Male Effect on Inbreeding

[grisaboy]

I read an article the other day about the effect of the number of males on inbreeding.  Unfortunately, I cannot find the web page where I found it.
Here is the Title and author for those that are better at searching than I am.
 >>Male Effect on Inbreeding

 >>F I R S T   D R A F T
 >>The effect of Male Numbers in a Population on the      Coefficient of Inbreeding
 >>by D. Caveny

Caveny was talking about animals in general, but I will try to summarize the article as I see how it relates to poultry...


Many of the outstanding exhibition strains of poultry have been developed using variations of inbreeding followed by line breeding.  This has resulted in outstanding exhibition birds but often the strains suffer from poor vitality, vigor and productivity.

So how do we develop a strain that has the outstanding traits that we desire without suffering from inbreeding depression?  

The key to avoiding inbreeding depression in a strain is to keep enough birds in your breeding pens so that the probability of mating close relatives is reduced.  It is especially critical to maintain enough males in your breeding program.

A coefficient of inbreeding can be determined by using the following formula.  (1/8M + 1/8F = In/Gen). Where M is the number of males and F is the number of females.  Mating full brother to full sister results in a coefficient of inbreeding of 0.25 where 25% of the genes of the parents are shared by all of the offspring.  The coefficient of inbreeding is used to determine how many generations it would take with your current number of breeders before you would reach an Inbreeding Coefficient equal to a full brother to full sister mating.

Some Examples:
# of Males    # of Females   # of Generations to reach 0.25 co-efficient
1      2      1
1      6      2
1      12      2
2      4      3
2      12      3
4      8      5
4      12      6
6      12      8
6      18      9
8      12      10
8      24      12
12      36      18      

As you can see, the number of males used in your program greatly increases the number of generations it takes before you reach a critical inbreeding coefficient.  If you keep 8 or more males,  you basically can maintain your strain indefinitely without going outside your strain for new blood.
This can be especially useful information for those of us that are working with rare strains where new un-related stock is difficult to obtain.

[grisaboy]

Well,  my chart didn\'t transfer very well.

The first number is males, The second number is females, and the third number is the number of generations before we reach the .25 Co-efficient of Inbreeding.

Curtis

[John]

the effect of the number of males

I haven\'t read the article you referred to, but the logic behind the idea is sound.
Very seldom do I breed one male over a group of females, although for experimental matings and in special cases I will mate one male over a special female or more.  My usual practice is to cull most breeders, after the breeding season, and only keep a few of the best.  I hatch and raise a large number of offspring and keep culling as they grow, once again keeping the best to use as breeders the following year.
The disclaimer is that there are always exceptions, but normally I put the best cockerels over the best hens and the best cocks over the best pullets.  I try to use a minimum of two males over any group of females.  One reason is to give me the highest percentage of fertility.  The other is for genetic diversity.  I generally change the males in the breeding pens on Sundays and Wednesdays, leaving the better male in for the longer 4 day period of Wednesday thru Sunday.
If a person only has four birds to breed from I can think of four ways to set up matings.  The first and least effective way is to use either one cock over three hens or three cocks over one hen.  All the offspring will share at least one parent and make them very closely related.  
Another idea is to mate two pairs separately.  This will give you two strains that do not share parents, but all offspring in each stain will be full siblings.  There are some instances when this mating is most useful.
The best mating, using only 4 birds, to achieve the most genetic diversity would be to use two cocks over two hens.  Put the hens in separate pens and rotate the two cocks between pens weekly or more often.  This will produce some offspring that share the same sire or dame and some that are full siblings, but also offspring that won\'t share either parent.  In this situation you wouldn\'t breed these offspring together (unless you know what mating each came from), but use the sire over the pullets and cockerels over the dames the following year.  

[Mike Gilbert]

Some of us are raising too many varieties for the resources we have in terms of breeding pens, rearing pens, and most importantly - TIME.    We understand the importance of maintaining a large gene pool, but our circumstances restrict us from it.    The best alternative I have found is NETWORKING with other breeders.    I am fortunate to have a neighbor, Bob Walchak, who raises many of the same varieties of Ameraucana bantams as I do.   I also utilize a few 4-H families to raise birds I don\'t have room or time for in exchange for picking out one or two select breeders later in the year.   John Blehm and I often exchange birds as well.
But your point is a good one.   It is the very reason I am disappointed that so many folks are intent on developing more and more new varieties when so many of the existing ones could be easily lost.   We have already had to re-create the silver bantam.   And I have created three seperate strains of brown red bantams.    My wheatens were practically resurrected from extinction early on because I kept too few breeders. Etc., etc. - you get the picture.

Mike G.

[John]

raising too many varieties for the resources

Boy, don\'t I know it.  I tried breeding all 16 varieties and found out that was way too much for my time, facilities and pocket book.  I plan to cut back further after I\'ve made some progress with a few improvement projects that I have been working on.  I hate to give up on them after putting a few years of breeding into them.
Eventually, I would like to concentrate of bantam and large fowl buff, silver, lavender and maybe brown red.  That would still be six to eight varieties.

[grisaboy]

I too am keeping too many varieties.
Currently I have 8 varieties of Ameraucana, 3 varieties of Modern Games and my daughter has 5 varieties of bantam cochins.  It is difficult to develop a viable, sustainable breeding program with this many varieties.  I plan on cutting back to just Silver and Lavendar Ameraucana bantams and Lavendar large fowl (with blacks to weave into the Lavendars).  And Birchen Modern Game bantams, just because I have been working on this strain for 10 years, and they are finally doing well at the shows.  My daughter can get by with two varieties of cochins.
It is so tempting to pick up Brown Reds or Buffs and work on them too.  But it is a much better use of pen space to just stick with fewer breeds and varieties.

Curtis