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A graduate exam seminar is a presentation of the student’s final research project for their degree.
This is an ALES PhD Final Exam Seminar by Jolet Kohler. This seminar is open to the general public to attend.
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Conference ID: 497839702
Thesis Topic: Characterization of rumen and hindgut development from pre- to post-weaning in Holstein dairy calves
PhD with Drs. Michael Steele and Leluo Guan
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 investigated the effect of the combination of milk replacer (MR) feeding rate (low or high) and processing of corn (whole corn or flaked corn) in textured calf starter (CS) fed to calves on growth performance, nutrient digestibility, rumen and hindgut fermentation and inflammatory biomarkers. Calves fed a high amount of milk had increased growth pre-weaning. However, these calves also experienced reduced growth during weaning and the increased pre-weaning growth advantage was compromised, resulting in similar body weights (BW) between treatments at wk 8. Calves fed high amounts of milk and whole corn 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, 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 only successful using surgical scissors, while colon biopsy tissue samples were successfully obtained by using an endoscope. Both tissue types were of optimum quality to be used for histology and molecular evaluation. Study 2 also characterized rumen fermentation and structural developmental, and serum inflammatory marker changes from pre- to post-weaning. Additionally, the colon transcriptome was evaluated for functional changes that may occur from pre- to post-weaning, as well as their relation to colon mucosa thickness, fecal starch and serum inflammatory marker changes. Calves were weaned at the end of 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 between pre-weaning and 2 wk post-weaning were observed, however, ruminal structure increased at wk 12. The inflammatory marker concentration remained constant pre- and post-weaning, 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. An upstream regulator gene, S100A12, of 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, the first study found that different amounts of MR in combination with CS containing flaked or whole corn can be fed to dairy calves because digestibility and rumen and hindgut fermentation parameters are more responsive to MR feeding rate than the processing of corn in CS or the combination of MR and processing of corn. Additionally, the second enhanced our understanding of the changes that occurs from pre- to post-weaning in the rumen and colon. Ruminal acidosis that calves experience pre- and post-weaning may not be a health concern based on unchanged inflammatory markers and intact papillae structural layers. Furthermore, the colon needs more investigation based on increased expression of S100A12 pre-weaning, which would suggest that MR feeding may induce colon tissue inflammation. All of these findings are important to the dairy industry given the key role nutrition plays in calf development, health, and ultimately the profitability of dairy operations.