The impact of an overweight body condition on pregnancy, parturition, and physical activity in the bitch

Abstract The aim of this study was to determine how an overweight body condition affects pregnancy success in the bitch. Fifteen client-owned medium-large breed bitches were enrolled for sixteen pregnancies from breeding to four weeks postpartum, grouped as lean (LE; body condition score, BCS, 4–5/9; n = 10) or overweight (OW; BCS 6–7/9; n = 6). A triaxial accelerometer (FitBark2) was used to monitor physical activity, quantified as “BarkPoints”. Serum progesterone (P4) and C-reactive protein (CRP) were measured alongside ultrasonographic conceptus growth of inner chorionic cavity diameter (ICCD) and biparietal diameter (BPD). Parturition duration was recorded. Placental microvascular density was quantified through CD31 immunolabeling of the endothelium. Data analysis included t-test, Fisher’s exact test, linear mixed-effects models, or generalized estimating equations; significance was set at P<0.05. LE bitches had significantly higher baseline BarkPoints, which gradually decreased until parturition. BarkPoints of OW bitches did not change through pregnancy, but increased during lactation. All bitches had an increase in BarkPoints in the last 4-6 hours prepartum. OW bitches had clinically notable increases in embryonic resorption rate and duration from 1st visible abdominal contraction to 1st puppy expulsion, although these were not statistically significant. No differences were seen between maternal BCS groups on conceptus growth, parturition duration parameters, placental microvascular density, serum P4 or CRP. In conclusion, an overweight maternal body condition may have clinically important albeit not statistically significant associations with reproductive parameters in this small cohort. Both body condition and reproductive stage (i.e., pregnancy and lactation) appear to affect habitual physical activity level of broodbitches. Lay Abstract Excessive body fat is suspected to negatively affect reproductive success in dogs, similar to other species. Thus, we aimed to determine if overweight dogs had negative pregnancy outcomes. Six overweight and 10 lean female dogs were monitored through pregnancy until the first four weeks of lactation. Lean dogs had higher baseline activity levels at home than overweight dogs. During pregnancy, lean dogs had a gradual decline in their activity that stayed low throughout lactation. Overweight dogs maintained their baseline activity levels throughout gestation, but increased during lactation. No differences were found between the two groups in embryonic growth rate, duration of labor, placental vasculature, or selected blood biomarker concentrations. We noted a potential clinically relevant higher early pregnancy loss and slower labor progression until the birth of the first puppy in overweight bitches, although this was not statistically significant. Although a relatively small number of dogs were included, the results point toward potential negative effects of obesity on canine reproductive performance.