I. INTRODUCTION
The AgriFutures Australia Chicken Meat Program funds research, development and extension activities for the benefit of the Australian chicken meat industry. Through the process of reviewing the 5-year strategic plan (RIRDC, 2014), the objectives were adjusted to align each objective with a stage of chicken meat production. This included the consolidation of all research related to the live chicken under a single objective, essentially acknowledging that the health, welfare, environmental and nutritional components of raising chickens are intricately linked. To this end, the aim is to invest in projects that are multi-faceted, while encouraging stronger collaborations between researchers and research institutes. Four projects with different nutritional focuses were contracted in 2019 and drawn together under the banner of the ‘Nutrition Program of Research’. The projects are separate; however, their milestone schedules, experimental design and outcomes are aligned, and overseen by a single industry steering committee.
II. PROJECT SUMMARIES
a) Optimising amino acid profiles and energy in reduced-protein diets.
In the literature, only two studies by Taherkhani et al. (2005, 2008) and one by Salehifar et al. (2012) have compared ‘ideal protein ratios’ in meat chickens. While these feeding studies resulted in poor overall bird performance, all three studies report tangible differences in growth performance in response to the ideal protein ratios of diets evaluated. The aim of this project is to investigate the amino acid requirements and validate ideal protein ratios of modern genotype meat chickens, in the context of reduced-protein diets containing high inclusion levels of crystalline amino acids, in experiments in which birds approach or surpass their genetic potential. It focuses on the constraints for least-cost feed formulation including ideal protein ratios, 4th limiting amino acid and energy requirements.
This project will include in vivo studies from 1-42 days post-hatch using wheat-based diets with 100 g/kg whole grain for grower diets and 150 g/kg whole grain for finisher diets. The relative importance of each supplemented amino acid will also be ranked. Further, excess fat deposition in meat chickens offered reduced-protein diets is a real challenge. Less energy is required to support intestinal absorption of crystalline amino acids (which are supplemented in the diet), compared to energy required for intestinal absorption of amino acids extracted from ingredients in the diet. Consequently, surplus dietary energy is deposited as fat. Therefore, the energy densities of reduced-protein diets could potentially be reduced without compromising performance. This could represent a substantial saving in feed cost.
b) Impact of non-starch polysaccharides in meat chicken diets.
Despite extensive evidence demonstrating the influence of NSPs on a range of processes involved in intestinal health and digestive efficacy (Amerah et al., 2009; Hetland and Svihus, 2001; Jørgensen et al., 1996; Bedford, 1996; Mayne et al., 2007), most commercial nutritionists do not formulate to NSP levels. This is likely because the optimum range in soluble and insoluble NSP level that nutritionists should be aiming for when formulating feed has yet to be defined, from both economic and bird health and welfare viewpoints. This project aims to provide the industry with these values, based on analysis of current commercial diets and research trials.
Furthermore, xylanase (an NSP-ase) supplementation is widely used in poultry diets to break down NSPs in the diet, but there is evidence to suggest that a combination of different NSP-ases may supply further benefits, partially by producing a range of different prebiotic oligosaccharides (Lee et al. 2017; Morgan et al. 2017). Consequently, this project will use both in vitro techniques and in vivo trials to explore the comparative advantages and disadvantagesof NSP-ase cocktails, from both an economic and practical viewpoint, in diets based on wheat or sorghum which have different levels of soluble NSP. Ultimately, the outcome of this project will be improved formulation of diets containing sorghum or wheat.
c) Branched-chain amino acids in wheat-based, crude protein-reduced diets.
Moderate reductions in dietary crude protein (e.g. from 210 g/kg to 175 g/kg) can be achieved without negatively impacting meat chicken growth rate. However, further reductions often have negative implications for feed conversion and increase fat deposition. While numerous factors contribute to this problem, this project aims to specifically investigate the involvement of the branched-chain amino acids (isoleucine, leucine and valine).
Reviews of leucine and branched chain amino acids provide further background to this issue (Li et al. 2011; Zhang et al. 2017). Leucine, in particular, has the potential to increase protein synthesis (Deng et al., 2014) and reduce fat deposition (Duan et al., 2015), and very high levels of leucine in meat chicken diets have produced positive responses (Yamazaki et al. 2006; Chen et al. 2016). Therefore, leucine is suspected to be critical to the implementation of reduced-CP meat chicken diets. A key objective for this project is to determine whether there are benefits to a higher inclusion of leucine in meat chicken diets, and to what extent the benefits rely on increases in leucine being coupled with increases in isoleucine and valine.
Currently, diets based on wheat or sorghum are formulated on the basis of digestible amino acids relative to lysine. However, this project may demonstrate that higher leucine levels are advantageous and that ratios of isoleucine plus valine to leucine will need to be taken into consideration in future.
d) The response of meat chickens to insoluble fibre and exogenous enzymes in reduced-protein diets.
The use of insoluble fibre in poultry diets has been applied in recent years to improve nutrient digestibility and improve intestinal development and bird health (Kheravii et al., 2018a, 2018b, 2018c). The inclusion of insoluble fibre in the diet improves digestion and the function of the intestines by stimulating the gizzard and increasing the retention time of digesta (Svihus, 2011).
Insoluble fibre also improves the secretion of digestive proteases and ultimately results in drier excreta (and therefore fewer wet litter problems). This project aims to determine whether improvements to bird outcomes on reduced-CP diets can be realised through the supplementation of different sources of insoluble fibre and protease in the diet.
This project will include in vivo studies from 1-42 days post -hatch to compare wheat and sorghum reduced-CP diets supplemented with added fibre and protease to examine the extent to which insoluble fibre can improve bird performance, and whether addition of protease is necessary, in the context of reduce-CP diets.
IV. DISCUSSION
Outcomes of these projects will be regularly provided through updates via various AgriFutures Australia publications and industry extension activities. There is the potential that the Program will be expanded to include other relevant components as they are raised as priorities by industry and/or identified by researchers.
Presented at the 30th Annual Australian Poultry Science Symposium 2020. For information on the next edition, click here.
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