Transcript Unit 1: Physiology of Reproduction

Unit 1: Physiology of
Reproduction
• The objective of unit 1 will be to create an
understanding of reproduction from the
physiological perspective.
• Topics covered in this unit:
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Male and Female anatomy
Hormone Function
Pregnancy
Parturition
AI
Reproductive Technologies
Unit 1: Physiology of
Reproduction
• Unit 1 will cover Chapters 10 + 11
• Why is knowledge of the fundamentals of
reproduction crucial?
Unit 1: Physiology of
Reproduction
• Female reproductive organs and function
– Ovary
• Produces the ova & female sex hormones
(estrogen & progesterone)
– Folliculogenesis
• Each follicle contains an ovum
• Development starts from deep within the ovary
with primordial follicles
• As a follicle develops, it produces more estrogen,
which continues its maturation
Unit 1: Physiology of
Reproduction
• Folliculogenesis cont.
– Each follicle goes through stages of
recruitment, selection, and dominance.
– As a follicle develops it can become:
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Primary
Secondary
Tertiary
Graafian
Degenerative (atresia)
Unit 1: Physiology of
Reproduction
• Folliculogenesis cont.
– Only the Graafian follicle can be ovulated
– Ovulation occurs when the follicle ruptures, releasing
the ovum
– After ovulation, follicular cells form the Corpus
Luteum
• The Corpus Luteum
– “yellow body” or callous on the ovary
– Produces progesterone (maintains pregnancy)
Unit 1: Physiology of
Reproduction
• The Oviduct
– Collects the ovulated ovum in the
Infundibulum which guides the egg into the
oviduct
– The site of fertilization
– A fertilized embryo migrates to the uterus
within 3-5 d
Unit 1: Physiology of
Reproduction
• Uterus
– Embryo attaches to the uterine wall to begin
development
– Some attach in the uterine horn (sow), others
in the uterine body (cow/mare)
– Guarded by the cervix (gatekeeper)
Unit 1: Physiology of
Reproduction
• The Vagina
– The “passageway” to the reproductive tract
– Female organ of copulation
– Environment changes depending on the stage
of reproductive cycle
– Also include the urethra
Unit 1: Physiology of
Reproduction
• Male Reproductive Organs
– Testicles
• Suspended from the body
• Produce testosterone
– Leydig or Interstitial cells
• Site of spermatogenesis
– Sperm begin development within the seminiferous
tubules
Unit 1: Physiology of
Reproduction
• The Epididymis
– Stores sperm for maturation
– Acquire the potential for fertilization
– Most mature spermatozoa are nearest the
Vas Deferens, while least mature are nearer
the testicles
– Some degenerate and are reabsorbed
Unit 1: Physiology of
Reproduction
• The Scrotum
– Two-lobed sac
– Serves two purposes:
• Protection
• Temperature regulation
– Can be 3-13º cooler than body temp.
– Tunica Dartos & cremaster muscles
• Responsible for raising and lower the scrotum
– Pampiniform plexus
• Acts as heat exchanger to cool blood as it enters the scrotum
– Begins functioning at puberty w/ hormone function 4060d prior to puberty
– What happens if this malfunctions?
Unit 1: Physiology of
Reproduction
• Vas Deferens
– Transport tube for sperm from epididymis to
urethra.
– Spermatozoa are stored in the ampulla of the
V.D. until the time of ejaculation
– Some species deposit sperm very quickly, and
some slowly (8-12 min.)
• Bull, horse, ram
• Boar, dog
Unit 1: Physiology of
Reproduction
• Urethra
– Canal extending from the bladder through the
pelvis to the end of the penis
– Carries both urinary waste and sperm
• The penis
– Male organ of copulation
– Virtually every species is different in form and
function
Unit 1: Physiology of
Reproduction
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Male Hormone Function
– Hormones stimulated and produced from the
Anterior Pituitary of the brain
1. Luteinizing Hormone (LH)-causes Leydig cells to
produce testosterone
2. Follicle-Stimulating Hormone (FSH)-stimulates
the seminiferous tubules to nourish developing
spermatozoa
– Hormone function can be influenced by
photoperiod (day length)
Unit 1: Physiology of
Reproduction
• Female Hormone Function
– Originate in the Hypothalamus and the Anterior
Pituitary
• Gonadotropin Releasing Hormone
• LH
• FSH
– Some Hormones also released from the female
reproductive organs
• Estrogen-follicle
• Progesterone-CL
• Prostaglandin-uterus
Unit 1: Physiology of
Reproduction
• All these activities make up the estrous
cycle
– Estrous cycles range from 14-29d and can
last anywhere from 12 hrs. to 9d
• Hormone function can be altered or
stimulated with hormone therapy
treatments
Unit 1: Physiology of
Reproduction
• Pregnancy
– Onset of gestation following fertilization
– Embryonic cell division every 20 hrs.
– The period of attachment in the uterus is
critical (20-30d cattle, 14-21d swine)-if no
attachment-embryonic death occurs
– Embryonic stage ends around 45d after
period of formation of major organs
– Fetal stage from 46d to birth
Unit 1: Physiology of
Reproduction
• Parturition
– Placenta is responsible for protecting the
fetus and exchanging nutrients and waste
with the mother
– Birthing is initiated with the release of cortisol
– Cortisol release causes progesterone to
decrease and estrogen, PGF2a, and oxytocin
to spike initiating uterine contractions
– Relaxin also released from the CL-stimulates
the pelvis
Unit 1: Physiology of
Reproduction
• Parturition cont.
– Abnormal birthing (dystocia) can result from
several problems
• Size of fetus
• Abnormal presentation
• Size of pelvic opening
Unit 1: Physiology of
Reproduction
• What has Artificial Insemination done for
the livestock industry?
– How does it fit?
– What are the drawbacks?
– Is it prominent in all of animal agriculture?
Unit 1: Physiology of
Reproduction
• Artificial Insemination
– First recorded in dogs in 1780, cattle & horses
in the early 1900’s
– Can increase the number of offspring from
one male
• Bulls – 30-50 females/yr natural, 200-400 units/wk
for AI (avg. 1 calf/1.5 units semen)
– Success of AI dependent on success of estrus
detection, quality semen, semen handling,
high fertility
Unit 1: Physiology of
Reproduction
• Semen Collection & Processing
– Collection of semen w/ and artificial vagina
– Male mounts a female in estrus, or trained to mount
an object
– May also collect semen manually (boar, dog), or by
electroejaculation
– Collection timing
• Bulls – 2x/d, 2d/wk
• Boars – every other day
• Shortening or extending the schedule may decrease number
of sperm/ejaculate
Unit 1: Physiology of
Reproduction
– Evaluated for:
• Volume, sperm concentration, motility,
abnormalities
– Mixed w/ an extender to dilute for more
volume (milk, egg yolk, buffer)
– 1 unit of cattle semen should contain 10m
normal, motile spermatozoa
– Can be stored and used fresh for only 24-48
hrs.
Unit 1: Physiology of
Reproduction
– Freezing semen
• What is it frozen in?
• Bull semen – can be frozen and stored for
indefinite time without loss of fertility
• Boars, stallions, rams – only modest success w/
frozen semen
• Inseminating the Female
– Conception rates depend on:
• Estrus detection, properly managed semen, timing
of insemination, insemination techniques, avoiding
stress
Unit 1: Physiology of
Reproduction
– Estrus Detection
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Signals time of ovulation, timing of insemination
What is the best indicator?
What are some other indicators of estrus?
What are some technologies that might be used to
detect estrus?
• What strategies might we use to detect estrus?
– Timing of Insemination
• Duration of estrus and timing of insemination
varies w/ species
• Exhibition of estrus doesn’t necessarily include
ovulation
– Sows at 3-5d after farrowing
Unit 1: Physiology of
Reproduction
• Insemination should occur as close to ovulation as
possible
– What is the rule of thumb in cows/sows?
• How common is AI?
– What industries use it the most?
– Which ones use it the least?
• Estrous Synchronization
– Controlling the estrous cycle and the female
expression of estrus
Unit 1: Physiology of
Reproduction
– Why use estrous synchronization?
– Where is it the most appropriate and cost
effective?
– Prostaglandins
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Causes regression of a CL
Cows will be in estrus ~3d after injection
Only effective in the presence of a functional CL
Heifers/cows must be in d 5 – 18 of estrous cycle
Unit 1: Physiology of
Reproduction
• One-injection system
– Observe heats for first 5d of breeding season and AI all
that exhibit heat
– Inject those not exhibiting heat on day 6
– All animals bred by day 11
– Can increase P.R. from 30-40% to 50-60%
• Two-injection system
– Inject all cows at day 1 and day 14
– All cows should exhibit estrus by day 19, or breed 76-80
hrs. after second shot
• Can be a good tool in well-managed herds
• What is a major risk w/ using Prostaglandin?
Unit 1: Physiology of
Reproduction
– MGA & Prostaglandin
• MGA – feed additive that suppresses estrus in
heifers
• Feed MGA for 14d, give Prostaglandin 19d after
last MGA feeding
– Most heifers should show estrus in 48-72 hrs
– Conception rate may be >80%
– Select-Synch
• Injection of GnRH 7d following Prostaglandin
– Heat detect 24-36 hrs to 5d after injection
– Should have ~70% exhibit estrus
Unit 1: Physiology of
Reproduction
– Co-Synch
• GnRH on day 0, Prostaglandin on day 7, second
GnRH on day 9 and breed
• Initiates ovulation
• May not exhibit estrus
– CIDR-B
• Use of intravaginal progesterone implant for 7d
• Inject prostaglandin on day 6
• Breed upon estrus detection from days 3-6 after
injection
Unit 1: Physiology of
Reproduction
– PG 600
• Pregnant mare serum gonadotropin
• Enhances fertility efficiency in swine
• Helps lower days returning to estrus after
farrowing, schedule breeding
– Natural estrus synchronization
• Most females will suppress estrous while nursing
young
• Removal of calf/piglet will help bring the cow into
heat
Unit 1: Physiology of
Reproduction
• Embryo Transfer
– What is ET?
– Why use ET?
– Can be costly - ~$1000/hd
– Superovulation
• Increase the number of ovulated ova
• May increase the number of harvested embryos
– How is ET performed?
– What components are essential?
Unit 1: Physiology of
Reproduction
– Sexed Semen
• What are the advantages/disadvantages?
• Reliability of 85-90%
Unit 1: Physiology of
Reproduction
• Unit 1 Assignment
– Chapter Review questions pgs & 209
• Pg. – 1, 2, 4, 7, 8, 9, 14, 16, 17, 18
• Pg. 209 – 2, 3, 5, 8, 9, 12
• Each question will be worth 2 points
– Bonus Question-What is the process of follicle
development called? (2 pts.)
– Due at the beginning of the next class period
– E-mailed homework is encouraged—please include
the course name/number in the subject line.