Efficiency is really the trait we are interested in, not weaning or yearling weight. A frame 5 calf that weighs 1,100 pounds at a year of age may be more efficient than a frame 6 calf that weighs 1,200 pounds at a year of age. Mature size is frequently ignored, but it is highly related to maintenance costs. Logically, extremes should be avoided. In addressing the topic of genetics for profit, I would indeed fail if I did not mention the importance of mating system.
Crossbred animals tend to out perform purebreds because of heterosis.
There is a significant amount of heterosis for fertility traits, some heterosis for growth traits, and little heterosis for product traits like quality and yield grades. The advantages of crossbreeding are greatest when you utilize a crossbred cow to produce a crossbred calf because you get improved fertility and milk production with the crossbred cow. Over the past 20 years, too many producers have focused their attention on one or two traits rather than the whole animal. In doing so, the industry and breeders have had a tendency to breed for extremes in several traits such as low birth weights, high yearling weights, large frame size, and high milk production. The next extreme may be muscling or ribeye area.