APSS 2013 Proceedings - The University of Sydney

Aust. Poult. Sci. Symp. 2013.....24
INTERACTION BETWEEN DIETARY PHYTASE, CALCIUM AND DIGESTIBLE
PHOSPHORUS LEVELS ON PERFORMANCE AND TIBIA ASH IN BROILERS
A. SACRANIE 1 , T. VAN GERWE 1 , J. DE LOS MOZOS 1 , A. GUTIERREZ DEL ALAMO 1 ,
A.J. COWIESON 2 and H. ENTING 3
Summary
A broiler study was conducted for 36 days with eight treatment groups in a 2 phytase x 2
calcium (Ca) level x 2 digestible phosphorus (dP) level experimental design. Birds exposed to
diets low in Ca, and standard in dP performed the best while the high Ca treatments induced
negative responses, especially in the first 8 days of experimentation. It was concluded that the
level of dP release from the high phytase inclusion was overestimated, while the higher Ca
levels included in the study impeded phosphorus (P) digestibility and bone development.
I. INTRODUCTION
The global availability of inorganic phosphates is limited; phosphorus (P) is the third most
expensive ingredient after energy and amino acids. Therefore sustainable animal production
requires optimal utilisation of P to reduce the cost of feeding. Over two thirds of P in plantbased
feedstuffs is not readily available in poultry as it is bound to phytic acid (PA), which
has been commonly thought to be due to the low levels of endogenous phytase (Bedford,
2000; Woyengo and Nyachoti, 2011). However, recent studies have suggested that this is not
the case, and in fact chickens possess adequate phytase activity in the intestinal mucosa. The
primary issue with phytate digestion is poor substrate solubility in the small intestine due to
cation (mainly Ca) interactions (Maenz and Classen, 1998; Cowieson, et al., 2011b). Calcium
is known to form insoluble complexes with phytate phosphorus (PP), which hinders phytase
activity (Angel, et al., 2002). Therefore, lowering dietary Ca levels can further improve the
effect of exogenous phytase on PP degradation. Recent studies have shown that when adding
phytase (500 FTU/kg), while at the same time lowering Ca in starter diets from 1% to 0.67%
in combination with reduced non-PP (nPP) levels does not impair young bird performance
(Létourneau-Montminy, et al., 2010; Powell, et al., 2011).
The use of exogenous phytase to assist the bird in degrading PP has become common
practice. In recent years, the use of higher levels of exogenous phytase, referred to as super
dosing, has been increasingly promoted as a method to release more PP and to alleviate the
antinutritive effects of phytate per se (Cowieson, et al., 2011b).
In this study, the interaction between dP, Ca and phytase levels was evaluated with
the aim of lowering inclusions of inorganic phosphates by optimising the hydrolysis of PP.
II. MATERIALS AND METHODS
Three thousand two hundred male Ross 308 broiler chickens were randomly distributed
amongst 80 pens, 40 birds per pen, giving 8 treatments with 10 replicates. Each pen, 2.5 x 1.6
m, was fitted with 1 feeder and 4 nipple cup drinkers. Birds had ad libitum access to feed and
water. From 0-3d, birds had 24 hours of light and from then on 18 hours of light and 6 hours
of darkness. At the start of the trial brooding temperature was set to 33°C and then reduced
incrementally to 20°C by 29 days. A description of treatments is shown in Table 1. A 3 phase
1 Poultry Research Centre, Nutreco R&D, Toledo, Spain.
2 Poultry Research Foundation, University of Sydney, Camden, NSW 2570, Australia.
3 Application and Solution Centre, Nutreco, Boxmeer, Netherlands.
19