It is equivalent to a PhD degree. The labeling of doctorates in Germany is different than the Anglo-Saxon, among others doctor in veterinary medicine are called Dr. Med Vet (see also Wikipedia page: https://en.wikipedia.org/wiki/Doctorate#Germany)
The Dr. med. vet. of Germany and in particular Hannover University is equivalent to Masters degree. It is not equivalent to Ph.D. Because Hannover University awards Dr. med. vet. as well as Ph.D. degree. How one University can award two equivalent degrees of different nomenclatures.