**3. Results**

#### *3.1. Longitudinal Growth in Non-Inbred Mouse Models*

Body weight was recorded in mice selected for high body mass at the age of 42 days (obese mouse model), in mice selected for high protein amount (lean mouse model), and in unselected controls (Figure 1). At an age of 11 weeks in females and 16 weeks in males, body weights were significantly di fferent between obese, lean, and control mice. Within groups, daily weight gains were highest in male or female controls at the age of 24.9 days or 20.9 days after birth. Lean mice elevated daily weight increases until an age of 26.3 days in males and 24.5 days in females. In obese mice, the daily weight gains peaked at the age of 26.7 days in male and 24.2 days in female mice. The absolute amount of daily weight increase amounted to 0.635 g/d and 0.59 g/d in male and female unselected controls, 1.99 g/d and 1.52 g/d in lean male and female mice, but 2.2 g/d and 1.7 g/d in obese male and female mice.

**Figure 1.** Body weight in male (left panel) and female (right panel) mice selected for high body weight (obese), for high protein amount (lean), and in unselected controls at an age of 2, 4, 7, 11, 16, 29, 42, and 54 weeks. (mean ± SEM; *n* = 8; due to high mortality, sample number was reduced to *n* = 4 at an age of 54 weeks in male obese mice; different letters (a, b, and c) indicate significant differences also in different genetic groups per gender, \*\*\*: *p* < 0.001; identical letters indicate no statistically significant difference).

#### *3.2. E*ff*ects of Age and Growth Selection on the Concentrations of IGF-1*

As a main e ffect of growth selection independent of age, IGF-1 was significantly increased in lean mice (*p* < 0.001) of both genders but only in obese male mice (*p* < 0.01) if compared to sex-matched unselected controls (Figure 2). As an e ffect of age and genetic group, in male obese mice, a significant (*p* < 0.001) increase of IGF-1 concentrations in serum was present between 2 and 4 weeks of age. In male lean mice, a similar increase was found between 2 and 7 weeks of age (*p* < 0.001). In males from both growth-selected mouse lines, IGF-1 concentrations decreased between 4 or 7 and 29 weeks of age (*p* < 0.01). Moreover, as an interaction of age and genetic group, in female obese and lean mice, increases of IGF-1 concentrations were found between 2 and 7 weeks of age (*p* < 0.001). However, a significant decrease of IGF-1 concentrations over time was only found in obese female mice between 7 and 54 weeks of age (*p* < 0.001).

**Figure 2.** Concentrations of insulin-like growth factor (IGF)-1 in serum from mice selected for high body weight (obese), for high protein amount (lean), and in unselected controls of both genders at an age of 2, 4, 7, 11, 16, 29, 42, and 54 weeks. Di fferent letters (a and b) indicate significant di fferences also with respect to di fferent genetic groups in each gender; identical letters indicate no statistically significant di fference. Sample information is provided by Figure 1 (mean ± SEM; \*\*: *p* < 0.01; \*\*\*: *p* < 0.001).

#### *3.3. E*ff*ects of Age and Gender on Levels of IGFBP2- to 4*

By direct comparison of longitudinal IGFBP profiles in serum from male and female unselected non-inbred mice (data not shown), IGFBP-2, -3, and -4 exhibited gender-related features: if compared to age-matched females, male mice had higher concentrations of IGFBP-2 (*p* < 0.01) and -3 (*p* < 0.001) at an age of 16 and 42 weeks, respectively, but lower concentrations of IGFBP-4 in serum (*p* < 0.001) at the age of 54 weeks.
