Pre-weaning plane of nutrition and Mannheimia haemolytica dose influence inflammatory responses to a bovine herpesvirus-1 and Mannheimia haemolytica challenge in post-weaning Holstein calves

摘要

The objectives of this study were to determinewhether plane of nutrition (PON) of milk replacerpreviously provided to calves, and dosage level ofMannheimia haemolytica (MH), influenced inflammatoryresponses to a combined viral-bacterial respiratorychallenge. Holstein calves (1 d of age; n = 30) wereassigned to treatments in a 2 × 3 factorial with preweaningPON and MH dose as main effects (n = 5 pertreatment). Calves were fed either a low (LPN; n =15) or a high PON (HPN; n = 15) from birth throughweaning. Calves fed LPN were fed 436 g of dry matter(DM) per day of milk replacer until weaning, and HPNcalves were fed 797 g of DM per day of milk replacerfrom d 1 to 10 and 1,080 g of DM per day from d 11until weaning. Calf starter and water were offered adlibitum. Calves were step-down weaned beginning at d54 and moved into an enclosed barn at d 70. Indwellingrectal temperature (RT) recording devices and jugularcatheters were inserted at d 80. Calves were challengedwith 1.5 × 10~8 plaque-forming units (pfu) per mL of bovineherpesvirus-1 (BHV-1) in each nostril at d 81 andwith either 10~6, 10~7, or 10~8 cfu of MH at d 84. Bloodsamples were collected at varying intervals relative toBHV-1 and MH challenges. Four LPN calves eitherdied or were euthanized soon after the 144-h observationperiod, whereas all HPN calves survived the entireobservation period. As dosage of MH administeredincreased, acute and systemic inflammatory responsesincreased. Higher doses of MH resulted in increasedleukocyte, neutrophil, and haptoglobin concentrationsin infected calves. Data from the current study suggestthat the highest dose, 10~8 cfu, triggered weaned calves’acute disease response, whereas the lower doses, 10~6and 10~7 cfu, caused more moderate inflammation anddisease. The effects of PON on inflammation responsesto the disease challenge indicated that calves previouslyfed the LPN diet had more severe pathophysiologicalresponses. Calves fed LPN showed higher peripheralneutrophil and leukocyte counts and serum haptoglobinconcentrations following the BHV-1 challenge. Additionally,following the MH challenge, LPN calves hadhigher peripheral neutrophil counts, neutrophil-tolymphocyteratios, and serum tumor necrosis factor-αconcentrations. These data demonstrate that higherdoses of MH increase the acute inflammatory responseand prolong inflammation, and that calves previouslyfed LPN responded more severely to the combinedviral-bacterial respiratory challenge.