On Monday, I began to discuss how we put together our breeding groups and had gotten to having put together the framework – the rams in columns and the ewes in rows – of our breeding charts. The next step is to determine the relationship coefficient between each of our rams of a breed with each of the ewes of the same breed. Yet, I think before we discuss the coefficients, we need to talk about inbreeding and linebreeding, both of which are important tools in any livestock breeding program. There is a fine line between inbreeding and linebreeding – and an old joke that says that the difference is simply one of success: if you end up with some terrible result, that was then called inbreeding, but if the resulting lambs were good quality, then we can call it linebreeding.
The difference is actually more one of degree than of results; if you are breeding close family members (like father to daughter, half-siblings, or any other immediate family relation), it is considered inbreeding, while the breeding of more distant family members within a family line is linebreeding (like cousin to cousin, grandfather to granddaughter, or aunt to nephew, for example). There are definite advantages to close breedings, but also inherent risks. The closer the breeding, the higher the risk – and the higher the risk, the higher the possible benefit, too. The closer the breeding, the more the genetics of the duplicated sheep will be doubled up at any one location, making the resultant lamb(s) more likely to breed true and accentuating positive or negative traits. That’s great for positive traits since we have a better chance of seeing those positive traits in the next generation, but if there is something truly bad in there, that trait could well threaten the viability of the lamb (there may be no next generation!).
Close breedings – either linebreeding or inbreeding – are useful when trying to lock in particular traits. By breeding two closer family members and having an offspring with numerous genetic duplications gives us a higher chance that the offspring will continue to produce future generations with the desired trait. Yet, breeding too closely or linebreeding less closely but for multiple generations can have other negative impacts on the newer generations of the flock. Close breeding and higher inbreeding coefficients (which reflect how much duplication appears in the pedigree of any one flock member) can result in a depression of fertility, growth and/or adult size, and health. The general rule of thumb is that too much inbreeding causes this type of depression – but there are exceptions to every rule, too. If one decides to use this tool, that shepherd needs to watch carefully for signs that new blood is necessary for the vitality of the flock.
It is important for me to carefully consider how closely I want any one pairing to be – and that is why I must fill in each breed’s annual breeding chart with the coefficient of relationship for each pairing. The coefficient of relationship increases for each ancestor that the pair has in common, with more immediate ancestors weighted more heavily than those that are more distant. This coefficient ranges between zero (not at all related) and one (full duplication of genetics like a sheep to itself), with 0.5 being the coefficient of relationship that occurs between full siblings. I have found over the years that the ideal range for any given breeding pair is not – as one would think – zero. We find that our best combinations do have some relationship to each other, and that the common ancestor is one in which the traits that we really want to see in the lambs were very strong. In general, we aim for a coefficient of relationship of 0.06 to 0.18, but will run a pair as high as 0.35 or even a bit higher if the common ancestor was an impressive sheep.
Calculating this coefficient would be tough going if I were doing this by hand, but once I identify one of my rams as a breeder, my sheep tracking software will calculate the coefficient of relationship for each breeding ewe of my flock. I simply need to fill in the chart for each individual ram and ewe pairing. Once entered, I usually fill the background of those cells that hold unacceptably high coefficients of relationship (0.45 and higher) in red, and those that are higher than I normally like in yellow. I am then ready to begin to put together my groups.
The first step is to determine how many of the rams in this particular breed will be running a breeding group. To do this, I quickly scan the yellow and red cells; if any one ram has quite a lot of these “danger” cells, I usually hold him until a future year when this is not the case. Each of the rams in the chart is here for a reason – he has traits that I hope will bring next year’s lambs closer to achieving one or more of my goals. I try to figure out which three or four rams of this breed will bring me closest to each of my goals while offering me enough genetic distance that each of my ewes can find a ram from among the group. This year, for example, I’ve decided to run four Romney groups (although I have six rams available): Korbin, ObiWan, Osiris, and Quest will each have a group. I’m still working on the Romeldale groups, but honestly, these charts seem to be a work in progress pretty much until the night before we put the into their groups. Beginning now, gives me time to adjust and readjust multiple times until I know that I am happy with how our groups have been arranged. After all, I still have four and a half weeks to think about it!