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

[Jacobflock at aol.com]

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
 
 
In a message dated 9/24/2009 7:46:32 A.M. Central Daylight Time,  
nlgrose at yadtel.net writes:

The role of inbreeding in fixing type on  purebreds is important to note, 
and it is equally important to understand that  it is not the end of the 
world in a breed. Inbreeding has to be done with  the understanding that 
heartless culling must also take place. Genetic  expansion from an inbred 
population can also happen if we pay attention  to our breeding practices. All of the 
Holsteins in the United States came from  a fixed herdbook of relatively 
few individuals. New combinations of old  bloodlines allow novel combinations 
of genes. (That doesn't mean it is  not also worthwhile to preserve inbred 
lines of old bloodlines.)
 
We can increase genetic diversity within the  purebred population by 
shortening generation interval (eating the old rams and  using new ones), and by 
looking to our ewe flocks as the foundation of the  breed. Those males are 
mostly just for show.
 
Neal


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