Methane (CH4) production from beef cattle occurs through a natural digestive process called enteric fermentation. This has increasingly become an area of focus due to environmental and efficiency concerns. There are several techniques to quantify gas fluxes from beef cattle such as an open circuit gas quantification system (OCGQS). The GreenFeed (C-Lock, Inc.) is an OCGQS, which has been validated in previous literature, that is capable of quantifying CH4, carbon dioxide (CO2), and oxygen (O2) from grazing beef cattle. However, few studies have reported the minimum number of spot samples to quantify gas fluxes from an individual animal, particularly in a grazing environment. No recommendations have been made to evaluate the number of spot samples for the calculation of metabolic heat production, using the gas fluxes quantified by an OCGQS. A minimum of 100 spot samples each were collected from 17 grazing animals using an OCGQS. The mean gas fluxes were computed starting from the first 10 visits (forward) and increasing by increments of 10 until 100 visits was reached and also from visit 100 moving back in time in increments of 10 (reverse). Mean gas fluxes were used to calculate individual animal metabolic heat production for each interval with both the forward and reverse approach. Pearson and Spearman correlations were computed between the full 100 visits and each shortened visit interval. Mean forward and reverse gas fluxes and metabolic heat production were also computed starting at 30 visits and increasing by 2 until 40 visits and vice versa. The minimum number of spot samples was determined when correlations with the full 100 visits were greater than 0.95. The minimum number of spot samples needed for accurate quantification of CH4, CO2, O2, and metabolic heat production were 38, 40, 40, and 36, respectively. Simultaneous collection of gas fluxes for the calculation of metabolic heat production would require at least 40 spot samples given the recommendations for gas flux components. Animals had an average of 1.2 visits/day to the OCGQS in this study. Therefore, animals met the required number of spot samples for quantification of metabolic heat production, CH4, CO2, and O2 in 29.5 ± 8.7, 30.5 ± 9.1, 31.8 ± 9.2, and 31.8 ± 9.2 d, respectively. There was large variation in the number of days needed to achieve the recommended number of spot samples. For this reason, protocols for the OCGQS should be based on the total number of spot samples, rather than a test duration. These recommendations can be applied to grazing cattle that typically have more infrequent visits. More research is needed to establish if the minimum number of spot samples would be fewer if animals have more frequent visits, although this is difficult in grazing settings.

中文翻译：

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2 使用 GreenFeed 系统放牧肉牛时所需的点样数量

肉牛通过称为肠道发酵的自然消化过程产生甲烷 (CH4)。由于环境和效率问题，这已日益成为人们关注的领域。有多种技术可以量化肉牛的气体通量，例如开路气体量化系统 (OCGQS)。GreenFeed (C-Lock, Inc.) 是一种 OCGQS，已在之前的文献中得到验证，能够量化放牧肉牛的 CH4、二氧化碳 (CO2) 和氧气 (O2)。然而，很少有研究报告量化单个动物气体通量的最低数量的点样本，特别是在放牧环境中。尚未提出使用 OCGQS 量化的气体通量来评估用于计算代谢产热的点样数量的建议。使用 OCGQS 从 17 只放牧动物身上采集了至少 100 个点样。平均气体通量是从前 10 次访问（正向）开始计算的，并以 10 为增量增加，直到达到 100 次访问，并且还从访问 100 次开始以 10 为增量向后移动（反向）。平均气体通量用于通过正向和反向方法计算每个时间间隔的个体动物代谢热产生。计算完整 100 次访问和每次缩短的访问间隔之间的 Pearson 和 Spearman 相关性。还计算了平均正向和反向气体通量以及代谢产热，从 30 次访问开始，增加 2 次直至 40 次访问，反之亦然。当与完整 100 次访问的相关性大于 0.95 时，确定现场样本的最小数量。准确定量 CH4、CO2、O2 和代谢产热所需的最少点样数量分别为 38、40、40 和 36。考虑到气体通量成分的建议，同时收集气体通量以计算代谢热产生将需要至少 40 个点样本。在本研究中，动物平均每天访问 OCGQS 1.2 次。因此，动物分别在 29.5 ± 8.7、30.5 ± 9.1、31.8 ± 9.2 和 31.8 ± 9.2 天内满足了代谢产热、CH4、CO2 和 O2 定量所需的点样数量。达到建议的现场样品数量所需的天数存在很大差异。因此，OCGQS 协议应基于现场样本总数，而不是测试持续时间。这些建议可适用于通常访问频率较低的放牧牛。需要更多的研究来确定如果动物更频繁地访问，最低点样本数量是否会更少，尽管这在放牧环境中很困难。