title: Off-site rearing of heifers reduces the risk of Mycobacterium avium ssp. paratuberculosis ELISA seroconversion and fecal shedding in a California dairy herd.
abstract: The objective of this cohort study was to evaluate whether rearing dairy heifers at different premises than the dairy of origin (off-site) reduced the risk of Mycobacterium avium ssp. paratuberculosis (MAP) infection more effectively than rearing on the dairy of origin (on-site). From 2003 to 2005, 3 cohorts of Jersey heifers were born on a single California dairy, with heifers in the first cohort raised on-site until first calving (n=797); heifers in the second cohort raised on-site until approximately 5 mo of age and off-site until about 1 to 2 mo precalving (n=791); and heifers in the third cohort raised off-site from d 1 until about 1 to 2 mo before first calving (n=797). Cohorts were sequentially enrolled, and heifers were followed until death, culling, or up to 6 yr of age. Heifers were tested annually for MAP infection by serum ELISA and bacterial culture of feces, from lactation 1 until they were 6 yr old, and all mortality and culling events were recorded. Compared with cohort 1, cohort 3 had lower hazards of seroconverting and shedding of MAP in feces, approximately 70 and 38%, respectively. Cohort 2 was not significantly different from cohort 1 for the same outcomes. Mortality hazards were only significantly different between cohorts before first calving, with calves raised completely off-site at lower risk than the remaining 2 cohorts. Additionally, the hazards for culling in cohorts 2 and 3 were only significantly different from cohort 1 after the first calving. To our knowledge, the current study is the first cohort study to evaluate the association between off-site heifer rearing and risk of MAP infection, mortality, and culling. Rearing heifer calves off-site, away from infected adult dairy cows, may have allowed for reduced exposure to MAP in the environment of the calves and, hence, served as a control strategy for Johne's disease.
authors.affiliation: Department of Population Health and Reproduction, School of Veterinary Medicine, University of California, Davis, One Shields Avenue, Davis 95616; Veterinary Medicine Teaching and Research Center, School of Veterinary Medicine, University of California, Davis, 18830 Road 112, Tulare 93274. Electronic address: saly@ucdavis.edu.
authors.forename: Sharif S
authors.initials: SS
authors.lastname: Aly
authors.affiliation: Veterinary Medicine Teaching and Research Center, School of Veterinary Medicine, University of California, Davis, 18830 Road 112, Tulare 93274; Department of Medicine and Epidemiology, School of Veterinary Medicine, University of California, Davis, Davis 95616.
authors.forename: Ian A
authors.initials: IA
authors.lastname: Gardner
authors.affiliation: California Animal Health and Food Safety Laboratory, Tulare Branch, 18830 Road 112, Tulare 93274.
authors.forename: John M
authors.initials: JM
authors.lastname: Adaska
authors.affiliation: California Department of Food Agriculture, Animal Health Branch, Sacramento 95814.
authors.forename: Randall J
authors.initials: RJ
authors.lastname: Anderson
mesh_terms: D000822:Animal Husbandry; D000818:Animals; D002140:California; D002417:Cattle; D002418:Cattle Diseases / Q000453:epidemiology / Q000382:microbiology*; D015331:Cohort Studies; D004797:Enzyme-Linked Immunosorbent Assay / Q000662:veterinary; D005243:Feces / Q000382:microbiology; D005260:Female; D016927:Mycobacterium avium subsp. paratuberculosis / Q000302:isolation & purification*; D010283:Paratuberculosis / Q000453:epidemiology / Q000382:microbiology*
keywords: cohort study; off-site heifer rearing; paratuberculosis; transmission risk