Identifying risk factors for mastitis in postpartum bitches

Mastitis in postpartum bitch is a disease that affects wellbeing of both dam and pups that rely on their mother’s milk as the sole source of nutrition during a critical growth period. Risk factors for canine mastitis have not been well-studied and this information could help veterinarians and breeders identify females that may need closer monitoring. Goal of this study was to identify risk factors for postpartum mastitis in bitch. We hypothesized that age, breed, litter size, and whelping interventions are associated with risk of developing mastitis in postpartum bitch. A retrospective cohort study was performed using data from 2 guide dog colonies over a 13-year period. A total of 2,489 whelpings occurred during study period. All bitches were monitored closely and mastitis was diagnosed by colony veterinarian. Risk factors examined were: colony, breed of dam, litter size, neonatal pup loss, age (in years), parity, dystocia, use of oxytocin during whelping, use of calcium during whelping, and if cesarean section was performed. Risk factors were evaluated individually and offered to the model if p < 0.20. A final model was built using a backwards-stepwise method and colony was forced into the model to account for colony-specific differences. Logistic regression ANOVA was performed using JMP Pro v. 14 (SAS Institute). Mastitis incidence was 8.9% (222 cases). Three significant risk factors were identified and offered to the model built; all were retained in the final model. First, mastitis risk increased as litter size increased and ROC analysis identified ≥ 9 pups as the optimal threshold. Bitches that had ≥ 9 pups (120/1,048 or 11.5% versus 7.1% in litters < 9 pups) were more likely to develop mastitis (OR = 1.67, 95% CI 1.26 - 2.21; p = 0.0003). Second, there was an effect of dam breed; Golden Retrievers (12.9% OR = 2.81, 95% C.I. 1.32 - 5.99; p = 0.0075) and Labrador Retrievers (8.6% OR = 2.05, 95% C.I 1.03 - 4.11; p = 0.0418) were more likely to develop mastitis compared to German Shepherd Dogs (4.8%). Finally, bitches that whelped naturally (9.4%) were more likely to develop mastitis compared to bitches that had cesarean section (5.7%) performed (OR = 1.70, 95% CI 1.04 - 2.76; p = 0.0332); therefore, bitches that underwent cesarean section had lower rates of mastitis. Surprisingly, bitches with singletons (3%) had lower mastitis risk than bitches with large litters, and neonatal (> 3 days) loss of pups did not affect mastitis risk. The dogma of older bitches having higher risk of mastitis was also not observed in our population. There is an effect of dam breed on mastitis risk and further studies examining more breeds are warranted.

Keywords: Canine, mastitis, risk factors

This manuscript was originally published in the journal Clinical Theriogenology Vol 12(3) Sept 2020.  Clinical Theriogenology is the official journal of the Society for Theriogenology (SFT) and the American College of Theriogenologists (ACT).  This content has been reproduced on the IVIS website with the explicit permission of the SFT/ACT.