title: Risk factors for and reproductive outcomes of phantom cows on New Zealand dairy farms.
abstract: OBJECTIVE
  To determine some of the risk factors for cows not observed in oestrus within 35-42 days of an unsuccessful artificial insemination (AI; phantom cows), and the reproductive outcomes and effect of treatment of phantom cows.
  
  
  METHODS
  Over 2 years, in dairy herds from the Waikato (n=10) and Canterbury (n=4) regions of New Zealand, pregnancy diagnosis was carried out 35-42 days after AI on cows that had been inseminated in the first 3 weeks after the start of mating (PSM) but had not been seen returning to oestrus. Risk factors for phantom cows were analysed using a generalised linear mixed effect model. In Year 1, all phantom cows were left untreated. In Year 2, phantom cows were categorised as having a corpus luteum (CL) (CL+ n=120), or having ovarian follicles≥10 (n=101) or <10 (n=40) mm in diameter. Cows with a CL were treated with cloprostenol or untreated and placed with bulls. Cows with no CL received intravaginal progesterone (P4) for 7 days, with injection of gonadotrophin-releasing hormone (GnRH) on Days 0 and 9, and cloprostenol on Day 7 followed by AI. Pregnancy diagnosis of all cows took place 100-120 days after PSM and interval to conception and final pregnancy rate determined.
  
  
  RESULTS
  Overall, of cows inseminated in the first 3 weeks after PSM that did not return to oestrus, 610/6,734 (9.1%) were phantom cows. From the final multivariable analysis, treatment for anoestrus, BCS≤4.0 at mating, being 2 or >6 years of age, and pure-bred, and decreasing interval between calving and mating, until 98 days post calving, were associated with increased odds of being a phantom cow. Compared to all other groups of cows, phantom cows had a longer interval to conception (p<0.001) and a lower final pregnancy rate (p<0.001). Treatment of CL+ cows or cows with follicles≥10 mm did not affect reproductive outcomes (p>0.3). For cows with follicles<10 mm treatment decreased the final percentage not pregnant (3/27; 11%; p=0.01) and interval to conception (21 days; p=0.02) compared with controls (7/13; 54% and 37 days, respectively).
  
  
  CONCLUSIONS
  Risk factors for phantom cows were identified that could be manipulated to reduce the number of phantom cows in a herd, in particular increasing BCS. Treatment of the majority of phantom cows did not improve reproductive performance.
authors.affiliation: a VetEnt , Te Awamutu , New Zealand.
authors.forename: E L
authors.initials: EL
authors.lastname: Cuttance
authors.forename: W A
authors.initials: WA
authors.lastname: Mason
mesh_terms: D000818:Animals; D002417:Cattle / Q000502:physiology*; D003008:Cloprostenol / Q000494:pharmacology; D003338:Corpus Luteum / Q000502:physiology; D004971:Estrus / Q000502:physiology*; D004973:Estrus Synchronization / Q000379:methods; D005260:Female; D007987:Gonadotropin-Releasing Hormone / Q000008:administration & dosage / Q000494:pharmacology; D007315:Insemination, Artificial / Q000662:veterinary*; D008297:Male; D009520:New Zealand; D011247:Pregnancy; D018873:Pregnancy Rate; D011374:Progesterone / Q000008:administration & dosage / Q000494:pharmacology; D012098:Reproduction; D012307:Risk Factors
chemical_list: D007987:Gonadotropin-Releasing Hormone; D003008:Cloprostenol; D011374:Progesterone
keywords: Phantom cow syndrome; dairy cattle; reproductive performance; risk factors