Breeding bloodline slaves for harvest

[AndrewTall]

I determined bloodline scores on a average of the two parents, as i thought the rules suggest?

That's the 2e standard which has the benefit of simplicity, but other systems are possible - and in this sort of case I'd consider tapering of some sort to represent the stretching of the bloodline

I also had Goblin society as polygamous as Females are very lowly ranked, More powerful Goblins get a bigger share of everything (women another status symbol), and there is a gender imbalance due to constant conflict and the males dying more often.

"Might makes right" tends to encourage male dominance, although it can flip if the men die off to the point that the survivors are heavily outnumbered. I'd expect it to undermine birth survival, etc however due to increased competition for resources between the wives and their children - infanticide and general competition wouldn't fix the breeding issue, but it would slow it somewhat.

In practice if its not causing issues then I'd ignore the issue, if it is then unblooded nobles, other noble houses, etc could see the children as a direct threat, the older children could try and take their parents place in time-honoured goblin fashion, bloodline hunters could proliferate, you could rule that the splitting bloodlines weaken faster, etc - whatever works.