Bogardan Dragonheart doesn’t lose any abilities when it becomes a Dragon.

Effects that modify Bogardan Dragonheart’s power or toughness (such as the effects of Force of Virtue or Giant Growth) will apply no matter when they started to take effect. The same is true for counters that change its power or toughness (such as +1/+1 counters).

Bogardan Dragonheart’s ability overwrites all previous effects that set its creature types, power, and/or toughness to specific values. Other effects that set these characteristics to specific values that start to apply after the ability resolves will overwrite that part of this effect.