Johann spent 10 days at daycare/boarding while we were on vacation. He had a lot of fun, but lost a lot of weight. He started at a lean and muscular 74 lbs, I'd guess that he lost about aroudn 8 lbs while we were gone. His ribs are all visible, spine sticks out a little bit, hip bones stick out. He's always been a lean and trim dog (good

)...but this has crossed into just plain skinny/scrawny. He lost some muscle as well.
Daycare owner feels horrible.

We had told her to increase his food (add lunches every day) to make up for the extra calories he'd burn off while playing all day. She also increased his total food given after she noticed he had started to lose weight (after consulting with our vet....we figured it was just the extra energy expenditure from playing for 8 hrs a day for 10 days straight).
We're continuing with him getting lunches until he gains back the weight he lost and have started adding meat or canned 95% meat food as well. He gets a raw egg twice a week normally, so we're planning on continuing that.
Before he went, he was eating around Orijen adult 2 cups AM, 1 cup for lunch (only at daycare) and 2 cups in PM. By the time we picked him up....he was eating around 3 cups AM/PM and 2 cups at lunch. No loose stools or any problems that would indicate overfeeding. We've put him back down to 2 cups with added canned food or meat in the AM/PM and a 1.5 or 2 cup lunch. He seems to be hungry and always gobbles his food up.
I'm going to bring him to the vet tomorrow to make sure he's otherwise healthy.
Any other ideas on healthy ways to get some weight back on him? I just want to sit there and feed him non-stop so he looks less starved.
Edited to add: Wanted to make sure it was clear that we aren't upset with Daycare owner about his weight loss or the care he got while we were gone. We planned on some weight loss (hence the increased food), but this was more than we'd expected.