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E p i c e n t r e
Issue 3

A review of

"A Genetic Analysis of the Exmoor Pony Population by Sneha Maroo BSc Hons"

This comprehensive study of the present Exmoor pony population was carried out at the Roslin Institute as a project leading to the Degree of Master of Science. It is not a thesis to be read by the innumerate but it presents an excellent genetic history of the breed leading up to the present. It defines the genetic problems which existed in the past, exist in the present, and could recur in the future if no decisive action is taken by the Exmoor Pony Society.

The pedigrees of 3834 ponies registered between 1910 and 1997 were examined. Genetic indices such as Effective Population Size, Inbreeding Coefficients, Rates of Inbreeding, Mean Kinship, Founder Representation, Founder Genome Equivalents, Gene Diversity, Pedigree Completeness, and Generation Intervals were calculated, analysed and where appropriate illustrated graphically. Mating systems were examined in some detail, and two separate regression analyses were carried out on the results. Period 1 examined results from 1953 to 1997 (approx. 5 generations); period 2 examined results from 1980 to 1997 (approx. 2 generations).

Conclusions noted that the Generation Interval has increased steadily over time and is now just below 10 years, but there is a move towards equality in the male and female Generation Intervals which is a deviation from normal animal breeding practice. Stallions are being kept too long and used because of sentiment.

Analysis of the Observed and Expected Inbreeding Coefficients showed that although there has always been a tendency to mate close relatives this has gradually decreased since 1967. This decrease is due to the establishment of breeding herds away from Exmoor and the interchange of stallions between these herds.

Inbreeding Coefficients increased dramatically around 1935 and again in 1949. These genetic bottlenecks occurred due the use of too few stallions. 12/13 (Sire of Caractacus, Grandsire of Crackshot in 1935) and 78/2 (Heatherman in 1949).

The overuse of certain sires because they won prizes at shows and because of sentimentality by breeders was shown to be critical to the breed since "by allowing a sire to have dozens of progeny and hundreds of grand-progeny genetic variation will be depleted over time". These conclusions agree with those in a paper by A. N. Copland on Exmoor Biometrics written for the EPS in 1994 and published in the Dartmoor Pony Society Diary in 1999.

This presentation by Sneha Maroo is well worth studying by those Exmoor breeders with a background in animal production and genetics. Her academic supervisor Dr. John Wooliams of the Roslin Institute indicated that the only limitation to the study was the lack of information about the foals which failed inspection and the reasons for failure.

by Alison Downing (e-mail )