Page 534 - Anatomy and Physiology of Farm Animals, 8th Edition

Poultry / 519

The presence of feathers is the hallmark domestic fowl are especially notable under
the wings. Feathers are replaced in most
of class Aves. Like the hairs of mammals,
VetBooks.ir feathers are keratinous in nature and grow birds once or twice a year, and in most spe-
from an epidermal follicle that encircles a
cies the molt proceeds in a sequential way so
dermal core. as not to render the bird flightless due to
The vascular feather pulp, an extension insufficient flight feathers. Anseriformes
of dermal tissue into the shaft of the feather, (ducks and geese), however, are unable to fly
is prominent only during growth. Trauma for several weeks during their molt.
that breaks the shaft of a large growing Chickens of breeds selected for high
feather (a so‐called “blood feather”) may egg production may molt after a typical 12‐
lead to considerable hemorrhage. month laying period. However, some birds
There are two main types of feathers may molt during this laying period, and
seen in poultry: contour feathers, which low‐producing hens often stop egg produc-
comprise the flight feathers and those that tion if they molt at this time. Restriction of
cover the body, and the fluffy down feathers food and water and decreasing periods of
(Fig. 30‐1). Both types possess a semirigid light will induce an entire flock to stop
shaft with multiple barbs arising from it laying and begin molting (a forced molt).
forming the vane. Contour feathers are During a forced molt, the reproductive
characterized by the orderly interlocking tract regresses and circulating levels of
nature of the barbs, whereas down feathers the hormones necessary to support egg
lack this systematic linking of barbs. production (prolactin, luteinizing hor-
Feathers are not uniformly distributed on mone [LH], estrogen, and progesterone)
the body of the bird, occurring instead in are significantly decreased. After a
well‐described feather tracts (Fig. 30‐2). forced molt, and after photoperiods and
Some locations on the bird’s body are rela- diets are corrected, hens typically enter a
tively free from contour feathers and these new laying period with improved egg
regions are the apteria (singular apterium). production. The use of forced molts as a
Used for thermal regulation, the apteria of management tool has become controver-
sial in part due to the restriction of food
and water required to induce the molt.
(A) (B) Although avian skin is nearly glandless,
domestic fowl have a large, well‐developed

Figure 30-1. (A) Down feather. (B) Contour
feather. Figure 30-2. Feather tracts on a chicken.