APSS 2013 Proceedings - The University of Sydney

Aust. Poult. Sci. Symp. 2013.....24
f) Environment and disease
Numerous non-nutritive factors can affect bird performance and hence have the potential to
affect the feed intake response of broilers to dietary energy (Applegate, 2012). It is beyond
the scope of this report to examine them in detail, but environmental factors of significance
include temperature, environmental contaminants such as ammonia, housing density, water
and feed availability and lighting programs. Disease challenge and immunological stress are
also important in defining bird response. The nature of these effects is complex but among
the mechanisms of action, partitioning of dietary energy as a result of increased heat
production and confounding effects on feed intake merit mentioning.
IV. RECENT RESEARCH
With the above factors in mind, research was undertaken to investigate the impact of dietary
energy, while attempting to minimize confounding factors (Cho, 2011). Diets were
formulated to contain 11.30, 11.86, 12.42 and 12.97 MJ/kg of ME using practical ingredients
(main ingredients – corn, wheat, barley, soybean meal, canola meal and canola oil), and fed
to Ross x Ross 308 mixed sex broilers housed in litter floor pens. The following aspects of
the experimental design were implemented to reduce confounding influences on broiler
response.
• Ingredient AMEn and apparent ileal amino acid digestibility were determined at 5-6
and 21 d of age in broiler chickens and diets were formulated using age appropriate
values.
• Diets were formulated on a digestible amino acid basis with ideal protein balance.
• Diets were formulated to maintain a constant ratio between the ether extract content
and AMEn of the diets.
• Diets were pelleted and fed in crumble or pellet form. Crumble and pellet quality, as
assessed by sieving (particle size) and pellet quality index procedures, demonstrated
minor differences among diets. To reduce the impact of ingredients on pellet quality,
pellet binders were added to the diets.
• Exogenous enzymes were used to negate the impact of soluble fibre found in wheat
and barley.
• Environmental conditions (temperature, ventilation) were optimized or specified (e.g.
space allocation).
• Anti-coccidial agents and growth promotants were used to minimize subclinical and
clinical disease.
In the first experiment, all diets were formulated to contain the digestible amino acid
requirements outlined by Aviagen (2007). The four levels of energy were fed from 0, 10 or
26 d of age until trial end at 35 d. Body weight and feed intake were monitored every 5 d for
the length of the trial. With minor exceptions, dietary energy did not affect feed intake
regardless of when treatments were initiated. Body weight gain increased and feed to gain
ratio (mortality corrected) decreased with dietary energy with significant effects most often
found during the starter and grower phases. The results demonstrate that this strain of broilers
did not increase feed intake to maintain the same energy intake. Effects of growth rate and
feed efficiency were similar to previous research but not to the same degree.
Because the levels of digestible amino acids in the first trial were relatively high, it
was of interest to examine the interaction of dietary energy with lower levels of dietary amino
acids. The second trial used the same ingredients and energy treatment levels, but these were
fed in combination with three levels of amino acid supplementation that approximated 90, 80
and 70% of Aviagen (2007) recommendations. Significant interactions were found for most
response criteria assessed. At the highest level of dietary amino acids, body weight and
111