Exactly Elbee. That quote sums it up exactly. Like I said before, heterosis is an increase in performance that you get when crossing two unrelated lines. It isn't just about weight gain in calves, though that is one trait that certainly benefits. It influences a whole host of traits.
shortyjock89 said:
This may sound stupid, but I have to ask. Would you benefit from heterosis if you bought a purebred bull to breed your purebred cows, only the bull is from waaayy different genetics than what you already have?
If the lines are very different, the answer is yes. However, the more drastic differences you see between the parents, the greater the heterosis. The very drastic crosses such as Bramhan to continental or British breeds get the most benefit.
Another thing to note about heterosis is that it doesn't just occur with that first cross....you get it on the next one as long as you use a different breed again. So say you have a Maine Angus cow, she has the full benefits of heterosis for herself, and then if you breed to Simmental, the calf still has 100% heterosis as well. But, if you cross back to one of the original breeds, then you don't get the maximum heterosis.
sjcattleco said:
The breeding program you describe is what 99% of purebred breeders do now.. out cross system...Also that type of breeding program is what EPD's are based on so they are promoted by acedemia because that is what they understand....
It's very difficult to efficiently incorporate dominance and epistatic effects (which are the causes of heterosis) into the models used to calculate EPDs, so you are right in that they aren't included, and it could give a little edge to the outbred animals. However, it is hardly because the academics don't understand. From comments on the cattle boards, I get the idea that people think academics are sitting behind some desk not knowing what a cow is. This couldn't be further from the truth. Most of the professors in the my department, especially the ones in animal breeding, grew up raising livestock. In fact, my advisor still has a small commercial beef herd to go home to after work. All of our current beef genetics grad students (yes, myself included) come from a beef farm. We are hardly out of touch. Yes, it is hard to perfectly model reality, especially in beef cattle where every guy can do whatever he wants in his own herd, but it doesn't mean that useful stuff can't still come out of the academic work. It's about doing the best we can, using as much information as possible, and constantly trying to improve.