Population analysis of the Staffordshire Bull Terrier breed by the English Kennelclub September 2015

  

 

Genetic analysis of the Kennel Club pedigree records of the UK Staffordshire Bull 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 Staffordshire Bull Terrier population, and statistics were calculated for the period 1980-

2014.

   

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: Staffordshire Bull Terrier

 

 

Figure 1: Number of registrations by year of birth

 

 

 

 

 

 

Trend  of registrations  over year of birth  (1980-2014) = 157.19 per year (with a 95% confidence interval of 75.40 to 238.97).

 

 

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

984

603

364

26

2

1

2.7

2.8

79.88

58.23

34.55

 

21.75

1981

3222

1057

572

70

3

1

5.63

7.72

83.4

62.63

41.46

29.27

1982

4287

1266

675

70

4

4

6.35

8.16

82.04

61.91

40.19

27.6

1983

5136

1477

819

91

4

3

6.27

8.3

81.83

62.11

40.38

27.82

1984

5761

1738

980

71

4

3

5.88

7.68

82.02

61.57

40.15

27.77

1985

6558

2056

1200

74

4

2

5.46

6.91

80.97

59.99

38.93

26.62

1986

6458

2072

1282

111

3

2

5.04

6.55

80.85

59.68

37.97

26.32

1987

6196

1974

1238

101

3

2

5

6.23

80.7

59.12

37.36

25.52

1988

6248

1941

1229

96

3

3

5.08

6.96

80.52

59.22

39.34

27.94

1989

7767

1754

1153

65

5

5

6.74

6.85

76.12

53.11

32.77

22.36

1990

6590

1452

996

63

5

5

6.62

6.55

75.78

53.2

32.85

21.88

1991

5850

1262

890

71

5

4

6.57

6.29

75.69

52.75

31.79

21.06

1992

5184

1111

777

65

5

5

6.67

5.92

74.71

51.45

31.02

20.14

1993

5629

1183

802

69

5

5

7.02

6.88

75.93

53.26

32.65

21.67

1994

6159

1320

854

58

5

5

7.21

6.83

76.81

54.18

32.57

20.96

1995

7198

1474

951

78

6

5

7.57

7.71

76.69

54.47

33.7

23.16

1996

8461

1693

1036

111

6

5

8.17

9

76.91

55.79

34.77

23.37

1997

9114

1800

1127

92

6

6

8.09

8.74

76.7

55.09

34.74

23.66

1998

9677

1884

1192

104

6

5

8.12

8.16

76.39

54.69

33.55

22

1999

9957

1935

1246

75

6

6

7.99

8.42

77.14

55.81

35.24

23.51

2000

10068

1985

1248

122

6

5

8.07

8.78

76.31

54.65

34.17

22.95

2001

10292

2007

1307

92

6

6

7.87

7.6

75.1

52.65

31.9

21.09

2002

10708

2070

1319

193

6

6

8.12

9.65

76.37

54.88

34.41

23.52

2003

11215

2163

1323

153

6

5

8.48

9.68

76.94

55.41

34.94

23.87

2004

12399

2302

1405

175

6

6

8.82

10.48

76.41

55.18

34.72

24.01

2005

13074

2445

1493

123

6

5

8.76

10.06

77.4

56.4

36.01

24.59

2006

12699

2348

1484

130

6

6

8.56

10.14

76.45

54.97

35

24.32

2007

12181

2239

1362

161

6

6

8.94

11.66

78.17

57.68

37.09

25.91

2008

10484

1955

1244

136

6

5

8.43

9.8

76.86

55.22

35.05

24.12

2009

8733

1625

1027

180

6

6

8.5

11.38

77.37

56.48

36.56

25.92

2010

8366

1578

969

147

6

6

8.63

12.52

78.54

58.28

38.57

27.87

2011

7093

1385

839

139

6

5

8.45

11.94

80.69

60.03

39.74

28.65

2012

6137

1194

742

127

6

6

8.27

11.24

80.22

59.39

40.08

28.97

2013

5840

1123

676

232

6

6

8.64

13.56

81.03

60.86

41.51

29.9

2014

4626

863

540

128

6

6

8.57

12.92

78.6

58.82

41.07

30.42

 

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) = 3.30

  

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

 

 

 

 

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 = 97.7

NB - this estimate is made using the rate of inbreeding over the whole period 1980-2014

  

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

3878

6645.4

5882.4

8881.4

10936

11434

6412.4

Total #sires Max #progeny Mean #progeny Median #progeny Mode #progeny SD #progeny

Skew #progeny

2175

264

8.9085

4

1

18.244

6.755

3984

362

8.3396

4

2

16.135

8.8088

2951

238

9.9665

6

5

15.195

6.4092

3637

330

12.209

7

6

20.402

6.6906

4203

545

13.01

7

6

22.166

8.5941

4371

451

13.079

7

6

23.844

8.3024

2517

504

12.732

6

6

28.289

8.6592

Total #dams Max #progeny Mean #progeny Median #progeny Mode #progeny SD #progeny

Skew #progeny

4510

35

4.2962

3

1

3.3747

1.9797

7425

27

4.4749

4

3

3.2516

1.8405

4741

36

6.2035

5

5

4.4117

1.9372

6295

44

7.0542

6

5

4.9343

1.8274

7495

54

7.2957

6

6

5.0254

1.8501

7803

50

7.3267

6

5

5.2133

1.9948

4657

39

6.8815

6

5

4.8885

1.6709

Rate of inbreeding Generation interval Effective pop size

0.016291

3.1446

30.692

0.006316

3.1284

79.163

0.009828

3.53

50.878

0.002389

3.4139

209.31

0.000744

3.4061

672.3

0.000473

3.2335

1057.1

0.015633

3.2589

31.985

 

 

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.

 

 

  

Comments

 

The rate of inbreeding in this breed has remained relatively steady over the whole period. However, this appears to be close to the level thought to be sustainable.

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.

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