The MSc thesis aimed to investigate the effect of diet, line and sex on apparent crude protein digestibility and crude fat digestibility in FHI (lean mouse line) and FLI (fat mouse line) lines. Two types of diet, HFD (high-fat diet) and LFD (low-fat diet), were tested separately by sex and line. The digestibility experiment was performed in two replicates, at six weeks of age (1ObPr) and 13 weeks of age (2ObPr). We found that the HFD feed had a more significant effect on digestibility parameters. At the end of the experiment, males had a higher body weight than females. The HFD-FHI group of males consumed the highest crude protein and crude fat intake, whereas the HFD-FHI group of females consumed the highest crude protein intake, and the HFD-FLI group consumed the highest crude fat intake. A better apparent digestibility of crude protein was calculated in HFD-FLI and HFD-FHI females compared to the other groups. Similar findings were also obtained for crude fat digestibility, as females of HFD-FHI and HFD-FLI had better crude fat digestibility than females on LFD and males of both lines, regardless of the type of feed. Our results confirmed previous studies in this mouse model that differences in feed intake cannot explain the phenotypic differences in body fat gain and body fat percentage between the fat and lean lines. For the most part, there were no differences in this parameter, and in males, the lean line even consumed statistically significantly more feed than the fat line. However, we have demonstrated some differences between the two lines and the effect of feed composition on apparent digestibility, which should be considered in further evaluation of phenotypic differences between the two genotypes.
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