Introduction
The weaning transition period is a critical phase in the developmental trajectory of Holstein calves, where diet changes dramatically from milk to solid feed. This shift poses challenges to the young ruminant’s digestive system, particularly the rumen. A study by Kim Yo-Han et al. published in The Journal of Veterinary Medical Science on June 6, 2019, provides valuable insight into how ruminal pH affects gene expression in the rumen epithelium, peripheral blood mononuclear cell (PBMC) subpopulations, and blood metabolites. This article delves into the findings of that study, emphasizing the physiological impacts on Holstein calves.
Methodology
In the study titled “Effects of ruminal pH on gene expression in the rumen epithelium, peripheral blood mononuclear cell subpopulations, and blood metabolites from Holstein calves during weaning transition,” researchers examined two groups of calves transitioning from a milk-based diet to solid feed. One group was fed calf starter with forage (Forage group, n=3), while the other received calf starter without forage (Starter group, n=4). Continuous measurement of ruminal pH was conducted, and samples for blood, rumen fluid, and rumen epithelium were collected at various time points around the weaning period.
Key Findings
The findings indicated that weaning led to increased ruminal pH and alterations in various blood metabolites such as blood urea nitrogen (BUN), beta-hydroxybutyrate (BHB), gamma-glutamyl transferase (GGT), total cholesterol (T-CHO), and phospholipid levels. Interestingly, a positive correlation was found between ruminal pH and CD8+ T-cell populations in the blood, hinting at possible immune system modulations linked to changes in the rumen environment.
Blood Metabolites and Immunity
Blood metabolites can serve as biomarkers for animal health and diet efficacy. Increases in BUN post-weaning may reflect greater protein breakdown or dietary protein excess, while changes in BHB concentration may signal shifts in energy metabolism due to dietary adaptation. Elevated GGT levels could indicate liver stress or adaptation to a new diet. The observed decline in T-CHO and phospholipids might be associated with changes in lipid metabolism as calves transition to solid food.
Ruminal Acidosis and Toll-Like Receptor 4 (TLR4)
Another significant finding is the association between ruminal pH and the immune response through TLR4, a recognition receptor for lipopolysaccharides (LPS) from gram-negative bacteria. It implies that changes in ruminal acidity could influence the expression of TLR4 and subsequent immune responses to microorganisms in the rumen.
Keywords
1. Weaning transition in calves
2. Ruminal pH impact
3. Holstein calf health
4. Blood metabolites in livestock
5. Rumen epithelium gene expression
Discussion
The study offers a broad perspective, encompassing the physiological, immunological, and metabolic adaptations occurring in Holstein calves during the weaning transition. The changes in ruminal pH and their associations with gene expression and immune cell populations underline the complex interactions between diet and calf health.
Alterations in blood metabolites not only signal the immediate dietary shift but may also foretell long-term health outcomes. The link between ruminal pH and TLR4 expression could be pivotal in understanding how rumen conditions influence systemic immune functions and could emerge as a focal point for preventing diseases associated with dietary transitions in ruminants.
The research further highlights the importance of dietary components, as the inclusion of forage in the diet correlated with differences in these physiological responses. It suggests that integrating forage into the weaning diet could potentially buffer against abrupt changes in ruminal pH, thus contributing to a smoother transition and better health outcomes.
Implications for Dairy Farming Practices
Dairy farmers and animal nutritionists can use these findings to design better weaning dietary strategies that support optimal rumen function and systemic health. Calves that smoothly transition during weaning are likely to grow into healthier, more productive dairy cattle.
References
DOI: 10.1292/jvms.18-0659
1. Berthon, P., Hopkins, J. (1996). Ruminant cluster CD14. Vet. Immunol. Immunopathol. 52: 245–248. doi: 10.1016/0165-2427(96)05568-7
2. Chen, Y., Oba, M., Guan, L. L. (2012). Variation of bacterial communities and expression of Toll-like receptor genes in the rumen of steers differing in susceptibility to subacute ruminal acidosis. Vet. Microbiol. 159: 451–459. doi: 10.1016/j.vetmic.2012.04.032
3. Connor, E. E., Baldwin, R. L., 6th, Li, C. J., Li, R. W., Chung, H. (2013). Gene expression in bovine rumen epithelium during weaning identifies molecular regulators of rumen development and growth. Funct. Integr. Genomics 13: 133–142. doi: 10.1007/s10142-012-0308-x
4. Kim, Y. H., Toji, N., Kizaki, K., Kushibiki, S., Ichijo, T., Sato, S. (2016b). Effects of dietary forage and calf starter on ruminal pH and transcriptomic adaptation of the rumen epithelium in Holstein calves during the weaning transition. Physiol. Genomics 48: 803–809. doi: 10.1152/physiolgenomics.00086.2016
5. Stefanska, B., Człapa, W., Pruszynska-Oszmałek, E., Szczepankiewicz, D., Fievez, V., Komisarek, J., Stajek, K., Nowak, W. (2018). Subacute ruminal acidosis affects fermentation and endotoxin concentration in the rumen and relative expression of the CD14/TLR4/MD2 genes involved in lipopolysaccharide systemic immune response in dairy cows. J. Dairy Sci. 101: 1297–1310. doi: 10.3168/jds.2017-12896
Conclusion
The study provides a gateway to a deeper understanding of the biological processes underpinning the weaning transition in Holstein calves. By exploring the interplay between ruminal pH, blood metabolites, and gene expression, it opens avenues for refining calf nutrition protocols, ultimately paving the way for healthier livestock and a more robust dairy industry. Further research is necessary to extend these findings and develop practical interventions.