Population analysis of the Schnauzer breed Genetic analysis of the Kennel Club pedigree records of the UK Schnauzer 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 Schnauzer 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: Schnauzer Figure 1: Number of registrations by year of birth Trend of registrations over year of birth (1980-2014) = 6.02 per year (with a 95% confidence interval of 3.93 to 8.11). 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 16 12 7 7 1 1 2.29 2.21 n/a n/a n/a n/a 1981 76 25 15 16 3 2 5.07 4.68 85.53 61.84 38.16 21.05 1982 116 26 16 21 5.5 1 7.25 6.69 87.93 56.9 33.62 18.1 1983 161 30 17 28 8 4 9.47 7.31 79.5 51.55 30.43 17.39 1984 138 31 19 27 6 2 7.26 6.15 81.16 54.35 29.71 19.57 1985 165 41 18 27 6.5 1 9.17 8.24 87.27 60 30.91 16.36 1986 186 39 21 35 7 2 8.86 7.88 80.65 52.69 29.03 18.82 1987 141 30 16 21 7.5 5 8.81 5.54 73.05 47.52 28.37 14.89 1988 172 36 21 21 7 1 8.19 5.97 77.91 50.58 23.84 12.21 1989 257 40 27 51 8 8 9.52 9.53 78.21 53.7 34.24 19.84 1990 207 37 24 24 7 4 8.63 5.59 72.46 47.83 22.22 11.59 1991 225 37 23 37 8 8 9.78 8.4 77.33 53.33 29.33 16.44 1992 242 40 28 23 7 7 8.64 4.87 71.07 44.21 22.31 9.5 1993 177 35 28 24 5.5 1 6.32 5.17 77.4 50.28 29.94 13.56 1994 223 42 30 31 5 4 7.43 7.03 80.72 60.09 32.29 24.66 1995 249 49 31 24 7 7 8.03 5.4 75.1 49 24.9 17.67 1996 256 47 27 37 8 4 9.48 7.96 78.13 53.52 32.42 14.45 1997 256 46 29 27 7 6 8.83 6.88 79.69 51.95 27.73 10.55 1998 315 51 28 37 9 3 11.25 8.77 75.24 51.43 29.84 11.75 1999 282 46 31 30 8 8 9.1 5.95 74.47 47.52 22.7 16.67 2000 261 37 24 43 7 6 10.88 10.43 78.16 57.09 31.42 16.48 2001 384 55 35 40 8 1 10.97 9.12 78.91 55.21 32.29 18.49 2002 373 55 32 64 8 1 11.66 13.35 81.77 60.32 37.53 30.03 2003 363 59 38 27 8 1 9.55 7.91 81.54 56.75 28.65 14.6 2004 360 56 34 38 9.5 1 10.59 8.63 80.83 55.28 23.61 17.22 2005 336 51 35 31 8 1 9.6 8.05 82.14 57.44 30.95 16.96 2006 361 56 36 51 8 1 10.03 10.07 79.22 55.68 35.46 24.65 2007 250 37 27 24 8 9 9.26 4.92 68.4 44 24.8 9.6 2008 313 54 35 31 7 1 8.94 8.09 84.66 59.42 31.63 18.21 2009 293 47 29 38 9 1 10.1 9.36 83.62 54.61 32.76 12.97 2010 291 50 33 41 6 1 8.82 9.75 86.25 62.89 34.02 26.46 2011 235 48 38 29 5.5 1 6.18 5.64 83.4 55.74 30.21 18.72 2012 299 50 33 27 8 1 9.06 7.3 83.28 51.84 24.08 17.39 2013 235 46 33 20 6 1 7.12 5.53 82.13 51.91 22.55 15.74 2014 205 33 29 20 7 3 7.07 4.09 72.68 40.98 21.46 9.76 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) = 3.92 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 = 105.4 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 101.4 184.2 214.8 271.6 348.2 310.6 253 Total #sires 47 59 70 73 93 95 106 Max #progeny 54 92 73 98 131 84 86 Mean #progeny 10.745 15.492 15.329 18.589 18.71 16.337 11.896 Median #progeny 6 9 9.5 12 10 9 7 Mode #progeny 1 1 1 2 1 1 1 SD #progeny 13.97 17.863 14.523 19.784 23.714 18.657 15.308 Skew #progeny 2.0414 2.3049 1.5506 1.8156 2.3361 1.6269 2.4527 Total #dams 88 130 131 155 172 180 161 Max #progeny 20 39 33 34 35 37 31 Mean #progeny 5.7386 7.0769 8.1908 8.7484 10.116 8.6222 7.8323 Median #progeny 5 6 7 7 8 7.5 6 Mode #progeny 1 1 8 7 1 1 1 SD #progeny 4.2521 6.179 5.7861 6.5778 7.8165 6.667 6.5319 Skew #progeny 1.1025 1.9222 1.5278 1.401 1.1724 1.3608 1.0761 Rate of inbreeding 0.033234 0.020861 0.003981 0.024427 0.013234 0.005672-0.00221 Generation interval 3.3277 3.2707 3.9979 3.8677 4.6063 3.8955 4.6106 Effective pop size 15.045 23.968 125.59 20.469 37.782 88.149 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 early 1990s. This represents a genetic bottleneck, with genetic variation lost from the population. Since the mid-1990s the rate of inbreeding has decreased, implying a slowdown in the rate of loss of genetic diversity (possibly through the use of imported animals). There appears to be extensive use of popular dogs as sires in this breed (the tail of the blue distribution 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