDGS. The backgrounding study was conducted utilizing 142 steer calves from multiple consignors. At the conclusion of the backgrounding study a finishing study followed in which pens of steers were reallocated to new treatments including a control and a single exogenous enzyme treatment.
Based on the in vitro batch culture results, cellulase, protease and Aspergillus oryzae extract (increased IVDMD of 7.7, 9.3 and 6.0% respectively compared to control) were selected for further evaluation using the in situ technique. Gas production reflects the generation of short-chain fatty acids and microbial mass which are utilized by the animal to meet their nutrient requirements. Compared with the control, all the enzyme treatments had higher dry matter digestibility in the in situ study. Consistent with the in vitro batch culture result, protease inclusion resulted in an increase of 9.9% ruminal dry matter digestibility (versus 9.3% for in vitro dry matter digestibility). Overall, these two techniques were utilized to identify an exogenous enzyme that can potentially increase dry matter and fiber digestibility of modified distillers grains in feedlot cattle.
There were no differences in body weight, average daily gain, dry matter intake, or feed efficiency due to treatment in the backgrounding study. Likewise no differences were observed in body weight, average daily gain, dry matter intake, or feed efficiency in the finishing study.
It is interesting that while the both in vitro and in situ digestibility was increased due the use of exogenous enzymes no differences were found in either the finishing or backgrounding studies in animal performance. Certainly the limited amount of experimental power in the feeding studies may have influenced these findings. The combined results of the laboratory and production studies indicate that further research would be needed to understand the impacts of exogenous enzymes on feed efficiency.