Aetiology and consequences of reproductive tract diseases in dairy cows : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Veterinary Science at Massey University, Palmerston North, New Zealand
Reproductive tract diseases of dairy cows are common world-wide and results in a decrease in reproductive performance. The research presented in this thesis evaluates the available diagnostic methods for reproductive tract diseases, including the quality of published reports describing these methods in dairy cows. To improve the accuracy of cow-side diagnostic tests for reproductive tract diseases more research is needed, specifically to establish optimal cut-points, timing of examination and test variability (i.e. intra- and interobserver agreement). Moreover, future manuscripts reporting on diagnostic methods for reproductive tract diseases could be improved by using checklists for quality of design and reporting as a guideline.
Research was also done to assess the presence of intrauterine bacteria in early postpartum New Zealand dairy cows and their association with the subsequent reproductive tract infection, inflammation and reproductive performance. The isolation of intrauterine bacteria, irrespective of type, at 23 days postpartum was associated with a decrease in pregnancy within three weeks for the start of the seasonal breeding programme (planned start of mating; PSM; P = 0.05). Escherichia coli isolated at 23 days postpartum tended to increase the time to pregnancy (P = 0.09). However, the presence of E. coli within the first week postpartum was not significantly associated with isolation of Trueperella pyogenes three weeks later (P = 0.53). An interesting finding was the positive association between the elevated recruitment of polymorphonuclear cells in the early postpartum period and a decreased time to pregnancy (P = 0.05).
Susceptibility data, based on minimum inhibitory concentration (MIC), was generated for a range of antimicrobials against E. coli and T. pyogenes from intrauterine origin. Between-herd and between age-group differences in MIC were detected (P = 0.05). Cows diagnosed with intrauterine E. coli with an MIC of =8 µg/mL at 23 days postpartum tended to be at lower risk of pregnancy within six weeks of PSM relative to an MIC of <8 µg/mL (P = 0.09). No interpretative criteria are available for MIC data of antimicrobials against uterine isolates. Hence, more research is required on pharmacokinetic and pharmacodynamic profiles for veterinary antimicrobials.
This thesis describes the first isolation of apparent antibodies to bovine herpesvirus type 4 and the DNA of bovine lymphotropic herpesvirus in New Zealand dairy cattle, both of which may play an important role in the pathogenesis of reproductive tract diseases. Further studies are required to investigate the true impact of these viruses.
The research presented in this thesis provided data useful for further improvement of diagnosis and treatment of reproductive tract diseases in dairy cows.