APSS 2013 Proceedings - The University of Sydney

Aust. Poult. Sci. Symp. 2013.....24
ARE WE TURNING CHICKENS INTO COWS: HOW MUCH GRASS DO FREE RANGE
BROILERS EAT?
M. SINGH 1 , T. DURALI 1 , T. WALKER 2 and A.J. COWIESON 1
Summary
Fourteen hundred and forty as hatched Cobb 500 broilers were divided equally among four
experimental treatments in a 2 x 2 factorial design, involving conventional or free range
production systems and diets with and without in feed antibiotics. Alkane concentrations in
the litter were measured and compared with alkane profiles of the intake components (grass,
diet pellets and woodchip) in order to estimate total grass intake from the range area. Grass
consumption was estimated to be 3.72-4.24 % of total “as fed” intake. Considering the
number of hours the birds spent on the range and the average feed intake from d21-42, this
equates to 1.55-1.78 grams of grass per bird per hour of range access in this study. Taking
into account grass consumption, range access resulted in an increase in feed intake by 4.1%
(P < 0.01) and FCR by 9-11 points (P = 0.082). It can be concluded that broilers reared under
free-range conditions eat a substantial quantity of grass. Under some circumstances this may
be advantageous, reducing the consumption of expensive pelleted feed. However, the nutrient
profile of grass is not complementary to the formulated ration and its consumption is likely to
lead to an array of nutritional and physiological changes for the bird. Further work is required
to explore the nutritional and health consequences of grass consumption for free-range
broilers, particularly considering energy, amino acid and mineral balance and the effect on
gastrointestinal physiology, immunology and microbiology.
I. INTRODUCTION
Free-range broilers and layers are less efficient converters of feed into saleable meat and eggs
and generally have higher mortality than conventionally-reared poultry. In broilers, the
performance gap has been quantified as a 10-12 point increase in FCR and a 2-3% increase
in mortality in free-range compared with conventionally-reared birds (Durali et al., 2012).
This increase in FCR, however, may still be under represented considering free range birds
also have access to supplementary feed sources on range. Although it has been established by
observation studies that chickens eat grass while on range (Glatz et al., 2005, Miao et al.,
2005), there have been minimal attempts to quantify the amount of grass consumed and its
effect on performance and digestibility in birds. Some of the methods that have been used so
far are by measuring reduction in sward height (Elbe et al., 2004), or comparing herbage
mass in areas grazed by hens to an area from which they have been excluded (Jondreville et
al. 2011). Other methods involve invasive procedures such as analysis of crop, gizzard and
faecal contents which cannot be repeated for individual birds (Antell and Ciszuk 2006;
Jondreville et al. 2011; Milby; 1961; Takahashi et al. 2006). One of the most suitable
methods is to use the n-alkanes (Hatt et al. 2001; Ordakowski et al. 2001; Premaratne et al.
2005). So far there have been very few attempts to use this methodology in birds. The first
reported study on use of alkanes in chickens was conducted by Hameleers et al (1996), who
were able to determine their faecal recovery. In another study, alkane analysis was used to
study intake and nutrient digestibility in pigeons (Hatt et al. 2001). Recently, soil and herbage
intake was measured for free range layers using this methodology to evaluate the impact of
nutrient restriction on ingestion (Jondreville et al. 2011). If grass consumption can be
1 Poultry Research Foundation, University of Sydney, Camden NSW 2570 Australia.
2 Poultry CRC, University of New England, Armidale NSW 2351 Australia.
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