Abstract
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.
Highlights
The contribution of the various biological traits to the improvements made is not well understood, this review provides a more detailed understanding of the interactions between their genetic change and the trends seen in both the energy use efficiency and the heat production rate
The results presented in this review demonstrate the fact that the energy use efficiency of broilers has been increased through artificial selection during the last decades, assuming that the scenario according to which there have been no major changes in the body composition of the birds is valid
The results show that the overall heat production rate (MJ/day) of the birds has increased via genetic selection over the decades, a fact that has previously not been demonstrated as far as the scope of this review could reveal
Summary
Modern chicken breeds are the result of billions of years of evolution by means of natural selection, on which artificial selection for commercial objectives has been applied. The greatest progress made in chicken genetics since their domestication has been witnessed in the latter half of the twentieth century, since the advent of industrial scale agriculture (Schmidt et al 2009). This can be attributed to developments made in quantitative genetics and the success of its commercial application (Siegel and Dunnington 1997). Broiler breeding methods can be summarised in the following steps: at the highest level, the pure-breeding lines are owned and controlled by the breeding companies These lines are subjected to full scale selection programs; it is from these
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