The sialoglycoconjugate content of human milk has been extensively studied.
However, little attention has been paid to the changes occurring in these
compounds in bovine milk during lactation. Since sialoglycoconjugates are v
ery abundant in milk from the early stages of lactation, they have been sug
gested to be important for the nutrition of the newborn during the first mo
nths of life. The distribution of sialoglycoconjugates (expressed as glycoc
onjugate-bound sialic acid) from four different stages of lactation (colost
rum, transitional, mature, and late-lactation milks) was investigated in fo
ur Spanish-Brown cows. All the fractions studied (total sialic acids, glyco
proteins, oligosaccharides, casein, and gangliosides) showed a similar tren
d. We found the highest values in the colostrum, these decreasing in transi
tional and mature milks and increasing again in late-lactation milk. We als
o found a selective change in the relative contents of glycoprotein- and ol
igosaccharide-bound sialic acids. In mature milk, the latter increased up t
o 80% (59% in colostrum) and the former decreased to 3.9% (35.3% in colostr
um). It would appear that the decrease in oligosaccharide-bound sialic acid
is compensated by the increase in glycoprotein-bound sialic acid. From the
se results, it is deduced that newborn infants or calves fed with infant fo
rmulas or milk replacers, respectively, should be supplemented with sialogl
ycoconjugates to approximate the composition of human and cow milk as far a
s is practicable.