Short communication: Replacement heifer mortality from weaning until second mating in seasonal-calving, pasture-based dairy herds in New Zealand

摘要

The primary aim of this prospective study was todetermine the postnatal mortality risk of replacementdairy heifers from weaning until the start of their secondmating period (~27 mo of age) in seasonal-calving,pasture-based dairy herds. Data were analyzed from 24farms from the Waikato (n = 15) and Canterbury (n =9) regions of New Zealand. All animals included in thestudy had an identified weaning date. From this pointonward, data on animals that were euthanized, died unassisted,were culled, or were sold were recorded by thefarmer on the home farm or by the grazier, accordingto animal location, and validated using calving, mating,culling, and sold records in their herd improvementdatabase (MINDApro LIC, Newstead, Hamilton, NewZealand). The mortality risk from weaning to the startof the second mating period was calculated by dividingthe number of deaths by the total number of enrolledanimals at weaning. Mortality rate was calculated bydividing the number of deaths over the study periodby the total days at risk, and reported as the mortalityrate per 100 cow years; this measure was also calculatedas the mortality rate per farm. A total of 3,770 animalsfrom 24 farms had data from weaning until the farmplanned start of mating when animals were ~27 mo old.The animal-level mortality incidence risk from weaning(~13 wk of age) to the start of their second mating(~27 mo old) was 2.7% (95% confidence interval: 2.2to 3.3%; 102 deaths/3,770 animals). The median farmlevelmortality incidence risk was 3.0%, with a rangeacross farms from 0 to 7.9%. There was a total of 102deaths over 2,429,362 cow days at risk, with the meantime at risk for the animals of 646 d. The animal-levelmortality was 1.53 deaths (95% confidence interval 1.26to 1.86) per 100 cow years from weaning to second matingstart date. The range in farm-level mortality ratewas 0 to 4.52 deaths per 100 cow years. The hazardof death did not change throughout the study period.The results from this study are difficult to comparewith international studies due to differences in studytiming and duration, reporting method (mortality riskvs. mortality rate), and concerns with data validation.However, to the best of our knowledge, the results fromthis study indicate that postweaning, postnatal mortalityunder the New Zealand seasonal-calving, pasturebasedsystem is lower than most other reported studies.