A Pairing Decision, Worked Through

Knowing the genetics is one thing. Using it when you have two real dogs in front of you, each with strengths and weaknesses, is another. This lesson works through one pairing decision step by step, the way an experienced breeder would reason through it.

You will see how health results, relatedness, temperament and the homes waiting for puppies all feed into one choice, and why the "obvious" option is not always the right one.

The situation

Dana breeds a medium-sized working breed on a small scale, one litter every year or two. Her female, Maple, is three years old, healthy and has an even, confident temperament. Dana is thinking about a first litter from her.

Maple's results so far:

• Hips and elbows screened through the national scheme, with results better than the breed's typical result.
• An eye examination by a veterinary ophthalmologist this year, with no inherited eye disease found.
• A DNA test for an inherited eye condition that follows simple recessive inheritance and has a validated test in this breed: clear.

Dana has two possible stud dogs.

Stud A lives twenty minutes away and has an impressive show record. He is DNA clear for the eye condition and his hip result is about average for the breed. He shares several ancestors with Maple: his grandfather is also Maple's grandfather on one side. The kennel club's calculator gives the planned litter a coefficient of inbreeding well above the breed average.

Stud B lives a long drive away. His owner is happy to share certificates. His hips and elbows are good, his eyes were examined recently with no disease found, and he is a carrier of the eye condition. His lines are almost entirely separate from Maple's, and the planned litter's inbreeding figure is below the breed average. Dana has met him: calm, friendly with strangers, keen to work.

Step 1: Check the results are real

Before comparing anything, Dana confirms each result from the source. She looks both dogs up in the public health database where results are recorded and asks to see original certificates for anything not listed. A result that is only reported by word of mouth is not a result.

She also checks that the eye condition test is one validated in this breed. A DNA test only helps if it is known to matter in the breed being tested.

Step 2: Work out what each pairing can produce

For the eye condition:

• Maple (clear) and Stud A (clear): every puppy will be clear.
• Maple (clear) and Stud B (carrier): no puppy can be affected, because Maple can only pass on a normal copy. On average about half the puppies will be carriers.

So Stud B's carrier status does not put any puppy at risk of the disease. It does mean Dana must test any puppy kept or sold for breeding, and tell buyers honestly what carrier status means.

Step 3: Weigh what the tests cannot see

This is where Stud A starts to look weaker. The close relationship means puppies are more likely to inherit identical copies of genes from the shared grandfather. That raises the risk of recessive problems that no test covers, and it tends to double up whatever faults the shared ancestor had. The above-average inbreeding figure is a cost the DNA result does not show.

Stud A's average hip result, paired with Maple's good one, is acceptable but does not improve on her. Stud B's good result is more likely to hold or improve the litter's odds for a many-gene condition, though it can never guarantee it.

Step 4: Temperament, purpose and structure

Health is necessary but not sufficient. Dana asks whether each stud would complement Maple. She has met Stud B and liked what she saw. She has only seen Stud A in the show ring, which tells her little about how he behaves at home or at work. Before deciding, she would want to meet him properly, and ask about his earlier litters: how the puppies turned out in temperament and health.

Step 5: Are there homes?

Finally, Dana checks her list of enquiries. She has several families she has already spoken to at length who suit the breed. If she did not, she would wait: a good pairing with no suitable homes is still a reason to delay.

The decision

Dana chooses Stud B. The pairing cannot produce puppies affected by the eye condition, brings in new lines, and improves the odds on hips and elbows. Her plan includes DNA testing any puppy intended for breeding and giving every buyer a written summary of both parents' results.

Notice what would change her mind. If Maple had been a carrier too, a carrier to carrier pairing could produce affected puppies, and Stud B would be the wrong choice. The decision is always about the pair, not either dog alone.

Before breeding, Dana also books Maple in with her vet for a pre-breeding check, because health testing for inherited conditions is not the same as a check that Maple is fit for pregnancy now. For what comes after the pairing, see raising and socializing a litter.