Monitoring of the sialylation and polysialylation status of sheep milk during early lactation.

The beneficial properties of sialylated biomolecules in milk are important for the optimal development of offspring. However, when assessing risk factors in food, the bioactivity of one sialic acid, N-glycolylneuraminic acid (Neu5Gc), is taken into account because Neu5Gc is supposed to induce proinflammatory responses and even cancer in humans. For these reasons, we determined the concentrations of the 2 main sialic acids found in mammals-Neu5Gc and N-acetylneuraminic acid (Neu5Ac)-in sheep milk during lactation. In addition, we examined the milk for polysialic acid (polySia), a bioactive Neu5Ac polymer. As previously observed in dairy cows, the levels of Neu5Ac, Neu5Gc and polySia decrease rapidly during the first days of lactation. However, in comparison to bovine milk, sheep milk contained significantly higher concentrations of Neu5Gc during lactation. Because of the different bioactivities of the analyzed sialic acids in mammals, the obtained results are important for human nutrition and feeding sheep offspring.