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Original
Article About Dexters
"The Founder Effect: Origins,
Characteristics and Future of the New Zealand Dexter Herd - Part 3"
by Tony
Cutten and Alex Meades
Gene Flow from NZ to Australia
Meadowpark Charles (registered in 1989 with the Australasian Dexter
Association prior to the formation of the NZ Dexter Breeders Association,
now the NZ Dexter Cattle Society) was the first graded up
purebred bull from Bookhams Robert and Shootlands Ben Macdhui lineage.
Meadowpark Charles had 3,000 straws drawn for the AI pool. Of these 1,000 went
to Australia and 2,000 stayed in NZ.
Analysis of the NZ Herdbook Electronic version (kindly performed by Mr.
Peter Lucking, Imani Stud of Tuakau, NZ Dexter Herd Registrar), shows that
Meadowpark Charles has sired 51 G1-G3 cows in NZ.
The 1,000 straws sent to Australia have resulted in a total of 107 progeny to Meadowpark Charles, including 14 bulls and 93 cows (the majority being G1
and G2 cows of Jersey origin). The 14 purebred Australian bulls have
sired 100 G1-PB cows (second generation) and 8 PB (second generation)
bulls. These second generation bulls have produced a further 7 third
generation registered bulls.
The two largest herds in Australia containing Meadowpark Charles’ progeny
are Elgin Park with 23 and Binowee with 30.
In addition, 14 Meadowpark embryos have gone to Australia to the Tabasco
stud. Notable among these progeny has been Maclee Tabasco, who won Champion
Junior Bull at a Queensland Show in 2000.
Gene Flow from Australia to NZ
Pat and Patsy Leek, Charming Stud, Horotiu, Hamilton, and Laurel Burnside,
Papakura, have imported live Dexters, some in-calf, from Australia since
1999. These include Volvo Lodge stock and are the first full blood live
imports from Australia. Llanfair's Finnigan, a US bull of English stock
registered in Australia, is being used by a number of breeders in NZ. Alex
Falkner, Silky Oaks Stud, Waitotara, has bred a number of Finnegan offspring
by flushing and embryo transplant in the last four years. At least eight PB
bulls from Finnegan are now working, including four Thymeout bulls bred by Ivan Allanson, Thymeout Stud, Wairarapa.
Gene Flow from Canada
Both Bradner Hilltop Dunstan (from the herd of June Goose) and Braco Shoeshine (Pat Freeman's
herd)
have been very influential AI sires over the last seven years in New
Zealand. In terms of absolute number of progeny, they are strongly
represented in the NZ Herdbook. In October 1999, 15 cows, yearlings and calves,
including some in-calf cows, were imported as a special project, "Operation
Import", from
Carol Davidson's Hiyu Stud, BC, Canada. The concept was to preserve the Hiyu genes in a relatively small and geographically isolated country. These
Hiyu Dexters are now dispersed to five or more Dexter herds in New Zealand.
Semen from two Hiyu bulls is also available in NZ.
Genetic Potential Contributions of Breeding Methods
A herd is usually made up of a number of working cows and a very few
bulls. That is, we farm cows not bulls. A model may be developed by which the
relative genetic contributions of bulls and cows can be estimated
depending on breeding method.
Beryl Rutherford (Woodmagic) suggests the breeding life of a cow (by
natural mating or AI) is 10 years and she will produce eight calves, four of
each sex. Using this information, a working cow will only contribute four
heifers to the gene pool. The assumption in the model is that bull calves
are culled. By comparison, the heifer selected for embryo transplant
breeding, will super-ovulate and be flushed, producing say 0-10 embryos. If
we assume two to four flushings yielding a maximum of 40 offspring, she will
produce 20 heifers (maximum). In practice, two flushings each of five embryos maturing to
calving, yielding say six heifers, may be more realistic. The same dam may
also produce a further three or four heifers by natural mating or AI, yielding a
lifetime contribution of 10 heifers. Potentially there is a 4:20 ratio (max)
or 5X potential contribution to the heifer gene pool when comparing the
natural breeding cow over her lifetime with the "flushing breeding
cow" in her lifetime. The more realistic alternative of 10 heifers
produced, would relate to a 4:10 ratio or 2.5X potential.
Considering a bull's potential contribution, a naturally serving bull in a
small Dexter herd of five breeding cows and used for three years would
produce 15 calves of which seven would be heifers. The assumption is he is then
culled. The AI bull quite obviously has high potential. Depending on his
quality and extent of semen collection and degree of marketing and
popularity of his straws, he might have a potential of 20-200 offspring in
multiple herds (though this estimate may be on the low side). He contributes 10-100
heifers in his breeding lifetime.
Given the limitation of these estimates it can be proposed that the relative
lifetime genetic contributions to the production of Dexter heifers is...
Natural breeding cow : flushed cow : naturally serving bull : AI
collected bull
= 4 : 10 : 7 : 100
The message is what we already know, viz. that "accelerated" breeding
methods have much greater potential to disseminate specific genotypes. There
is an order of magnitude (approximately tenfold) greater potential of
AI, in particular, to spread genes. Similarly the flushed cow may produce
about double the number of heifer offspring that a naturally mated/AI mated
cow would. Great care needs to be exerted by decision makers in embarking
on these methods because of potential to magnify not only desirable but
undesirable traits into the greater herd.
Conclusions
New Zealand has a small Dexter herd derived by the founder effect from three
English blood lines - (Summerdale, Woodmagic and Marsh lines - these have
been identified by A.J. Sheppy).
Following constraints on importation due to the BSE outbreak,
Shadwell bloodlines (Sheppy's Line 3) were imported from Canada. The foresight and judgment
of the founding members, principally Alex and Anne Meades, in their selection
of the original Dexter sire genes, have irrevocably cast the genetic base of
the NZ herd. The original genes will always dominate the NZ Dexter herd.
Second, third and fourth cross descendants from these animals now form the
core of our Dexters. Subsequent introductions of individual animals or semen
are entering a defined gene pool and their overall effect will be
accordingly diluted. These more recent introductions from Australia and
Canada of semen, frozen embryos and live animals will have a limited effect
on the established herd.
In the rapidly expanding number of small herds, a great heterogeneity of
Dexter types will be produced - the good, the bad and the downright
indifferent. As Hamish Ensor (Glenaan) states, "Owners will love their
Dexters to bits", and the result will be very limited culling, if any. Until
owners halter train calves with potential, exhibit at breed shows, learn to
develop "an eye" for the Dexter type and transfer this experience into
informed breeding and selection decisions, they will not progress. The ideal
to aim for is the independently judged animal, recognizable as from a
particular stud herd, and conforming to the agreed Dexter standard.
Acknowledgments
Peter Lucking (Imani) DCSNZ Herd Registrar for genealogy analysis,
assistance and advice.
Nancy Edge (Klonyke) President DCSNZ for critical advice and photographs.
Peter Ludlam (Harbourview) Dexter photographs.
Canadian Dexter Cattle Association's excellent website.
My long-suffering partner Marion, from whom I gained the love of Dexters.
References
Canadian Dexter Association pedigree information website
www.clrc.ca/cgi-bin/query.cgi?_association=17
Ensor, Hamish (Glenaan) (2002) personal communication.
Lucking, Peter (Imani) (2002) personal communication. Herdbook extracted
data.
Meades, Alex (Meadowpark) (2001) personal communication and photographs.
Rutherford, Beryl (Woodmagic) (1998) The grass roots perspective, in Proceedings
of the First
World Congress, Cirencester, UK. Pages 61-68.
Sheppy A.J. (1998) Bloodstock, breed structure and the influence of artificial
insemination in
Dexter cattle, in Proceedings of the First
World Congress, Cirencester, UK. Pages 146-167.
Stevenson, Jeff (Ruahine) 2002 personal communication.
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