Abstract
Simple SummaryThe livestock sector is a significant contributor to global greenhouse gas emissions, with cattle representing 62% of CO2 emissions. Genetic selection is a tool that has the potential to reduce emissions from rumen fermentation and can be adopted in grazing and feedlot systems. Therefore, the purpose of this study was to evaluate steers from a new line of the Canchim breed (5/8 Charolais, 3/8 Zebu) derived by genetic selection improvement, and formed and maintained as a closed herd since 1998, in regards to performance, carcass dressing, and enteric methane emissions, when compared with the old line formed and maintained as a closed herd since 1960. Animals from the new line of the Canchim breed should be used for rearing on pasture to obtain greater liveweight gain. However, genetic improvement in Canchim breed does not guarantee animals with lower methane emissions under grazing conditions. For the finishing feedlot phase, increased liveweight gain, improved feed conversion, and a better carcass dressing percentage are obtained using animals from the new line of Canchim breed. The new line also leads to higher daily feed intake and higher daily liveweight gain, but with the same methane emissions per kg of animal liveweight than the other lines.The present study aimed to investigate whether different lines of a composite breed (5/8 Charolais × 3/8 Zebu), formed at different times, and genetically improved, would result in differences in animal performance, enteric methane emissions, and carcass traits. Forty-six Canchim steers (15 months, 280 ± 33 kg liveweight) from three different lines were used: old, new, and their cross. These three breed lines were considered the treatments (arranged in four randomized blocks based on initial liveweight) and were evaluated under grazing and feedlot conditions in relation to the performance and emission of enteric methane. During the grazing period, the new line was found to be superior to the old only in relation to the average daily liveweight gain (0.692 vs. 0.547 kg/day), and with no differences in relation to the cross line (0.692 vs. 0.620). In the feedlot finishing phase, only the average daily liveweight gain was significantly higher in the new line compared to the cross and old line (1.44 vs. 1.32 and 1.23 kg/day). The new and cross lines demonstrated higher dry matter intake when compared to the old line (10.25 and 10.42 vs. 9.11 kg/day), with the crossline animals demonstrating the best feed conversion. The new line showed higher enteric methane emissions compared to the old line (178 vs. 156 g/day). The line had an effect on the carcass dressing of the animals, with greater fat thickness in carcasses from the new and cross lines than the old line (4.4 and 3.8 vs. 3.2 mm). Canchim cattle selected for improved productive performance characteristics does not guarantee animals with lower methane emissions under grazing conditions; while in feedlots, can lead to increased daily feed consumption, and hence, to higher emissions of methane.
Highlights
Livestock farming is a fundamental activity for maintaining the current society
The line of the animals had a significant effect on average daily gain (ADG) (p < 0.001); the animals from the new line presented higher averages than the old line, while the animals belonging to the cross line did not differ from those of the new lines
The superior daily LW gain displayed by the new line during the rearing period was a result of the use of improved bulls to form this line, since feed intake did not differ between the animals of the two lines, as was the case in relation to the cross line
Summary
Livestock farming is a fundamental activity for maintaining the current society. By 2050, the world’s population is expected to reach 9.1 billion people. According to Oliveira Silva et al [2], ruminant animals are the largest cause of agricultural externalities in terms of land use and emissions of greenhouse gas (GHG), such as methane (CH4 ). In 2010, agriculture accounted for 5.5 gigatonnes of carbon dioxide equivalent (GtCO2 eq) of global emissions, with 2.1 GtCO2 eq of this total resulting from of enteric fermentation by these animals [3]. The approach adopted by the Intergovernmental Panel on Climate Change (IPCC) for GHG inventories, while adequate, does not take into account the mitigating options that exist within each activity. For example, have significantly lower emissions when we take into account atmospheric carbon dioxide (CO2 ) that is absorbed by grasses and added to the stock of carbon (C) in the soil [4]. A similar effect occurs when more efficient animals are used [7]
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