title: Effects of oestrus synchronisation and fixed-time artificial insemination on the reproductive performance of dairy heifers.
abstract: OBJECTIVE
  To compare the reproductive performance of heifers after oestrus synchronisation and fixed-time artificial insemination with non-synchronised heifers bred by herd sires.
  
  
  METHODS
  Heifers from 10 spring-calving herds were randomly divided into two groups by herd, breed and age. Heifers in one group (the synchronised group, n = 478) were synchronised with a combination of progesterone, oestradiol benzoate and PGF2alpha, and inseminated 50-54 hours after progesterone treatment. Returns to first service were resynchronised with progesterone treatment 16-21 days after the fixed-time artificial insemination. Heifers in the other group (the control group, n = 470) did not receive any treatment and were bred by herd sires.
  
  
  RESULTS
  The conception rate of synchronised heifers to the fixed-time artificial insemination was 51.2% and to the artificial insemination after resynchronisation 40.4%. The pregnancy rate at the end of the breeding season was lower (p<0.001) for the synchronised (92.9%) than for the control (97.2%) group. The interval from start of breeding to calving was earlier for synchronised (295.9 +/- 22.5 days, mean +/- s.d.) than for control (298.5 +/- 17.3 days) heifers.
  
  
  CONCLUSIONS
  Results from this study indicate that the oestrus synchronisation programme used in the present study can reduce reproductive performance by increasing the empty rate compared with natural mating.
authors: Livestock Improvement Corporation Ltd, Private Bag 3016, Hamilton, New Zealand. zxu@lic.co.nz
authors: Z Z
authors: ZZ
authors: Xu
authors: L J
authors: LJ
authors: Burton