Metabolic changes in obese pregnant mares

Abstract

Pregnancy in mares is associated with insulin dysregulation (Fowden et al. Equine Veterinary Journal. 1984; 16(4), 239-246), which is exacerbated by obesity (Pardié et al. International Congress on Animal Reproduction. June 2022; p204, W71). We studied the effect of body condition score (BCS) on metabolic variables in Criollo pregnant mares. Criollo pregnant mares (n=41) were categorized according to their BCS (scale 1-9, Henneke et al. Equine Veterinary Journal. 1983; 15(4), 371-372) as obese (7 to 9 BCS, n=26) or normal BCS (<7, n=15). Animals were grouped into three gestational periods; between 3 and 5 months (mo) of gestation (period I), 8 and 9 mo (period II) and the last mo of gestation (period III), BCS was determined and serum was obtained for biochemistry determination in every period. Biochemistry variables were determined by spectrophotometer, insulin by immunoradiometric assay and all variables were analyzed by ANOVA using a mixed procedure including BCS group, observation (time of gestation) and their interaction. The cut off value used was P<0.05. Glucose concentration was affected by gestation (P<0.0001), BCS (P=0.017) and their interaction (P=0.0005). Glucose concentrations were greater in obese than normal weight mares (82.3±2.7 vs 72.0±2.1 mg/dL, P=0.0046). Insulin concentration was affected by gestation (P<0.01) and BCS effect trended towards significance and its concentrations tended to be greater in obese comparedto normal mares (15.4±1.3 vs 11.2±1.7 mUI/L, P=0.065). Cholesterol concentrations were markedly affected by the gestational period (P=0.0006), tended to be affected by the BCS, but their interaction was not significant. Cholesterol increased during gestation from period I to II (80.1±1.8 vs 93±3.1 mg/dL, P=0.0009) remaining stable thereafter. Obese mares tended to have greater cholesterol concentrations than normal weight mares (92±3 vs 86.8±2.3 mg/dL). Triglycerides concentrations were not affected by any fixed effect. Urea concentration was affected both by gestation (P=0.02) and BCS (P=0.0004), but their interaction was not significant. The urea concentration increased during gestation from period I to II (49.3±1 vs 53.2±1.5 mg/dL, P=0.03). Urea concentration was higher in the normal weight group (55.5±1.1 vs 48±1.4 mg/dL, P<0.05). Creatinine concentrations were affected by gestation (P<0.001) and BCS (P<0.02), but the interaction between them was not significant. The creatinine concentration increased during gestation from periods I to II (P=0.0002) with the most significant increase between periods II and III (P=0.04). Creatinine concentrations were greater in the obese group (1.31±0.04 vs 1.12±0.02 mg/dL), P<0.05. This study shows that there is are metabolic adaptations during gestation, and even though this may be physiological, it could be altered by the degree of body reserves in obese mares.