I didn't mean to upset anyone. This is a sore subject with me. However, yes linebreeding is inbreeding. If you have line-bred cattle, then you just have to accept the fact that you have in-bred livestock, dogs, whatever (hopefully not kids). You might experience some short-term gains as some of you suggest, however long-term line breeding will ALWAYS result in negative gene concentrations, statistically.
If you are "line breeding" you are "in breeding". If you are going to sell the animals for beef. It does'nt matter if you get a little inbreeding. Most producers who use the battery of bulls method wind up with some inbreeding. The problem with line/in breeding is that while trying to enhance some positive traits you will always, yes always, be advancing some inferior traits that will, yes will, make it to the surface sooner or later.
I'm sure inbred deer die off as one of you suggested when negative gene concentrations occur, but that is not a logical comparison with dometic animals. Do you want your cows to die off? We humans compensate for the deficiencies in our stock when something goes amiss and too often it's too profitable to cull a super producing animal because of one small defect. So we propagate it for it's benefits and down the road the negative aspects bite us in the hiney. Show horses today have feet that are too small for their weight. These show horse genes make it into work horse stock. Many show Arabs have backs that are too long to support riders (they are supposed to have one less vertebrae and short backs), many dog lines have hip dysplasia, hel), bull dogs can't even deliver naturally anymore. All births are cesarian. Domestic turkeys can't breed. Every Butterball is A.I.d because we breed them for breasts that are so big they cannot mount for breeding. Hemophilia used to run rampant in the royalty of Europe. It was a hugh problem for them, because they liked their cousins and were trying to keep pure, royal blood in the family. My examples are of the extreme, but my point is that if you are getting in/line breeding in your stock I would eat them if I was you and if you don't your heifers are going to be purchased by someone who will breed them and eventually or handiwork is going to affect us all. I simply won't accept inbreeding in my livestock if I can help it. My calves performance proves my point.
It happens all the time and most registered producers do line-breed to some degree. They are trying to enhance growth, milk, IMF, Ribeye area, etc. Their goal is not necesarily lbs of calf in the fall. Line breeding IS the reason we have common genetic maladies showing up in dogs, horses, cattle, etc. It IS the reason we experience herterosis today. Heterosis is seen when breeding composites of any species. Composites are statistically healthier and stronger that pure breed stock. Most calf producers, other than purebred producers, choose to cross two or more different lines i.e. Angus and Hereford for this reason. It always benefits the producer to do so becasue he/she statistically produces more lbs of beef with fewer health problems. It happens because the pure breeds are too genetically similar and crossing the breeds brings a positive genetic diversity 99.9% of the time.
If I was wrong, heterosis wouldn't even be a word.