You don't give the age of the female producing the small litter w/slugs. If you bred her at 2 years and again the following season this could have caused the problem. My Albino and Het Limburg females are not bred until 3 years and with good size(the males will breed at 18 months) The average clutch size is 6. Give your female a year off and try to put on more size before breeding again.