Very interesting! I have a strain of mice that I got from the pet store, a very prolific albino strain that has up to 16 babies at a time. I have changed food a few times, I started out making my own mix from different feeds from the feed store (oats, corn, etc.) They seemed to do poorly on it, so I switched to Mazuri 6F. Then switched again to a generic lab block (which molded easily) then went back to Mazuri 6F. I did notice that initially I was getting mostly males, then on the cheap stuff got mostly females. Now I get about a 50:50 ratio on Mazuri. I thought it was some weird genetics that changed from generation to generation, I didn't even think about the food being the cause!