Cattle are more motivated for a high-concentrate diet than Sudan grass hay, despite low reticulorumen pH.

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 ±â€…169 and 1,380 ±â€…254 µA, respectively, mean ±â€…SE, P = 0.01). Lower motivation to access SG was further demonstrated through fewer visits to the SG (2.4 ±â€…0.4 vs. 5.3 ±â€…0.6 #/d, P < 0.01), and less SG consumed than TMR (32.0 ±â€…0.1 vs. 74.0 ±â€…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.

Feedlot cattle are at risk of subacute ruminal acidosis, a digestive disorder, because their diets are typically high in concentrates or grains and low in forages. Grains have the potential to be digested rapidly in the animals' rumen, causing an increase in acidity. In contrast, forages slow the rate of digestion and can prevent a rapid or chronic drop in rumen pH, thereby mitigating this problem. Our objective was to measure how motivated finishing cattle are to access Sudan grass hay when fed a high-concentrate diet. Cattle with free access to other feed accessed one of two treatments, either Sudan grass hay or additional grain, by voluntarily opening an electrified barrier. The current applied to the barrier increased exponentially every 24 h until the animal stopped touching it. Animals were simultaneously administered a wireless telemetry bolus to measure reticulorumen pH. Cattle offered Sudan grass hay and accessed the forage more often as pH depression increased in severity. However, cattle willingly interacted with a higher electric current to access grain than Sudan grass hay, despite experiencing chronic low reticulorumen pH.