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Variability Among Morning And Evening Milk
Compositions During The Lactation
V. M.-R. Arnould 1,2,, N. Gengler 2,3, and H.
Soyeurt 2,3 1 CONVIS s.c., Ettelbruck,
Luxembourg 2 University of Liège, Gembloux Agro
Bio-Tech, Animal Science Unit, Animal Breeding
and Genetics Group, Gembloux, Belgique 3 Fond
National pour la Recherche Scientifique
(F.N.R.S.), Bruxelles, Belgique.  Financed by
National Research Fund, Luxembourg (AFR
PHD-09-119RE)
Abstract
Differences in milk composition between morning
and evening milk are documented for major milk
components. This study extended research to milk
fat composition. Milk samples were collected
between October 2007 and November 2011 in 491
Luxembourg farms and analyzed by MIR
spectrometry. The milk contents of saturated
(SFA) and unsaturated fatty acids (UFA) were
predicted from the recorded MIR spectral data. As
expected, the milk composition and, especially,
the milk fat composition, were affected by AM /
PM milking during the lactation. Therefore
adjustments for morning / evening milking are
required before using it jointly. Differences in
composition could allow different uses of milk.
Objective
Material and method

• To Analyse the milking-to-milking variability in
  milk and milk fat quality.

• Data.
• Holstein cows (n32,339 cows from 491 herds) in
  first lactation (5 lt DIM lt 366).
• Data set
• 130,997 records in morning milking data (AM)
• 125,384 records in evening milking data (PM)
• Fatty acids predicted from FOSS milk spectrum
  (Mid-Infared spectrometry) saturated (SAT) and
  unsaturated fatty acids (UFA)

Milk fat

• Model
• Fixed effects Herd date of test
• Classes of 15 days in milk
• Classes of age at calving
• Random effects Additive genetic effect
• Permanent environment
• Residual effects
• Variances components estimated by REML
  (Restricted Maximum Likelihood )
• The significance of differences was evaluated by
  Student t-test

NS
NS
NS
NS
Figure 1. Difference in milk fat percentage
according the milking time and the season during
the first lactation.
Milk fat composition

• There were no significant difference between AM
  and PM milk fat percentage
• BUT SAT was higher in the evening milking (fig.
  2 and 3).
• SFA/UFA was lower during the evening milking
  (fig. 3).
• There were also some variations in milk fat
  composition according to the milking time and the
  season.

• Heritability is defined as proportion of
  observable differences between individuals that
  is due to genetic differences
• Daily heritability values for SAT were AM 0.33
  0.01
• PM 0.38 0.01

Figure 2. SAT (g/dl milk) and UFA (g/dl milk)
contents during the first lactation and
according to the milking time and the season.
Figure 4. Evolution of SAT daily heritability
values accros lactation and according to the
milking time
Conclusion

• Milk fat composition varies with the season
  (summer vs. winter) but also with the milking
  time (AM vs. PM).
• These observations could allow the
  diversification of dairy products by season and
  milking time

Figure 3. Evolution of SAT (g/dl milk) during the
first lactation and according to the milking time
and the season.
Contact varnould_at_ulg.ac.be
valerie.arnould_at_convis.lu
The first author acknowledges the financial
support of AFR/FNR (Aide à la Formation
Recherche/Fonds National de la Recherche
Luxembourg) PhD grant (AFR PHD-09-119-RE).
CONVIS s.c. and Luxembourg farms are
acknowledged for providing data.