I think the baby should be fine. The problem could be for you. By straining you could really hurt your back or pelvis due to the ligaments beginning to soften.
There was a few times in my first PG that I was a bit gung-ho about lifting things. At the time I was working in a bottle shop and was too impatient to wait for one of the guys so I'd lift things myself. Slabs of beer and cartons of wine aren't exactly light. Sometimes I wonder now if that may have contributed to the sore back I have now.

I hope your doggie was ok!