Alternative Approaches to Antimicrobial Use and Injection Site in Cattle

Bovine herpesvirus-1 (BHV-1) is a viral pathogen that contributes to bovine respiratory disease (BRD) complex. Characterized by inflammation of the upper respiratory tract and trachea and accompanied by nasal lesion and discharge; BHV-1 has the ability to undergo latency in neurological tissue and recrudesce upon stress-induced immunosuppression. Immunostimulatory products are recently available for control of cattle diseases and may reduce the impact of stress-induced immunosuppression, but their efficacy to control the various pathogens involved in BRD is poorly understood. Furthermore, most injectable cattle products have a label indication for intramuscular or subcutaneous administration in the neck but some producers, primarily dairy, choose to administer injections in the ischiorectal fossa (RF); therefore, research on the efficacy and tissue reactivity of alternative injection sites is needed. Experiment 1 investigated the effect of a DNA immunostimulant (Zelnate, Bayer Animal Health) on recrudescence of BHV-1 after dexamethasone challenge administered for 3 consecutive days in beef cattle and Experiment 2 determined the efficacy of the RF as an alternative injection site. In Experiment 1, steers (n=10) and heifers (n=10) were administered 40 mg of dexamethasone i.v. 166-d subsequent to a controlled BHV-1 challenge (1.0 x 108 PFU per nostril). On day 1, calves were administered 2 mL of DNA immunostimulant (Zelnate; ZEL) or sterile saline (CON) i.m. Hematological variables, BHV-1 isolation from nasal swabs, presence of nasal lesions, BHV-1-specific antibody titers and rectal temperature were evaluated daily (0600) for 12 days after dexamethasone challenge. Results indicate that the DNA immunostimulant altered
eosinophil concentration but did not mitigate BHV-1 recrudesce. In Experiment 2, 28 Jersey steers were administered a modified-live virus (MLV) respiratory vaccine (Pyramid 5, Boehringer Ingelheim Animal Health USA) s.c in the neck region (NECK) or in the RF. Blood samples were collected to analyze BVDV-specific antibody titer, performance data was analyzed, and injection site lesions at harvest were observed. Results indicate that MLV respiratory vaccine administration in the RF did not cause injection site lesions and the humoral vaccine response was similar to NECK. The use of a DNA immunostimulant did not mitigate recrudescence of BHV-1 in dexamethasone challenged beef calves previously administered BHV-1 and the RF may be an effective route of administration for MLV. Further research investigating the efficacy of DNA immunostimulants in different disease challenge models is needed to ensure safe use in beef calves and research determining the effects of other commonly administered animal health products in the RF should be further explored.