My daughter's 4 year old whippet, Jet, who is healthy, typically sleepy, but has to be very active to keep up with his 1 year old very playfully active beagle/American staffy friend, Maja. Despite eating both fresh meat and kibble twice a day, Jet can't seem to hold onto his condition. When he is on his own for a couple of weeks, he beefs up. What can we add to his food to give him a boost to keep in good condition when he has to keep up with Maja? I've read that eggs can be added, but how often?