Animal Doctor

This achievement is unlocked by completing the twenty-third mission in the game, which has you treating a sick cow. Head to the cow icon behind the Animal Hospital to begin, which will start you with identifying which cow is sick. Interact with the one closest to Farmer Harris, which you'll have to do three times. You'll then have to go to the dispensary two times to get various items to treat the cow, after which you will unlock the achievement.