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

Sub-acute ruminal acidosis (SARA), a disorder characterized by chronic low ruminal pH, occurs in feedlot cattle fed high-concentrate diets. Forages slow digestion and reduce acid production. Thus, 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 contextualize the results with digestive health. Twenty-eight animals fed a high-concentrate ration ad-libitum had access to 4 L one of two treatments (n=14/treatment) fed once a day behind a barrier: 1) SG, or 2) an additional offering of the normal ration (TMR). To access a treatment, the steer voluntarily pushed his muzzle against an electrified barrier. The electrical current was increased exponentially every 24 h (0, 156, 312, 625, 1250, 2500, 5000 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. Rumen pH averaged 3.0±1.2 and 2.3±0.9 h/d below 5.6, for SG and TMR, respectively, meeting 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 3x less willing to interact with higher currents than TMR (mean maximum current touched: 469±169 and 1380±254 mA, 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). 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. There was no relationship between any measure of treatment use and pH depression for TMR animals (P≥0.3). These findings provide evidence that cattle are motivated for Sudan grass hay when experiencing chronic low reticulorumen pH. However, the findings also contribute to the mixed evidence about motivation for forage in this life stage, because, overall TMR was valued more highly than SG. Indeed, despite widespread pH depression, TMR cattle contrafreeloaded for additional concentrate, demonstrating unexpectedly high motivation for this resource.