Effects of bovine respiratory disease on immune response, animal performance, nitrogen balance, and blood and nutrient flux across total splanchnic tissues in beef steer

Objectives were to evaluate the effects of bovine respiratory disease (BRD) on immune response, cattle performance, carcass characteristics, visceral organ mass, apparent nutrient digestibility, nutrient retention, and blood flow and net flux of nutrients across the portal-drained viscera (PDV) and liver. Steers were challenged with bovine viral diarrhea virus (BVDV) and/or Mannheimia haemolytica (MH).;Findings and Conclusions: Steers challenged with BVDV and/or MH showed alterations in the immune system that were ultimately reflected in decreased performance and nitrogen balance. In addition, plasma amino acid concentrations were decreased and liver removal increased suggesting enhanced turnover of endogenously released amino acids. These changes in amino acid metabolism induced by BRD suggest that amino acid requirements are different for cattle undergoing an acute immune challenge and can remain increased even 14 days after the immune challenge occurs even though clinical or physiological manifestations of disease are no longer detectable.