You may find with the smaller prey items, that he may eat better. If that turns out to be the case, you can always try feeding him in shorter intervals. If your normal schedule is once every week, then change it to once every 5 days. If you were expecting the pups to average 25 grams apiece, and you would normally feed 4 in 4 weeks, then that's 100 grams of food in 28 days. if you do once every 5 days and they average 18 grams apiece, that's approximately 100.8 grams in 28 days.