Population analysis of the French Bulldog breed Genetic analysis of the Kennel Club pedigree records of the UK French Bulldog population has been carried out with the aim of estimating the rate of loss of genetic diversity within the breed and providing information to guide a future sustainable breeding strategy. The population statistics summarised provide a picture of trends in census size, the number of animals used for breeding, the rate of inbreeding and the estimated effective population size. The rate of inbreeding and estimated effective population size indicate the rate at which genetic diversity is being lost within the breed. The analysis also calculates the average relationship (kinship) among all individuals of the breed born per year and is used to determine the level of inbreeding that might be expected if matings were made among randomly selected dogs from the population (the expected rate of inbreeding). Summary of results The analysis utilises the complete computerised pedigree records for the current UK Kennel Club registered French Bulldog population, and statistics were calculated for the period 1980-2014. 1
Figure 1: a plot of number of registrations by year of birth, indicative of any changing trend in popularity of the breed, followed by the yearly trend in number of animals registered (and 95% confidence interval). Breed: French Bulldog Figure 1: Number of registrations by year of birth Trend of registrations over year of birth (1980-2014) = 127.40 per year (with a 95% confidence interval of 72.38 to 182.42). 2
Table 1: census statistics by year, including sire use statistics. Table 1: by year (1980-2014), the number of registered puppies born, by the number of unique dams and sires; maximum, median, mode, mean and standard deviation of number of puppies per sire; and the percentage of all puppies born to the most prolific 50%, 25%, 10% and 5% of sires. year #born #dams #sires puppies per sire %puppies sired by most prolific sires max median mode mean sd 50% sires 25% sires 10% sires 5% sires 1980 38 28 20 6 1 1 1.9 1.41 73.68 52.63 26.32 15.79 1981 86 40 27 13 3 1 3.19 2.76 80.23 53.49 33.72 15.12 1982 124 41 28 15 3 1 4.43 3.87 81.45 55.65 32.26 12.1 1983 126 42 23 25 3 2 5.48 5.66 81.75 59.52 33.33 19.84 1984 121 40 23 16 4 4 5.26 4.1 77.69 52.89 26.45 13.22 1985 148 50 25 17 5 2 5.92 4.02 77.03 45.95 29.05 11.49 1986 173 59 35 19 3 2 4.94 4.58 79.77 58.96 35.84 20.81 1987 179 61 39 20 4 2 4.59 3.63 75.98 51.4 29.05 17.88 1988 151 49 34 19 3 3 4.44 4.16 76.16 58.28 30.46 21.85 1989 252 72 37 36 4 2 6.81 6.91 82.94 57.54 34.52 22.62 1990 245 73 40 29 4 3 6.13 6.19 80.82 57.96 35.1 22.04 1991 226 70 41 28 4 3 5.51 5.34 78.32 54.42 33.63 21.68 1992 247 77 45 28 4 2 5.49 5.32 77.33 52.63 34.01 21.86 1993 272 89 51 22 3 2 5.33 4.84 81.62 58.46 30.88 20.22 1994 318 88 53 25 5 2 6 5.37 78.93 54.72 30.82 21.7 1995 244 74 37 19 6 1 6.59 4.7 79.1 48.77 26.23 14.34 1996 199 67 42 19 4 1 4.74 4.43 79.4 57.79 31.66 18.59 1997 194 58 38 25 3 2 5.11 5.45 81.44 60.82 38.14 24.74 1998 204 56 37 22 4 1 5.51 5.34 82.84 56.86 36.76 20.59 1999 243 70 34 50 4.5 1 7.15 8.89 82.72 62.55 34.57 27.57 2000 176 59 36 30 3 1 4.89 5.48 82.39 58.52 37.5 26.14 2001 217 65 43 27 3 3 5.05 4.83 78.8 57.14 30.88 19.82 2002 286 83 57 17 4 1 5.02 3.85 78.32 51.05 28.67 16.43 2003 354 102 57 30 5 1 6.21 5.65 83.05 55.93 30.51 18.64 2004 352 110 67 19 4 1 5.25 4.12 79.55 52.84 28.69 14.2 2005 388 127 84 32 3 1 4.62 5.47 85.31 63.92 37.63 24.23 2006 597 181 115 29 3 1 5.19 5.56 85.09 62.14 37.35 22.95 2007 773 236 149 32 4 1 5.19 5.72 85.25 60.41 35.96 23.16 2008 1175 319 198 39 3 1 5.93 6.92 86.72 65.45 39.4 24.09 2009 1581 427 248 60 4 1 6.38 7.33 84.5 61.73 36.31 22.45 2010 2362 591 292 65 5 1 8.09 9.11 85.1 62.19 36.62 24.13 2011 3178 848 447 69 4 1 7.11 9.27 86.94 65.61 40.56 26.59 2012 5229 1283 624 87 5 1 8.38 10.69 86.54 66.32 40.56 26.2 2013 7018 1614 682 131 6 1 10.29 13.56 85.78 65.82 40.94 27.29 2014 9164 1901 744 163 7 4 12.32 16.27 85.05 65.56 42.48 28.14 3
Generation interval: the mean average age (in years) of parents at the birth of offspring which themselves go on to reproduce. Mean generation interval (years) = 3.20 Figure 2: a plot of the annual mean observed inbreeding coefficient (showing loss of genetic diversity), and mean expected inbreeding coefficient (from random mating ) over the period 1980-2014. Expected inbreeding is staggered by the generation interval and, where >2000 animals are born in a single year, the 95% confidence interval is indicated. Figure 2: Annual mean observed and expected inbreeding coefficients 4
Estimated effective population size: the rate of inbreeding (slope or steepness of the observed inbreeding in Figure 2) is used to estimate the effective population size of the breed. The effective population size is the number of breeding animals in an idealised, hypothetical population that would be expected to show the same rate of loss of genetic diversity (rate of inbreeding) as the breed in question. It may be thought of as the size of the gene pool of the breed. Below an effective population size of 100 (inbreeding rate of 0.50% per generation) the rate of loss of genetic diversity in a breed/population increases dramatically (Food & Agriculture Organisation of the United Nations, Monitoring animal genetic resources and criteria for prioritization of breeds, 1992). An effective population size of below 50 (inbreeding rate of 1.0% per generation) indicates the future of the breed many be considered to be at risk (Food & Agriculture Organisation of the United Nations, Breeding strategies for sustainable management of animal genetic resources, 2010). Where the rate of inbreeding is negative (implying increasing genetic diversity in the breed), effective population size is denoted n/a. Estimated effective population size = 132.3 NB - this estimate is made using the rate of inbreeding over the whole period 1980-2014 5
Table 2: a breakdown of census statistics, sire and dam usage and indicators of the rate of loss of genetic diversity over 5 year periods (1980-4, 1985-9, 1990-4, 1995-9, 2000-4, 2005-9, 2010-14). Rate of inbreeding and estimated effective population size for each 5-year block can be compared with the trend in observed inbreeding in Figure 2. Table 2: by 5-year blocks, the mean number of registrations; for sires the total number used, maximum, mean, median, mode, standard deviation and skewness (indicative of the size of the tail on the distribution) of number of progeny per sire; for dams the total number used, maximum, mean, median, mode, standard deviation and skewness of number of progeny per dam; rate of inbreeding per generation (as a decimal, multiply by 100 to obtain as a percentage); mean generation interval; and estimated effective population size. years 1980-1984 1985-1989 1990-1994 1995-1999 2000-2004 2005-2009 2010-2014 Mean #registrations 99 180.6 261.6 216.8 277 902.8 5390.2 Total #sires 77 90 134 114 161 540 1739 Max #progeny 34 78 83 82 51 91 325 Mean #progeny 6.3896 9.9333 9.7463 9.5 8.5963 8.3574 15.496 Median #progeny 3 6.5 5 5 4 4 6 Mode #progeny 1 4 2 1 1 1 1 SD #progeny 7.3164 11.949 12.335 12.511 10.744 11.936 25.977 Skew #progeny 1.976 3.2493 3.0074 3.0741 1.9848 2.9197 4.156 Total #dams 139 200 277 249 312 1001 4674 Max #progeny 17 16 27 33 19 26 31 Mean #progeny 3.5396 4.495 4.7184 4.3494 4.4359 4.5075 5.7653 Median #progeny 3 4 4 4 4 4 5 Mode #progeny 1 2 3 1 1 1 5 SD #progeny 2.8546 3.0572 3.4505 3.2729 3.4036 3.7043 4.1888 Skew #progeny 1.8467 1.1573 2.1548 3.2385 1.3268 1.4925 1.5899 Rate of inbreeding 0.032411 0.010356 0.021094 0.000662 0.01501-0.02816-0.01972 Generation interval 3.4295 3.2036 3.2046 3.5629 3.4819 3.0255 2.4876 Effective pop size 15.427 48.279 23.704 754.83 33.311 n/a n/a 6
Figure 3: a histogram ( tally distribution) of number of progeny per sire and dam over each of the seven 5-year blocks above. A longer tail on the distribution of progeny per sire is indicative of popular sires (few sires with a very large number of offspring, known to be a major contributor to a high rate of inbreeding). Figure 3: Distribution of progeny per sire (blue) and per dam (red) over 5-year blocks (1980-4 top, 2010-14 bottom). Vertical axis is a logarithmic scale. 7
Comments As with most breeds, the rate of inbreeding was at its highest in this breed in the 1980s and 1990s. This represents a genetic bottleneck, with genetic variation lost from the population. However, since the early 2000s the rate of inbreeding has been negative, implying moderate replenishment of genetic diversity (possibly through the use of imported animals). It appears that the extensive use of popular dogs as sires has increased (the tail of the blue distribution increasing in figure 3). It should be noted that, while animals imported from overseas may appear completely unrelated, this is not always the case. Often the pedigree available to the Kennel Club is limited in the number of generations, hampering the ability to detect true, albeit distant, relationships. 8