Artificial selection of broiler chickens for commercial objectives has been employed at an unprecedented magnitude over the recent decades. Consequently, the number of days, total feed and in turn energy, required to raise a broiler to slaughter weight, have decreased dramatically. Feed provision is the poultry industry's biggest environmental hotspot; hence, understanding the interactions between the birds' genetic change and their energy use efficiency forms the necessary starting point for quantifying and predicting and thereby mitigating the future environmental impact of the poultry sector. This review assesses the consequences of artificial selection on the following traits: digestive efficiency, body composition and utilisation of metabolisable energy for growth and metabolic activity. The main findings were (1) the digestive system has been subjected to much physical change due to selection in the recent decades, but this has not led to any apparent change in digestion efficiency. (2) Both the energy intake per day and the metabolic heat production rate have increased in the recent decades whilst (3) the efficiency of utilising energy for growth has also increased; this is due to an increased growth rate, so that broilers reach slaughter weight more quickly and therefore need to allocate less energy overall to metabolic processes, with the exception of growth. (4) There may have been a reduction in the tendency to waste feed through spillage and carry out energetically expensive behaviors. There is a discrepancy in the literature with regards to the influence of selection on body composition and its contribution to feed efficiency. In this review, two scenarios are demonstrated, whereby body composition either has or has not altered via artificial selection. Understanding the effects of artificial selection on the traits that relate to the feed efficiency of the broilers will contribute towards the reduction of the environmental impacts that arise from such systems.

Modern broiler chickens are a major animal husbandry success story, both in terms of efficient resource utilisation and environmental sustainability. However, continuing artificial selection for both efficiency and rapid growth will be subject to both biological limits and animal welfare concerns. Using a novel analytical energy flow modelling approach, we predict how far such selection can go, given the biological limits of bird energy intake and partitioning of energy. We find that the biological potential for further improvements in efficiency, and hence environmental impact reduction, is minimal relative to past progress already made via artificial selection. An alternative breeding strategy to produce slower-growing birds to meet new welfare standards increases environmental burdens, compared to current birds. This unique analytic approach provides biologically sound guidelines for strategic planning of sustainable broiler production.

This work is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International licence Newcastle University ePrints-eprint.ncl.ac.uk Tallentire CW, Mackenzie SG, Kyriazakis I. Can novel ingredients replace soybeans and reduce the environmental burdens of European livestock systems in the future?.

This work is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International licence Newcastle University ePrints-eprint.ncl.ac.uk Tallentire CW, Mackenzie SG, Kyriazakis I. Environmental impact trade-offs in diet formulation for broiler production systems in the UK and USA.

Purpose There is increasing public concern over standards of farm animal welfare, yet the majority of sustainability studies of livestock have thus far focused only on environmental performance and profitability. Where social analysis has been carried out, there has yet to be a consistent methodology developed that incorporates animal welfare into social life cycle assessment (S-LCA). A framework was developed to assess animal welfare, using conventional broiler chicken meat production in Europe as a case in point. Methods Data were collected on stocking density, mortality, and carcass condemnation rate from conventional chicken meat production systems in Europe. The quantitative risk of each welfare indicator was characterised in accordance with the Social Hotspots Database methodology based on best to worst farm performances, i.e. quartiles of the data collected for each indicator. The overall animal welfare impact was assessed using a weighted sum methodology, which accounted for the level of risk animals were exposed to for each indicator and the animal lifespan. From this, a Social Hotspot Index (SHI) could be calculated for the animal welfare impact associated with the functional unit, which was 1 kg of chicken meat production. The animal welfare impact of four European countries was then compared. Results and discussion The countries assessed displayed a range of values for overall animal welfare impact; the country with the best animal welfare had a SHI for animal welfare impact of 0.14, whilst the worst had a SHI for animal welfare impact of 0.72. Farms that kept more birds per building had an increased overall animal welfare impact. Animal welfare, determined by negative welfare indicators, was worse in more recently established farm buildings due to increased flock size. Conclusions A methodology that incorporates animal welfare indicators into S-LCA was developed that is both scalable and related to welfare assessment frameworks. Although only some specific negative welfare indicators were considered here, the methodology could easily accommodate additional negative indicators and even positive welfare indicators as advancements are made in the understanding of animal welfare. Hence, this study provides a springboard for further development of S-LCA, animal welfare assessment and, ultimately, improved animal welfare in livestock systems.