Center for Animal Welfare, Department of Animal Science, University of California, Davis, Davis, CA 95618, USA.
J Anim Sci. 2024 Jan 3;102. doi: 10.1093/jas/skae049.
Subacute ruminal acidosis (SARA) is characterized by chronic low ruminal pH, and occurs for feedlot cattle fed high-concentrate diets. Forages slow digestion and reduce acid production. We aimed to assess how motivated finishing cattle are to access forage (Sudan grass hay, SG) via their willingness to interact with an electrified barrier. Reticulorumen pH was measured to relate the results to digestive health. Twenty-eight animals fed a high-concentrate ration ad libitum had access to 4 L of one of two treatments (n = 14/treatment) fed 1×/d behind a barrier: 1) SG or 2) an additional offering of the normal ration (total mixed ration [TMR]). To access their treatment, the steer voluntarily pushed his muzzle against an electrified barrier. The electrical current was increased exponentially every 24 h (0, 156, 312, 625, 1,250, 2,500, 5,000 µA) until the animal ceased accessing it. Visits to the treatment were recorded continuously 24 h/d and reticulorumen pH was measured every 10 min. Time with a reticulorumen pH below 5.8 was 348 ± 101 and 280 ± 76 min/24 h for SG and TMR animals, respectively; these durations meet the criterion for SARA. However, animals with access to SG were less likely to advance to the next current than TMR animals (P < 0.01) and were approximately 3× less willing to interact with higher currents than TMR (mean maximum current touched: 469 ± 169 and 1,380 ± 254 μA, respectively, mean ± SE, P = 0.01). Lower motivation to access SG was further demonstrated through fewer visits to the SG (2.4 ± 0.4 vs. 5.3 ± 0.6 #/d, P < 0.01), and less SG consumed than TMR (32.0 ± 0.1 vs. 74.0 ± 0.0 %/d, P < 0.01, measured as % due to weight differences of SG and TMR). Overall, finishing cattle valued the TMR more than SG, likely because of differences in the quantity offered, palatability, and familiarity. When rumen health was considered, SG animals visited more often (r = 0.5, P = 0.09) and showed fewer failed attempts (r = -0.5, P = 0.06) to access forage as the severity and duration of pH depression below 5.6, for example, increased. No measures of treatment use were related to pH depression for TMR animals (P ≥ 0.31). These findings provide evidence that cattle are motivated for Sudan grass hay when experiencing chronic low reticulorumen pH. However, they also contribute to the mixed evidence about the motivation for forage in this life stage, because, overall TMR was valued more highly than SG. Despite widespread pH depression, TMR cattle contrafreeloaded for additional concentration, demonstrating unexpectedly high motivation for this resource.
亚急性瘤胃酸中毒（SARA）的特征是瘤胃 pH 值慢性偏低，常发生于采食高精料日粮的牛。粗饲料能减缓消化速度并减少酸的产生。我们旨在评估育肥牛接触粗饲料（苏丹草干草，SG）的意愿，通过它们与通电障碍物互动的意愿来评估。通过测量瘤胃 pH 值来将结果与消化健康联系起来。28 头自由采食高浓缩日粮的动物可以选择接触两种处理方法（n=14/处理）中的一种：1）SG 或 2）额外提供正常日粮（全混合日粮[TMR]）。为了获得他们的治疗，公牛自愿将他的口鼻部推向通电障碍物。电流每 24 小时呈指数增加（0、156、312、625、1、1250、2500、5000 µA），直到动物停止接触它。24 小时连续记录访问次数，每 10 分钟测量一次瘤胃 pH 值。瘤胃 pH 值低于 5.8 的时间分别为 SG 动物和 TMR 动物的 348±101 和 280±76 分钟/24 小时；这些持续时间符合 SARA 的标准。然而，与 TMR 动物相比，SG 动物接触更高电流的可能性较小（P<0.01），与 TMR 相比，接触更高电流的意愿也降低了约 3 倍（平均最大电流接触：469±169 和 1380±254 μA，分别为平均值±SE，P=0.01）。通过 SG 的访问次数较少（2.4±0.4 与 5.3±0.6 #/d，P<0.01），SG 的摄入量低于 TMR（32.0±0.1 与 74.0±0.0%/d，P<0.01，基于 SG 和 TMR 重量差异进行测量），进一步证明了对 SG 的较低访问动机。总体而言，育肥牛比 SG 更看重 TMR，这可能是由于提供的数量、适口性和熟悉程度的差异。当考虑瘤胃健康时，随着 pH 值低于 5.6 的严重程度和持续时间的增加，SG 动物访问的频率更高（r=0.5，P=0.09），尝试失败的次数更少（r=-0.5，P=0.06）。TMR 动物的任何治疗使用措施均与 pH 值下降无关（P≥0.31）。这些发现提供了证据表明，当牛经历慢性低瘤胃 pH 值时，它们对苏丹草干草有动力。然而，它们也增加了关于这个生命阶段对粗饲料的动机的混合证据，因为总体而言，TMR 比 SG 更受重视。尽管 pH 值普遍下降，TMR 牛还是会为额外的浓缩物反刍，这表明它们对这种资源的动机出乎意料地高。
