Long‐Term Feeding of an in‐House Prepared High‐Fat Diet to Leptin‐Deficient Mice

Abstract

Obese animal models are used in obesity or obesity‐related disease research. Many obese models are gene‐specific knockout or transgenic rodents frequently fed high‐fat diets (HFD). Pellet‐type HFD are commercially available and have been widely used to induce and maintain obesity in mouse models. In nutrition experiments, however, meal‐form diets are preferred due to the convenience in preparing various treatment diets. Although young obese mice are often used in research mostly at less than 20 weeks of age, older mice may be more appropriate for mimicking adult or elderly human obesity. However, information on the survival rate and body weight (BW) changes of ob/ob mice fed HFD for over 6 months is very limiting. Therefore, we fed leptin‐deficient ob/ob mice and wild‐type mice for over 120 weeks with a HFD in meal form prepared in‐house. A total 709 BW and age data (224 data from ob/ob mice and 485 data from wild‐type mice) ranging from 6.3 to 77.7 g BW for 41 animals were collected from 3 to 127 weeks of age. A HFD (34.3% energy from fat) was prepared in‐house to contain 49% ground corn, 30% soybean meal (protein 48%), 20% fat powder, and 1% vitamin‐mineral premix. The fat powder is a protein‐coated fat product mainly composed of 80% lard, whey, and casein. All animals had free access to diet and water. Individual BW of mice was measured with approximately two‐week intervals. The survival rates of ob/ob and wild‐type mice were calculated. To develop growth curves of ob/ob mice and wild‐type mice fed a HFD, Gompertz and Logistic growth models with three parameters in the equation were employed. The survival rates of ob/ob mice fed a HFD were 72.7, 54.5, and 45.5% at the age of 50, 60, and 70 week, and those of wild‐type mice were 95.2, 90.5, and 61.9%. Estimated growth models of ob/ob mice fed a HFD as a function of age (week) were: BW, g = 61.36 × e−2.56×e^−0.13t with AIC = 1,694 in Gompertz model and BW, g = 60.65 × (1 + 7.04 × e−0.18t) −1 with AIC = 1,719 in Logistic model. Estimated growth models of wild‐type mice fed a HFD as a function of age (week) were: BW, g = 28.94 × e−1.75×e^−0.13t with AIC = 3,171 in Gompertz model and BW, g = 28.23 × (1 + 4.85 × e−0.25t) −1 with AIC = 3,198 in Logistic model. The age at point of inflection in Gompertz model showed that the maximum growth rate of ob/ob mouse and wild‐type mouse was at 7.22 and 4.19 weeks of age, respectively. The BW at inflection in Gompertz model of ob/ob mouse and wild‐type mouse was 2.93 and 1.43 g, respectively. Taken together, Gompertz models resulted in greater fitness to the growth curve of ob/ob mouse fed HFD compared with Logistic models. Suggested growth curves and survival rate data for ob/ob mouse fed a HFD may be used for designing long‐term experiments or planning to use elderly obesity models. Further research is warranted to develop growth models for other model animals for obesity or nutrition research.Support or Funding InformationThis work was supported by the National Research Foundation of Korea (NRF) grant funded by the Korea government (MSIP) (No. 2016R1A2B2015665).