A common misunderstanding about NI is that it cannot happen in a queen’s first litter of kittens, i.e. a type B queen has to be exposed to type A blood to raise the anti-A antibodies. This is incorrect since type B queens have naturally occurring high levels of anti-A antibodies in their blood regardless of the number of litters they
have had.
Therefore, NI can occur in the kittens from the first litter of a type B queen. Whilst most type B queens have high levels of anti-A antibodies in their blood, the levels do vary and some type B queens may produce lower levels. This may be responsible for some cases where type B queens appear to have litters with no apparent NI issues.