Original Research ARTICLE
The effect of abnormal reproductive tract discharge on the calving to conception interval of dairy cows
- 1Graham Centre for Agricultural Innovation, Charles Sturt University, Australia
- 2School of Animal and Veterinary Sciences, Charles Sturt University, Australia
- 3Department of Large Animal Clinical Sciences, College of Veterinary Medicine, Michigan State University, United States
- 4Sydney School of Veterinary Science, Faculty of Science, The University of Sydney, Australia
Prolonged calving-to-conception interval (CCI) can increase economic loss in cattle. We investigated the effect of post-calving abnormal reproductive tract discharge (ARTD) on CCI in dairy cows and quantified the relationship of ARTD and associated risk factors with CCI.
The source population was dairy cows that calved in the study period on three pasture-based, year-round calving farms in the Riverina, NSW, Australia. Farm records and records from veterinarians’ visits were analysed. ARTD was defined as the presence of reproductive tract discharge according to the following classification: per vaginum purulent discharge ≥21 days post-calving or mucopurulent discharge >26 days post-calving.
The incidence of ARTD was calculated. A Kaplan-Meier survivor function was used to estimate median time to conception post-calving dependent on the presence or absence of ARTD. Mixed effects Cox-proportional hazard models were used to estimate the direct and indirect effects of ARTD, and other potential risk factors on CCI such as body condition score (BCS), ambient temperature and milk yield. Model structures were guided by a directed acyclic graph of potential risk factors for ARTD.
The incidence of ARTD in lactations was 16% (95% CI 13.8-18.5%) and did not differ significantly between the three farms (P >0.05). The median CCI was 176 days and 118 days for lactations with and without ARTD, respectively (P <0.01). The rate of pregnancy following calving in cows with ARTD was significantly decreased relative to the rate of pregnancy in cows without (total effect hazard ratio = 0.62, se = 0.18, P =0.01). High peak milk yield (>32 L) and parity >2 also significantly extended CCI. We did not observe an effect of BCS or ambient temperature on CCI.
The incidence of ARTD in the current study was consistent with clinical endometritis (considered a major source of ARTD) reported in other studies. In contrast – and despite regular veterinary assessment and treatment of on the farms in this study – ARTD extended CCI. Evaluation of the economic impact of ARTD on dairy farms in this region is warranted, and methods to identify high risk cows and develop effective interventions are required.
Keywords: Dairy, Cow, Calving to conception interval, Endometritis, Holstein, Friesian
Received: 17 Mar 2019;
Accepted: 08 Oct 2019.
Copyright: © 2019 Hay, Gunn, Abuelo and Brookes. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.
* Correspondence: Dr. Victoria J. Brookes, School of Animal and Veterinary Sciences, Charles Sturt University, Wagga Wagga, Australia, email@example.com