Diapositive 1

1
Within and Across Breeds Differences in Fatty
Acids Profiles of Milk and Milk Fat in Dairy
Cows H. Soyeurt1,2, P. Dardenne3, P. Mayeres1,4,
C. Croquet1,5, S. Vanderick1, C. Bertozzi4 and N.
Gengler1,5 1 Gembloux Agricultural University,
Passage des Déportés 2, B-5030 Gembloux, Belgium,

E-mail soyeurt.h_at_fsagx.ac.be 2 F.R.I.A., B-1000
Brussels, Belgium 3 Walloon Agricultural
Research Centre, Quality Department, B-5030
Gembloux, Belgium 4 Walloon Breeders Association,
B-5530 Ciney, Belgium 5National Fund for
Scientific Research, B-1000 Brussels, Belgium
Objective Improving the nutritional quality of
milk fat by animal selection ? The variability
within and across breeds in fatty acid (FA)
profile of cow milk was studied with the
predicted concentrations of FA by Mid-Infrared
(MIR) Spectrometry for each milk sample and with
mixed model theory.
3
Results
Figure 1  Differences in fatty acids composition
in milk (standardized units) compared to
Holsteins.

• Methods
• After calibration, the FA contents of cow milk
  was predicted by MIR Spectrometry.
• From April to June 2005, 600 milk samples were
  analysed from 275 cows derived to 6 breeds (Dual
  Purpose Belgian Blue (DPB), Holstein-Friesian
  (HOL), Jersey (JER), Montbeliarde (MON) and Red
  and White (RED).
• Single trait mixed model Fixed effect herdtest
  date, number of lactation, stage of lactation and
  regressions on breed composition effects as a lot
  of animals were crossbred, when FA contents in
  fat were analyzed a regression on of milk fat
  was added
• The variation within and across breeds in the
  activity of delta-9 desaturase was also studied
  with the same mixed model.

Figure 2 Differences in fatty acids profiles in
milk fat (standardized units) compared to
Holsteins.
Figure 3 Differences in activity of delta-9
desaturase (standardized units) compared to
Holsteins.
DPB lowest fat (MG) but C181 and C182 9-cis,
12-cis not the lowest concentrations (Figure 1) ?
unsaturated FA proportion in fat might be high ?
In fact, the fat of DPB contained the lowest
proportion in saturated FA (SAT) (Figure 2) ?
These observations might be explained by the
higher activity of delta-9 desaturase for this
breed (Figure 3). JER very high difference in
monounsaturated fatty acids (MONO) ? not lowest
delta-9 desaturase activity. RED and MON high
proportion of SAT ? low delta-9 activity. To
estimate the differences within breed, the
repeatability for each studied traits were
estimated and the obtained results were high with
values between 43 and 61 . Future studies should
show if this is also an indication for reasonable
high heritabilities.