From what i have read and heard the main reason for slugging out would be more on the male not injecting enough sperm to fertilize the eggs. I could be wrong but in the ton of research i have done that's usually the cause. This will be my first breeding season and i have a virgin male and female. Female being 4 yrs and 2000g male being 1.5 yrs and 900g. she is developing just fine and last count was 8 follicles over 20-25mm (estimated). I wish the best of luck for you when you do breed.
an infertile egg and a slug are totally two different things.