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

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Classes of days in milk

Summer_SAT_AM Summer_SAT_PM

Winter_SAT_AM Winter_SAT_PM

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.

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)

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.

Abstract

Milk fat composition

Contact: varnould@ulg.ac.be

valerie.arnould@convis.lu

ObjectiveTo Analyse the milking-to-milking variability in milk and

milk fat quality.

Data.

Holstein cows (n=32,339 cows from 491 herds) in first lactation (5 < DIM < 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)

Material and method

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.

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SAT UFA

NS **

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Classes of 15 days in milk

AM PM

Figure 3. Evolution of SAT (g/dl milk) during the first lactation and according to the milking time and the season.

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

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

Conclusion

NSNS

Model: Fixed effects: Herd * date of test

Classes of 15 days in milkClasses of age at calving

Random effects: Additive genetic effectPermanent

environmentResidual effects

Variances components estimated by REML (Restricted Maximum Likelihood ) The significance of differences was evaluated by Student t-test

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

3.80

3.90

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AM AMPM PM

***

NSNS

Milk fat

Variability Among Morning And Evening Milk Compositions During The Lactation