Beef cattle are often fed high-concentrate diet (HCD) to achieve high growth rate. However, HCD feeding is strongly associated with metabolic disorders. Mild acid treatment of grains in HCD with 1% hydrochloric acid (HA) followed by neutralization with sodium bicarbonate (SB) might modify rumen fermentation patterns and microbiota, thereby decreasing the negative effects of HCD. This study was thus aimed to investigate the effects of treatment of corn with 1% HA and subsequent neutralization with SB on rumen fermentation and microbiota, inflammatory response and growth performance in beef cattle fed HCD. Eighteen beef cattle were randomly allocated to three groups and each group was fed different diets: low-concentrate diet (LCD) (concentrate : forage = 40 : 60), HCD (concentrate : forage = 60 : 40) or HCD based on treated corn (HCDT) with the same concentrate to forage ratio as the HCD. The corn in the HCDT was steeped in 1% HA (wt/wt) for 48 h and neutralized with SB after HA treatment. The animal trial lasted for 42 days with an adaptation period of 7 days. At the end of the trial, rumen fluid samples were collected for measuring ruminal pH values, short-chain fatty acids, endotoxin (or lipopolysaccharide, LPS) and bacterial microbiota. Plasma samples were collected at the end of the trial to determine the concentrations of plasma LPS, proinflammatory cytokines and acute phase proteins (APPs). The results showed that compared with the LCD, feeding the HCD had better growth performance due to a shift in the ruminal fermentation pattern from acetate towards propionate, butyrate and valerate. However, the HCD decreased ruminal pH and increased ruminal LPS release and the concentrations of plasma proinflammatory cytokines and APPs. Furthermore, feeding the HCD reduced bacterial richness and diversity in the rumen. Treatment of corn increased resistant starch (RS) content. Compared with the HCD, feeding the HCDT reduced ruminal LPS and improved ruminal bacterial microbiota, resulting in decreased inflammation and improved growth performance. In conclusion, although the HCD had better growth performance than the LCD, feeding the HCD promoted the pH reduction and the LPS release in the rumen, disturbed the ruminal bacterial stability and increased inflammatory response. Treatment of corn with HA in combination with subsequent SB neutralization increased the RS content and helped counter the negative effects of feeding HCD to beef steers.

肉牛经常饲喂高浓度饲料（HCD）以实现高生长率。但是，HCD喂养与代谢紊乱密切相关。用1％盐酸（HA）对HCD中的谷物进行轻度酸处理，然后用碳酸氢钠（SB）中和，可能会改变瘤胃发酵模式和微生物群，从而降低HCD的负面影响。因此，本研究旨在调查用1％HA处理玉米并随后用SB中和对饲喂HCD的肉牛的瘤胃发酵和微生物群，炎症反应和生长性能的影响。将18头肉牛随机分为三组，每组分别喂养不同的饮食：低浓度饮食（LCD））（精矿：草料= 40:60），HCD（精矿：草料= 60:40）或基于处理过的玉米（HCDT）的HCD，其精料/草料比与HCD相同。HCDT中的玉米浸泡在1％HA（wt / wt）中48小时，并在HA处理后用SB中和。动物试验持续42天，适应期为7天。在试验结束时，收集了瘤胃液样品以测量瘤胃pH值，短链脂肪酸，内毒素（或脂多糖，LPS）和细菌菌群。在试验结束时收集血浆样品，以确定血浆LPS，促炎细胞因子和急性期蛋白（APPs）的浓度）。结果表明，与LCD相比，饲喂HCD具有更好的生长性能，这是因为瘤胃发酵模式从醋酸盐向丙酸，丁酸和戊酸转变。但是，HCD降低了瘤胃pH值，增加了瘤胃LPS释放以及血浆促炎细胞因子和APP的浓度。此外，喂食HCD会降低瘤胃中细菌的丰富度和多样性。玉米的治疗增加抗性淀粉（RS）内容。与六溴环十二烷相比，饲喂六氯二苯并对二恶英可降低瘤胃脂多糖和瘤胃细菌菌群，从而减少炎症并改善生长性能。总之，尽管HCD具有比LCD更好的生长性能，但喂食HCD可以促进pH降低和瘤胃中LPS的释放，扰乱瘤胃细菌的稳定性并增加炎症反应。用HA结合随后的SB中和处理玉米可以增加RS含量，并有助于抵消将HCD饲喂牛肉所带来的负面影响。