In Exp. 1, graded levels of xylanase (8,000, 16,000 and 24,000 BXU/kg) were supplemented to diets containing 15% each of corn DDGS, corn germ meal, and wheat middlings (with all diets containing 250 FTU/kg of phytase supplementation) for a balance trial with pigs weighing 75-80 kg to compare apparent total tract digestibility (ATTD) of the diets. A positive effect of xylanase supplementation was demonstrated in hemicellulose digestibility with the highest supplementation (24,000 BXU/kg of xylanase) indicating that degradation of insoluble fiber (i.e., arabinoxylan) by the non-starch polysaccharide degrading enzyme supplementation had occurred. This was then associated with a slight increase of energy retention and an energy uplift at approximately 33 kcal/kg for pigs fed that enzyme level.
In Exp. 2, graded levels of phytase (500, 1,000, and 2,000 FTU/kg) were supplemented to grower-finisher diets containing 13% of corn germ meal and 15% each of corn DDGS and wheat middlings that also contained no xylanase or added xylanase (24,000 BXU/kg) to compare growth performance, carcass characteristics, and ATTD (for pigs weighing 110-120 kg). All pigs had free access to feed from 25 to 125 kg body weight. Phytase supplementation clearly increased growth rate and feed efficiency as well as carcass leanness and lean gain, and also increased P digestibility with improvements in the ATTD of dry matter, fat, and fibrous components as supplementation levels increased resulting in an energy uplift of about 44 kcal/kg. However, there was no effect of xylanase supplementation on growth performance, carcass characteristics, and nutrient digestibility which was different from Exp. 1 suggesting that the efficacy of xylanase in pig diets may be dependent on the content of substrates, duration of feeding, feeding regime, and pig age.
In summary, xylanase supplementation can improve fiber digestibility in corn-based diets containing a large amount of byproducts. Also, phytase supplementation can improve digestibility of P and fiber as well as growth performance and carcass leanness. However, when swine producers use xylanase in pig diet, many factors affecting xylanase efficacy (e.g., amount and type of byproducts, age of pig, number of days of supplementation) should be considered to obtain maximized responses.
• 1. Xylanase supplementation can improve fiber digestibility in corn-based high fiber diets. However, the xylanase response in growing pigs may vary depending on, supplementation level, feeding regime, feeding duration, and age or body weight of pig.
• 2. Phytase supplementation in P-adequate diets can improve growth rate, feed efficiency and carcass leanness as well as digestibility of dry matter, fat, and fiber components in addition to the expected improvement in ATTD of P.
• 3. No significant interaction between xylanase and phytase supplementation on growth performance, carcass characteristics, and nutrient digestibility were observed. However, there may be a potential interaction between these enzymes in feed efficiency in which xylanase supplementation in the phytase-supplemented diets had a slight improvement in feed efficiency over the response with only phytase supplementation.
• 4. Xylanase supplementation to the high by-products diets could uplift the energy release about 33 kcal/kg under limit-fed condition whereas phytase supplementation to the high by-products diets could uplift the energy release about 44 kcal/kg.
