I don't know if this is possible but I breaded Tier 5 horses 6 times and every time I got a T6 female. The horses level was 30 and 29 or 30 and 30 for max gain. According to the horse calculator my chances are as follows 6M(18%), 6F(26%), 7M(22%), 7F(26%), 8M(8%). So what are the chances of landing a T6 female 6 times in a row. So I jumped to the conclusion that if you breed a 5m horse with a 5m horse you will always get a T6 female. The 5m is the model of the horse on fams horse calculator. It's the horse you get from questing that has 100% sprint and 100% instant accel. So if you don't want a T6 female don't smash 2 5m's together or if you want 1 just smash two 5m's together. Just some info I would like to share with the community.