[BLOG] The "critical period" : something breeders need to be aware of

 When I finished my veterinary curriculum, there were plenty of things I wasn't aware of concerning puppies & kittens. The term "critical period" clearly did not ring a bell... Today, I know better. I understand why this term is essential, especially when you have - or will have- puppies & kittens. I understand why it is important to always discuss it with our breeders. 


The "critical period" (which is the literal translation of the french term - in English it is often referred to as "immunity gap") happens in all puppies & kittens. It has potential consequences, especially in a breeding structure.


What is it ?


In previous posts (see here ) we touched on the importance of colostrum in newborns, this first milk of the mother which contains a high concentration of antibodies that will provide the puppy / kitten that drinks it its first immune system. The slideshare below shows you what happens as the puppy / kitten grows : this initial immune system will progressively wane off. Some antibodies will be destroyed, some will be consumed in contact with some of the pathogens in the environment... and growth per se will obviously decrease their concentration too. 



Now pay attention to those two lines that are present on the chart :

- the red line is what we refer to as the "protection threshold" : when antibodies' concentration is above this line, puppies/kittens are considered protected by the antibodies they received from their mother ;


- the blue line represents the "vaccine neutralisation threshold" : if a vaccine is administered while the puppy/kitten antibodies' concentration is above this line, everything it contains will be neutralized by those maternal antibodies. The vaccine will therefore be inefficient because of what we refer to as "interference of the maternal antibodies". 


If you take a good look at the slideshare again, you realize that there is a period during the life of a puppy or a kitten when their antibody concentration will be below the red line... but also above the blue line. When this occurs, they are no more protected by the maternal antibodies. But there are still too many of them for vaccination to be efficient. This is what we call the critical period.


When does it happen ?


Unfortunately, the critical period indeed do not happen at a given moment on a given puppy /kitten (it's biology we are dealing with, which means lots of factors of variation...).


It indeed depends  on :


- The amount of colostrum the puppy / kitten drank right after birth. The more is drunk, the more antibodies are absorbed ;


- The antibodies contained in the colostrum ; the colostrum contains antibodies against diseases the mother has been vaccinated for OR that she suffered from ; remember that when it comes to infectious diseases, antibodies are disease-specific. No vaccination or no exposure to a given disease from the mom = no colostrum protection transferred to the neonates for this specific problem.


- The speed of growth of the puppy / kitten ; the faster they grow, the faster the protection provided by the colostrum will be "diluted" ;


With all those variation factors, you understand therefore that it might vary between litters, but it might also vary from one puppy / kitten to another within the same litter !


The critical period usually occurs between 4-12 weeks in puppies & kittens, more often between 5-8 weeks. 


What are the consequences ? 


Maybe you have heard about puppies or kittens developing diseases they were vaccinated for right after being vaccinated. Sometimes people assume it is because the vaccines did not work (we discuss this in one of our e-book, you can read it here). The truth is, very often,  this happens because unfortunately the vaccination was performed during the critical period. 


Instead of stimulating the immune system, the vaccine was neutralized by the remaining maternal antibodies... and the puppy and kitten left unprotected.


Obviously vaccination protocols do take the critical period into account and current vaccine recommendations will be adequate for most cases. But because of all the variation factors, you understand why breeders are somehow more predisposed to face this kind of situation. 


The use of vaccine titers can today definitely help to better assess when to start vaccinating your puppies and kittens. This is something I definitely encourage you to discuss with your veterinarian.


In case this type of problem ever occurs in your kennel or cattery, be aware that vaccination protocols can be re-adapted. The information I always recommend you bring to your veterinarian is at what age the problem occurred in the puppies or kittens. This data is essential to redefine a vaccination protocol that will better suit your cattery or kennel. 

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