Page 477 - Anatomy and Physiology of Farm Animals, 8th Edition

462 / Anatomy and Physiology of Farm Animals

(IVF). One ejaculate of a bull can be divided the rate of embryo loss (miscarriage)
into as many as 500 breeding doses, and if
VetBooks.ir properly handled, each portion has a good increased. Scientists have since devel-
oped methods to identify if potential
probability of resulting in conception.
Semen can also be frozen and stored for breeding stock carry the mutated gene
and the frequency of the mutated gene
years. The division of a semen sample into has fallen in recent years from 8% to 2%.
multiple breeding doses and the freezing of It is estimated that this single mutation
semen for long‐term storage require the has caused more than 500,000 spontane-
addition of cryoprotectants to increase the ous abortions and cost the dairy industry
volume of the sample and protect the sper- more than $420 million in pregnancy
matozoa during freezing. Interestingly, the losses; nonetheless, economists estimate
characteristics and composition of the that the increase in milk production as a
most effective solutions vary with semen result of Chief’s genetics are responsible
samples from different species and even for a $35 billion dollar increase in indus-
within species. This suggests that sperma- try production since the 1960s.
tozoa from different species have unique
metabolic and/or structural differences
and the spermatozoa from each male may Hormones of Male Reproduction
respond differently to cryopreservation
(freezing). While sperm that leave the Endocrine Regulation of Testicular
testicle are immotile and incapable of ferti- Function
lization, by the time they reach the tail of
the epididymis 8 to 11 days later they are Follicle‐stimulating hormone (FSH) and
capable of fertilization. Collection of sper- luteinizing hormone (LH) are glycopro-
matozoa from the tail of the epididymis tein hormones (see Chapter 13) from the
following the untimely death of a male or adenohypophysis (anterior pituitary gland)
at castration can be an effective means of and are the primary endocrine regulators
genetic preservation; most epididymal of testicular function. Their overall effect is
sperm is cryopreserved and used for IVF. to stimulate testicular function, so both are
While the efficient use of semen tech- considered to be gonadotropins. FSH pro-
nologies for breeding is advantageous to motes spermatogenesis by its actions on
producers, the risk of spreading genetic the germ cells in the seminiferous tubules
mutations along with certain desired and the sustentacular cells that support the
traits must also be considered. In popu- development of the spermatozoa. LH acts
lation genetics, the “founder effect” is a on testicular interstitial cells to promote
type of population bottleneck that can the secretion of androgens, primarily tes-
have perilous outcomes as a result of the tosterone. The testosterone produced by
loss of allelic variation in the population. the interstitial cells is necessary for the
As an example, the dairy bull Pawnee completion of spermatogenesis, so both
Farm Arlinda Chief (“Chief”) sired FSH and LH are required for normal
16,000 cows that were prolific milk pro- spermatogenesis.
ducers. These cows in turn produced A single hormone from the hypothala-
500,000 granddaughters and more than mus, gonadotropin‐releasing hormone
2 million great‐granddaughters. In fact, (GnRH), stimulates the release of both
Chief’s genes account for 14% of all DNA FSH and LH from the gonadotropes of the
in Holstein cows, and with this comes adenohypophysis. Negative feedback to
the prevalence of a lethal mutation for the hypothalamus to regulate GnRH is
the gene Apaf1. As Chief’s mutated gene provided by serum testosterone, which is
spread through the breed, the mutation produced by testicular interstitial cells
went unnoticed; however, as his genetics when stimulated by LH. Testosterone also
began to appear in both dams and sires, has direct effects on the adenohypophysis