Grant: Collaborative Research and Development Grants

Growing and finishing beef cattle in North America are typicallyfed high grain diets (> 90 % grain, DM basis) to achieve maximum productivityin a cost-effective manner. A limitation to feeding grain-based diets is the perceived increase in the prevalence of digestive disorders, particularlysub-acute ruminal acidosis. Sub-acute acidosis is characterized bybouts of low pH in the rumen caused bythe accumulation of acids. Acidosis negativelyaffects feed (fiber) digestion, nutrient absorption from the rumen, and is an animal welfare concern. The incidence of ruminal acidosis has been measured in dairycattle using ruminocentesis as a method to collect data from numerous cows (>500) across manyherds. However, there are challenges with ruminocentesis including: high labour requirement; risk for peritonitis; and that it onlyresults in a single-data point in time for each animal to determine predicted risk. More recently, studies have evaluated the prevalenceand severityfor ruminal acidosis using indwelling pH meters. These systems provide comprehensive data regarding ruminal pH patterns over an extended duration. This data can then be used to characterize the prevalence, incidence, and severityfor ruminal acidosis based on, for example, days on feed and timing of feeding using group-fed cattle. While it is expected that feedlot cattle mayexperience ruminal acidosis, there are currentlyno known studies that document the incidence, prevalence, or severityin feedlot cattle throughout the finishing period. This research will determine critical risk periods for ruminal acidosis throughout the finishing period and will determine the incidence, prevalence, and severityfor ruminal acidosis. This will include the use of both small-pen and commercial-scale feeding operations. Furthermore, we will evaluate whether cattle experiencing more severe ruminal acidosis have altered ruminal absorptive and barrier functions.As such, the proposed research will provide the fundamental knowledge needed to quantifythe impact of ruminal acidosis on feedlot cattle as well as identifying critical risk periods so that strategies can be developed to minimize the risk, prevalence, and severityof ruminal acidosis in feedlots.