ESS Population Analysis

Royal Kennel Club Population Analysis

In January 2026, the RKC released the final versions of their individual Breed Population Analysis reports for each of 222 recognised breeds.  The reports were based on the records of RKC registered dogs born between 1990 and 2021 and looked at trends in registration, litter size, breeding practices and genetic diversity.  

One of the strongest warnings in the ESS report is the continued influence of the popular sire effect and echoes an earlier KC Population Analysis Report published in 2015 (which looked at dogs registered between 1980 and 2014).  When a small number of males are used repeatedly, the gene pool narrows rapidly.  Even in populations with robust numbers, this can quietly undermine long-term breed health.  Less diversity means more risk of inherited disease and inbreeding depression (e.g. reduced fertility, increased puppy mortality, faulty immune systems, etc.).

Here are some of the key findings of the 2026 ESS Population Analysis Report:

• Based on the rate of inbreeding calculated for ESS born between 1990 and 2021, the effective population size was estimated at 44, compared with 45 in the 2015 report.  (Effective population size may be thought of as the total genetic variation of a breed’s ‘gene pool’, not the size of the population itself.  Large populations can have a low EPS and small populations a high EPS.  An EPS of less than 50 puts a breed at critical risk of inbreeding depression - ideally it should be over 100.)

• Average COI for dogs born in 2021 was 11.2%.  There was a significant and negative association between COI and litter size – litters with higher COIs tend to be smaller.

• The average genetic relationship (AGR) among dogs assumed to be alive is 18.8% - i.e. the average ESS in the current population is more related to any other dog in the population than first cousins, but not as closely as half-siblings.  (While COI looks at a specific litter, AGR measures how closely an individual dog is related to the entire breed population. Dogs with a low AGR are genetically "rare" and highly valuable for maintaining diversity.)

• The percentage of males used in breeding was low, which poses a risk to genetic diversity.

• Across time, there was strong evidence of popular sire use.

• Sires with stud book numbers and imported sires had significantly higher numbers of litters.

• The number of imported dogs significantly increased over time, with a simultaneous increase in the percentage of litters produced from imported parents.

There are practical steps breeders and owners can take to preserve valuable genetic diversity.  This includes:

• Choosing less closely related mates.

• Avoiding repeated use of popular sires.

• Considering both COI and AGR (population diversity) when planning matings.

• Supporting genetic diversity over short-term success.

Every mating matters.  Informed breeding today can protect the future health and welfare of the breed.

You can read the full 2026 ESS Population Analysis Report and the earlier 2015 Report by clicking on the links below.

For further guidance on managing and maintaining genetic diversity, visit the RKC website HERE.