APSS 2013 Proceedings - The University of Sydney

Aust. Poult. Sci. Symp. 2013.....24
III. ADDITIVE EFFECTS OF PROTEASE AND OTHER DIETARY ENZYMES
Effects of protease on poultry diets do not appear to be completely limited to protein
digestion, but can also affect the digestibility of other nutrients. McAllister (1993), for
example, reported increased digestion of corn starch with the use of a serine protease in a
rumen in vitro model, which the author attributed to the disruption on the protein matrix in
starch granules. Similarly, protein digestibility can also be affected by the presence of other
dietary enzymes. Effects of carbohydrases and phytases on amino acid digestibility have been
demonstrated and appear to involve a reduction of endogenous amino acid losses (Cowieson
et al., 2008; Rutherfurd et al., 2007). It has also been suggested that phytases reduce the
association of phytate and protein in the gizzard and proventriculus, increasing protein
solubility (Yu et al., 2012). However, as effects of proteases and other dietary enzymes are all
dependent on the amount of undigested amino acids present in the digestive tract, increments
in amino acid digestibility from different enzymes cannot be additive. Therefore, the nutrient
contribution from protease and other dietary enzymes in practical diets should not be
determined in isolation.
Romero et al. (2012) conducted a series of studies to better understand the complex
interactions of protease with different dietary ingredients and other enzymes. Two studies
with 432 21-day or 288 42-day-old Ross-308 broiler males evaluated changes on the ileal
energy contribution of substrates in response to xylanase and amylase without, or with
protease in four broiler diets. The studies used a 2 x 2 x 3 factorial arrangement of treatments
with two base grains (corn-soybean-meal; or wheat-soybean-meal diets); two fibrous protein
ingredient levels (with, or without 10% corn-DDGS and 5% canola meal); and three enzyme
levels. At 12 d or 32 d, three enzyme levels were applied: a negative control (NC); NC with
xylanase from T. reesei and amylase from B. licheniformis; or NC with xylanase from T.
reesei, amylase from B. licheniformis, and protease from B. subtilis (Axtra XAP; Danisco
Animal Nutrition, DuPont Industrial Biosciences). At 21 d or 42 d, birds were euthanised;
ileal digesta was collected, pooled per cage, and analysed to determine the apparent
digestibility of energy, starch, fat, and protein. The increment of ileal energy digestibility of
starch, fat, and protein was calculated as the mean change on the coefficient of apparent ileal
digestibility of the enzyme treatment compared to the respective control treatment, and
multiplied by the measured nutrient content in the diet and the assumed gross energy content
of each substrate (starch=4.2 kcal/g; fat=9.4 kcal/g; protein =5.5 kcal/g).
Starch digestibility increased with xylanase/amylase (97.8% at 21 d; 96.6% at 42 d) and
xylanase/amylase/protease (97.9% at 21 d; 97.0% at 42 d) compared to the NC (96.3% at 21
d; 93.4% at 42 d) across diets. There were no differences between xylanase/amylase and
xylanase/amylase/protease on ileal starch digestion. Xylanase/amylase (84.4%) and
xylanase/amylase/protease (85.8%) gradually increased protein digestibility (P < 0.05) at 21 d
(NC=82.7%); but only xylanase/amylase/protease (85.1%) increased protein digestibility
compared to the NC (82.4%) at 42 d. Both xylanase/amylase (83.3%) and
xylanase/amylase/protease (84.0%) increased fat digestibility compared to the NC (80.2%) at
21 d. At 42 d, xylanase/amylase (86.6%) increased fat digestibility compared to NC (86.6%);
and xylanase/amylase/protease (89.4%) further increased fat digestibility compared to
xylanase/amylase.
26