A pedigree is a record of ancestry, not a laboratory result. It tells you who a puppy's parents and grandparents were and whether those dogs were registered, but it does not state the puppy's MDR1 genotype, and it cannot be read as a certificate of drug tolerance. The only document that speaks to drug sensitivity is a genetic test result tied to an identified dog, and that document has to be requested, dated, and read carefully.
Owners who follow daily life with a dog in continental Europe often encounter breeding traditions and paperwork that differ from North American practice, and general-interest writing on that world, such as a Czech dog journal, can help a new owner understand how pedigrees, breeding records, and kennel customs are presented abroad. None of that replaces a genotype report, but it does explain why the paperwork a breeder hands over can look thorough while still saying nothing about the MDR1 gene.
What does a pedigree show about MDR1 status?
A pedigree shows lineage and registration. It lists ancestors, often across several generations, with titles, kennel names, and registration numbers. It confirms that the dogs in the pedigree were entered in a stud book and that the litter was recorded. What it does not show is any individual dog's MDR1 genotype, because the MDR1 gene is not part of the registration record. A pedigree can be complete and correct and still leave the question of drug sensitivity entirely open.
This matters because MDR1 status is inherited, and a dog can carry a defective allele without ever having been exposed to a drug that would reveal it. A pedigree with no history of adverse drug reactions is not evidence of a clear genotype. Reactions are often unrecognized, attributed to something else, or never reported. The absence of a note in a pedigree is the absence of a note, nothing more.
Some breed clubs and registries do record health screening results alongside pedigree data, and a breeder may keep those records. That is useful, but it is a separate document. Ask for it as a separate document, and read it as one.
How is a test result matched to a puppy?
A genotype report is only meaningful if it is tied to one animal. The report should carry the dog's registered name or call name, an identifier such as a microchip number or registration number, the laboratory that performed the analysis, the date the sample was collected or received, and the date the report was issued. Without those elements, a result is a piece of paper that could belong to any dog in the kennel.
Timing matters as much as identity. A result from a parent does not describe a puppy. A result from an earlier litter does not describe a later one. If a breeder offers a genotype for the dam and the sire, that is helpful background, but it is not the puppy's result. The puppy's own sample, collected after birth and identified to that puppy, is the document that answers the question.
Owners should also check what the test actually detects. Laboratories differ in which mutations they report and in how they name the genotypes. A report that uses different terminology than the one a veterinarian expects can still be valid, but it needs to be read in the laboratory's own terms. If anything is unclear, the laboratory that issued the report is the right place to ask, not an online forum.
Which questions should be put in writing before the puppy leaves?
Verbal assurances are difficult to rely on later, especially across borders and languages. A short written exchange, by email, covers the essentials and creates a record both parties can refer to.
Ask, in writing:
- Has this puppy been genotyped for MDR1, and if so, can I receive a copy of the report?
- If the puppy has not been tested, have the dam and sire been tested, and can I receive those reports?
- Which laboratory performed the testing, and what mutations does its panel include?
- What identifier links the report to this specific puppy?
- If no testing has been done, is the breeder willing to arrange it, and who covers the cost?
- Has any dog in the kennel ever shown signs after receiving ivermectin or another drug associated with MDR1 toxicity?
A breeder who has done the testing can usually answer these quickly. A breeder who has not may still be a careful, responsible breeder, but the owner then knows that the genotype is unknown and can plan accordingly.
How the answer guides the first year of parasite prevention
If a puppy is confirmed affected, meaning it carries two copies of the defective allele, prevention has to be built around that fact. Many heartworm preventives are formulated at doses that are safe for affected dogs, while others are not, and the difference is a matter of active ingredient and dose, not brand loyalty. A veterinarian who knows the genotype can select a product and a schedule that avoid the drugs of concern.
If the puppy is a carrier, with one copy, the practical implications are usually milder, but the information still matters for breeding decisions later and for the owner's understanding of what could be passed on. If the puppy is clear, the owner has a baseline that is worth keeping with the medical record.
If the genotype is unknown, the cautious approach is to treat the puppy as potentially affected until testing is done. That means avoiding the drugs on the list of concerns, reading labels rather than assuming, and telling every veterinarian who sees the dog that the status is unresolved. It also means testing at the first convenient opportunity, because a known result is easier to work with than a permanent unknown.
The anaesthetic conversation
Elective surgery, including spaying or neutering, is often the first time an owner has to discuss drug sensitivity with a clinic. The conversation is short if the genotype is known: the veterinarian notes the result in the record and chooses drugs accordingly. The conversation is longer if the genotype is unknown, because the clinician has to weigh the risk of an adverse reaction against the risk of withholding a needed procedure.
Owners can make that conversation easier by bringing the genotype report to the appointment, by naming the laboratory and the date, and by asking directly whether any drug in the planned protocol is one that affected dogs should avoid. A written question in the record is more useful than a memory of a phone call.
The same logic applies to any drug that crosses the blood-brain barrier, not only anaesthetics. The genotype, once known, follows the dog for life. The paperwork that establishes it is worth keeping in the same folder as the vaccination record and the pedigree, because it is the one document that turns a general warning about MDR1 into a specific instruction for one animal.
The figures and testing rules summarized above come from the WSU MDR1 programme, which maintains the reference laboratory for the MDR1 mutation and publishes the genotype interpretations that guide ivermectin and anaesthetic decisions. Owners who want to confirm a puppy's status, or who need the underlying documentation for a breeder or veterinarian, can request testing and review the programme's published guidance directly. The questions listed in this article reflect that source, so any result discussed with your veterinarian should be read against it.