This is a very interesting post on Medium about the dogs the Soviets sent into space in the 1950s:
While the US test rocket programme used monkeys, about two thirds of whom died, dogs were chosen by the Soviets for their ability to withstand long periods of inactivity, and were trained extensively before they flew. Only stray female dogs were used because it was thought they’d be better able to cope with the extreme stress of spaceflight, and the bubble-helmeted spacesuits designed for the programme were equipped with a device to collect feces and urine that only worked with females.
Training included standing still for long periods, wearing the spacesuits, being confined in increasingly small boxes for 15-20 days at a time, riding in centrifuges to simulate the high acceleration of launch, and being placed in machines that simulated the vibrations and loud noises of a rocket.
The first pair of dogs to travel to space were Dezik and Tsygan (“Gypsy”), who made it to 110km on 22 July 1951 and were recovered, unharmed by their ordeal, the next day. Dezik returned to space in September 1951 with a dog named Lisa, but neither survived the journey. After Dezik’s death, Tsygan was adopted by Anatoli Blagronravov, a physician who later worked closely with the United States at the height of the Cold War to promote international cooperation on spaceflight.
They were followed by Smelaya (“Brave”), who defied her name by running away the day before her launch was scheduled. She was found the next morning, however, and made a successful flight with Malyshka (“Babe”). Another runaway was Bolik, who successfully escaped a few days before her flight in September 1951. Her replacement was ignomoniously named ZIB — the Russian acronym for “Substitute for Missing Bolik”, and was a street dog found running around the barracks where the tests were being conducted. Despite being untrained for the mission, he made a successful flight and returned to Earth unharmed.
A good piece of trivia from the piece: Laika wasn’t the original name for the most famous of Russian space dogs; it was named Kudryavka (Russian: Кудрявка, meaning Little Curly) before its name was changed.