Diurnal Ruminal pH and Temperature Patterns of Steers Fed Corn or Barley-Based Finishing Diets

SIMPLE SUMMARY: Cattle in feedlots are typically fed diets with a high proportion of cereal grains. While feeding high-energy grain-based diets is advantageous for growth and performance, it can also contribute to an increased likelihood of metabolic issues. Different feedstuffs have unique digestive utilization, which may lead to different cattle performance outcomes. Barley is fermented to a greater extent in the rumen, compared to corn, and can lead to an increased likelihood of digestive disorders. To further our understanding of the use of barley and corn in cattle feedlot diets, we evaluated the effect of diets on ruminal pH, temperature and feed intake events using continuous rumen monitoring technology. While mean ruminal pH was not different between corn or barley-fed steers, barley-fed steers had greater ruminal pH change throughout a 24 h period. Barley-fed steers also exhibited greater variation in ruminal pH. Additionally, intake patterns were different between corn- and barley-fed steers in which corn-fed steers consumed more feed the first 6 h directly after feeding while barley-fed steers consumed more feed later in the day. Presumably these intake patterns could be influenced by differences in the diurnal patterns of ruminal pH between corn and barley. By evaluating ruminal dynamics on a diurnal scale, we will enhance our understanding of utilization of different feedstuffs in beef feedlot diets. ABSTRACT: This study evaluated the effects of corn or barley finishing diets on ruminal pH and temperature and their relationship to feed intake events using continuous reticulorumen monitoring of feedlot steers. Average daily ruminal pH and temperature were not impacted (p ≥ 0.17) by diet. However, diet did affect daily variation of ruminal pH and temperature (p < 0.01). Average hourly ruminal pH displayed a diet by hour post-feeding interaction (p < 0.01), where barley-fed steers had greater (p < 0.01) ruminal pH than corn-fed steers at 0, 1, 18, 19, 20, 21, 22 and 23 h post feeding, but had lower (p ≤ 0.05) ruminal pH than corn-fed steers at 6, 7, and 8 h post-feeding. Variation in ruminal pH hour post-feeding also displayed a diet by hour post-feeding interaction (p < 0.01), where barley-fed steers had greater (p ≤ 0.03) variation in ruminal pH at hours 1–17 post-feeding but did not differ (p ≥ 0.16) at 0, 18, 19, 20, 21, 22 and 23 h post-feeding. Additionally, average hourly ruminal temperature exhibited a diet by hour post-feeding interaction (p < 0.01). In summary, basal grain interacted with time post-feeding influencing ruminal pH and temperature in feedlot steers.