Breeding for efficiency in the broiler chicken: A review

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.

Differences in muscle histidine‐containing dipeptides in broilers

“…the synthesis of non‐proteinogenic dipeptides. Selection for fast growth and high feed efficiency has been very successful and has resulted in large decreases in the number of days and the amount of feed required to reach market slaughter weight . Effects of this selection on important body composition traits (e.g.…”

“…breast yield, body fatness) are more variable; however, it has in general resulted in leaner animals with higher breast yield, which also depends on the weight of these traits in the composite breeding goals. According to the review by Tallentire et al ., there is some indication that higher protein deposition has been achieved through selection for efficient growth by lowering protein breakdown; however, net protein turnover seems not to be affected. In contrast, Dransfield and Sosnicki showed that protein turnover is higher in muscles of slow‐growing birds.…”

“…Selection for fast growth and high feed efficiency has been very successful and has resulted in large decreases in the number of days and the amount of feed required to reach market slaughter weight. 20 Effects of this selection on important body composition traits (e.g. breast yield, body fatness) are more variable; however, it has in general resulted in leaner animals with higher breast yield, which also depends on the weight of these traits in the composite breeding goals.…”

Differential immune response to Eimeria maxima infection in fast‐ and slow‐growing broiler genotypes

“…This was highlighted by Swaggerty et al who reported that chicken genotypes which produce high levels of IL‐6, CXCLi2 and CCLi2 in response to Eimeria tenella infection have reduced lesional scores in the caeca. In Europe, although fast‐growing broiler genotypes are commonly used in poultry production, the use of slower‐growing genotypes is beginning to emerge . However, nothing has been reported regarding immune phenotypes in fast and slow growing broilers in response to Eimeria infection, which may determine whether fast or slow growing broilers may differ in their underlying resistance to Eimeria .…”

“…In Europe, although fast-growing broiler genotypes are commonly used in poultry production, the use of slower-growing genotypes is beginning to emerge. [19][20][21] However, nothing has been reported regarding immune phenotypes in fast and slow growing broilers in response to Eimeria infection, which may determine whether fast or slow growing broilers may differ in their underlying resistance to Eimeria.…”