Agriculture and Agri-Food Canada, Lethbridge, Alberta, Canada.
J Anim Sci. 2012 Aug;90(8):2727-32. doi: 10.2527/jas.2011-4681. Epub 2012 Mar 9.
An experiment was conducted to determine whether using ruminally cannulated cattle affects the estimate of enteric methane (CH(4)) emissions when using the sulfur hexafluoride (SF(6)) tracer technique with samples taken from a head canister. Eleven beef cattle were surgically fitted with several types of ruminal cannula (2C, 3C, 3C+washer, 9C; Bar Diamond, Parma, ID). The 2C and 3C models (outer and inner flanges with opposite curvature) had medium to high leakage, whereas the 9C models (outer and inner flanges with the same curvature) provided minimum to moderate leakage of gas. A total of 48 cow-day measurements were conducted. For each animal, a permeation tube containing sulfur hexafluoride (SF(6)) was placed in the rumen, and a sample of air from around the nose and mouth was drawn through tubing into an evacuated canister (head canister). A second sample of air was collected from outside the rumen near the cannula into another canister (cannula canister). Background concentrations were also monitored. The methane (CH(4)) emission was estimated from the daily CH(4) and SF(6) concentrations in the head canister (uncorrected). The permeation SF(6) release rate was then partitioned based on the proportion of the SF(6) concentration measured in the head vs. the cannula canister. The CH(4) emissions at each site were calculated using the two release rates and the two CH(4):SF(6) concentration ratios. The head and cannula emissions were summed to obtain the total emission (corrected). The difference (corrected - uncorrected) in CH4 emission was attributed to the differences in CH(4):SF(6) ratio at the 2 exit locations. The proportions of CH(4) and SF(6) recovered at the head were greater (P < 0.001) for the 9C cannulas (64% and 66%) compared with the other cannulas, which were similar (P > 0.05; 2C, 6% and 4%; 3C, 17% and 15%; 3C+washer, 19% and 14%). Uncorrected CH(4) emissions were ± 10% of corrected emissions for 53% of the cow-day measurements. Only when more than 80% of the SF(6) escaped via the rumen did the difference between the uncorrected and corrected CH(4) emissions exceed 20%. We concluded that using cannulated cattle introduces more variability into the SF(6) technique used with a head canister, a technique that is already highly variable. Thus, use of cannulated animals is not recommended when using the SF(6) technique with head canister. However, if cannulated cattle are used, the cannulas need to be tight-fitting to minimize leakage, and large animal numbers are needed to overcome the additional variability.
进行了一项实验，以确定在使用头部收集器时，使用六氟化硫（SF6）示踪技术，使用瘤胃插管的反刍动物是否会影响肠道甲烷（CH4）排放的估计值。给 11 头肉牛进行了手术，使用了几种类型的瘤胃插管（2C、3C、3C+垫圈、9C；Bar Diamond，Parma，ID）。2C 和 3C 模型（具有相反曲率的外凸缘和内凸缘）泄漏量中等偏高，而 9C 模型（具有相同曲率的外凸缘和内凸缘）的气体泄漏量最小或中等。总共进行了 48 次奶牛日测量。对于每头动物，将一个装有六氟化硫（SF6）的渗透管放置在瘤胃中，并通过管道将口鼻周围的空气样本吸入抽空的收集器（头部收集器）中。从靠近插管的瘤胃外部收集到另一个收集器（插管收集器）中的第二个空气样本。还监测了背景浓度。甲烷（CH4）排放量是从头部收集器中每天的 CH4 和 SF6 浓度中估算出来的（未校正）。然后，根据在头部和插管收集器中测量的 SF6 浓度的比例，对渗透 SF6 释放率进行了划分。使用两个释放率和两个 CH4：SF6 浓度比计算每个部位的 CH4 排放。将头部和插管排放相加，得出总排放量（校正后）。CH4 排放量的差异（校正后-未校正）归因于两个出口位置的 CH4：SF6 比值的差异。与其他插管相比，9C 插管回收的 CH4（64%）和 SF6（66%）比例更大（P<0.001），而其他插管相似（P>0.05；2C，6%和 4%；3C，17%和 15%；3C+垫圈，19%和 14%）。对于 53%的奶牛日测量，未校正的 CH4 排放量在校正排放量的±10%范围内。只有当超过 80%的 SF6 通过瘤胃逸出时，未校正和校正的 CH4 排放量之间的差异才会超过 20%。我们得出的结论是，使用插管牛会给使用头部收集器的 SF6 技术带来更多的变异性，而该技术已经具有很高的变异性。因此，当使用 SF6 技术与头部收集器时，不建议使用插管动物。但是，如果使用插管牛，则需要使用紧密配合的插管来最小化泄漏，并且需要大量的动物来克服额外的变异性。
