I would ring everyone of your clients, and ask them about there situation, and share your situation.
We are all faced with challenges, and those clients may have ideas, they may also want to get a break from their pets. They maybe equally concerned you have closed.
If you have a large database of clients, split the work load across your staff, and record feed-back. Maybe do a session with staff first to generate some questions and confidence. Those clients may also have friends with pets.
Set a target with the business, and share with clients i.e if we used to take 20 pets a day, lets aim for 10.
If your clients a close by maybe a ‘walk-by’ and wave.
Personal contact is key, its the most real and its your point of difference.