Often, doctors will first recommend hormonal suppression — usually in the form of birth control pills — to prevent fluctuations in estrogen and progesterone levels throughout the month. (health.com)
Spay / neuter is the only permanent, 100 % effective method of birth control for dogs and cats. (peachtreehillsvet.com)
It is the estrogen in other types of birth control pills that decreases milk supply and thus makes nursing more difficult. (breastfeeding.lifetips.com)