Page 552 - Anatomy and Physiology of Farm Animals, 8th Edition

Poultry / 537

chickens who have been laying for Male Reproductive System
VetBooks.ir extended periods. Osteoporosis, a pro- Testes in domestic birds are normally paired
gressive decrease in mineralized bone
and located cranioventral to the kidneys
leading to bone fragility and increased
risk for fractures, is recognized in lay- (Fig. 30‐9). Like the ovaries, testes are
ing flocks and is believed to contribute smaller outside of breeding seasons and will
to the syndrome cage layer fatigue, in increase markedly in size during breeding
which birds are found paralyzed in periods. The microscopic appearance of an
their cage. Numerous fractures may be avian testis is similar to a mammalian testis
found involving the ribs and long bones in that it primarily consists of seminiferous
of such birds. Loss of structural bone tubules surrounded by an interstitium that
may also accompany egg laying and contains Leydig cells. The process of sper-
forced molting as the result of nutri- matogenesis in the tubules is similar to that
tional deficiencies. for mammals and is promoted by follicle‐
Calcium carbonate deposition within stimulating hormone (FSH) and luteinizing
the eggshell also requires the localized hormone (LH). However, unlike in mammals,
formation of carbonate ions within the spermatogenesis occurs in avian testes
shell gland. This generation of carbonate found normally within the body cavity,
ions is dependent on carbonic anhydrase where they are maintained at normal core
activity within the gland. Under the influ- body temperature.
ence of carbonic anhydrase, CO from The ductus deferens (deferent duct)
2
blood perfusing the gland is used to pro- conveys sperm from the testis to a raised
duce carbonate ions. Laying chickens papilla on the lateral aspect of the urodeum.
subjected to abnormally high environ- Male birds do not possess accessory sex
mental temperatures (heat stress) typi- glands; the ejaculate is composed of sperm
cally have declines in egg production and scant additional secretions produced by
and in the shell quality of eggs that are the testes and the walls of the ducts.
produced. The decline in shell quality On the ventral floor of the proctodeum
is associated with a reduction in blood of roosters and male turkeys there lies a
PCO , as a result of hyperventilation copulatory organ, the phallus, which is
2
induced by heat stress. The lower CO nonprotrusible (i.e., does not form a pro-
2
is believed to adversely affect the abil- truding copulatory organ). The phallus has
ity of the shell gland to produce car- erectile tissue within it, and during copula-
bonate ions. Heat‐stressed birds also tion the engorged tissue forms a groove
reduce food intake, which would also that conveys the ejaculate from the open-
contribute to the decline in egg quan- ings of the deferent ducts to the surface of
tity and quality. the phallus. During the act of breeding, the
Prostaglandin, predominantly from proctodeum is everted and the phallus
the postovulatory follicle as well as some pressed against the vent of the female so as
from the preovulatory follicle, is also to facilitate the transfer of ejaculate. Drakes
necessary for ovipositioning. Arginine and ganders (and, incidentally, male swans
vasotocin (AVT) stimulates uterine con- and ostriches) have a protrusible phallus
tractions during oviposition. Like oxytocin that, when erect, is about 5 cm long. Its tip
in mammals, AVT is released from the is spiraled and is introduced into the cloaca
neurohypophysis, and its plasma levels rise of the female during copulation. Large,
significantly shortly before and peak heavily muscled birds that are desirable
during oviposition. Unlike mammals, birds for human consumption are unable to
have one small peptide hormone, AVT, physically complete the mating process.
that functions in both the regulation of Artificial insemination is widely used in
urine osmolality and the regulation of commercial poultry operations, particu-
uterine contractions. larly for turkeys.