APSS 2013 Proceedings - The University of Sydney

Aust. Poult. Sci. Symp. 2013.....24
II. MATERIALS AND METHODS
All experimental procedures in this study were conducted in accordance with the University
of Sydney Animal Ethics Committee. A total of 720 day old male Ross 308 chicks were
obtained from a commercial hatchery (Baiada Poultry Pty Ltd, Marsden Park, NSW) and
randomly allocated to cages. Birds were maintained in an environmentally controlled room
set at 31 °C for the first five days and this was reduced by 0.5 °C per day until 24 °C (day
21). The photoperiod was 23h:1h (light:dark) for the first five days and then 18h:6h
(light:dark) thereafter.
For the first 7 days, all birds were fed a standard commercial broiler starter diet which
provided 11.8 MJ/kg AME, 228g/kg CP, 8.8 g/kg Ca and 4.4 g/kg avP (Vella Stock Feeds,
Plumpton NSW). On day 7, all birds were individually weighed, wing tagged and randomly
allocated to one of 15 dietary treatments in a completely randomised design. Diets were fed
as a mash based on corn and soybean meal and were formulated to be nutritionally adequate
except for total Ca and avP. Diets were clustered around three total Ca + avP densities of 12,
13.5 and 15 g/kg with five varying ratios of total Ca:avP (4:1, 2.75:1, 2:1 and 1.14:1) within
each density. To calculate the apparent ileal digestibility (AID) coefficients for crude protein
(CP), energy and minerals, an indigestible marker (Celite 281, Filchem Australia Pty Ltd,
Castle Hill, NSW, Australia) was added to diets at a concentration of 20 g/kg. Treatments
were replicated five times with eight birds per replicate cage. Feed intake and individual
body weight were recorded weekly. Ileal digesta samples were collected from individual
birds on day 28 of the study according to the procedures of Ravindran et al. (2005). Samples
were frozen at -20 °C and freeze dried thereafter.
The gross energy (GE) of diets and excreta were determined using a Parr 1281
adiabatic bomb calorimeter (Parr Instrument Company, Moline, IL, USA) that was
standardised with benzoic acid. Nitrogen concentration of samples was determined by the
Dumas method using a FP-428 nitrogen analyser (LECO ® Corporation, St. Joseph, MI, USA)
as described by Sweeny (1989). Samples were wet acid digested using nitric acid and
hydrogen peroxide prior to the determination of mineral concentration by inductively
Coupled Plasma-Optical Emission Spectroscopy using a Perkin Elmer OPTIMA 7300 (Perkin
Elmer Inc, Waltham, MA, USA) (Peters et al., 2003). The acid insoluble ash component of
dried diets and ileal digesta samples were determined according to the method of Siriwan et
al. (1993).
Performance data were surface mapped using the Thin Plate Spline procedure of the
fields package (R Development Core Team, 2011). Treatments are represented as dots
overlaid on the contour plots. Interrogation of the data was performed using a quadratic
function. Treatment differences were considered significant at P < 0.05.
III. RESULTS AND DISCUSSION
The interaction between formulated dietary total Ca and avP on feed intake (FI) for the
experimental period are presented in Figure 1. Broilers fed diets with high avP (> 5.0 g/kg)
and high Ca (> 10.0 g/kg Ca) had the greatest FI. Feed intake increased as avP increased
between 2.4-3.0 g/kg but was less influenced above 4.0 g/kg avP where Ca concentration
became dominant. These results are in agreement with Perney et al. (1993) who showed that
feed intake of broilers was reduced at low avP and was increased as greater avP was
provided. Since P is essential for many physiological processes, it may be that when birds
are fed low avP diets reduced consumption of high Ca diets may be a response to restore Ca
and P homeostasis. However, the mechanisms governing this relationship are yet to be
defined.
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