Instructions
Open the"Minecraft" installation directory and locate your server folder. In the folder there should be a file named "Server.properties."
Open the "Server.properties" file with a text editor. You will see various lines of information relating to your server.
Locate the line "spawn-animals=true." Change "true" to "false" to turn off animal spawning completely. Do the same for the line "spawn-monsters=true" if you wish to turn off monster spawns.
Add the line "natural-spawn-rate=#" where "#" is the chance percentage of an animal spawning. Increase the number to decrease the speed at which animals will spawn. For example, if you want a very slow spawn rate of animals then change the number to 99, which will give animals only a one percent chance of spawning.
Save and close "Server.properties" and load your "Minecraft" server.