Page 524 - Anatomy and Physiology of Farm Animals, 8th Edition

Anatomy and Physiology of the Mammary Glands / 509

cistern is continuous with a gland cistern. percentage of lipids in the milk. Diets high
in protein promote a slight increase in the
The teat is hairless, but hair is found at the
VetBooks.ir base of the teat and on the gland. percentage of protein in the milk, but this
effect is much less than the effect of energy
on milk lipid content. The amount of car-
Mammary Glands of the Horse bohydrates in milk (lactose, or milk sugar)
does not routinely change with diet. The
The mammary glands of the mare consist percentage of lipids and protein in milk is
of one teat on each side attached to half of also highest early in lactation. In cattle, the
the udder. Each teat has two streak canals percentages are relatively high in the first
and two teat cisterns, each of which is con- few weeks after calving and then decrease
tinuous with a separate system of ducts over the next 3‐4 months. Later in lacta-
and alveoli (occasionally a gland has a third tion, the concentrations of lipids and
set of ducts). There appears to be no com- proteins again increase as total daily pro-
munication between ducts or cisterns duction (pounds of milk per day) decreases.
within the same half of the udder. Most of the lipids in milk are in the
The suspensory apparatus is arranged form of triglycerides, and these are the
as in the cow, although it is not as robust. primary source of dietary energy in milk.
The udder and teats of the mare are Triglycerides are composed of three fatty
covered with thin, fine hair and with acids and glycerol. The fatty acids for the
numerous sebaceous and sweat glands. synthesis of milk triglycerides may be
derived from the blood or synthesized
within the mammary gland. Nonruminant
Physiology of Lactation mammary glands use blood glucose both
for energy and as a source of carbon for the
Composition of Milk synthesis of the fatty acids. The glycerol is
derived mostly from glucose catabolism in
Milk contains all the nutrients necessary the process of glycolysis. The mammary
for survival and initial growth of mamma- glands of ruminants depend on blood ace-
lian neonates. The nutrients in milk include tate and β‐hydroxybutyrate to provide
sources of energy (lipids and carbohy- carbon for fatty acid synthesis, with acetate
drates), proteins to provide amino acids, being the primary source. The acetate and
vitamins, minerals (ash) for electrolytes, β‐hydroxybutyrate in ruminants are pro-
and water. The relative amounts of these duced as volatile fatty acids by fermentative
nutrients in milk vary among species metabolism by microorganisms in the
(Table 29‐1). rumen. These volatile fatty acids are
Maternal diet and the stage of lactation absorbed into the blood and thereby become
also affect the composition of milk. Diets available for synthesis of milk fat in the
high in nonfiber carbohydrate sources of mammary gland. Most milk triglycerides
energy are associated with increases in the have fatty acids with chains 4 to 14 carbon

Table 29-1. Typical Values for Constituents of Milk in Grams per Liter

Species Lipids Lactose Protein Total Minerals (Ash) Calcium
Cow 38 48 37 7.0 1.3
Mare 16 50 24 4.5 1.0
Ewe 70 40 60 8.0 1.9
Sow 80 46 58 8.5 2.0
Doe 40 45 35 7.8 1.2