Hi @jennygail - welcome to the farmOS community! 
Currently, the livestock module provides a “Medical” log type, so you can record when you give your animals medical treatments.
However, it does not yet have the ability to track inventory of medical supplies. This is something that we plan to add in the future, though, and some of the work is already done.
Here are some of the relevant discussions in the issue queue:
- https://www.drupal.org/project/farm/issues/2401531
- https://www.drupal.org/project/farm/issues/2912091
- https://www.drupal.org/project/farm/issues/2916551
Ultimately, the way it will work is you will be able to create assets to represent the different types of medical supplies you have, along with inventory levels for each. Then, when you create a Medical log (to record that medicine was given to an animal) you will reference that inventory and decrement it accordingly.
This is how animal head counts are currently tracked in farmOS - but we need to do a little more work to allow that to be used more generally for other asset types.
Love to hear any ideas you have for how to make this easy/intuitive!