title: Resynchronising returns to service in anoestrous dairy cows in the South Island of New Zealand.
abstract: OBJECTIVE
  To investigate the effect of targeted resynchronisation of cows treated for non-observed oestrus before the planned start of mating (PSM), that were not detected in oestrus or pregnant 23 days after treatment (phantom cows), on the proportion pregnant at 42 days after PSM and the end of mating.
  
  
  METHODS
  Farm staff from eight herds in two regions of the South Island of New Zealand identified 1,819 cows not showing oestrus by 10 days before PSM. These cows were treated with intravaginal progesterone for 7 days, and I/M gonadorelin 10 days and 1 day before PSM. Three days before PSM they were injected with cloprostenol and equine chorionic gonadotrophin, with fixed time artificial insemination (FTAI) at PSM. By 23 days after PSM, 1,218 cows had not returned to oestrus. Of these, 161 cows confirmed not pregnant by transrectal ultrasonography were randomly assigned to no treatment (control group; n=74) or were resynchronised 25 days after PSM using the same treatment programme as above, with FTAI 35 days after PSM (n=87). All cows that returned to oestrus were artificially inseminated until 42 days after PSM, when natural mating was used. All cows were examined using transrectal ultrasonography 80 to 90 days after PSM to confirm conception dates.
  
  
  RESULTS
  Of the 1,819 anoestrous cows treated before PSM, 526 (29 (95% CI=23.1-34.0)%) had not been observed in oestrus by 23 days after PSM and had not conceived, so were diagnosed as phantoms cows. For resynchronised cows, 42/87 (48 (95% CI=37.8-58.8)%) were pregnant by 42 days after PSM compared to 21/74 (28 (95% CI=18.1-38.7)%) control cows (p=0.009). At the end of mating 58/87 (67 (95% CI=56.6-76.7)%) cows in the resynchronised group were pregnant and 46/74 (62 (95% CI=50.9-73.2)%) in the control group (p=0.554). The hazard of conception from 21 to 42 days after PSM was 1.9 (95% CI=1.07-3.12) times greater for resynchronised than control cows (p=0.026).
  
  
  CONCLUSIONS
  In cows not observed in oestrus and treated before PSM, resynchronisation increased the proportion pregnant by 42 days after PSM.
  
  
  CONCLUSIONS
  The benefit of resynchronisation depends on the number of anoestrous cows before PSM and the number of phantom cows after PSM. However at the herd-level it is likely that providing advice to reduce the known risk factors for cows not being observed in oestrus before the PSM may well be more cost effective than identifying and treating a sub-population of phantom cows.
authors.affiliation: a Centre for Dairy Excellence , 20 Wilson Street, Geraldine 7930 , New Zealand.
authors.forename: A J
authors.initials: AJ
authors.lastname: Bates
authors.affiliation: b North Canterbury Veterinary Clinics , PO Box 58, Culverden 7391 , New Zealand.
authors.forename: A G
authors.initials: AG
authors.lastname: Kenyon
authors.affiliation: c Institute of Veterinary, Animal and Biomedical Sciences, Massey University , Private Bag 11222, Palmerston North , New Zealand.
authors.forename: R A
authors.initials: RA
authors.lastname: Laven
authors.affiliation: d Vetlife Temuka , 35 King Street, Temuka 7920 , New Zealand.
authors.forename: J C
authors.initials: JC
authors.lastname: McDowell
mesh_terms: D000282:Administration, Intravaginal; D000780:Anestrus; D000818:Animals; D002417:Cattle; D006063:Chorionic Gonadotropin / Q000627:therapeutic use; D003008:Cloprostenol / Q000008:administration & dosage / Q000627:therapeutic use; D003612:Dairying / Q000379:methods; D004973:Estrus Synchronization / Q000379:methods*; D005260:Female; D007987:Gonadotropin-Releasing Hormone / Q000008:administration & dosage / Q000627:therapeutic use; D007273:Injections, Intramuscular / Q000662:veterinary; D007315:Insemination, Artificial / Q000379:methods / Q000662:veterinary; D009520:New Zealand; D011247:Pregnancy; D011374:Progesterone / Q000008:administration & dosage / Q000627:therapeutic use
chemical_list: D006063:Chorionic Gonadotropin; D007987:Gonadotropin-Releasing Hormone; D003008:Cloprostenol; D011374:Progesterone
keywords: Anoestrous; dairy; progesterone; resynchronisation; seasonal calving