Extensively raised beef cattle contribute to the highest levels of enteric methane (CH4) gas emissions among all livestock. Expensive techniques and logistics hinder monitoring of such gas. Therefore, the objective of this study was to use an inexpensive laser methane detector (LMD) apparatus to determine the enteric CH4 levels from a herd of beef cows raised on semi-arid rangelands. A total of 24 cows were selected from Boran and Nguni cows (n = 12 per breed) from two different farms. The parities of the cows were as follows: parity 1 (n = 6), parity 2 (n = 6), parity 3 (n = 6) and parity 4 (n = 6). An observer used a hand-held LMD to measure enteric CH4 emissions plumes during the late afternoon hours when the animals were resting (either standing or lying down). Point measurements (expressed in ppm/m) were taken for six consecutive days and repeated once after every three months. The ratio of CH4 output per kilogramme DMI was not different in within-breed and between-breed in both seasons. Generally, the dry season recorded the highest CH4 output per kilogramme of live weight of cow. For example, Boran cows in parity 2 produced the highest output of 1.0 ± 0.04 g CH4 per kilogramme live weight of cow while Nguni cows in parities 1, 2 and 4 each produced 0.9 ± 0.04 g CH4 per kilogramme live weight of cow in the dry season. All the animals maintained optimal body condition scores in both seasons (ranging between the lowest of 3.2 ± 0.01 and the highest of 3.4 ± 0.01). Based on the results of the study, it is concluded that cows from both herds produced higher CH4 per kilogramme live weight of cow in the dry season while maintaining optimal body condition scores in both seasons.

中文翻译：

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在广阔的干旱牧场上饲养的精选肉牛群产生的肠甲烷

在所有牲畜中，大量饲养的肉牛导致最高的肠内甲烷（CH4）气体排放。昂贵的技术和物流阻碍了此类气体的监测。因此，本研究的目的是使用廉价的激光甲烷检测器（LMD）来确定半干旱牧场上饲养的一头肉牛的肠CH4水平。从两个不同农场的Boran和Nguni母牛中选出了24头母牛（每个品种n = 12）。母牛的奇偶校验如下：奇偶校验1（n = 6），奇偶校验2（n = 6），奇偶校验3（n = 6）和奇偶校验4（n = 6）。在动物休息（站立或躺下）的午后时间，观察员使用手持式LMD测量肠内CH4排放羽流。连续六天进行点测量（以ppm / m表示），每三个月重复一次。在两个季节的品种内和品种间，每公斤DMI的CH4产出比没有差异。通常，旱季记录的每公斤活牛体重CH4产量最高。例如，平价2的Boran奶牛的最高产量为每公斤牛活重1.0±0.04 g CH4，而平价1、2和4的Nguni牛在干燥状态下的每公斤活重为0.9±0.04 g CH4季节。所有动物在两个季节中均保持最佳的身体状况评分（介于最低3.2±0.01和最高3.4±0.01之间）。根据研究结果，