title: A longitudinal study of reproductive performance and management of 82 dairy herds in the Waikato region with differing policies on the routine use of induction of parturition.
abstract: OBJECTIVE
  To describe the reproductive performance and management practices over three lactations in dairy herds that had different policies on the routine use of induction of parturition; to describe any change in outcomes in herds that ceased inductions during the study period; and to investigate other herd-level factors associated with reproductive performance.
  
  
  METHODS
  From 2002 to 2004 inclusive, a longitudinal study was undertaken in 82 herds in the Waikato region of New Zealand. The main outcome variables were the percentage of cows pregnant after 8 weeks of mating (8-week in-calf rate) and the percentage of cows not pregnant at the end of mating (final empty rate). Data were obtained from pregnancy diagnosis records from a veterinary practice and from an electronic database, and a questionnaire. Herds were classified as either not using inductions in the three lactations (Nil; n=14), ceased inductions in the second or third lactation (Transitional; n=12), or continuing to induce (Continuing; n=56).
  
  
  RESULTS
  Nil herds had a higher 8-week in-calf rate (p=0.01) than Transitional or Continuing herds (83%, 78% and 79%, respectively). The final empty rate in Nil and Transitional herds was similar (10.2% and 9.9%), tended to be greater in Nil than in Continuing herds (10.2% vs 9.0%; p=0.06) and was greater in Transitional than in Continuing herds (9.9% vs 9.0%; p=0.04), respectively. Multivariable modelling found that 8-week in-calf rates were additionally associated with year of lactation, interval from the planned start of calving (PSC) to the median calving date, duration of artificial insemination, and 21-day submission rate; and that final empty rates were associated with year of lactation, predominant breed, percentage of the herd calving within 40 days of the planned start of mating (PSM), the total duration of mating, and the 21-day submission rate, but not the herd induction policy. A change to ceasing routine use of induction tended to be associated (p=0.07) with a 2.5% increase in the final empty rate in the lactation of change.
  
  
  CONCLUSIONS
  The reproductive performance of herds was associated with induction policy, in addition to other factors. Herds that ceased induction had a greater 8-week in-calf rate but a greater final empty rate than those that continued. The higher empty rate in Nil herds was partly due to their shorter duration of mating.
  
  
  CONCLUSIONS
  Herdowners and their advisors planning to cease routine use of induction should plan for an increase in the final empty rate in both the lactation of change and in the longer term, and undertake measures to mitigate against this effect.
authors.affiliation: Animal Health Centre, Morrinsville, New Zealand. ccompton@ahc.co.nz
authors.forename: C W R
authors.initials: CW
authors.lastname: Compton
authors.forename: S
authors.initials: S
authors.lastname: McDougall
mesh_terms: D000822:Animal Husbandry; D000818:Animals; D002417:Cattle / Q000502:physiology*; D003612:Dairying; D005260:Female; D007774:Lactation; D008137:Longitudinal Studies; D009520:New Zealand; D011247:Pregnancy; D012098:Reproduction / Q000502:physiology*