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New Mexico | your using basically strait Angus bulls ( generation after generation ).
The NH inbreed factor for NH is high. Looks to be in the 20 to 25% range for bulls tested so far.
Generally a cow will not carry an NH factor calf very long ( lots of 6 week abortions ).
Especially the past 2 years folks are starting to figure out that the "mystery" open cows are in fact caused by NH, lots of other diseases or supposed problems have been chased, but the problem on many has in fact been NH.
American Angus Association has a real good search link (tool) for NH carriers and or NHF ( NH free bulls ).
Looked like approx 11,305 head of the popular bull ( lines ) have been tested back 3 or 4 generations. Looks like approx 23+% of em ( 2,520 head ) are positive NH thus are NHC ( NH Carrier ) bulls.
Bottom line is if You've saved hiefers out of NH defect bulls for a couple 3 generation and thus say 50% of your cows are NH positive...then You use some NH factor bulls on em....75% of those will abort early ( before preg testing ).
The NH factor is a 50% heritable defect, bull or cow. That means 2 generations of positives is a 75% offspring factor etc.
btw, if your cleaning up NH.....might as well clean up the AM defect too. Some bulls ( the popular bulls ) tested are both NH carriers and AM carriers too.
Best way to clean up most of the current Angus defect which were basically caused by to much line breeding is perhaps to use say Hereford or Char bulls every other generation.
Bottom line on the black bulls, is DO some homework before buying the ones You like. There appears to be right at a 25% chance of purchasing a defect.
Keep in mind, most the exotic or composite bulls who are now black also have an almost equal chance of carrying the NH and / or AM defects too. That means one has to homework their background genetics too from the Angus side.
Edited by Markwright 11/8/2009 17:57
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Update on conception problems
