Population analysis of the Airedale Terrier breed Genetic analysis of the Kennel Club pedigree records of the UK Airedale Terrier 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 Airedale Terrier 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: Airedale Terrier Figure 1: Number of registrations by year of birth Trend of registrations over year of birth (1980-2014) = -18.66 per year (with a 95% confidence interval of -25.90 to -11.41). 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 343 195 97 23 2 1 3.54 4.54 85.71 67.64 43.15 27.7 1981 1025 260 110 63 4 2 9.32 12.18 88.78 70.73 43.71 27.61 1982 1329 291 97 104 7 3 13.7 17.4 87.58 66.29 41.46 27.16 1983 1398 308 112 74 6 1 12.48 14.81 88.05 66.88 38.77 25.04 1984 1412 313 127 100 6 1 11.12 15.78 87.82 69.33 47.03 28.9 1985 1371 295 112 67 7 1 12.24 13.31 86 63.02 35.52 23.63 1986 1375 316 113 95 7 3 12.17 14.8 84.58 63.49 39.42 26.91 1987 1071 237 106 53 6 1 10.1 11.46 84.97 65.45 38.75 21.85 1988 1319 267 108 80 7 6 12.21 14.2 84.53 63.61 39.12 23.28 1989 1415 220 106 63 8 4 13.35 13.93 82.47 61.48 37.67 20.21 1990 1243 180 91 122 9 7 13.66 16.03 81.01 60.1 36.44 26.15 1991 1058 163 84 79 8 7 12.6 13.43 76.94 58.88 36.77 22.59 1992 1042 150 72 92 9 8 14.47 17.39 81.86 64.01 40.21 28.02 1993 930 125 64 64 10 6 14.53 14.36 80.65 58.28 34.19 19.35 1994 1014 144 70 88 9.5 7 14.49 14.54 79.59 57.89 33.63 24.06 1995 1222 170 80 92 9 7 15.28 17.35 81.34 60.64 37.73 25.7 1996 986 151 74 56 9 7 13.32 11.24 78.19 57.51 27.89 17.55 1997 1163 164 80 74 9.5 1 14.54 14.8 80.91 58.3 35.43 22.18 1998 913 127 67 88 10 11 13.63 14.36 77.88 56.74 36.25 21.8 1999 872 138 67 80 8 1 13.01 16.17 83.83 63.65 42.55 24.89 2000 975 148 64 105 10.5 6 15.23 16.64 81.13 57.64 34.26 22.46 2001 889 136 62 182 9 1 14.34 25.93 84.25 66.59 47.58 36.56 2002 1011 146 71 75 9 7 14.24 14.12 81.8 59.25 34.42 22.26 2003 877 144 64 76 8 1 13.7 15.69 85.06 64.77 36.83 22.01 2004 964 133 53 95 11 2 18.19 20.63 84.85 63.59 37.14 25.21 2005 783 130 66 80 8 1 11.86 15.81 86.08 67.94 46.74 25.42 2006 851 125 70 67 8 1 12.16 12.85 83.67 62.04 33.73 23.03 2007 904 125 63 78 9 1 14.35 16.68 85.51 64.93 37.72 22.79 2008 850 126 67 85 9 1 12.69 13.83 82.59 59.41 36.47 21.29 2009 586 88 63 61 7 6 9.3 9 79.18 55.29 29.69 18.43 2010 579 89 53 54 8 1 10.92 10.39 79.27 54.75 32.47 22.8 2011 610 95 45 63 9 1 13.56 13.33 85.41 59.84 34.26 16.89 2012 612 99 56 62 7 1 10.93 13.85 86.27 66.5 44.77 28.27 2013 548 77 40 70 9 1 13.7 15.79 82.66 63.14 39.6 23.72 2014 580 76 43 110 9 6 13.49 17.39 81.21 60.52 36.38 25.86 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) = 4.02 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 = 25.6 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 1101.4 1310.2 1057.4 1031.2 943.2 794.8 585.8 Total #sires 306 282 210 210 164 180 135 Max #progeny 216 282 297 214 300 184 207 Mean #progeny 17.987 23.22 25.171 24.548 28.738 22.067 21.689 Median #progeny 6 9 11 12 12 10 9 Mode #progeny 1 1 8 1 1 1 1 SD #progeny 32.742 36.592 37.424 33.401 45.16 32.107 35.985 Skew #progeny 3.3173 3.6274 3.4747 2.9297 3.5467 2.943 3.2608 Total #dams 971 971 536 515 451 407 289 Max #progeny 27 31 50 43 46 44 37 Mean #progeny 5.6684 6.7446 9.8507 10.01 10.455 9.7592 10.131 Median #progeny 4 6 8 8 8 8 9 Mode #progeny 1 3 7 8 8 1 1 SD #progeny 4.9479 5.2426 6.7558 7.1126 7.7663 7.4289 7.5132 Skew #progeny 1.5919 1.549 1.5537 1.4398 1.3525 1.4673 0.93616 Rate of inbreeding 0.038956 0.032628 0.0378 0.05801 0.021383 0.0001839-0.032294 Generation interval 3.4045 3.7493 4.4379 3.9026 4.0781 4.0949 4.5872 Effective pop size 12.835 15.324 13.227 8.6192 23.383 2718.4 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 mid-2000s 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