To assess gastrointestinal development in this study,ruminal concentrations of SCFA, blood BHBA, and fecalstarch percentage were measured. Ruminal SCFAconcentrations were used as a marker of microbialfermentation in the rumen. On d 35 of life, before stepdownweaning, ruminal fluid concentration was <50mM, which agrees with some previous reports (Anderson,1981; Lesmeister et al., 2004; Laarman et al., 2012)but contrasts other reports that showed higher concentrationsduring the first month of life (Rey et al., 2012).Interestingly, the SCFA and butyrate concentrations ofcalves the week before weaning were higher in 8WWcalves, indicating greater microbial fermentation withinthe rumen before weaning. The end-products of microbialfermentation, namely butyrate and propionate,have been shown to induce ruminal growth (Baldwinet al., 2004). The greater concentration of microbialend-products available to trigger ruminal developmentmay be one contributing factor to improving the transitionto weaning. The age- and diet-dependent factors ofmicrobial and epithelial functional development duringweaning in the rumen require further exploration.
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