Most dairy farms are trying to push the envelope from the conventional 4L of milk replacer per day to a higher volume to support lean structural growth of replacement heifers. Concerns of ruminal leakage resulting in fermentation has been cited as a concern, but is that based on an incomplete picture?  We know microbial protein offers a nearly perfect alignment of amino acid requirements for the bovine, however nutrition programs have discounted milk replacer to exclusively providing rumen undegradable protein (RUP) – protein that skips the rumen and is absorbed in the abomasum.Marcos Marcondes, researcher from the Miner Institute, wanted to see if feeding higher volumes would change the flow of protein and energy to the calf and the physiology of the rumen, due to leakage. To test this question he fed a standard rate and double rate of milk replacer with colbalt to mark and track the flow of digestion through preweaned animals.Leakage was found in the rumen on both treatments, but the results were positive. Energy, in the form of volatile fatty acids, and microbial protein added to the fuel for these growing animals.  Listen in to better understand the kinetics of digestion and questions that still remain for this phase of production.Topics of discussionInfluence of different amounts of milk replacer on esophageal leakage, rumen fermentation characteristics, gastrointestinal tract passage rate, and microbial crude protein synthesis of nursling animals#2xAg2030; #journalofdairyscience; #openaccess; #MODAIRY; #prewean; #dairycalves; #microbialprotein; #MinerInstitute; #kinetics; #dairysciencedigest; #ReaganBluel;