Particle size of calf starter: Effects on digestive system development and rumen fermentatio

Starter intake before weaning is the conditional factor to rumen development and thus to a successful transition at weaning. Rumen development can be negatively affected when the particle size of starter is too small, resulting in abnormal papillae and hyper-keratinization of the rumen epithelium. Two common strategies to increase particle size of starter are to add forage to the diet, or to reduce the processing of grain. The two strategies were tested, and the literature was reviewed in regards to the effects of forage on starter intake.;The effects of forage on starter intake in pre-weaned dairy calves were reviewed as research studies have yielded inconsistent results. Discrepancies in the literature come from differences in starter ingredient composition, forage source, particle size of starter and forage, and intake level. All of these factors will affect calves' intake response to forage in their diet. Some important factors that will affect intake, such as starch content and particle size of starter, were often not reported, which limited the analysis of this review. It was also noted that segregating intake by wk, particularly for pre-weaned vs. post-weaned periods, when reporting intake data would help to determine the level of forage intake that impacts starter intake.;Effects of grain processing in calf starter were evaluated in young calves. A series of 3 trials were conducted to determine effects of whole or ground oats in starter grain on reticulorumen fermentation and digestive system development of pre-weaned calves. In all trials a fixed amount of starter (containing 25% oats either ground and pelleted or whole) was offered daily; orts were fed through the cannula in trials 1 and 2. Calves were randomly assigned to all pelleted starter or pellets plus whole oats.;Additionally, the effects of increasing particle size of calf starter by changing the particle length of straw were evaluated in young calves. Two trials were conducted to determine effects of straw particle size in calf starter on rumen fermentation and development. Holstein calves (n = 45) were housed in individual pens; bedding (wood shavings) was covered with landscape fabric to completely avoid consumption of bedding. Milk replacer was fed at 12% of birth body weight/d and water offered free choice. Calves were randomly assigned to 4 treatments differing in geometric mean particle length (Xgm) of straw comprising 5% of starter dry matter. Straw was provided within the pellet at manufacturing (PS, 0.82 mm Xgm) or mixed with the pellet at time of feeding at Xgm of 3.04 (SS), 7.10 (MS), or 12.7 (LS) mm.;Particle size of calf starters can be modified by changing grain processing or by adding forage. Factors such as intake level and ingredient and chemical composition will influence the effects of particle size on rumen fermentation and rumen development. Calves can tolerate lower rumen pH levels than adult cattle, however, high intake of starters with short particle size and high starch concentration increase the risk of reaching pH levels that can negatively impact calf health. (Abstract shortened by UMI.).