English Shepherds have a relatively large number of distinct dam founder lines available. Our studies have identified 41 dam lines by pedigree; analysis of genetic data reveal at least 16 maternal haplotypes in the breed. For a comparison, a 2015 study of 368 breeding female dogs found only 3 maternal haplotypes present in Hovawarts in Germany (the country of origin).
The number of maternal haplotypes present in a breed is one indicator of genetic diversity. Mitochondrial DNA (mtDNA), which is thought to be important in energy metabolism, is inherited exclusively through dam lines; the number of dam lines and their representatives correspond to the number and frequencies of mtDNA haplotypes in a population.
Here is an update on the current status of dam lines in English Shepherds and trends in their representation across the breed using ESCR data available through 2021 (most recent year with complete litter registration information).
Dam Line Statistics for 2019-2021
# Dams = 368
# Dam founder lines = 28
# Litters ~ 564
Number of Litters/ Dam Line: there is a large range in number of litters per line with many lines having very small numbers of litters while a few lines produce a majority of the litters. This skew in the representation of dam lines is reflected in the fact that the “median” (50th percentile) number of litters per line is only half that of the “average” (number of litters that each line would produce were the lines all equally well represented). In fact, over 67% of dam lines reproduced at a “below average” rate over the past generation. This fact reflects ongoing change in the breed population and carries important implications for the future.
Range = 1-108
Median = 10.5
Average = 20
For 2021 (183 dams) : the age at breeding and recording of health (hip) testing were reviewed for dams producing litters in 2021.
Age of dams (at breeding):
Range = 7 – 106 months
Median = 37 ½ months
% with hip score in ESCR = 11%
Chart identifying founder line and key descendants that bring the line forward to present:
Trends in Representation of Dam Lines
Comparison of the percentage of litters attributable to each dam line during two intervals, 2013- 2018 and 2019-2021, reveals a significant increase for the dam line carried through Cedar Creek Maggie Mae (increase from 3% to 7%). Overall, the dam line coming through Butcher’s Cassie Sue and Susie Q remains by far the most common line, accounting for roughly 20% of litters in both intervals.
Many lines appear from ESCR registrations to be in a precarious position, with just a handful of dams or litters carrying them forward. Eleven recognized dam lines had no litters registered between 2019-2021.
Discussion
Our previous reports on dam lines noted that English Shepherds as a breed have retained a larger number of dam founder lines and unique maternal haplotypes than many other breeds. We have identified 41 founder dam lines altogether, ten of which have limited pedigree available due to their status as step in dogs, and 16 distinct maternal haplotypes.
The majority of litters, however, come from just 5 maternal lines with 4 documented maternal haplotypes (missing data for one line). It appears that a great deal of the potential diversity within the breed resides in dam lines that are in danger of disappearing. As this happens, lines that are more widely represented run the risk of increasing levels of inbreeding as generations pass and the availability of unrelated dogs for breeding diminishes.
Most females will only have one or two litters in their breeding career and will be retired by the time they are 4-5 years old (see previous breed report). That being the case, dam lines that fail to reproduce over a 5 year interval are likely to be lost to the breed.
Questions:
- What can be done to raise awareness of the need to maintain a diversity of lines in each generation?
- What motivation is there for individual breeders to select breeding stock that help preserve diversity within the breed?
- What benefit or cost do those breeders experience?
- What can the wider breed community do to support conservation minded breeders?
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Reference: https://aab.copernicus.org/articles/58/335/2015/aab-58-335-2015.pdf
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