Systematic Assessment of Mortalities in Calves at Commercial Calf Ranches and the Association Between Cause of Death and Season

As breeding practices in dairy industry shift toward the use of beef semen, the number of calves sent off-site for rearing has increased. The limited literature describes mortalities by season, sex, or breed within calf ranches. The objectives were to identify primary and co-morbidities at necropsy in calf ranches and determine whether causes of death varied by season, sex, breed, or ranch. Systematic necropsies (n = 243) were performed monthly over 12 months at four ranches by technicians with diagnoses confirmed by veterinarians. Mortalities were classified as respiratory (RESP), gastrointestinal (GI), septicemia (SEPT), or other (OTH) based on gross necropsy findings. A subset from ranches with 12 months of necropsy data (n = 175) was analyzed using generalized linear and multinomial models to evaluate associations between RESP diagnoses or GI lesion locations and 4-month periods, sex, breed, and ranch. Respiratory disease was most common (67.5%), followed by GI (11.5%), SEPT (9.5%), and OTH (11.5%). Most (86.0%) lacked co-morbidities; RESP (7.0%) and OTH (3.7%) were the frequent primary diagnoses with co-morbidities. No significant associations were detected with time, sex, breed, or ranch (<i>p</i> ≥ 0.11 for RESP; <i>p</i> ≥ 0.13 for GI). Although inferences were limited by sample size, findings provide insight into calf mortalities and co-morbidities in commercial ranches.