Page 541 - Anatomy and Physiology of Farm Animals, 8th Edition

526 / Anatomy and Physiology of Farm Animals

chamber is the proventriculus or glandu- Foie gras (literally fat liver in French,
lar stomach, which provides pepsin and
VetBooks.ir hydrochloric acid for enzymatic digestion. pronounced fwah′ grah) is a food prod-
uct made from the liver of ducks or geese.
The proventriculus is demarcated clearly
by a constriction from the second cham- It has been made uniquely creamy and
(to some palates) delicious by the forced‐
ber, the gizzard (muscular stomach or feeding of the bird on corn. Because of
ventriculus muscularis). It largely fills the the role of the liver in digestion, this
lower left of the body cavity. The highly force‐feeding results in accumulation of
keratinized mucosa on the inside of the fat in the liver, which becomes markedly
gizzard, the cuticle, forms a thick, leathery enlarged as a result. The production of
sheet, which is removed during processing foie gras is controversial, as many people
for human consumption. perceive that the practice produces a
Crops and gizzards are unique to avian state of ill health for the birds, and the
digestive systems and contribute to the effi- force‐feeding technique may result in
ciency with which many wild and domestic injury or death of the bird.
birds can utilize whole, intact seeds, includ- As in mammals, the longest segment of
ing grains, as part of their diet. The crop the small intestine is the jejunum. In many
moistens food and provides for temporary adult domestic birds, the jejunum retains a
storage after swallowing, and the gizzard remnant of the embryonic connection to
provides a muscular force to grind and the yolk sac, Meckel’s diverticulum, which
crush foodstuffs so that they can be more assumes an immune function after retrac-
effectively digested. Hard particles, such tion of the yolk sac before hatching.
as grit or gravel, consumed with food The short ileum terminates at the large
contribute to the ability of the gizzard to intestine, a point demarcated clearly in
properly grind intact seeds, and a source domestic birds by the presence of paired
of such particles should be part of the ceca. These blind‐ended diverticula of the
diet of birds fed this diet. Grit is not nec- colon are 10 to 25 cm in ducks, chickens,
essary for diets that are finely ground or and turkeys, and 22 to 34 cm in geese. The
in mash form. Neither the crop nor the paired ceca of domestic birds and wild
gizzard secretes enzymes to contribute to birds that eat seeds (granivores) provide a
enzymatic digestion of foodstuffs. site for the digestion of fiber by microor-
The small intestine of birds is not ganisms. The resulting volatile fatty acids
remarkably different from that of mammals. are absorbed from the ceca. Cecal diges-
The duodenum forms a distinctive loop tion is of little importance in domestic fowl
with the pancreas sandwiched between fed highly digestible feeds. The colon itself
descending and ascending parts. The pan- is relatively short and straight, terminating
creas communicates with the lumen of at a sphincter interposed between the large
the ascending duodenum through three intestine and the cloaca, an expanded
ducts in gallinaceous birds and usually via region that is common to the gastrointesti-
two (sometimes three) in Anseriformes. nal and urogenital tracts.
The ascending limb of the duodenum also The cloaca is partially divided into three
receives the two bile ducts. These carry named portions by encircling ring folds of
bile from the liver directly (the hepatoen- muscle covered with mucosa. Receiving the
teric duct) and from the gall bladder terminus of the colon is the coprodeum, a
(the cysticoenteric duct). The liver of dilated region that temporarily holds feces.
domestic birds consists of two lobes, sim- It is divided by a ring fold from the next
ply referred to as the right and left lobes. compartment, the urodeum. The urodeum
These lie in the ventral body cavity against features the openings of the two ureters in
the sternum and body wall. The digestive the dorsal aspect of the lumen. Just lateral
functions of the liver, small intestine, and to these are openings for the seminal ducts
pancreas are similar to those for mammals. in male animals. In most female domestic