MILK PROTEINS 197Figure 4.28 Model of the basic 7s immunoglobulin (Ig) molecule showing two heavy and two
light chains joined by disulphide bonds: V, variable region; C, constant region; L, light chain;
H, heavy chain; 1, 2 and 3 subscripts refer to the three constant regions of the heavy chains;
CHO, carbohydrate groups; Fab refers to the (top) antigen-specific portion of the Ig molecule;
Fc refers to the cell-binding effector portion of the Ig molecule (from Larson, 1992).
suckling and persist for about 3 months, although the calf is able to
synthesize its own Ig within about 2 weeks. It is, therefore, essential that a
calf should receive colostrum within a few hours of birth, otherwise it will
probably die. The human baby obtains Ig in utero and hence, unlike the calf,
is not as dependent on Ig from milk (in fact its intestine is impermeable to
Ig). However, the Ig in human colostrum is beneficial to the baby, e.g. it
reduces the risk of intestinal infections.
As regards the type and function of Ig in colostrum, mammals fall into
three groups (Figure 4.30) - those like the cow (i.e. other ruminants), those
like the human, and some, e.g. the horse, with features of the other two
groups (Larson, 1992).