Potential climate performance of modern fast- and slow-growing broiler genotypes

Genetic selection aiming to improve the feed efficiency is believed to have a significant role in reducing the environmental impacts of livestock production. The aim of this study was to quantify the global warming potential of a wide range of modern fast-growing and slow-growing broiler genotypes under conditions where they are expected to meet their performance objectives set by breeding companies. The global warming potential was estimated for scenarios where the birds were fed on conventional and soy-free diets with different levels of balanced protein. Life cycle assessment approach based on the ISO 14040 standards was used to quantify the greenhouse gas emissions arising from the production. The results show that the fastest-growing genotypes have the lowest global warming potential when achieving their performance objectives, the difference being over 1 kg CO₂e per kg eviscerated carcass, compared to the slowest-growing genotypes. As the faster growth rate reduces the time to reach the slaughter weight (ranging from 38 days to 61 days between the genotypes), up to 13 MJ less energy per bird is lost as heat during the whole growth cycle and therefore less feed is needed. The improvement of feed efficiency is important because the feed-related emissions have a high contribution to the overall greenhouse gas emissions of broilers, ranging from 88 - 92%, when fed with the traditional soya-based diet. Additionally, differences in the body composition also have an effect on the energy consumption of the birds and on the corresponding greenhouse gas emissions. The protein sources in diets have generally high greenhouse gas intensity, and therefore reducing the protein concentration of the diet may, in some cases, reduce the global warming potential. On the other hand, this effect is limited by the adverse effect on the growth rate of the birds. In cases where protein sources with lower emission intensity can be used, the reduction of the protein concentration in the diet does not bring any further improvement to the climate performance of broiler production. In contrast, in such cases, low protein diets increase the emissions as a result of the longer growth cycle. In conclusion, the differences in Global Warming Potential of modern broiler genotypes are related to the differences in their efficiency of the use of feed energy. This efficiency is dependent on the growth rate of the birds, although the differences in body composition also have some effect.