The Effect of Contract-Rearing on the Health Status of Replacement Dairy Heifers

SIMPLE SUMMARY: In this study, we set out to compare the health of contract- vs. conventionally reared replacement dairy heifers. Contract-reared heifers are raised off-farm on another farm by another farmer, for a fee. A total of 120 dairy farmers were enrolled in the study: 55 farmers were rearing their own heifers (control farmers; CFs), and 65 were sending heifers to a contract-rearing farm (source dairy farmers; SDFs). Over two years, we monitored approximately 5500 replacement heifers from these farms to check for signs of ill health using a calf health scoring system that involved individually examining each animal at four farm visits (twice annually). Additionally, faecal and nasal swabs were taken from a proportion of heifers with clinical signs of diarrhoea and respiratory disease. Overall, the results indicated few differences in the health and infectious status of home-reared versus contract-reared heifers. Additionally, the number of source dairy farms represented and mixing of heifers from multiple farms at the rearing unit were not associated with an increased incidence of respiratory disease or diarrhoea among contract-reared heifers. Therefore, it was concluded that contract-rearing did not result in adverse health outcomes for replacement dairy heifers. ABSTRACT: The aim of this study was to compare the health status of contract- vs. conventionally reared replacement dairy heifers over a 2-year period. A total of 120 dairy farmers were enrolled in the study in spring 2018: 55 farmers were rearing their own heifers (control farmers; CFs), and 65 were sending heifers to a contract-rearing farm (source dairy farmers; SDFs). Between spring 2018 and autumn 2019, approximately 5500 replacement heifers from these farms were monitored for signs of ill health during four farm visits using a modified version of the Wisconsin calf health scoring system. Additionally, faecal and nasal swabs were taken from a proportion of heifers with clinical signs of diarrhoea and respiratory disease to determine the associated aetiological agents. Results indicate few differences in the health status and pathogen exposure status of home-reared versus contract-reared heifers. Additionally, the number of source dairy farms represented and commingling of heifers from multiple origins at the rearing unit were not associated with an increased incidence of respiratory disease or diarrhoea among contract-reared heifers. It was concluded that contract-rearing did not result in adverse health outcomes for replacement dairy heifers. This is the first study to demonstrate this finding in a robust, longitudinal, herd-level population study.