1. Animal Breeding &
Genomics Centre
Whole Genome Scan:
QTL for Milk Fat Composition in
Summer
Nazir A Ganai
Tuesday 24th
March 2009
2. Animal Breeding &
Genomics Centre
Milk Genomics Initiative
Aim: Identify opportunities to use genetic variation to
improve milk quality characteristics
Milk quality:
Milk-Protein composition
Milk-fat composition
Improve:
Technological efficiency (production of cheese, butter)
Innovative dairy products (e.g. promoting human health)
3. Animal Breeding &
Genomics Centre
Milk Fat composition
Importance
Major energy component - 2.25 times caloric value of CHOs
Farmers: for economics
Industry: for quality dairy products
Designer Milk: for good health
An (indirect) aim of the Milk Genomics Initiative
MGI aims to find the QTL / genes underlying the variation of milk fat
composition
Ultimately propose genetic interventions to alter the milk fat composition for
good health and/or better processing qualities
4. Animal Breeding &
Genomics Centre
Human versus Cow milk composition
Constituent Human
milk
Cow milk
Protein % protein 1.3 % 3.5%
Casein : Whey protein 40:60 80:20
Fat % fat 3.9% 4.0%
Saturated 1.8 g/100g 2.5
Mono-Unsaturated 1.6 1.0
Poly-unsaturated 0.5 0.18
6. Animal Breeding &
Genomics Centre
Milk Fatty acids and human health
Type of Fat Role Effect
Sat. Fatty Acids Lauric acid (12:0)
Palmitic acid 16:0
Myristic acid
Raise LDL Cholestrol
•Atheroseclerosis
•High BP
•CHD
Trans fatty acids Trans 18:1
Unsat. Fatty
acids
Oleic acid cis 18:1
Linoleic acid 18:2
Linolenic acid 18:3
Lower LDL Cholestrol Good for health
7. Animal Breeding &
Genomics Centre
Milk Fat Profile
• 400 different FA in milk
• Different ways to classify
•Origin in Milk
•Short / Medium Chain: synthesized de novo
•Long Chain : preformed-
•Melting point:
•Saturated
•Un saturated
•Biological properties
•Good for health
•Bad
9. Animal Breeding &
Genomics Centre
Variability in milk fat composition
Environmental:
FA profile highly sensitive to the kind of feed
Summer milk fat – low in saturated, high in unsaturated
Trait Summer Winter
UFA 29.24 25.5
C18trans 2.14 1.50
CLAcis 9, tr 11 0.56 0.39
C18:3 cis9,12,15 0.50 0.41
C16:0 29.0 32.6
10. Animal Breeding &
Genomics Centre
Heritability
Short and medium chain 0.23 to 0.57
Long chain FA 0.12 to 0.33
Genes involved in biosynthesis of milk : > 40
To find genes causing genetic variation :
difficult
Therefore, the first approach to is find QTL
underlying the genetic variation
11. Animal Breeding &
Genomics Centre
Aim
To find QTL for milk fat composition in summer
Compare the results with winter milk fat analysis
12. Animal Breeding &
Genomics Centre
Material & Methods
• Resource population
• 1905 Cows
• 398 herds
• 7-sire families
• Milk sampling
• Summer
• Marker Map: 1341 SNPs over 29 autosomes
• Analysis: Multi-marker regression analysis
16. Animal Breeding &
Genomics Centre
Detection of DNA regions
Using 1341 Single Nucleotide Polymorphisms
(SNPs) as genetic markers
Ind 1 CACCGCGCCT GGTCCC G TTT TGGCTATTCT
CACCGCGCCT GGTCCC G TTT TGGCTATTCT
Ind 2 CACCGCGCCT GGTCCC A TTT TGGCTATTCT
CACCGCGCCT GGTCCC A TTT TGGCTATTCT
Genetic markers can be used to reconstruct the
inheritance from parents to offspring
23. Animal Breeding &
Genomics Centre
Conclusion (for summer milk fat)
Detected 4 QTL on BTA14, 15, 26 and 27 for summer milk fat
composition.
QTL on BTA14 significantly influenced most of the traits, both saturated
and unsaturated.
QTL on BTA15 influenced the saturated FA only (C4:0 and C17:0).
QTL on BTA26 specifically influenced MUFA. The source of such FA
in milk is the desaturation activity of enzyme SCD, for which the gene
has been already mapped to BTA26.
QTL on BTA27 specifically influenced odd-chain Saturated FA.
The origin of such FA is different from even-chain FA.
24. Animal Breeding &
Genomics Centre
Summer vs Winter milk fat composition
Similarities:
Only two QTL on BTA14 and BTA26 influence the same traits in both
seasons.
Differences:
3 QTL on BTA6, 16, 29 influenced fat composition in winter milk only.
QTL on BTA27 is influenced fat composition in Summer milk only.
All the suggestive QTL on 23 other autosomes influenced different traits
in two seasons.
This lack of consistency :
background effects like : epistasis and environmental
interactions,
less powerful experimental design (half-sib structure) for QTL analysis.
25. Animal Breeding &
Genomics Centre
Opportunities for genetic selection
Health Promoting
(low fat %)I beleive there is a
long way before we
can modulate the
milk fat composition
for a Designer Milk
through marker
assisted selection !!
Quality characteristics are mainly related to milk-fat and milk-protein composition.
Improvements may imply technological efficiency, such as production of cheese or butter, where you can think of yield or colour.
Improvements may also imply innovative products, such as products promoting human health.
Some examples of products with beneficial effects on human health are given on the next slide.