Feeding high-grain diets leads to the release and accumulation of short-chain fatty acids in the rumen. The subsequent prolonged decline in ruminal pH can lead to subacute ruminal acidosis (SARA). Accumulation of short-chain fatty acids can cause proliferation of rumen papillae to increase absorption surface, subsequently leading to a thickening of the rumen mucosa. The aim of this study was to evaluate the appropriateness of continuous measurements of the rumen mucosa thickness (RMT) as a diagnostic tool for SARA in dairy cows compared with continuous measurements of ruminal pH. The study used 6 lactating Simmental cows switched from a moderate-grain (MG) diet with 40% concentrate (dry matter basis) for 1 wk to a high-grain (HG) diet with 60% concentrate (dry matter basis) for 4 wk. Reticuloruminal pH was recorded with indwelling sensors throughout the trial. Rumen mucosa thickness was measured by transabdominal ultrasound at 4 d during the MG diet and 23 d during the HG diet. Mean RMT increased from 4.7 ± 0.19 mm in the MG diet to 5.3 ± 0.17 mm in the HG diet, whereas daily mean reticular pH decreased from 6.8 ± 0.01 in the MG diet to 6.5 ± 0.01 in the HG diet. Older cows (>3 lactations) had increased RMT, associated with higher reticular pH throughout the experiment. The higher RMT and pH level in older cows underlines their lesser susceptibility to SARA during high-grain feeding. In conclusion, RMT can successfully be measured using linear ultrasound probes, commonly used by veterinary practitioners as rectal probes. By combining noninvasive RMT measurements with the lactation number of the individual cows in a herd, this study suggests that RMT is a viable option for diagnosing SARA. Further research, using a larger number of cows with different lactations numbers, is needed to establish a cut-off RMT indicating the risk of SARA.

喂高谷物饮食会导致瘤胃中短链脂肪酸的释放和积累。瘤胃pH值随后的长时间下降可能导致亚急性瘤胃酸中毒（SARA）。短链脂肪酸的积累会引起瘤胃乳头的增殖，从而增加吸收表面，从而导致瘤胃粘膜增厚。这项研究的目的是评估与连续测量瘤胃pH值相比，连续测量瘤胃粘膜厚度（RMT）作为奶牛SARA的诊断工具的适用性。该研究使用了6头泌乳的西门塔尔奶牛，从1 wk的40％精粉（以干物质为基础）的中粒（MG）日粮改为4 wk的60％浓缩粉（以干物质为基础）的高谷物（HG）日粮。在整个试验中，使用留置传感器记录网状pH。在MG饮食期间4 d和HG饮食期间23 d，通过腹腔超声测量瘤胃黏膜厚度。平均RMT从MG饮食中的4.7±0.19 mm增加到HG饮食中的5.3±0.17 mm，而每日平均网状pH值从MG饮食中的6.8±0.01降低到HG饮食中的6.5±0.01。在整个实验过程中，年龄较大的母牛（> 3次泌乳）的RMT升高，且网状pH值较高。高龄奶牛的RMT和pH值较高，这说明它们在高谷物喂养过程中对SARA的敏感性较低。总之，可以使用兽医通常用作直肠探针的线性超声探头来成功地测量RMT。通过将无创RMT测量值与牛群中个体母牛的泌乳数结合起来，这项研究表明，RMT是诊断SARA的可行选择。需要进行进一步的研究，使用更多具有不同泌乳次数的母牛，以建立表明SARA风险的临界RMT。