Electrophoretic characterization of proteins and milk stability of cows submitted to feeding restriction

Abstract

The objective of this work was to evaluate the feeding restriction effects on milk yield and on its electrophoretic protein profile, and to relate them to milk stability to the alcohol test. Two experiments were carried out with Jersey cows: in the first one, the effect of 40% feed restriction was evaluated on semiconfined cows; in the second one, the effect of 30% reduction in total digestive nutrients was evaluated on confined cows. Protein fractions were determined by electrophoresis and their quantification was done by image analysis. Milk samples were classified according to their stability in the 72°GL‑alcohol test. The 40% feed restriction for semiconfined cows decreased milk yield, but it did not change milk protein contents and stability; in this case, unstable milk showed larger contents of β‑casein and total proteins, but lower κ‑casein in comparison to stable milk. The 30% restriction of energy supply for confined cows did not reduce milk yield, but decreased the percentage of serum bovine albumin and milk stability; in this case, unstable and stable milk did not differ as for protein fractions.