Population analysis of the Irish Wolfhound breed Genetic analysis of the Kennel Club pedigree records of the UK Irish Wolfhound 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 Irish Wolfhound 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: Irish Wolfhound Figure 1: Number of registrations by year of birth Trend of registrations over year of birth (1980-2014) = -9.75 per year (with a 95% confidence interval of -13.97 to -5.53). 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 193 116 59 15 2 1 3.27 3.07 82.9 58.55 32.64 18.65 1981 489 142 85 28 4 1 5.75 5.98 84.25 61.55 36.81 19.84 1982 603 149 80 33 5.5 1 7.54 7.08 82.75 58.04 32.5 18.74 1983 679 152 81 34 5 1 8.38 8.74 86.3 63.03 34.9 19.15 1984 708 158 82 59 5.5 1 8.63 10.57 86.44 65.82 40.11 24.58 1985 701 140 70 77 6 1 10.01 12.79 84.02 66.19 41.94 28.96 1986 706 139 66 100 5 1 10.7 15.55 86.69 68.41 45.47 28.33 1987 590 116 68 41 7 1 8.68 8.28 81.02 57.29 34.24 17.12 1988 828 143 83 71 7 1 9.98 10.67 81.88 58.7 33.94 22.1 1989 827 135 77 81 8 1 10.74 11.22 82.35 56.47 32.29 21.28 1990 667 108 64 46 8 6 10.42 8.81 76.16 53.07 29.84 17.24 1991 751 130 68 63 7 1 11.04 11.78 84.29 62.32 35.69 19.44 1992 561 106 71 59 5 1 7.9 9.67 86.99 64.35 38.15 27.27 1993 613 114 69 43 6 1 8.88 8.8 83.69 58.08 33.61 18.43 1994 572 113 73 38 6 1 7.84 7.19 81.64 56.29 30.42 20.63 1995 632 110 66 32 8 7 9.58 7.55 76.42 53.16 30.54 14.72 1996 514 97 60 35 7 2 8.57 7.67 80.93 56.61 31.13 18.09 1997 592 103 58 50 7 1 10.21 9.59 82.26 58.28 32.09 19.93 1998 535 94 59 36 7 5 9.07 7.08 77.2 52.52 28.22 17.01 1999 536 99 62 40 6.5 1 8.65 8.47 82.46 59.89 32.84 18.28 2000 561 92 57 34 8 1 9.84 8.06 80.39 53.83 29.77 15.86 2001 545 92 59 34 8 1 9.24 7.61 79.63 54.13 29.54 16.7 2002 494 88 56 42 7 1 8.82 8.66 83.4 58.7 34.82 20.45 2003 381 70 55 28 5 1 6.93 5.59 81.63 53.28 28.35 16.8 2004 445 87 65 34 6 1 6.85 5.84 80 51.91 30.11 17.08 2005 514 100 72 28 7 1 7.14 5.55 79.18 50.39 26.85 17.12 2006 400 79 60 22 5.5 1 6.67 5.29 80.5 53.25 26.5 15 2007 490 94 68 34 6 1 7.21 7.52 85.51 60.61 35.92 18.98 2008 428 78 58 33 6 1 7.38 6.37 82.71 56.07 28.04 16.36 2009 390 89 70 34 3 1 5.57 6.44 86.67 61.79 36.67 27.18 2010 317 79 61 49 2 1 5.2 7.62 90.22 67.82 41.32 29.02 2011 370 78 56 52 6 1 6.61 8.42 87.57 62.16 40.81 27.57 2012 316 66 48 31 4 1 6.58 7.04 88.29 63.29 36.08 17.41 2013 307 75 56 38 3 1 5.48 6.62 87.3 64.5 40.39 24.76 2014 225 45 34 31 4 1 6.62 7.3 84 62.22 36 25.78 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) = 3.59 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 = 222.2 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 534.4 730.4 632.8 561.8 485.2 444.4 307 Total #sires 232 217 215 188 194 228 192 Max #progeny 88 181 223 145 110 106 170 Mean #progeny 11.478 16.825 14.712 14.936 12.5 9.7412 7.9844 Median #progeny 5 8 8 9 7 6 3 Mode #progeny 1 1 1 7 1 1 1 SD #progeny 16.628 24.656 23.258 17.978 15.145 12.533 15.627 Skew #progeny 2.4934 3.4528 4.915 3.1051 2.6286 3.4256 6.725 Total #dams 513 495 439 394 358 366 295 Max #progeny 29 37 35 30 23 26 28 Mean #progeny 5.191 7.3758 7.205 7.1269 6.7737 6.0683 5.1966 Median #progeny 4 6 6 7 6 5 3 Mode #progeny 1 1 1 1 1 1 1 SD #progeny 4.5374 5.5663 5.1293 4.9562 4.7482 4.8147 4.9165 Skew #progeny 1.8738 1.5063 1.2846 1.2592 0.90428 1.1458 1.48 Rate of inbreeding 0.016288 0.005689 0.007938 0.019292-0.00405-0.00937-0.02696 Generation interval 3.6268 3.3762 3.6471 3.6703 3.5074 3.6822 3.6666 Effective pop size 30.697 87.888 62.988 25.918 n/a 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 2000 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 eased a little (the tail of the blue distribution shortening 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