[Jacob-list] Inbreed/Linecross/Breed genetic variability

[Neal and Louise Grose]

It's true that Holsteins are more inbred than we would like. The thing is, they are more genetically diverse than they were in 1880, and are now MORE genetically diverse than the other dairy breeds. Numbers are important. Ayrshires are an example of a great breed that has become a genetically dead end because of overselection for a narrow end-result. At the Madison Dairy Expo, there will be almost as many Ayrshires as Holsteins in the show, despite the tremendous differences in cattle numbers in production. This means that the majority of Ayrshires are selected for show; whereas very few Holsteins are selected for show characteristics. 25% of the top 100 Holstein sires in AI today are sons of "Oman", but there are barely 25 bulls used in the entire Ayrshire breed, most of them are from just a few bull-sires.

Fred's statement:
"Unrelated rams are the key and I suggest keeping the concept of "effective population" in mind at breeding season.  A flock of one ram and 30 ewes is an effective population of 4.  A flock of 3 rams and 30 ewes is an effective population of 12.  Multiple rams are the key." 

Is one that I have been trying to get across for some time. The only thing that makes a ram "good" is that he sires good offspring. Why not use the best sons of a ram instead of using the same ram year after year? The sons are more genetically diverse than the original ram and provide and opportunity to reselect good offspring that preserve the diverse characteristics expressed from the flock. The cliché "the ram is half the flock" is a warning as well as an adage. We would rather have 3 rams be half the flock.

Neal Grose

  ----- Original Message ----- 
  From: Jacobflock at aol.com 
  To: nlgrose at yadtel.net ; jacob-list at jacobsheep.com 
  Sent: Friday, September 25, 2009 8:24 PM
  Subject: [Jacob-list] Inbreed/Linecross/Breed genetic variability


  Interesting that the Holstein be mentioned.  I recall a party ... five years ago? ....  hosted by Gary and Gail Anderson in the California wine country ... don't recall the occasion for the party it was that good... but I met Harvey Blackburn over a glass of wine .. I corresponded with him previously but a glass of wine waxed over my shyness ... and he was talking about these black and white animals.  The subject was genetic diversity within a breed (not cross breeding between breeds) and he mentioned Holstein cows: Sixteen million of these that represent abouyt 85% of the cow population (distinguiished from cattle).  As Harvey tells it, he comes out in the morning and says to the 16 million "Get in a line facing me".  He then says "You all look the same.  But if anyone of you is not related to another in the line, take four steps forward."  Do you know how many would step forward?  Yup, twenty five.  This is the ultimate line breeding and the ultimate loss of breed genetic variability.  A lot of milk and cheese but all the cows are related to the same few bulls who were probably State Fair winners.  You know the drill.  Angus cattle are probably in a similar fix.

  Some inbreeding can be positive, some line cross breeding is positive.  Keep the line but keep the door open for linecross breeding.  Don't get painted into a corner.  If all the animals in the flock are closely related, inbreeding and inbreeding depression are fait accompli.  Unrelated rams are the key and I suggest keeping the concept of "effective population" in mind at breeding season.  A flock of one ram and 30 ewes is an effectiive populatiuon of 4.  A flock of 3 rams and 30 ewes is an effective population of 12.  Multiple rams are the key.  The inbreeding coefficient per generation for the 1 ram/30 ewe flock is aboiut 13%; in the second case it is a little over 4%.  Multiple rams, not ewes, is the key to genetic variation and reduced inbreeding.

  I recommend the ALBC book "Managing Breeds for a Secure Future" which has a lot of basics and how to info.

  Fred Horak
  St. Jude's Farm
  1165 E. Lucas Road
  Lucas, TX 75002
  972-727-0900
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