Page 530 - Anatomy and Physiology of Farm Animals, 8th Edition

Anatomy and Physiology of the Mammary Glands / 515

absorbed and consumed immunoglobulins Cessation of Lactation
are digested in a manner similar to other
VetBooks.ir ingested proteins. Closure is the term Daily milk production reaches a maximal

given to the changes that occur in the
gastrointestinal tract that prevent the con- value at some point after lactation begins and
then gradually declines over time in most spe-
tinued absorption of intact IgG. Failure of cies. The decline in milk production is associ-
passive transfer, or decreased levels of ated with a gradual decrease in the number of
IgG measured in the blood at 24 to active alveoli and an increase in the relative
36 hours after birth (foals <400 mg/dL; amount of connective tissue. Mammary
calves <1,000 mg/dL) is highly corre- gland involution is the term describing the
lated to decreased survival rates in those conversion of a milk‐secreting gland with
neonates. Consumption or oral admin- milk‐filled alveoli to one characterized by
istration of any substance, including small, nonsecreting alveoli surrounded by an
water, can result in closure of the gastro- extensive amount of connective tissue.
intestinal tract; therefore, it is essential Extending the period of lactation is economi-
that neonates are provided with ade- cally important for some species (e.g., dairy
quate, good quality colostrum before cows), but not all (e.g., piglets may be weaned
any other substances. prior to peak milk production by sows).