A breeder who has actually screened the litter's parents can hand you a laboratory report with the dog's registered name, the test date, and a genotype result. A verbal assurance that "the lines are clean" is not a result, because MDR1 status is a laboratory finding, not an impression. Before any deposit leaves your account, ask to see the document itself, and ask how that result will shape the preventive care the puppy receives after pickup.
What proof of MDR1 screening should a breeder show?
The proof is a report issued by a laboratory, not a summary written by the seller. On it you should be able to read the dog's registered name or chip number, the laboratory's name, the collection or receipt date, and a genotype: clear, carrier, or affected. Those three words carry different meanings, and the report should state which one applies rather than leaving you to guess from a phrase like "tested normal."
Ask whether the result belongs to the sire, the dam, or both. A single tested parent tells you only half of what you need. If the breeder tested one dog and not the other, the untested parent's status is unknown, and the litter's possible genotypes widen accordingly.
Ask for the original, not a retyped copy. Screenshots and typed summaries are easy to alter and impossible to verify. A PDF or paper report from the laboratory, with its own formatting and reference numbers, is what you can check against the laboratory's records if you choose to.
If the breeder says the test was done "years ago," that is usually fine, because MDR1 genotype does not change over a dog's life. What matters is that the dog tested is the dog being bred, and that the identity on the report matches the identity on the pedigree and the registration papers.
This is the same discipline that applies to every other claim in a sale, and it is the approach set out in an Aussie breeder's evidence: documents first, assurances second. A breeder who expects to be asked will have the paperwork ready.
Why is a verbal assurance not enough?
A verbal assurance cannot be checked, cannot be dated, and cannot be attached to a specific dog. "We have never had a problem" describes the breeder's experience, not the puppy's genotype. Those are different things, and only one of them travels home with you.
MDR1 sensitivity is inherited, so the relevant question is not whether problems have appeared before but what the parents' genotypes are. A carrier bred to a carrier can produce affected puppies even in a kennel that has never seen a reaction. The absence of past incidents is not evidence of a clear genotype; it may simply mean the breeder has not used the drugs that would reveal it.
There is also a practical problem with memory. Breeders handle many dogs, many litters, and many years. A result recalled from memory may be accurate, or it may belong to a different dog, a different litter, or a test that was discussed but never sent. The report removes that ambiguity.
Finally, a verbal assurance gives you nothing to act on later. When your veterinarian asks about the puppy's MDR1 status before prescribing a preventive, "the breeder said it was fine" is not a status. A genotype is.
How does MDR1 screening sit beside eye and hip checks?
MDR1 screening is one line in a set of health documents, and it behaves differently from the others. Eye and hip evaluations are examinations performed at a point in time, and their results can change as a dog ages. MDR1 is a genotype: it is set at conception and does not change, so a single valid result lasts the dog's lifetime.
That difference matters when you read a folder of paperwork. Hip and eye results are typically issued by examining bodies after a physical assessment, and they carry a date that tells you how current the evaluation is. An MDR1 report carries a date too, but for a different reason: it tells you when the sample was submitted, not when the status might expire.
Ask to see all three together, and ask which dogs they cover. A breeder may have hip and eye results on the dam and MDR1 results on the sire, or the reverse. What you want is a complete picture of both parents across all three categories, not a strong result in one area standing in for silence in another.
If a document is missing, the useful question is whether it exists and can be produced, or whether it was never obtained. Those are different situations, and the answer tells you something about how the kennel is run.
What should the answer change about the puppy's care?
The genotype should follow the puppy into your veterinarian's office. If the puppy is clear, routine parasite prevention can be chosen without MDR1 as a limiting factor. If the puppy is a carrier, the practical risk is low for the dog itself, but the status matters if that dog is ever bred. If the puppy is affected, drug selection becomes a genuine clinical constraint, and your veterinarian needs to know before the first prescription, not after a reaction.
Ask the breeder how the result will be communicated: on the sales contract, in a separate health record, or verbally at pickup. Written is better, because it survives the trip home and the change of veterinarians.
Ask also what the breeder knows about the puppy's parents' status in combination. Two clear parents produce clear puppies. A clear parent and a carrier parent produce a mix, and the individual puppy's status cannot be assumed from the parents alone. That is why testing the puppy, or at least recording the parents' genotypes accurately, has practical value beyond the sale.
Questions to bring to the first conversation
Write them down before you call, so the conversation does not drift. Which dogs were tested, and can I see the reports? What are the genotypes, in the laboratory's own words? Will the result appear in writing with the puppy's paperwork? Who do I contact if my veterinarian has a question about the result?
A breeder who answers these directly, and who can produce the documents, is giving you something a reassuring sentence cannot. The deposit is the point at which you still have leverage. Use it to ask for paper.
Once the deposit question is settled, the same paperwork trail continues on the other side of the sale. Buyers who want the MDR1 result to survive the trip home, and breeders who want it recorded where a veterinarian can find it, face a second set of decisions about documentation and timing. A companion article walks through how a result is read in a breeding decision, where it belongs in the puppy's file, and how it carries into the first year of preventive care, using the purchase file in France as a worked example of the record a new owner should expect to receive.
The screening figures and testing rules described above come from the WSU MDR1 programme, the laboratory that developed and continues to run the mutation test for collies and related breeds. Its published guidance explains why a verbal assurance from a breeder carries no weight, how MDR1 results sit alongside eye and hip checks, and what a positive or carrier result should change in a puppy's daily care. Owners can read the source material directly before the first conversation with a breeder.