There are few studies on the composition of fatty acids and how they change the bone marrow fat of young animals depending on nutrition. Therefore, the proximate and fatty acid composition of metatarsal bone marrow from fawns of farm fallow deer after a summer of grazing and the winter feeding was compared. Due to the size and nature of the data, parametric or nonparametric tests were used. Fatty acid composition was determined by gas chromatographic analysis. After the winter feeding, bone marrow contained more fat (83.11% vs. 75.09%, p < 0.05) and less fat free dry matter (5.61% vs. 13.76%, p < 0.05) compared to the pasture period. Moreover, there was a significantly higher amount of saturated fatty acids (23.34% vs. 21.60%, p < 0.001), more trans fatty acids (2.99% vs. 2.34%, p < 0.005), and conjugated linoleic acid isomers (1.04% vs. 0.83%, p < 0.01), compared to post winter feeding, which in turn contained significantly more total cis-monounsaturated fatty acids (54.65% vs. 58.90%, p < 0.001). The percentage of polyunsaturated fatty acids (including n-3 and n-6) was not affected by feeding season. In conclusion, it was shown that young male farm fallow deer were better nourished after the winter period, during which they were kept in properly prepared rooms and fed fodder prepared by people.