Transcript Genetics and Breeding: Reproduction

GENETICS AND BREEDING
3025A
REPRODUCTION
I.
REPRODUCTION IN
MALES
A. After sexual maturity of the
male, sperm production is
continuous under most
conditions.
B. Testosterone is the primary
male sex hormone responsible
for:
• The growth, development, and secretory
activity of the accessory glands.
• The survival of spermatozoa.
• The secondary sex characteristics, crest,
male voice, and sex drive.
C. “Semen” is the fluid
ejaculated by the male for
reproductive purposes. It is made
up of:
• Fluid from the many accessory glands.
• Sperm cells.
D. The amount of spermatozoa
and total volume of seminal fluid
varies in each species.
E. Spermatozoa may be stored
in the epididymis for several
days.
• In the female, sperm will survive for 24-96
hours.
• If frozen for artificial insemination, it will
last many years.
II. REPRODUCTION IN
FEMALES
A. Most farm animals reach
sexual maturity in 4-24 months;
at this time the follicles begin to
develop, then:
• The female comes in heat (estrus).
• The follicle containing the maturing ovum
bursts.
• The egg is ovulated and travels down the
oviducts to a point at which it can be
fertilized by the sperm.
B. The age of puberty varies
between species and individuals.
C. Puberty is brought on by
hormone secretions, primarily of
estrogen.
III. ESTRUS AND THE
ESTROUS CYCLE.
A. Estrus in farm animals is the
time the female has or is about to
ovulate and is “receptive” to the
male
B. The first estrous cycle begins
at puberty and is the interval
between two estrous periods
while the animal is not pregnant.
C. There are four different
phases of the estrous cycle.
1. Proestrus, the phase just
before estrus.
• The vaginal wall thickens in preparation to
receive the fertilized egg.
• The ovary is about to release the ovum.
2. Estrus is the time for
acceptance of the male and
normally coincides
approximately with ovulation.
3. Matestrus is:
• The period immediately following estrus.
• If conception has taken place the uterus
prepares for pregnancy.
• The fertilized egg will settle and attach
there.
4. Diestrus occurs between
metestrus and proestrus and is the
longest period of the cycle.
D. Non-pregnant females
normally express both inward
and outward signs of heat
throughout the year. It includes:
• Noise and aggressive behavior.
• Swelling of the external portions of the
reproductive tract.
• Color change of the vaginal wall.
E. Estrous cycles stop after
conception.
F. Estrous cycles begin again
soon after parturition (birth), in:
•
•
•
•
Sows: 1-5 days post-partum
mares: 5-10
Cows: 30-60
Ewes are seasonal breeders
G. Control of estrus cycles by
hormone injections and
management schemes.
H. Synchronizing estrus cycles.