Failure of Passive Transfer
A newborn's failure to absorb enough antibodies from its mother's first milk, leaving it dangerously vulnerable to infection unless caught and treated within a short window after birth.
Also known as FPT, Failure of Passive Immunity Transfer, Passive Transfer Failure
Newborn puppies, kittens, foals, calves, lambs and kids arrive with an immune system that's ready to work but has never met a single germ. In these species the placenta blocks almost all antibody transfer to the baby before birth, so each one starts life with barely any defence of its own. That defence has to arrive after birth, carried in the mother's first milk. Colostrum is thick with antibodies, mostly a type called IgG, and for a short stretch after birth the newborn's gut can absorb those large antibody molecules whole, straight into the bloodstream, rather than simply digesting them like ordinary food. Failure of passive transfer, often shortened to FPT, is what vets call it when that handover doesn't go to plan and the newborn ends up without enough antibody in its blood to fight off infection.
Two things make this urgent. The first is the clock. The gut's ability to pull antibodies into the bloodstream fades quickly and then shuts entirely. In puppies, the process appears to start within four to eight hours of birth and is essentially finished by sixteen to twenty-four hours, based on a study feeding colostrum to newborn beagles at set intervals after whelping. In kittens, absorption works best within the first sixteen hours of life and generally stops by around twenty-four hours. In farm species, colostrum given after roughly eighteen to twenty-four hours does little beyond feeding the newborn, because the gut can no longer pass antibody molecules through. Once that window has closed, colostrum is still good nutrition, but the antibodies in it mostly stay in the gut instead of reaching the blood. The second thing is the consequence: a newborn without that antibody cover is left wide open to infection, and problems like blood poisoning (sepsis) and death in the first weeks of life show up far more often in newborns that missed the handover.
Plenty of ordinary situations can cause it: a mother who produces too little colostrum or colostrum of poor quality, one who leaks milk before giving birth, a hard delivery that leaves her too sore to let the newborn nurse, a very large litter where the smallest get pushed off the teat, a premature or weak baby with no suck reflex, or an orphan with no colostrum source at all. It happens even under good management: on four New South Wales studs, 16% of foals had failed transfer outright and a further 17% had only partial transfer, which is why testing for it is routine on many breeding farms rather than something reserved for foals that already look unwell.
When to involve your vet
In horses and farm animals, a blood test measuring IgG is standard, with quicker in-clinic estimates available alongside the more precise lab test. In foals, above 800 mg/dL is considered adequate, 400 to 800 mg/dL counts as partial failure, and below 400 mg/dL is complete failure. Puppies and kittens are harder to test for antibody levels directly, so vets rely more on the newborn's history, risk factors and how it grows over the first couple of days, stepping in when the overall picture looks wrong.
Call your vet the same day, not tomorrow, if a newborn:
- hasn't nursed within the first two to four hours of life
- is being kept away from the mother, or the mother has no milk to give
- is losing weight, or not steadily gaining, in the first days of life
Timing decides what's still possible. Within the absorption window, colostrum from the mother, a donor of the same species, or a colostrum bank can still be given by bottle or tube, and getting it in early matters more than exactly where it comes from. Once the gut has closed, antibody has to arrive another way: foals typically receive an intravenous plasma transfusion, while kittens can be given serum from a healthy, vaccinated cat by injection. Both are procedures for a vet to carry out, not something to attempt at home. Prevention beats treatment here, so it's worth watching that every newborn genuinely feeds early and asking for help quickly if one doesn't.
This is general information, not a diagnosis. A newborn that isn't thriving is always worth having seen.
