IAD 202
Livestock Production &
Development
Wolfgang Pittroff
Lecture 3
Introduction into Reproductive
Physiology
Functional anatomy, cyclicity and seasonality
of reproduction, environmental effects on
reproduction, species differences, problems
specific to low input systems
Reproduction
Reproduction
• The purpose of reproduction is at first sight
rather obvious: maintain life
• When examining sexual reproduction in
more detail, another, equally important
purpose emerges: re-arrange genes, allow
continuous adaptation to (environmental)
change
Reproduction
• Like nutrition, reproduction is a key bottle neck in
livestock development
• The main reason for reproductive problems in
low input systems is nutrition
• But there is also a great deal of ignorance about
reproductive physiology, proper herd and flock
management, and health problems causing
reproductive failure
• Reproduction (=> population dynamics) is a
theme where many management problems
converge
Introduction into Functional
Anatomy and Physiology of
Reproduction
1. Male Reproduction
Male Reproduction and
Gametogenesis
• Formation of sperm
• Deposition of sperm into the female
• Governed by hormones and the autonomic
nervous system
• Subject to elaborate hormonal, neural,
muscular and thermal regulation systems
Schematic Overview
Comparative Anatomy Male Reproductive Organs
Ductulus efferens
Testis
• Seminiferous tubules (organizing
structure of the testes) occupy the
largest portion of each testicle –
spermatozoa are produced here
• Tubules strengthened by
connective tissue extensions from
an external capsule
Testis
• Important cell types:
– Sertoli cells (nurse function for
developing spermatozoa, also called
sustentacular cells): inside seminiferous
tubules
– Leydig cells (also called interstitial cells,
secreting testosterone): outside
seminiferous tubules
(Sertoli cells)
Interstitium( Leydig cells)
Sertoli Cells
• Sertoli cells: are interspersed between and
envelop developing spermatids and their
precursors in the seminiferous tubules
• Adjacent Sertoli cells form a blood-testis
barrier that serves to control the
environment within the tubule and
prevents spermatozoa from entering the
interstitium
Epididymis
• Spermatozoa pass from the tubules
through the ductulus efferens to the
head of the epididymis (a long tube
connecting the epididymis and urethra)
• Spermatozoa mature here prior to
ejaculation (through the ejaculatory
duct in the prostatic urethra)
Epididymis
• Epididymis is a huge tube: 100 to 500
feet long!
• Travel time for sperm cells 10 to 15
days, depending on species
Epididymis
Interesting:
• Sperm production is coordinated along the
seminiferous tubules in such a way that
specific geographic areas engage in the
production at the same time – leads to
wave-like production of sperms
Seminal fluid - Function
• Survival of sperm! Contains electrolytes,
fructose, ascorbic acid, vitamins,
prostaglandins
• Prostaglandins (hormones) react with
cervical mucus and make it more receptive
to sperm; cause smooth muscle
contraction facilitating transport of sperm
toward the ovaries
Spermatogenesis
• Entire process of transformation of stem
cells (spermatogonia) to spermatozoa.
• Goals:
– Reduce chromosome set (reductive division,
or meiosis)
– Multiply (multiplicative division, mitosis)
Environmental effects
Psychological effects
Hypothalamus
Stimulus
GnRH
Inhibition
Pituitary
LH
FSH
Testis
Sertoli Cells
Leydig Cells
Inhibin
Testosterone
Stem Cells to Germ Cells
(Gametes)
• Males: continuous replenishment – one
cell resulting from the initial mitosis
replaces the parent stem cell, the other
become spermatozoa
• Females: no replacement of stem cells –
finite number over the lifespan of the
organism
Factors affecting male
reproductive function
• Puberty: levels of hormones produced in the
brain increase, trigger differentiation and
development
• Photoperiod: Small ruminants experience
testicular regression during periods of increasing
day length; restored with decreasing
photoperiods. In stallions, decreasing
photoperiod reduces testicular function
• Body composition plays a role – extremely
undernourished animals cease testosterone
production
Reproductive Manipulation
• Objectives:
– Rapid propagation of desirable genetic
material
– Prevention of sexually transmitted diseases
– Use of highly valuable genetic material
(horses)
– Conservation of endangered breeds and
species
– Facilitation of creation of genetically modified
organisms (GMO’s)
Artificial Insemination
• Number of sperm in one
insemination dose in artificial
insemination (AI):
– 10 million in cattle
– 125 million in sheep
– 2 billion in pigs and horses
2. Female Reproduction
Female Reproduction and
Gametogenesis
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Production and storage of oocytes
Fertilization
Development of the embryo
Birth
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Parts of the female reproductive
system
Ovaries
Ovarian (Fallopian) tubes
Uterus
Vagina
Vulva
Cow reproductive
tract
Functional Anatomy
• The ovum (egg) is expelled from the ovary
and received by the infundibulum and
carried to the uterine tube, where
fertilization normally takes place during
passage of the ovum to the uterus. Within
the uterus, the fertilized egg develops into
an embryo and fetus, and then leaves the
uterus through vagina and vulva as a
newborn animal (neonate).
Ovaries
• Paired glands – development of oocytes
and production of hormones. Equivalent
of testes
• In cow and horse, rectal palpation
relatively easy due to somewhat loose
suspension
Cow ovary
Pig ovary
What exactly happens at
ovulation?
Ovulation
• The total duration of follicular development
is around 6 months, but the final phase is
much shorter – ranging from about 12 to
35 days in farm animals
• This is part of the estrous cycle
Ovulation
• The cascade of events leading to
ovulation is initiated by the
preovulatory LH surge.
After ovulation – Corpus
luteum
• After ovulation, the cell mass of the follicle
transforms and changes to the production of
a different steroid (progesterone)
• If the ovum is not fertilized, the CL regresses
• If pregnancy occurs, the CL may last
throughout the gestation period
• CL has the richest blood supply in the body
Corpus luteum
• Important:
– When granulosa cells begin the formation of
the CL, they switch from estrogen production
to the production of progesterone
– Progesterone is important for the
maintenance of pregnancy, and in some
species, for the expression of estrus
Corpus luteum
– Sometimes the CL fails to regress
(retained CL) – this is an important cause
of temporary infertility in dairy cattle
– A number of follicles may develop without
rupturing – cystic condition of the ovary.
Treatment: with LH-releasing hormone
causing LH release leading to rupture of
the follicles
– Regression of the CL in farm animals
influenced by the uterus (endometrium)
(hysterectomy prolongs CL life)
Why is the understanding of the
estrous cycle important?
• Reproductive management must
understand species specific differences in
reproductive physiology
• If reproduction does not work, what is the
problem? Nutrition? Males? Disease?
Fertilization
Ovum Transport
• At the time of ovulation, the fimbriae of the
fallopian tubes (oviducts) have strong blood flow
and are in close contact with the ovary
• The fimbriae show contractile activity that
sweeps the ovulated oocyst(s) [ova] into the
infundibulum
• Contraction of the oviduct muscles and
movement of mucosal cilia transport the ovum
toward the uterus
Fertilization
• They key to successful fertilization is the
meeting of oocyte and spermatocytes at
the right place, and the right time
• If you use AI, your timing of insemination
must coincide with the arrival of the oocyte
• Fertilization usually takes place in the
uterine tubes
Fertilization
• Both males and females can cause failure
of fertilization
• In the reproductive evaluation of males,
quality and motility of sperm is judged
• Motility is not important for movement
inside the female tract but for penetration
of the oocyte
Normal and
abnormal
bovine
spermatozoa
Capacitation
• Changes required to penetrate the Zona
pellucida and fertilize
• Takes several hours, and involves
production and release of enzymes that
modify the spermatozoon
• This process is called ‘capacitation’
Fertilization
• Fusion of male and female
gametes
• Second maturational division
(shedding another polar body) is
not completed until fertilization
occurs
• First step of fertilization: passage of
the spermatozoon through the
Zona pellucida – aided by enzymes
released from the sperm cell
(acrosome)
Fertilization
• Important! Fertilization in most
species takes place in the
uterine tube (fallopian tube,
oviduct)
Post-fertilization
polyspermic zygote
(rabbit)
Note: sperms that ‘did
mot make it’
Early Embryogenesis
• Product of fertilization is a one-cell zygote
• It follows a series of divisions leading to a
hollow sphere – the blastocyst
• Embryo is the term for blastocyst until
there is a differentiation of the organ
systems and placenta – at that stage, it is
called a fetus
• Note: Some sources use the term for the
two-cell stage or later
Early Embryogenesis
• The zygote is transported down the uterine
tube into the uterus as the blastocyst is
being formed
• Takes about 4 days post coitus in
ruminants
• This developing new organism is
nourished by ovum (egg) yolk until
attachment in the uterus occurs –
remember: oogenesis: keep the good
stuff!
Early Pregnancy
• Implantation begins 2-5 weeks after
conception (primates: 1 week after
ovulation)
Placentation in the Mare
Placentation in the Pig
Maternal Recognition of Pregnancy
• The maternal organism must recognize
the presence of an embryo in the uterus
• CL must be maintained (progesterone!)
• Uterine derived PGF2α must be inhibited
• Interaction between embryo and
endometrium provides signals for
maintenance of CL
Maternal Recognition of Pregnancy
• In ruminants, early embryos produce a
protein (Interferon tau) that drastically
reduces the production of PGF2α by the
uterus – the CL is maintained
• Mechanisms differ between species –
dogs don’t need one because their pattern
of progesterone secretion does not
change
Maternal Recognition of Pregnancy
• Failure of recognition may be an important
cause for early embryonic death – narrow
time window
• Ultrasound diagnostics allow earlier
detection now
Placenta
• Development of extraembryonic
membranes is called placentation
• Collective name for the membranes is fetal
placenta
• Trophoblastic cells of the embryo
participate in the formation of the placenta
Fetus and placenta of the horse
Placenta
• There is no direct connection between the
blood supply of the fetus and the mother
• Umbilical chord is connected to the
placenta – nutrients come in through the
chorion
• Note that the direction of circulation of
blood is opposite in the developing fetus
Pregnancy Testing
• Early detection of pregnancy is
economically important in farm animals
– Cows: rectal palpation, 30-45 days
– Sheep: ultrasound, 30-45 days
– Pigs: ultrasound, 30-70 days
Cattle embryo 31 days
48 days fetus and membranes (cattle)
Placenta and fetus in situ (sheep)
Parturition
• Termination of pregnancy – three
stages:
– 1. Uterine contractions, dilation of cervix
• 2-6 hrs in cow and ewe, 2-12 hours in sow
– 2. Delivery of fetus: combination of
uterine and abdominal contractions
forces the fetus through the birth canal
– 3. Delivery of placenta
Parturition
• Hormonal regulation: progesterone
declines rapidly in the last 48 hours of
gestation in the cow, estrogen levels
increase, but decline just prior to
parturition
• Corticosteroid and prolactin levels behave
like estrogen
Parturition
• Fetus senses stress, increases cortisone
(cortisol) production
• Cortisol causes the placenta to produce
estradiol
• Estradiol in turn causes the uterus to
produce relaxin, leading to dilation of the
cervix
• Species differences in hormone secretion
patterns
Parturition
• External signs:
– Swelling of the vulva, discharge of
mucous
– Relaxation of abdominal wall, sinking
of the rump
– Behavior: restless, retreat, frequent
urination
• Dystocia: Difficult birth of any kind
Begin stage 2 labor in ewe
Stage 2 labor in a goat
Lambing ewe between two lambs
Lamb – head and shoulders out
Dystocia – not a happy calf
Uterus prolapse
Common Reproductive Problems in
Low Input Systems
• Reproductive problems are rampant in low
input systems
• Major problem is ignorance and infection
pressure, combined with nutrition
problems
• Veterinary services deficient in many
places
• Lack of integration of veterinary care with
nutritional management
Reproductive Problems
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Choice of breeding animals
Lack of reproductive evaluation
Anestrus, silent estrus
Nutrition causing or compounding
problems
• Absence of stringent culling
• High incidence of sterility
• Failure to interpret herd parameters
correctly
Reproductive Problems
• Cystic ovaries: luteal cysts or follicular
cysts (cause not very clear)
• Fertilization failure
• Embryonic mortality (higher in tropical
areas)
• Infectious abortions (notably brucellosis,
leptospirosis, trichomoniasis, neosporosis)
• Dystocia; Retention of placenta
Reproductive Problems
• In males:
– Infections (orchitis caused by brucellosis,
tuberculosis; epididymitis caused by
brucellosis and viral infections)
– Cryptorchidism
– Lack of libido
– Homosexual orientation (sheep)
– Sperm quality
What do you think of this bull? Why did the producer select it?
What do you think of this bull?
What do you think of this bull?