Milk proteins as a feed restriction signature indicating the metabolic adaptation of dairy cows

Milk production in dairy cows is affected by numerous factors, including diet. Feed restriction is known to have little impact on milk total protein content but its effect on the fine protein composition is still poorly documented. The objective of this study was to describe the effects of two feed restriction trials of different intensities on the milk protein composition of Holstein cows. One restriction trial was short and of high intensity (SH), the second was long and of moderate intensity (LM). Feed restriction decreased the milk protein yield for caseins under the LM trial and of all six major milk proteins under the SH trial. These decreased yields lead to lower concentrations of αs1-, αs2- and β-caseins during the SH trial. The milk proteome was affected as a function of restriction intensity. Among the 345 proteins identified eight varied under the LM trial and 160 under the SH trial. Ontology analyses revealed their implication in carbohydrate, lipid and protein metabolisms as well as in the immune system. These proteins reflected adaptations of the animal and mammary gland physiology to feed restriction and constituted a signature of this change.