The influence of microbial phytase on the ileal amino acid digestibilities in three
cereals (corn, sorghum, and wheat), four oilseed meals (soybean meal, canola meal,
cottonseed meal, and sunflower meal) and two cereal by-products (wheat middlings and
rice polishings) was determined using 5-wk-old broilers. Supplementation of microbial
phytase (1,200 FTU/kg) improved (P < 0.001 to 0.10) the digestibilities of protein
and amino acids in all feedstuffs, but the magnitude of response varied depending
on the feedstuff and the amino acid considered. Mean digestibility of the 15 amino
acids in the feedstuffs without and with phytase were: corn, 78.0 and 80.4%; sorghum,
74.7 and 79.4%; wheat, 77.7 and 84.6%; soybean meal, 82.2 and 85.5%; canola meal,
78.7 and 80.7%; cottonseed meal, 70.8 and 74.2%; sunflower meal, 76.7 and 80.2%; wheat
middlings, 70.8 and 73.4%; and rice polishings 62.1 and 66.9%, respectively. When
individual amino acids were considered, the increments in digestibility were relatively
higher for threonine and valine. This effect was consistent across all feedstuffs.
The observed variations in response among feedstuffs were influenced by the inherent
protein digestibility, but not by dietary phytic acid concentration. No correlations
were determined between the dietary concentrations of phytic acid and phytase responses
in terms of protein digestibility (r = 0.20; P > 0.31) and mean amino acid digestibility
(r = 0.12; P > 0.51); however a significant negative correlation was observed between
inherent protein digestibility and phytase responses in protein digestibility (r =
-0.42; P < 0.03). It appears that solubilities of phytate salts and protein, and their
influence on the degree of phytate-protein complexing in different feedstuffs, may
be more relevant than total phytic acid concentrations. Interestingly, dietary phytic
acid concentrations were negatively correlated with inherent protein (r = -0.81; P
< 0.001) and mean amino acid (r = -0.85; P < 0.001) digestibilities of the feedstuffs
evaluated in this study.