Download BOVINE GENOME MAPPING AT ROSLIN INSTITUTE

EXECUTIVE SUMMARY
SLP LINK Projects LK0602
Bovine Genome Mapping
Start date: 01/04/1996
Partners:
Sponsor:
End date: 31/03/1998
Roslin Institute
Meat & Livestock Commission
Milk Development Council
Ministry of Agriculture, Fisheries & Food (now Defra)
Future improvements in cattle breeding will be enhanced by a clearer understanding of
the genetic control of desirable characteristics. Molecular techniques, such as the use
of DNA markers can be used in combination with current selection approaches for more
effective cattle breeding. Once a genetic marker for a trait of interest has been found,
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animals carrying the marker can be easily identified (by a blood test, for example).
Breeders can then select the appropriate animals for their breeding programmes. It is
not the intention of this work to produce genetically modified animals.
Most commercially important traits in farm animals, such as growth or milk yield, vary
considerably between individuals.
These highly variable (or quantitative) traits are
controlled by several genes located at ‘quantitative trait loci’ (QTL). A QTL is an area of
chromosome where one, or more, of the genes determining a particular trait are
located. To date, little is known about the QTLs which affect commercially important
characteristics. However, recent advances in molecular biology techniques, arising in
part from the human genome project, will make the identification and study of QTLs
possible.
The Roslin Resource Herd was established with the aim of identifying QTLs affecting
characteristics commonly selected for in breeding programmes. The herd comprises of
three generations of cross-bred cattle. The crosses are between the most widely used
dairy breed, the Holstein-Friesian, and a popular beef breed, the Charollais, which has
been selected over many generations for excellent feed efficiency, conformation and
lean tissue growth rate. The Roslin Resource Herd allows us to study a number of
characteristics not easily measured in commercial herds such as meat and milk quality,
and animal health and fertility. Assessments of these commercially important traits are
made both on the farm and in the laboratory. Simple on-farm measurements include
weight-for-age and feed consumption. Laboratory research involves determining meat
and milk composition, and assessing the functioning of an animal’s immune system.
The chromosomal region containing a QTL is located by examining whether the
inheritance of a region of chromosome coincides with the inheritance of a particular
trait. The Roslin Resource Herd was created to map the genes involved in a large
number of traits. The herd has been bred by crossing between cattle of breeds that are
different in both appearance and genetic background. The experimental herd allows a
large number of detailed measurements to be made under standardised conditions.
These measurements include simple on-farm measurements of daily weight gain, and
milk yield, through to detailed laboratory measurements to determine, for example,
meat composition and the functioning of the immune system in response to mastitis
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pathogens.
Three generations of cattle have been used in the study. Initially purebred Charollais
bulls were mated with Holstein cows, to produce a first generation cross. The first
generation cross bred cows were then mated either with other first generation cross
bred bulls or Charollais bulls, while the first generation cross bred bulls were mated with
Holstein cows.
This produced a second generation of crossbred cattle that were
measured for a wide range of traits. In all about 500 second generation cross bred
calves have been produced.
The second generation bulls were reared with their mothers as suckler calves to 6
months of age, when they were transferred to a standardised concentrate based
management regime and were recorded for feed conversion efficiency, growth rate,
conformation and immune response to a range of disease agents. On reaching the
target 550Kg slaughter weight, the bulls were slaughtered at a commercial abattoir and
carcass traits recorded. Samples were collected and analysed for composition and
eating quality. Large variation was seen in all the traits measured. Preliminary analysis
of feed efficiency and immune traits has shown that there is a large genetic influence on
the variation between individuals.
The second-generation crossbred heifers were raised as dairy calves. They were
separated from their mothers at 24 hours of age, and then bucket-reared until weaning.
Following weaning, they were raised on a silage based regimen and feed recorded for
their first 12 months, during which time their immune response to various vaccinations,
and onset of oestrus were recorded. As adults the heifers are currently being recorded
for calving performance and milk production traits, including mastitis incidence and milk
quality.
All animals have been genotyped with a panel of DNA markers that cover all the
chromosomes, which will allow the inheritance of chromosomal regions to be tracked
through the generations. The juvenile data and data from the bulls is now complete and
analysis is underway to correlate the trait and DNA data to localise the genes involved
in the various traits. Once analysed, information on the location of genes controlling a
wide range of traits will be available and will be used to aid the design of breeding
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programmes and in the section of animals as breeding stock. The information will also
serve as the starting point for identifying the genes involved.
CONTACT
Dr John L Williams
Roslin Institute (Edinburgh)
Roslin
Midlothian
Scotland
EH25 9PS
Tel: 0131 5274310
Fax: 0131 4400434
[email protected]
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