A moderate transition of beef heifers to a 90% concentrate diet as a model for subacute ruminal acidosis induced alterations in feeding behavior, rumen environment, reticulorumen motility, and blood acid-base status

Authors: EGERT-MCLEAN, AMANDA - University Of Kentucky; SAMA, MICHAEL - University Of Kentucky; Klotz, James; MCLEOD, KYLE - University Of Kentucky; KRISTENSEN, NIELS - Danish Agriculture & Food Council; HARMON, DAVID - University Of Kentucky

Submitted to: Canadian Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/4/2020
Publication Date: 7/21/2020
Citation: Egert-McLean, A.M., Sama, M.P., Klotz, J.L., McLeod, K.R., Kristensen, N.B., Harmon, D.L. 2020. A moderate transition of beef heifers to a 90% concentrate diet as a model for subacute ruminal acidosis induced alterations in feeding behavior, rumen environment, reticulorumen motility, and blood acid-base status. Canadian Journal of Animal Science. 101(1):85-95. https://doi.org/10.1139/cjas-2019-0218.
DOI: https://doi.org/10.1139/cjas-2019-0218

Interpretive Summary: The work conducted in this paper addresses the problem with cattle having depressed feed intake when their diet is transitioned from a high-forage to a high-grain diet. This diet transition is common practice in feedlots during the finishing phase prior to slaughter. The unique component of this research is establishment of a causal relationship between ruminal acidosis or decrease rumen pH caused by the transition to a high-grain diet and rumen motility. Specifically, this study showed a reduction in rumen motility during this dietary transition. This decrease in motility influenced feed intake at a time when maximal intake is desirable. These results will mostly benefit other researchers in this area of study, as the work further characterizes a problem in finishing cattle. However, it moves the research one step closer to developing a solution from which stakeholders would benefit from greatly.

Technical Abstract: The objective of this study was to characterize a moderate dietary transition from a 70% to a 90% concentrate diet, to induce subacute ruminal acidosis (SARA), with regards to a variety of behavioral and physiological responses in cattle. Eight ruminally-cannulated Angus crossbred beef heifers were housed inside in individual stalls and adapted to a 70% concentrate, high-moisture corn-based diet (T70) provided ad libitum. Measurements of feeding behavior, ruminal pH and temperature, rumen motility, liquid passage rate, and blood acid-base status were conducted to establish baseline values on T70. Then, all animals were switched to a 90% concentrate, high-moisture corn-based diet (H90) fed ad libitum, and measurements were repeated to characterize the transition period for the first (d1 H90) and second (d2 H90) days of high-grain feeding. Daily feed intake was manual measured by difference of DM given and DM remaining in orts. Feeding behavior was characterized using an algorithm previously described (Egert-McLean et al., 2019) from feed disappearance from feed bunks. Time for consumption of quarterly daily intake was calculated by modeling of feed disappearance data using exponential one phase decay. Ruminal pH and temperature was monitored every min using rumen data loggers in the ventral sac. Rumen motility was recorded continuously using a water-filled balloon inserted into the ventral sac attached to a pressure transducer. Liquid passage rate was estimated by an intraruminal pulse-dose of Cr:EDTA and disappearance of Cr over time. Data were analyzed as a randomized complete block design with repeated measures using SAS 9.4. Ruminal pH results confirmed that animals were experiencing subacute ruminal acidosis; mean ruminal pH was reduced on both days of high-grain feeding (P<0.001) and the time ruminal pH was below 5.6 progressively increased from T70 to d1 H90 and d2 H90 (P<0.001). Meal size, duration, and frequency were not affected by the dietary transition. However, consumption rate of feed was increased on d1 H90 (P<0.04), which likely influenced the depression in ruminal pH. Ruminal contraction amplitude was reduced (P<0.001) on both days of H90 feeding compared to T70. While contraction duration was reduced on d1 H90, duration returned to T70 levels by d2 H90 (P<0.0001). Although rumen motility was reduced by this SARA challenge experienced during a typical feedlot dietary transition, it did not slow passage rate nor influence voluntary DMI.