The aims of the current study were to estimate the prevalence of enteropathogens in calves in Norwegian dairy herds, evaluate the clinical consequences of protozoal infections, and identify risk factors for diarrhea. The 135 participating herds were randomly selected from those in The Norwegian Dairy Herd Recording System that had at least 15 cow-years. Each herd was followed for 1 yr. Fecal samples from calves with (n = 68) or without (n = 691) diarrhea were analyzed for the presence of Cryptosporidium, Giardia, and Eimeria species. Diarrheic samples (n = 191) were assayed for rotavirus group A, bovine coronavirus (BCoV), Cryptosporidium, and Escherichia coli F5 by antigen ELISA. Blood samples (n = 1,348) were analyzed for antibodies against BCoV and rotavirus. Potential risk factors for diarrhea were analyzed by using Cox regression analysis adjusted for herd frailty effect. Rotavirus and Cryptosporidium were the most commonly detected enteropathogens in diarrheic samples. A high level of Cryptosporidium shedding or BCoV seropositive calves in a herd was associated with an increased risk of diarrhea. Other factors found to increase the risk of diarrhea were use of slatted concrete floor in group pens versus other floor types [hazard ratio (HR) = 8.9], housing of calves in free-stalls compared with tie-stalls (HR = 3.7), purchasing of calves into the herd versus not purchasing calves (HR = 4.1), and calves being born during winter compared with other seasons of the year (HR = 1.5).

The aims of this study were to estimate the seroprevalence of respiratory agents in Norwegian dairy calves and to identify risk factors for respiratory disease. The participating 135 herds were randomly selected from those in The Norwegian Dairy Herd Recording System with at least 15 cow years. Each herd was followed for 1 yr. Blood samples from calves of >150 d of age (n = 1,348) were analyzed for antibodies against parainfluenza virus 3, bovine coronavirus (BCoV), bovine respiratory syncytial virus (BRSV), and Mycoplasma bovis. Calves reported to have been on pasture (n = 139) were tested for antibodies against Dictyocaulus viviparus. Seroprevalences for parainfluenza virus 3, BCoV, BRSV, and D. viviparus at the calf level were 50.2, 39.3, 31.2, and 4.3%, respectively. No calves were antibody positive for M. bovis. Calves in herds with BCoV-seropositive calves had an increased risk of respiratory disease compared with herds in which BCoV antibodies were not detected [hazard ratio (HR) = 3.9], as had calves in herds in which the majority (>54%) of the sampled calves were seropositive for BRSV (HR = 2.7). Other factors found to increase the risk of respiratory disease in calves were shared housing with cows during the first week of life compared with separate housing (HR = 16.7), a larger herd size (>50 cow years) compared with smaller herds (HR = 8.2), more than an 8-wk age difference between calves housed together in the same group pen compared with having pen mates of a more similar age (HR = 3.9), previous recordings of diarrhea compared with no recorded diarrhea (HR = 3.9), and leaving calves with dams for >24 h after birth compared with earlier separation (HR = 3.5).

A novel SYBR Green based real-time RT-PCR assay for detection of genogroup III bovine noroviruses (BoNoV) was developed and the assay applied to 419 faecal samples from calves with and without diarrhoea. The samples were obtained from 190 Norwegian dairy and beef herds. BoNoV was detected in 49.6% of the samples from 61.1% of the herds indicating that BoNoV is ubiquitous in Norway. The overall prevalence was not significantly different in diarrhoea and non-diarrhoea samples. Analyses of polymerase gene sequences revealed both genotype III/1 and III/2 with genotype III/2 (Newbury2-like) being the most prevalent. Detected capsid sequences were restricted to Newbury2-like and the chimeric Bo/Thirsk10/00/UK strain. The RNA polymerase genotypes of the circulating BoNoVs in Norway were predicted by melting temperature analysis. Additional data from a challenge experiment suggest that a high proportion of young calves are shedding low levels of BoNoV for a prolonged time after recovering from the associated diarrhoea. The findings may explain some of the discrepancies in detection rates from previous studies and explain why some studies have failed to detect significant prevalence differences between calves with and without diarrhoea. It may also shed new light on some epidemiological aspects of norovirus infections.