beefalo giving birth non stop

i started to tame a beefalo little before of spring. In spring it enters in heat and spawn a little beefalo, i though this is normal so i ignored it. I let the beefalo and his child with a salt lick to wait for his heat to finish and when i come there was a lot of little beefalos. I killed all of them so i dont have a herd inside of my pen wasting the salt licks. Summer start, no heat and the beefalo spawn another child