Chapter 4: Considerations for Mixing Cats and Kittens

Shelter staff and foster parents are tasked with caring for and adopting out animals who are healthy and well-socialized pets for their future adoptive homes.  We want growing animals to be able to experience the world and we want adult animals to be able to express their normal behaviors and have interactions that would enrich their lives. It is important to balance these mental/emotional needs with medical health needs, including preventing the spread of infectious disease. Kittens, in particular, are highly susceptible to infectious disease and special consideration must be given to when it is or is not reasonable to mix them together; in addition, there are some important details to keep in mind when mixing unrelated cats of any age.

Limitations on capacity - staff, time, and/or number of foster homes or amount of cage space - can pose challenges to providing the care necessary to move animals efficiently and safely to the point of adoption. These challenges may lead some shelters to make a choice to mix unrelated cats or kittens together just in order to find more “space.”  However, that choice often leads to more challenges rather than fewer if the choices of which cats to mix are not balanced against the ability to screen for and recognize signs of infectious disease.

All Cats and Kittens

Does the shelter have adequate screening and monitoring practices in place to identify animals with signs of infectious disease?

Cats showing signs of infectious disease should not be co-mingled or housed in groups. Signs to watch for include:

  • Sneezing, nasal discharge, squinting/swollen eyes, ocular discharge
  • Vomiting, diarrhea, poor appetite
  • Itchy skin (pruritis), visible external parasites, suspicious areas of hair loss, Wood’s positive skin lesions
  • Unexplained weight loss, history of littermate with sudden death

Screening for these signs must begin at intake and monitoring should continue daily for the duration of the animal’s time in the shelter.

Infectious disease may be brewing in apparently healthy cats. The time between being infected with a pathogen and showing signs of illness is called the incubation period. During the incubation period an animal may be contagious to other animals but appear healthy. The incubation period for panleukopenia is well established, typically 5-7 days but can go up to 14 days. A cat is unlikely to be incubating panleukopenia if they appear healthy for 7 days, and the chances are slim if no signs have been seen for the past 14 days. For this reason, cats who have at least 7 days (and ideally 14 days) of a well-documented, healthy medical history in the shelter make better choices than cats with an unclear history.

Additionally, the incubation period for ringworm is 2-4 weeks. If cats are being screened for suspicious lesions (as well as other signs of infectious disease) at intake, receiving a wood’s lamp examination at intake, and are checked again prior to being mixed, this will help to limit the spread of ringworm between cats in your shelter.

Does the shelter routinely vaccinate all cats and kittens at time of intake (or as soon as they reach 4 weeks of age) and every 2 weeks thereafter?

Vaccination is a key component of preventing disease outbreaks. The panleukopenia component of the FVRCP vaccine in particular offers robust protection from disease, but it does take at least 5 days for the vaccine to provide full immunity. Furthermore, the presence of maternal antibodies may prevent a vaccine from successfully immunizing a kitten, so it is important that they get re-vaccinated every 2 weeks while they are in the care of the shelter or until they reach the age of 20 weeks. 

Kittens < 20 weeks old

The benefits may be worth the risks for mixing unrelated kittens together when combining pairs of single orphaned kittens who risk missing out on critical opportunities for socialization with other cats. In other cases, the risks of combining kittens probably outweigh the benefits. While shelters may choose to mix kittens together for other reasons, this often poses significant risk for welfare and health for other individuals and possibly for the population as well. 

There are several factors that should be weighed before mixing animals from different sources together in any situation:

Do not mix sick kittens with other (healthy or sick) kittens.  Much like children in daycare, if one kitten is sick, chances are all of them are going to get sick. But in kittens the stakes are higher, because the illness could be life threatening. Kitten’s immune systems are developing from the day they are born but it takes time to develop a robust immune system. Furthermore, because kittens may have received antibodies from their mother soon after birth (that are important but can interfere with immunization), they may not be immunized by the vaccines they receive until the levels of maternal antibodies fall below a certain threshold. Because we can never be certain when that threshold is, kittens must be vaccinated every 2 – 3 weeks until 20 weeks of age when all maternal antibodies are known to have subsided.  Also, even though 2 unrelated kittens may have signs of upper respiratory disease, you cannot be certain the disease is being caused by the same pathogen so mixing them together may result in complicating their upper respiratory infections.

Considerations when using surrogate queens:

Putting orphan kittens with an unknown history with a queen with older kittens may be a very risky choice for all of the kittens. Even if apparently healthy, the new kittens may be incubating disease that could affect the queen or other kittens she is nursing. Older kittens often also outcompete orphans for the milk they need to grow and thrive.

Queens provide more than just food and a warm snuggly pillow to their kittens. Kittens receive colostrum from their mothers in their first nursing sessions after birth. Colostrum serves to offer some immune protection from infectious disease until kittens develop an immune system of their own. Unfortunately, kittens are only able to absorb colostrum for the first 24 hours of their life, and queens only produce it soon after queening. Kittens who miss out on receiving colostrum are at high risk for disease and fading kitten syndrome. The colostrum-deprived orphans have a poor prognosis, and if/when they become ill they may put the queen’s original kittens at risk.

NOTE: Kittens do not receive any immune benefits through nursing after the first 24 hours of life. Vaccinating a queen provides no immunity to her nursing kittens. Kittens who are 4 weeks or older should each receive their own vaccinations (or start once they reach 4 weeks of age), repeating as described above.

In addition, overloading a queen with more than her litter or with sequential litters may cause health and welfare risks for the queen. The nutritional needs of nursing queens are high, and caring for orphan kittens will take a toll on her physical health unless nutritional needs are maintained. Furthermore, it is important to maintain consideration for the behavioral needs of the queen over time.

Imagine the worst case scenario when making a choice to mix kittens and weigh that against your goals for socialization and/or foster home placement. If you decide to mix 2 unrelated litters of kittens, imagine the consequences if a serious disease were to spread to all individuals: 

What if you placed 1 orphan baby with a nursing queen and her 4 kittens? If either group is harboring disease, all 5 of these kittens (and possibly the queen) are now at risk.  The benefits of putting the orphaned kitten in this group to save his life may ultimately jeopardize 5 other lives.

What if you placed 2 single orphaned kittens together? In this scenario, even if the worst happens, only these 2 kittens are put at risk for disease. As singletons, these kittens have a relatively high risk of developing behavioral problems that can reduce their adoptability. The choice to combine them carries some disease risks, but also offers real socialization benefits. The risks of 2 kittens remaining alone versus living together does not multiply the risk additional animals.

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