The in situ nylon bag technique (ISNBT) is traditional and necessary for the evaluation of ruminant feed, but there are exists some disunity operation schemes. Therefor, we select one way that varying SS:SA to determine the effects of it on feed degradation in the rumen. Eight Yunnan semi-fine wool sheep fitted with permanent ruminal cannul as were used and the nylon bags containing different sample size with fixed surface area. The results demonstrated that increasing the ratio of sample size to nylon bag area (SS:SA) lowered the effective dry matter (DM) degradability of rye straw. There was no difference in degradability with SS:SA ratios of 12.5 and 20.85 mg/cm² but DM degradability was reduced (P < 0.05) at SS:SA ratios of 29.17 and 37.5 mg/cm². At these higher SS:SA ratios DM degradability was also reduced (P < 0.05), at incubation durations of less than 36 h. A similar picture was obtained for rye straw crude protein (CP) degradability, although the effects of sample size and incubation time were less marked. In the case of the concentrated feedstuff, soybean meal, ruminal degradation was almost complete at 36 h and there was a trend for higher effective degradability (ED) at the lower SS:SA ratios. These results show that with a standard nylon bag with external dimensions of 6 × 10 cm, increasing the amount of sample, thus raising the ratio of sample size to bag surface area (SS:SA ratio) reduces feed degradation. It is recommended that sample size influenced feed degradation in the nylon bag technique and a sample weight of 2.5 g (SS:SA about 20 mg/cm²) should be used for evaluation of roughage and 3 g (SS:SA about 25 mg/cm²) for evaluation of concentrated diets for sheep using this technique.

该原位尼龙袋法（ISNBT）是传统的和必要的反刍动物饲料的评价，但也有一些存在分裂操作方案。因此，我们选择一种改变SS：SA的方法来确定其对瘤胃饲料降解的影响。使用八只装有永久性瘤胃导管的云南半细羊毛羊，以及装有不同样品大小且表面积固定的尼龙袋。结果表明，增加样品尺寸与尼龙袋面积之比（SS：SA）会降低黑麦秸秆的有效干物质（DM）降解能力。SS：SA比率为12.5和20.85 mg / cm ^2时，降解性没有差异，但 SS：SA比率为29.17和37.5 mg / cm ^2时，DM的降解性降低了（P <0.05）。²。在这些较高的SS：SA比值下，DM的可降解性也降低了（P <0.05），孵育时间少于36小时。尽管样品量和孵育时间的影响不太明显，但黑麦秸秆粗蛋白（CP）的可降解性得到了相似的图像。在浓缩饲料豆粕的情况下，瘤胃降解在36 h几乎完全完成，并且在较低的SS：SA比下存在较高的有效降解率（ED）的趋势。这些结果表明，使用外部尺寸为6×10 cm的标准尼龙袋，可以增加样品量，从而提高样品尺寸与袋表面积的比率（SS：SA比率）可以减少饲料降解。建议在尼龙袋技术中，样品大小影响进料降解，样品重量为2.5 g（SS：SA约为20 mg / cm ²）用于评估粗饲料，并使用此技术将3 g（SS：SA约为25 mg / cm ²）用于评估绵羊的浓缩日粮。