Weight loss resistance: A further consideration for the nutritional management of obese Equidae

Abstract Evidence-based, weight loss management advice is required to address equine obesity. Changes in body mass (BM), body condition score (BCS), heart (HG) and belly circumference (BG), direct (ultrasonographic) and indirect (D 2 O dilution, bioelectrical impedance analysis [BIA]) measures of body fat as well as indices of insulin resistance (IR) were monitored in 12 overweight (BCS ⩾ 7/9) horses and ponies of mixed breed and gender for 16 weeks. Animals were randomly assigned to two groups (Group 1, n  = 6, BCS 7.6/9 ± 0.6, 489 ± 184.6 kg; Group 2, n  = 6, BCS 8.1/9 ± 0.6, 479 ± 191.5 kg). Daily dry matter intake (DMI) was restricted to 1.25% BM as one of two, near-isocaloric (DE ∼0.115 MJ/kg BM/day), forage-based diets (Group 1, 0.8% BM chaff-based feed: 0.45% BM hay; Group 2, 1.15% BM hay: 0.1% BM nutrient-balancer). Statistical modelling revealed considerable between-animal heterogeneity in proportional weight losses (0.16–0.55% of Week 1 BM weekly). The magnitude of weight loss resistance (WLR) or sensitivity to dietary restriction was independent of diet or any measured outset variable and was largely (65%) attributed to animal identity. Predicted rates of weight loss decreased over time. BCS and BIA were poor estimates of D 2 O-derived body fat%. Reciprocal changes in depths of retroperitoneal and subcutaneous adipose tissues were evident. Changes in BG were associated with losses in retroperitoneal fat and BM ( r 2 , 0.67 and 0.79). Indices of IR improved for 9/12 animals by Week 16. For obese animals, weight loss should be initiated by restricting forage DMI to 1.25% BM. Subsequent restriction to 1% BM may be warranted for WLR animals.