Page 529 - Anatomy and Physiology of Farm Animals, 8th Edition

514 / Anatomy and Physiology of Farm Animals

the sight of the suckling offspring. It can newborn domestic animals. One of the
unique differences between colostrum
also be inhibited by emotionally disturbing
VetBooks.ir stimuli, such as dogs barking, other loud and typical milk is that colostrum con-
and unusual noises, excess muscular activ-
globulins produced by the immune
ity, and pain. Stressful stimuli increase the tains a high concentration of immuno-
activity of the sympathetic nervous system of the dam. These immunoglobu-
system, which can also inhibit the milk lins (Ig) are concentrated in the milk by
ejection reflex. This inhibition occurs both selective transport by the epithelial cells
at the level of the hypothalamus via an lining the alveoli and are needed by the
inhibition of oxytocin release and at the neonate to provide immune protection
level of the mammary gland, where sympa- against infectious agents in the environ-
thetic stimulation can reduce blood flow ment until the immune system of the
and directly counteract the effect of oxy- offspring has matured and is functional.
tocin on myoepithelial cells. Oxytocin Colostrum consumption is especially
release typically occurs as a surge within a important in domestic farm animals
minute or two after initiation of the reflex because of limited transfer of immuno-
by some tactile or environmental stimulus, globulins from the dam to the fetus via the
and the plasma half‐life of oxytocin (a placenta. In some mammals, including
small peptide hormone) is but a few min- humans, transfer of immunoglobulins via
utes. Hence, milking or suckling should the placenta occurs to a greater extent, so
begin in close association with stimuli consumption of colostrum by neonates is
known to stimulate oxytocin release, such less important. The primary immuno-
as washing the udder and stimulation of globulin that must be absorbed by the
the teats. If failure to get an adequate stim- neonatal gastrointestinal tract into the
ulus for milk ejection, possibly because of systemic circulation is immunoglobulin G
inadequate preparation before milking, (IgG); nonetheless, the presence of other
becomes habitual, the lactation period may immunoglobulins (IgA, IgE, IgM) are also
be shortened by excessive retention of milk important for providing the humoral
in the udder. immune response. IgA in particular is
Essentially all the milk obtained at any produced by the intestinal mucosa and is
one milking is present in the mammary able to neutralize pathogens and endotox-
gland at the beginning of the milking or ins. Most neonates are born with limited
nursing period. However, milking usually amounts of body fat and other sources of
does not remove all of the milk in the metabolic energy; therefore the primary
gland. Up to 25% of the milk in a gland sources of energy in colostrum are milk
may remain after milking. Some of this proteins and lipids. Colostrum is also a
residual milk can be removed after injec- source of energy because colostrum has a
tions of oxytocin, but the routine use of relatively low concentration of lactose.
such injections tends to shorten the lacta- Recall that progesterone inhibits develop-
tion period. ment of enzymes necessary for lactose
synthesis until just prior to parturition.
The colostrum of most species also tends
Colostrum to have relatively high concentrations of
vitamins A and D and iron, but some spe-
Colostrum is the first milk produced by cies differences in composition do exist.
the mammary gland and is recognized by In most domestic neonates, it is only dur-
its yellow color; it is often given the name ing the first 24 hours of life that passive
“liquid gold.” Upon delivery of the new- transfer, or the absorption of intact IgG from
born, early ingestion of colostrum is the gastrointestinal tract into the blood, can
imperative for the survival and vitality of occur. After this period, IgG cannot be