Characterization of rumen and hindgut development from pre- to post-weaning in Holstein dairy calves

Jolet Kohler
2020
In the dairy industry, the development of heifer calves is of high importance as it impacts health, future productivity and farm profitability. Nutrition is one aspect of heifer management that plays a key role in calf development and health. Therefore, the first study (Chapters 2 and 3) investigated the effects of the combination of milk replacer (MR) feeding rate and processing of corn grain in calf starter (CS) fed to calves on growth performance, nutrient digestibility, rumen and hindgut
more » ... mentation and inflammatory biomarkers. There were 4 treatments (n = 12 per treatment) with a 2 × 2 factorial arrangement of either: 1) MR feeding rate of 0.749 kg (LO) or 1.498 kg (HI) of MR/d; and 2) whole corn (WC) or flaked corn (FC) in textured CS. All calves were weaned by reducing MR allotment by 50% during wk 6. Calves fed HI had increased growth pre-weaning. However, these calves also experienced reduced growth compared with calves fed LO during weaning. Moreover, the increased pre-weaning growth advantage was compromised, resulting in similar body weights (BW) between treatments at wk 12. Calves fed HIWC had reduced fecal pH at wk 8, which may be an indication of hindgut acidosis, however, inflammatory biomarkers were unaffected. The first objective of study 2 (Chapter 4) was to develop a method to collect tissue samples longitudinally from the rumen and colon of calves that can later be used for histological and molecular analysis without sacrificing animals. Collection of rumen biopsy tissue samples was successful using surgical scissors, but not by using an endoscope, while colon biopsy tissue samples were successfully obtained using an endoscope. Both tissue types were of optimum quality for histology and molecular evaluation. Study 2 also characterized rumen fermentation and structural development, and amyloid A (SAA) and LPS binding protein (LBP) concentration changes from pre-to post-weaning (Chapter 5). iii Additionally, the colon transcriptome was evaluated for functional changes at the molecular level that may occur from pre-to post-weaning, as well as their relation to colon mucosa thickness, fecal starch, inflammatory markers, SAA and LBP changes (Chapter 6). Six calves were fed MR (150 g/L) at 15% of BW adjusted weekly. Calves were weaned by reducing milk allocation by 50% during wk 6. Ruminal pH was below 5.8 for approximately 936.3 min/d pre-weaning and remained below 5.8 for approximately 388.1 min/d at wk 12, indicating calves underwent ruminal acidosis during weaning. Rumen adaptation may take several wk post-weaning because no structural differences were observed between pre-weaning and 2 wk post-weaning, although ruminal structure had increased at wk 12. SAA and LBP concentrations remained constant pre-and postweaning, suggesting the depressed ruminal pH did not evoke a systemic inflammatory response. Expression of six genes (AQP8, SLC7A8, SLC13A2, SLC9A3, SLC6A14, SLC40A1) involved in nutrient transport decreased from pre-to post-weaning and was negatively associated with CS intake and fecal starch concentrations. An upstream regulator gene -S100A12of inflammation and tissue growth also decreased in expression from pre-to post-weaning and was positively associated with colon mucosa thickness and negatively associated with fecal starch and CS intake. Responsive genes identified in this study may be used as gene markers in the future. In summary, based on findings observed in Chapters 2 and 3, different amounts of MR in combination with CS containing flaked or whole corn can be fed to dairy calves without affecting digestibility, rumen and hindgut fermentation or inflammatory parameters. Furthermore, digestibility and rumen and hindgut fermentation are more responsive to MR feeding rate than the processing of corn in CS. Additionally, Chapters 5 and 6 enhanced our understanding of the changes that occurs from preto post-weaning in the rumen and colon, respectively. Ruminal acidosis experienced by calves preiv and post-weaning may not be a health concern based on unchanged inflammatory markers and intact papillae structural layers. The colon also needs more investigation based on increased expression of S100A12 pre-weaning, which suggests that MR feeding may induce colon tissue inflammation. v Preface This thesis is an original work by Jolet Köhler and consist of five chapters that originated from two studies. Study 1 contributed to chapters 2 and 3 which received research ethics approval from the University of Alberta Animal Care and Use Committee for Livestock (AUP00002303). Study 2 contributed to chapters 4, 5 and 6 which also received research ethics approval from the University of Alberta Animal Care and Use Committee for Livestock (AUP00002010).
doi:10.7939/r3-8vxv-bc28 fatcat:7xp2rp2rpjhudapo2m4hxfoc4q