WATCH | Thor the lion has vasectomy after siring five cubs in a year 12 March 2021 - 10:08 By Reuters A lion had a vasectomy on Thursday after his Dutch keepers decided he had sired enough cubs. Thor, 11-years-old, had fathered five cubs with two lionesses in the past year, staff at Burgers' Zoo in Arnhem said. Veterinarian Henk Luten said it was the first time in his 35-year career at the zoo that he had carried out the procedure on a lion. “Why are we doing it? Because he's a proven breeder. We have a lot of offspring and we don't want to have him overpopulating the genetic pool,” Luten said.