Objective: A cross-sectional study of seasonally-calving dairy cows in south-western Victoria to quantify the prevalence of anoestrus and to assess the effect of body condition score (BCS), days in milk (DIM) at mating start date (MSD) and age on the likelihood of being diagnosed as anoestrus.
Methods: Age, DIM and BCS details were collected from 1795 cycling and 1399 cows diagnosed as anoestrus in five seasonally-calving dairy herds in Victoria. Multivariable logistic regression was used to quantify the association between BCS, DIM and age and the probability of being diagnosed as anoestrus.
Results: The apparent prevalence of anoestrus in cows that took part in the study was 44% (95% confidence interval (CI) 42-46%). The risk of anoestrus increased with decreases in DIM and BCS. There was a significant interaction between BCS and DIM. For cows >90 DIM at MSD (the reference category) the odds of anoestrus in cows with BCS <4.00 was 8.05-fold (95% CI 3.2-20.2) that of cows of BCS ≥4.50. The risk of anoestrus decreased with increases in cow age. Cows aged 2 and 3-5 years had 2.4-fold (95% CI 1.79-3.22) and 1.4 (95% CI 1.11-1.77) odds of anoestrus, respectively, compared with cows aged ≥6 years.
Conclusion: Reproductive management to maximise the number of days calved at MSD and nutritional management to ensure cows are in BCS >4.5 at mating will reduce the prevalence of anoestrus in Victorian dairy herds.
Keywords: anoestrus; dairy cattle; reproduction; seasonal calving.
© 2016 Australian Veterinary Association.