Are you linebreeding—or inbreeding?

 “If it works, it’s linebreeding, if it doesn’t it’s inbreeding.” This line may bring a smile, but it also points to a worrisome reality. Many breeders aren’t clear about the distinction between linebreeding and inbreeding, and don’t have the information they need to make good decisions about their improving their herd.

Most people know the meaning of “inbreeding,” that is, the mating of closely related animals, such as father to daughters, or brothers to sisters.  And most know that inbreeding concentrates genes to such an extent that it brings a high risk that recessive genes for lack of fertility, small size, and other negative characteristics will be expressed.  What is less well understood is that over time this practice can undermine the quality of the herd. Ken McDowall, the breeder who created the Rotokowa Devon herd, explains, “It’s equivalent to walking down a mountain ridge that gets continually narrower until it’s a knife edge; when you get to the point when the ridge crumbles, there is no way to turn around.”

Linebreeding concentrates genes as well; it can concentrate desirable traits, such as a large volume of high-quality meat; or concentrate undesirable traits, such as a tilted udder or other structural problem. Unlike inbreeding, however, linebreeding can benefit the herd overtime, if used properly as a tool and not as an end in itself. The common practice of using the terms “linebreeding” and “inbreeding” interchangeably ignores the potentially negative problems of inbreeding. Inherent in all breeding programs is the need to constantly assess by eye appraisal, rejecting inferior animals.  This is especially relevant with close breeding. If known weaknesses in the parents show up in the progeny, the inferior animal should be culled from the herd.
So, how do you linebreed without creating the problems associated with inbreeding?  These are two key points to remember about linebreeding:

• Linebreeding mates animals that are related, but not too closely.
• Linebreeding is a tool to reach a specific goal, not an end in itself. Animals should not be bred just because they are related, but for a specific purpose: to fix a particular desired trait or to correct a particular problem.

Recognized authorities from the 18th century to the present day agree on these basic principles and only differ in some particulars, such as how close is too close, as evidenced by the descriptions here:

1. Laurence Winter in the book, Animal Breeding (1939)says, “Inbreeding brings about segregation and thereby brings out desirable, undesirable, and indifferent expressions of characters.  It brings out many undesirables that the breeder did not realize were in his stock.  More undesirables are brought to light than desirables....the breeder intent on fixing type is likely to overlook less conspicuous factors, such as fertility, longevity and even growth rate.” Regarding the acceptable degree of closeness, Winter’s definition of inbreeding includes matings of “full brother and sister, parent and offspring, or half brother and half sister.”  Linebreeding, according to Winter, can include “cousins, half cousins, half uncle and niece, granddaughter and grandsire, double grandsons and granddams, etc.” His conclusion is that the general breeder will do well to continue linebreeding (according to his description) and avoid inbreeding.
   
   
2.  Jim Lents says in his book The Basis of Linebreeding (1991), “ Linebreeding is a long-range plan which requires that the breeder have firmly fixed in his mind his ideal animal and be willing to always to stay the course in the pursuit of this ideal…line breeding is inseparably linked to selection.  It concentrates both desirable and undesirable characteristics and requires total honesty and rigid selection…If the animals in each generation exhibiting undesirable characteristics are not rigidly culled, then the breeder’s ideal will never be approached and breeding program will be a failure.”
   
   
3. In a fascinating book Genetic Heritage (1996) about horse breeding, Ken McLean offers his formula for determining a safe degree of relationship. “If the same ancestor in the top half (sire) and bottom half (dam) of a pedigree appears within two, three and four generations, we call this closeness “inbreeding.”  If it occurs from the fourth generation onwards, i.e. further removed in the pedigree, we call this “linebreeding.” His advice for purchasing broodmares is, “Look at form and function rather than just the pedigree.”
   
   
4. According to Genetic Prehistory in Selective Breeding (2001), by Roger J. Wood and Vitezslav Orel, Robert Bakewell, the famous eighteenth breeder, was “aware of the uncertainties of heredity…Breeding stock had to be carefully selected on the basis of form as well as blood, in every generation, supported by wise and consistent husbandry.” He learned of “the dangers associated with inbreeding without progeny testing…Breeders were sometimes tempted to consider ancestry sufficient in itself as a guide to being ‘well bred.’  This was a trend Bakewell himself deplored.” Bakewell was also famous for “breeding the best to the best regardless of the relationship” and would at times inbreed if it met his goals.  But he would breed closely despite close relationship, not because of it.
   
   
5. Ken McDowall, from New Zealand, recommends the following procedure for determining suitable mates, based on his experience developing the Rotokawa Devon herd over a period of almost 30 years. On the first breeding of a heifer, place the pedigree of all the bulls being considered (In Ken’s case, available from his own herd or AI) on a table with the pedigree of the heifer.  Reject any bulls that appear in the first two generations of the heifer’s pedigree.  Then go to the field, look at the heifer and try to pair her with a bull (of the unrelated group) that complements any perceived deficiencies, i.e. pick a bull with a great loin if she lacks loin, etc.  Evaluate the resulting calf and any subsequent “get” of this pairing and continue to breed her this way if it is successful. 
   
   Because Ken was always breeding with five or six bulls from his own herd, what transpired over time was that the sires chosen as breeding bulls have the same sires appearing in their pedigrees in the 5th and 6th generation back. This is how his prepotent bulls were able to transmit their condensed genes without ever getting “too close” and thus generating the problems inherent in inbreeding. Ken was also faithful about culling and had no tolerance for defects.  Because this method of breeding was so successful at fixing longevity, Ken had to make a practice of culling cattle when they reached fourteen years of age, just to make room in the herd for replacement females.

With all the information above, it should be clear that a “double bred” or “triple bred” animal is not necessarily a good choice for your breeding program. You would have to have access to a number of the progeny of that animal and evaluate them in order to evaluate the worth of the sire or dam. The ads that tout “Our bulls are linebred” bear investigation to understand what the breeder means by that.

A summary list of linebreeding basics:

• Linebreeding is a tool for concentrating desired genes and characteristics—not a goal in itself.
• The form and functionality of the animal should be the first criteria—not relationship.
• Breeding too close repeatedly may undermine the herd through lack of fertility, lack of size, durability, and fixing of undesirable structural problems.
• Careful linebreeding—avoiding inbreeding—can produce prepotent bulls that will stamp their progeny with their own desirable traits.
• Many producers feel they need to change bulls every two years to avoid breeding “too close.” A bull (or semen from an outside bull) may be used repeatedly over many years if a regimen to avoid inbreeding is followed faithfully, as Ken McDowall does.
• Animals that are structurally or functionally defective should be culled.
• Nutritional needs of breeding stock must be well met to allow expression of the animals’ potential.

Contact Ridge Shinn at 413-477-6500 or ridge@bakewellrepro.com .

Reprinted from Stockman Grass Farmer, Jan 2010