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Evolution of milk composition, milk fat globule size, and free fatty acids during milking of dairy cows

Abstract : The objective of this study was to measure milk composition (fat, protein, and calcium contents; fatty acid profile), milk fat globule size, and free fatty acid content throughout milking. Composition was measured from milk samples collected every 1 min during morning milking in 2 previously published experiments. Experiments 1 and 2 used 9 and 6 dairy cows, respectively. From the beginning to end of milking in experiments 1 and 2, lactose content decreased (−0.45 percentage units), as did protein content (−0.28 and −0.17 percentage units, respectively). In contrast, fat content increased (+5.66 and +5.57 percentage units, respectively). Milk fat globule size increased (+1.51 and +0.43 μm, respectively),whereas free fatty acid content (measured after 24 h of storage at 4°C) decreased quickly during the first minutes (−0.45 mEq/100 g of fat from time point 1 to time point 4 in experiment 1, and −0.85 mEq/100 g of fat from time point 1 to time point 5 in experiment 2), and then largely stabilized, with a slight tendency to increase toward the end of milking period in experiment 2 (+0.32 mEq/100 g of fat). The evolution of milk fatty acid composition depended on the experiment. From the beginning to the end of milking, the concentration of C16:0 consistently increased (+3.4 wt/wt % in experiment 1 and +3.3 wt/wt % from time point 2 to time point 7 in experiment 2), whereas the C18:1/C16:0 ratio increased during the first minutes of milking and then slightly decreased (−0.050 in experiment 1 and −0.031 from time point 2 to time point 7 in experiment 2). Calcium content decreased in experiment 2 (−58 mg/kg). In conclusion, milk composition changed greatly during milking, suggesting that different mechanisms are involved in synthesis and excretion, depending on the type of milk component.
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https://hal.inrae.fr/hal-03131023
Contributor : Catherine Hurtaud <>
Submitted on : Thursday, February 4, 2021 - 9:41:37 AM
Last modification on : Thursday, April 29, 2021 - 3:10:04 PM

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Catherine Hurtaud, Marion Dutreuil, Élise Vanbergue, Jocelyne Guinard-Flament, Lucile Herve, et al.. Evolution of milk composition, milk fat globule size, and free fatty acids during milking of dairy cows. JDS Communications, American Dairy Science Association, 2020, 1 (2), pp.50-54. ⟨10.3168/jdsc.2020-18473⟩. ⟨hal-03131023⟩

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