Abstract

Increasing greenhouse gas (GHG) emissions from anthropogenic activities have contributed to global warming and consequently to climate change. Among all sources of emissions, the agricultural sector accounts for just under a quarter, mainly because of the intensification of food production systems necessary to supply the growing demand of the population. As ruminal fermentation is the largest source of methane emission in the livestock industry, emission by cattle has become the focus of studies. The aim of this study was to evaluate enteric methane emission and emission intensities of Nellore cattle at different ages submitted to levels of intensification of the grazing system. Twenty-four animals per cycle (age of 21.8 and 13.1 mo in cycles 1 and 2, respectively) were randomly distributed across different grazing systems: irrigated pasture with a high stocking rate (IHS), dryland pasture with a high stocking rate (DHS), recovering dryland pasture with a moderate stocking rate (DMS), and degraded pasture with a low stocking rate (DP). Methane emission was measured using the sulfur hexafluoride technique in each season of the cycle. Intensive systems provided higher yields of good-quality forage as well as superior animal performance when compared with DP. Methane yields were different between seasons and cycles. Methane emissions per average daily weight gain and dry matter digestible intake were different between treatments. Differences in the results were observed when they were analyzed per hectare, with the highest gain yield (P = 0.0134), stocking rate, weight gain, carcass production, and total methane emission (P < 0.0001) being found for the intensive systems. There were no differences in emissions per weight gain or carcass production between production systems, while a difference was observed between cycles (P = 0.0189 and P = 0.0255, respectively), resulting in lower emission intensities for younger animals. We conclude that more intensive systems resulted in a higher kilograms production of carcass per hectare; however, animals at 19 mo of age raised in the IHS and DMS systems had a lower emission intensity in kilogram of CO₂-eq. per kilogram of carcass. Moderate intensification (DMS) using animals at about 19 mo of age might be an effective strategy to mitigate GHG emissions from Brazilian tropical pastures. Further studies are needed to understand the relationship between increasing productivity and decreasing environmental impacts, especially methane emission from ruminants.

中文翻译：

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肉牛生产中的牧场集约化会影响甲烷排放强度。

摘要

增加温室气体 ( GHG)) 人为活动的排放导致全球变暖，进而导致气候变化。在所有排放源中，农业部门占不到四分之一，这主要是因为为满足人口不断增长的需求所必需的粮食生产系统的集约化。由于瘤胃发酵是畜牧业甲烷排放的最大来源，牛的排放成为研究的重点。本研究的目的是评估不同年龄 Nellore 牛在放牧系统集约化水平下的肠道甲烷排放和排放强度。每个周期 24 只动物（周期 1 和周期 2 的年龄分别为 21.8 和 13.1 个月）随机分布在不同的放牧系统中：高放养率的灌溉牧场（IHS )、高放养率 ( DHS ) 旱地牧场、中等放养率 ( DMS )恢复旱地牧场和低放养率 ( DP )退化牧场。在循环的每个季节使用六氟化硫技术测量甲烷排放。与 DP 相比，集约化系统提供了更高的优质草料产量以及优异的动物性能。甲烷产量因季节和周期而异。平均每日体重增加的甲烷排放量和干物质可消化摄入量在处理之间不同。每公顷分析时观察到结果的差异，其中增益产量最高（P= 0.0134)、集约化系统的放养率、体重增加、胴体产量和甲烷排放总量（P < 0.0001）。生产系统之间每增重或屠体产量的排放量没有差异，而在周期之间观察到差异（分别为P = 0.0189 和P = 0.0255），导致年轻动物的排放强度较低。我们得出的结论是，更集约化的系统导致每公顷更高的胴体产量。然而，在 IHS 和 DMS 系统中饲养的 19 个月大的动物的 CO ₂千克排放强度较低-eq. 每公斤胴体。使用大约 19 个月大的动物进行适度集约化 (DMS) 可能是减少巴西热带牧场温室气体排放的有效策略。需要进一步研究以了解提高生产力与减少环境影响之间的关系，尤其是反刍动物的甲烷排放。