1960's series involving genetically modified animals to serve as soldiers and servants. They were indistinguishable from humans except for a mandated mark on the palm of the hands. The author (who I can't recall) was fairly well known at the time.
Brian Stableford's Dies Irae Trilogy
The Days of Glory, (Ace 1971)
Ten millennia had passed since the creation of the Beasts, and those ten thousand years had obliterated the original purpose of Adam December and the construct surgeons.
Ten millennia had passed since the word WAR was forgotten and remembered; and that word wiped out ten thousand years of peaceful coexistence.
Ten millennia, one thousand decades, ten thousand years .. and for the first time Humans and Beasts were dying throughout the galaxy.
But it should have been expected: man had created the Beasts in his own image, and unfortunately, the Beasts were just like him.
The first of the brilliant science fiction trilogy of the Dies Irae, by the talented author of CRADLE OF THE SUN
The other two books in the trilogy are:
- In the Kingdom of the Beasts, (Ace 1971)
- Day of Wrath, (Ace 1971)
Check out the other covers and see if they look familiar.