Risk factors for stillbirths and mortality during the first 24h of life on dairy farms in Hokkaido, Japan 2005-2009.
This was a retrospective cohort study using data from the insurance scheme provided by the Japanese Mutual Aid Association (NOSAI). The population of interest comprised all cattle born on NOSAI-client farms in the Japanese prefecture of Hokkaido, Japan for the period 1 April 2005-31 March 2009. The outcome of interest was whether or not at least one calf was stillborn, had died during delivery or died during the first 24 hours of life for a given calving event, termed first 24h mortality risk. A mixed-effects logistic regression model was developed to identify explanatory variables associated with first 24h mortality risk. The final data set comprised details of 1,281,737 calving events on a total of 5172 dairy herds from 19 NOSAI branches located throughout the prefecture of Hokkaido. Throughout the study period 7.68 (95% CI 7.64-7.73) of every 100 calving events had at least one calf that was either stillborn, dead at the time of delivery or dead during the first 24h of life. Factors that were positively associated with an increase in first 24h mortality risk included delivery during the colder months of the year (November-March), being of Wagyu breed, having a multipara dam, multiple (as opposed to single) birth deliveries, and delivery in larger herds. ​After adjusting for the fixed effects included in our multilevel model, 89% of the unexplained variation in first 24h mortality risk was at the calving event level. We propose that the data recording requirements of the NOSAI scheme are extended to include details of calving events (e.g. the presence or absence of dystocia) and details of the way in which calves are managed post delivery. This would allow more subtle risk factors for calf mortality to be identified which, in turn, will lead to refinement of recommendations for calf management during the first 24h of life in this area of Japan.
Global Agro-Medicine Research Center, Japan; Obihiro University of Agriculture and Veterinary Medicine, Inada-cho, Obihiro, Hokkaido 080-8555, Japan.
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Kayano
Field Centre of Animal Science and Agriculture, Japan; Obihiro University of Agriculture and Veterinary Medicine, Inada-cho, Obihiro, Hokkaido 080-8555, Japan. Electronic address: kadohira@obihiro.ac.jp.
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Kadohira
Faculty of Veterinary and Agricultural Sciences, The University of Melbourne, Parkville 3010 Victoria, Australia.
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Stevenson
D000818:Animals; D000831:Animals, Newborn; D002417:Cattle; D002418:Cattle Diseases / Q000453:epidemiology* / Q000209:etiology / Q000401:mortality; D015331:Cohort Studies; D003612:Dairying; D007564:Japan / Q000453:epidemiology; D016015:Logistic Models; D012189:Retrospective Studies; D012307:Risk Factors; D050497:Stillbirth / Q000453:epidemiology / Q000662:veterinary*
Dairy; Epidemiology; Japan; Multilevel modelling; Peri-natal mortality