To investigate the risk factors for neonatal calf diarrhoea, a cross-sectional study was conducted on 97 New Zealand dairy farms. Faecal specimens from 1283 calves were scored as liquid, semi-solid or solid, and analysed for bovine rotavirus (BRV) and coronavirus (BCV), enterotoxigenic K99(+)Escherichia coli (K99), Salmonella spp. and Cryptosporidium parvum. Calf- and farm-level data were collected by means of a questionnaire and the odds of liquid faeces calculated using mixed effects logistic regression models. Among the infectious agents, only C. parvum (odds ratio [OR] = 2.6; 95% confidence interval [CI], 1.3-5.6; P = 0.02), BRV (OR = 2.7; 95% CI, 1.3-5.9; P = 0.01) and co-infection with more than one agent (compared with mono-infection: OR = 2.5; 95% CI, 1.3-4.8; P = 0.01) were associated with increased odds of liquid faeces in calves which were 9 to 21 days old. Housing of calves in open barns so exposing them to the weather was also associated with increased odds of liquid faeces compared with closed barns (OR = 2.1; 95% CI, 1.1-12.2; P = 0.03). Vaccinating cows against calf enteropathogens (OR = 0.2; 95% CI, 0.1-0.9; P = 0.03), administering waste milk (from mastitis and/or containing antibiotics; OR = 0.4; 95% CI, 0.1-0.8; P = 0.01), the sex of calves (females compared to males OR = 0.2, 95% CI, 0.07-0.7; P <0.01), and the use of straw for bedding (OR = 0.2; 95% CI, 0.03-0.9; P = 0.03) decreased the odds of liquid faeces. Conversely, in calves that were 1 to 5 days old, only K99 was associated with liquid faeces (OR = 4.6; 95% CI, 1.2-16.1; P = 0.02). In this age group, the odds of liquid faeces were smaller on farms where females took care of the calves, compared with males (OR = 0.4; 95% CI, 0.01-0.9; P = 0.04).

Cryptosporidium isolates from diarrheic foals in New Zealand (n ‫؍‬ 9) were identified as C. parvum, subtyped at two polymorphic loci, and compared with human (n ‫؍‬ 45) and bovine (n ‫؍‬ 8) isolates. Foal C. parvum isolates were genetically diverse, markedly similar to human and bovine isolates, and carried GP60 IIaA18G3R1 alleles, indicating a zoonotic potential.

This study provides epidemiological estimates of the prevalence of calves' enteropathogens in New Zealand, which could be used for infection risk assessment or estimation of the environmental loads of pathogens shed in cattle faeces.

The fact that Cryptosporidium parasites were identified in 18% of faecal specimens from foals analysed for this agent in 2005-2007 by the participating laboratory indicated that infection with this agent in foals is not uncommon. Collectively, the results of this and previous studies performed in New Zealand indicate C. parvum is a cause of diarrhoea in newborn foals, potentially accounting for a proportion of cases empirically diagnosed as foal heat diarrhoea. It is therefore advisable to take precautions when handling diarrhoeic foals, until this potentially zoonotic agent is ruled out in the laboratory.

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