1. Anne Laarman, M.Sc. Ph.D. Student University of Guelph alaarman@uoguelph.ca

2. VFAs (incl. butyrate) Starter Acidotic pressure Protein Epithelium

3.  With low pH, fermentation bacteria start to die off Starter VFAs (incl. butyrate) Acidotic pressure Protein Epithelium

4. Milk Hay Milk Hay Starter Weaning Experiment set-up for investigating the role of calf starter in rumen pH and metabolic adaptations

7. Duration of Acidosis (pH < 5.8) Area under the curve (pH < 5.8) Time of Day pH

8.  Calves that consume more hay have a higher rumen pH Laarman et al., 2012. In press

9.  Calves that consume very little hay are at greater risk of more rumen acidosis (pH < 5.8) Laarman and Oba, 2011

10. Milk & HayMilk & Hay & Starter Average pH6.42 ± 0.10 6.27 ± 0.12 Duration Rumen Acidosis, min/d 101 ± 100 237 ± 126 Area under the Curve, pH*min/d 49.3 ± 36.5 64.2 ± 47.4 Total VFA, mM 64.6 ± 8.6 99.1 ± 8.1 * Butyrate, % Total 7.9 ± 1.9 15.6 ± 1.7 * Hay DMI, kg/d 0.23 ± 0.07 0.34 ± 0.8 Starter DMI, kg/d N/A0.76 ± 0.04 Hay consumption appears unrelated to calf starter intake Laarman and Oba, 2011

11.  Hay intake increases with age  Doesn’t appear directly related to feeding program De Passillé et al., 2011

12. Milk & HayMilk & Hay & Starter Average pH6.42 ± 0.10 6.27 ± 0.12 Duration Rumen Acidosis, min/d 101 ± 100 237 ± 126 Area under the Curve, pH*min/d 49.3 ± 36.5 64.2 ± 47.4 Total VFA, mM 64.6 ± 8.6 99.1 ± 8.1 * Butyrate, % Total 7.9 ± 1.9 15.6 ± 1.7 * Hay DMI, kg/d 0.23 ± 0.07 0.34 ± 0.8 Starter DMI, kg/d N/A0.76 ± 0.04 Despite higher VFA concentrations, calves fed calf starter did not have lower rumen pH Laarman and Oba, 2011

13. Changes in gene expression suggest epithelium is adapting on a metabolic level Milk & Hay Milk & Hay & Starter NHE-30.82 ± 0.12 0.37 ± 0.12* NHE-20.84 ± 0.16 0.86 ± 0.17 MCT-10.53 ± 0.23 1.45 ± 0.22* Laarman et al., 2012

15. Milk & Hay Milk & Hay & Starter Carbamoyl phosphate synthetase 8.67 ± 1.10 9.90 ± 1.10 Ornithine transcarbamoylase 1.34 ± 0.11 1.64 ± 0.11 * Arginosuccinate synthetase 1.56 ± 0.29 2.67 ± 0.29 * Arginosuccinate lyase 0.99 ± 0.10 1.44 ± 0.10 * Arginase 1.74 ± 0.32 3.21 ± 0.32 * Laarman et al., 2012. In press Calf starter increases gene expression of 4 out of 5 urea cycle genes

16.  Feeding solid feed can affect gene expression in rumen epithelium and liver  pH regulation in epithelium  Urea cycle in liver  Roughage can help manage rumen pH  Developing rumen adapts to increased acidotic pressure from calf starter fermentation

17.  Dr. Tom Wright, University of Guelph  Dr. Brian McBride, University of Guelph  Dr. Masahito Oba, University of Alberta  OMAFRA HQP Program  Japanese Federation of Dairy Co-Ops  Agriculture and AgriFood Canada