WK 3 (Spermatogenesis & controlled breeding) Flashcards
Function of gene SrY
Y chromosome contains male determining gene
This switches on ‘structural genes’ in autosomal chromosomes that cause development of male genital system
The testis
Has 2 functions:
- Production and transmission of male genes (spermatozoa)
- Production of reproductive hormones (androgens)
Testis consist of seminiferous tubules (sperm maturation occurs)
Testicular parenchyma
Consists of 2 discrete compartments:
- Within seminferous tubules
- Sertoli cells present
- Sperm development - Between seminferous tubules
- Leydig cells present - where testosterone is made under influence of LH
- Androgens synthesised
Blood testis barrier
Blocks blood and associated immune cells from getting in to where the sperm are developing.
This is important because at a certain point in the spermatogenic cycle the cells become different than self and if immune cells could see them they would attack them
Damage to blood testis barrier affects spermatogenesis as immune cells kill developing sperm so ejaculate contain less sperm until damage is resolved
Sertoli cell
Sertoli cell influences spermatogenesis:
- Spermatocytes receive testicular proteins via sertoli cell gap junctions
- Spermatocytes and spermatids are physically anchored to the sertoli cell
- Sertoli cell removes material from the elongating spermatid during cytoplasmic condensation
All sertoli cells linked to each other by gap junctions to provide network for communication throughout tubule
Sertoli cells play critical role in mediating the actions of hormones on spermatogenesis
3 phases of spermatogenesis:
- Mitotic proliferation
- Meiotic division
- Cytodifferntiation (spermiogenesis)
Spermatogenesis - Phase 1: Mitotic proliferation
Produces large numbers of cells (spermatogonia A0-A4)
Spermatogonia are diploid and genetically identical
Occurs in basal compartment of tubule
Doesn’t need to occur in adluminal compartment (blood testis barrier) as cells are still self-cells
There is a point at which some of these cells (after a couple of divisions), revert back to an earlier version of themselves
- go from being spermatogonia (A4) to (A1)
- In order for there to constantly be sperm produced, the testes has to maintain a population of these (A1) spermatogonia - does this by a subset of the divided spermatogonia regenerating and reverting back to (A1) spermatogonia
Spermatogenesis - Phase 2: Meiotic division
No longer referred to as spermatogonia but spermatocytes
Generates genetic diversity (chromatids exchange genetic material)
Halves chromosome number (haploid)
Spermatocytes to spermatids
Occurs in adluminal compartment of tubule (non-self cells)
Spermatogenesis - Phase 3: Cytodifferentiation
Packages genes for delivery to oocyte
Elongating spermatids –> spermatozoa
Final stage of spermatogenesis
Re-packaging of this cell from something round and passive (just floats) to what we see as a sperm (motile – Head- Tail)
Sertoli cell removes material from the elongating spermatid during cytoplasmic condensation (cytoplasmic droplet)
Occurs right at the top near the lumen
This process is happening from the basement membrane pushing up towards the lumen
- Most immature cell types can be found at the basement membrane and then as they get more and more developed they make their way further up to the top, closer to the lumen before they get released
Process isn’t perfect – things go wrong - apoptosis
- Reduction in efficiency can be targeted by treatments later on down the track to increase number of sperm generated
What percentage of normal sperm is expected in production animals used for breeding?
90%
The rate of spermatogenesis is…..
The rate of spermatogenesis is CONSTANT
Spermatogenic wave
Refers to how there are different stages of division occurring along the seminiferous tubule
How is a constant supply of sperm maintained?
Different stages of spermatic division are occurring at different sites along the seminiferous tubule .
In every species, if you multiply the cycle of the seminiferous epithelium by 4.5 you will get the number of days for complete spermatogenic cycle
E.g. Rams
Each site along the seminiferous tubule is at a different stage of division so each site takes 10.5 days to release sperm but the complete spermatogenic cycle of 1 cell through all the divisions and re-packaging takes 47 days or 4.5 seminiferous epithelium cycles (as at each site, at each stage there is layers of cells at different stages of maturation – basement membrane up to seminiferous epithelium)
I.e. spermatogonia is at one of 8 stages of maturation – different spermatogonia are in different phases so every 10.5 days sperm is being released from a particular site of the tubule, (each site has layers of cells underneath that are not ready to be released yet) but the journey of those cells up until the point of release would have taken 47 days
As each site is at a different stage of division, one site is always going to be at stage 8 at any given point in time meaning there is ALWAYS a constant supply of sperm
if each site was at the same stage of division sperm release would be pulsatile and it would take 10.5 days for new release of sperm (not practical)
10.5 days of seminiferous epithelium cycle refers to the very top layer of this picture – i.e. it takes 10.5 days for the top layer of spermatids to mature and be released BUT it takes 47 days for the most basic cell to go work its way up from the basement membrane and be released into the lumen
Complete spermatogenic cycle = spermatogonia (A1) spermatozoa
Cycle of seminiferous epithelium = just the very edge/outer layer (right near lumen) = the releasing of sperm into seminiferous lumen
Endocrine control of spermatogenesis
GnRH pulse generator is located in hypothalamus
GnRH pulses elicit release of FSH and LH from the anterior pituitary gland, which stimulates release of steroid hormones from the testes
Both LH (or T) and FSH are required to initiate spermatogenesis
- Puberty
- Seasonal anoestrous
But only LH or Testosterone (and DHT) are required to maintain spermatogenesis
Hypothalamus releases GnRH feeds back to pituitary –> Anterior lobe of pituitary produces LH –> LH acts on the Leydig cells inside of testes (in interstitial space) —> LH is converted into testosterone testosterone –> acts on sertoli cells –> developing germ cells and supports spermatogenesis
FSH promotes B spermatogonia indirectly via Sertoli cells, feedback via differentiating germ cells to Sertoli cells, affecting Inhibin production
DHT (dihydrotestosterone)
Potent form of testosterone
Testosterone is transformed into DHT by an enzyme called 5 reductase
Inhibin in males
Produced by the sertoli cells
Feedback to the pituitary which regulates the amount of FSH produced
Can the timing or rate of spermatogenesis be changed?
NO
However the efficiency of spermatogenesis CAN be changed
- So the rate of sperm production can be altered
The rate of sperm production and efficiency of spermatogenesis is governed by:
- Length of cycle (CONSTANT)
- Weight of the testes
- Sperm production/unit weight of testis
- Number of spermatogonia feeding into cycle (can be altered
- Extent of cell loss at each stage of the cycle (can be altered)
Factors effecting the efficiency of spermatogenesis
Breakdown of the blood-testis barrier
Irradiation
Heat & cryptorchidism
Diet
Drugs/toxic agents
Disease
Endocrines
i.e. factors that effect: weight of testes & sperm produced/unit weight of testes
Efficiency of spermatogenesis - Breakdown of blood-testis barrier
Caused by:
Mechanical injury - lowers sperm count
Autoimmune orchitis
Aspermatogenesis
Breakdown leads to auto-immune attack on sperm cells - infertility
Efficiency of spermatogenesis - Irradiation
Dividing cells are susceptible to irradiation damage causing wave of maturation depletion in adult, possibly complete loss of spermatogonia in fetus
Efficiency of spermatogenesis - Heat & cryptorchidism
Spermatogenesis only occurs 4-7 °C below body core temperature
Spermatocytes, spermatids particularly sensitive to local heating
Temperature controlled by:
- Cremaster muscle (regulates height of testes)
- Scrotal sweat glands
- Pampiniform plexus (hot arterial blood exchanging blood with the cooler venous blood before reaching the testes)
Cryptorchids:
Undescended testis – needs to be removed or can cause cancer
No spermatogenesis
Efficiency of spermatogenesis - Diet
Deficiencies causing testicular degeneration: Vitamin A Essential fatty acids Some amino acids Zinc Vitamin B via pituitary
High energy or protein food can stimulate testes via action on hypothalamus and pituitary gland, e.g. lupin grains
- Feeding lupins increases the pulsatility of GnRH pulse generator, making more GnRH –> more LH –> more testosterone
Of no additional use when diet is adequate
Efficiency of spermatogenesis - Drugs/toxic agents
Agents causing testicular degeneration:
- Cadmium salts
- Cytotoxic drugs
- Some antibacterial drugs
- Corticosteroids (via pituitary gland)
- Alcohol
Dividing cells are susceptible to cytotoxic or antibacterial drug damage causing wave of maturation depletion in adult , possibly complete loss of spermatogonia during prolonged treatment
Efficiency of spermatogenesis - Disease
Disease causing oligospermia
- Genetic abnormalities
- Mumps (adults)
- Local Inflammation
Temporary or permanent oligiospermia may arise from local over-heating during inflammation or breakdown of blood-testis barrier
Efficiency of spermatogenesis - Endocrines
Both LH and FSH are required to initiate spermatogenesis
LH or testosterone (and DHT) maintain spermatogenesis
Affect of breeding season on GnRH (males)
Less GnRH in non-breeding season –> less Lh –> less testosterone –> reduced spermatogenesis
Affects some species more than others (merinos not so affected)
Male effect - GnRH pulses
GnRH pulses dramatically increase
Nutrition stress - Testosterone release
Reduces testosterone through reduced LH secretion
Effect of stress on testosterone production
Reduced testosterone through reduced LH via generalised negative feedback of corticosteroids
Post spermatogenesis and spermiogenesis
When elongated spermatids are released from sertoli cells its is known as spermiation
- At this point they change from spermatids to spermatozoa – they are still not motile
Once sperm have detached from the sertoli cell they are transported to the epididymis
Transport of sperm to the epididymis
When sperm is released from Sertoli cell it is immotile
Tubular fluid secreted by sertoli cells:
- High in K+ (renders sperm immotile)
- Low in Na+
- High in inositol, glutamic acid, some amino acids
- Inhibitor of acrosin
- Androgen binding protein (some spp.)
Rete testes absorbs fluid
- Fluid going in at one end out the other –> sperm floating along
Rete testes –> Efferent ducts –> Epididymis
Once sperm reach the efferent ducts there is more active movement via cilia and smooth muscle contraction
Secretions of tubules, and possible active ion transport from rete testis, draw soerm to:
Rete testis (absorption of water) –> Efferent ducts (Epithelial cilia, smooth muscle contraction) –> Epididymis
Epididymal Structure
Caput (Head)
- Fluid from sertoli cells reabsorbed
- Thus sperm are concentrated 100-fold
- Sperm subsequently transported by muscles in epididymis
Corpus (body)
- Modification of environment and sperm maturation
Cauda (tail)
- Sperm storage
Passage through epididymis takes 6-14 days
When sperm leave the testes are they fertile?
No - They have to go through epididymal maturation
Sperm in the caput (head) of the epididymis
Sperm are:
Immotile
Infertile
Proximal cytoplasmic droplet (result of repackaging by sertoli cell - round cell into elongated cell, a little bit of cytoplasm from the round cell remains
(When cytoplasmic droplet is called proximal = close to the head, distal = close to the Tail)
Sperm in the cauda (tail) of the epididymis
Sperm are:
Forward progressive motile
Fertile
Will either have:
- A distal cytoplasmic droplet
OR
- It will have lost its cytoplasmic droplet
Androgen
Supports sperm maturation via rete testis or blood
Epididymal maturation (brief)
Sperm structure
Sperm membranes
Sperm metabolism
Sperm motility
Epididymal maturation - Sperm structure
Loss of surplus cytoplasm (removal of cytoplasmic droplet)
Condensation of nuclear chromatin by disulphide bridges – less susceptible to damage from reactive oxygen species found in female tract
Epididymal maturation - Sperm membranes
Addition of surface glycoproteins to stabilize plasma membrane
Membrane fluidity and lipid composition change - more robust and enables it to undergo a further maturation event called capacitation
- Cholesterol selectivity metabolized shifting balance towards diaglycerol and unsaturated fatty acids
Epididymal maturation - Sperm metabolism
Depression of metabolic activity to prolong life of cell
Increased dependence on external fructose for energy production
Epididymal maturation - Sperm motility
cAMP content of tail increases allowing acquisition of motility
Anatomy of the penis - Shaft
Corpus spongiosum (urethra) and corpus cavernosum (main body) act as blood reservoirs during erection
Os penis in dog
Anatomy of the penis - Glans penis
Glans penis = End part
Tom covered in androgen dependent spines (if you castrate spines disappear)
Alpaca has a stiff spine
Boar corkscrew shape
Fibroelastic penis
Bull, boar, ram
Limited erectile tissue
Presence of sigmoid flexure
- Allows the penis to be retracted into the body until erection
- Sigmoid flexure held by retractor penis muscles
- Contract retractor muscles - penis held in sheath
- Relax retractor muscles - penis protrudes
Musculovascular Penis
Stallion, Human
Large corpus cavernosum fills with blood during erection
No sigmoid flexure
Retractor penis muscle in stallion
Erection - Psychogenic stimuli
Visual cues
- Mating in others – induces erection and can stimulate the release of oxytocin which pushes some sperm from the tail of the epididymis up into the urethra = high sperm counts in ejaculates and helps animal to jump/mount
- Lordosis (female exhibiting standing heat)
Olfactory cues
- Sniffing of vulva
- Female urination
- Pheromones
- Androgens, Boar mate (nasal spray
product for pigs – causes ejaculation)
Penile erection - Nervous Stimulation
Erection induced by:
- Visual cues
- Olfactory cues
- Tactile stimulation of penis and perineum
- Pudendal nerve (afferent somatic
innervation)
- Pudendal nerve (afferent somatic
Complex series of neural signals:
- Efferent innervation of penis controls erection
Pelvic nerve (parasympathetic) promotes erection - Non-andrenergic, cholinergic + non-andrenergic, non-cholinergic
Hypogastric nerve (sympathetic) suppresses erection - Andrenergic innervation
Pudendal nerve (somatic) promotes
Flacid penis
Adrenergic neurons are part of the sympathetic nervous system –> Neurotransmitter is Norepinephrine (NE) which makes smooth muscle cells contract
NANC neurons = parasympathetic neurons while penis is non-erect they are not firing (switched off)
Erect penis
Erectile stimulus causes Adrenergic neurons to be switched off and NANC neurons to be switched on
NANC neuron’s neurotransmitter is Nitric oxide (NO)
Nitric oxide activates an enzyme called Guanylate cyclase
Guanylate cyclase converts GTP to cGMP (cyclic GMP)
cGMP causes smooth muscle to relax
Another enzyme PDE5 stops things from getting out of control by converting cGMP back to GMP and as levels of cGMP are diminished so to is the erectile response
- Viagra inhibits PDE5 allowing cGMP to build up to higher levels
An erection is NOT a contraction of muscles, it is actually a relaxation of muscles - the smooth muscle relaxes which allows corporal sinusoids to fill with blood
Erection process
Parasympathetic neurons fire, release nitric oxide (NO) from terminals, activates enzyme (guanylate cyclase)
- Causes arterial dilation and increased blood flow into corpus cavernosa (smooth muscle is relaxing)
- Intracorporal pressure increases, compressing emissary venules; blood ‘trapped’ (deep arterial inflow vs surface venous outflow –> means increased pressure blocks venous drainage)
Relaxation of the retractor penis muscle
- Straightening of the sigmoid flexure
Seminal Plasma
A product of the accessory sex glands
Sperm + Seminal plasma = Semen
Accessory sex glands include:
- Seminal vesicles
- Prostate
- Bulbourethral gland
- Ampulla gland
Major contribution to seminal plasma - Ram
Large seminal vesicles
Small prostate
Major contribution to seminal plasma - Bull
Large seminal vesicles
Small prostate
Major contribution to seminal plasma - Pig
Large bulbourtheral
Large prostate
Large seminal vesicles
Major contribution to seminal plasma - Dog
Large prostate
No seminal vesicles
Major contribution to seminal plasma - Cat
Large prostates
No seminal vesicles
Seminal plasma bull
Seminal plasma derived from accessory sex glands:
- Prostate gland
- Seminal vesicle
- Ampulla
Ejaculate volume of bull
2-10ml
Ejaculate volume of dog
2-15ml
Seminal plasma - stallion
Large ampulla
Large prostate
Small seminal vesicle
Additional bulbourethral gland
Ejaculate volume - stallion
30-300ml
Ejaculate volume - Boar
150-500ml
Products of prostate gland
Citric acid, acid phosphatase, Zn, Mg, antiagluttinin
Products of seminal vesicles
Fructose
Prostaglandins
Inositol
Buffers
Products of bulbourethral gland
Proteins
Mucin (siallic acids, galactose, sugars)
Products of preputial gland
Pheromones
Products of accessory sex glands
Energy source, e.g. glucose, fructose - has to be monosaccharide in order to be metabolised
Buffering agents - protect against pH change - important as vagina is an acidic environment
Seminal plasma proteins - change the way that sperm mature and the way they interact with the female tract
E.g. in sheep without seminal plasma proteins sperm cannot enter the cervix
Antioxidants
Ejaculation
Primarily a result of stimulation of the glans penis
Causes contraction of smooth muscles surrounding vas deferens, seminal vesicles and prostate
- Urethralis
- Ischiocavernous
- Bulbospongiosus
Two stages:
- Emission and Expulsion
Emission occurs:
- Movement of sperm and seminal plasma into urethra
Spermatozoa and seminal plasma expelled
Emission:
- Sperm move from epididymis to Ductus deferens to urethra - Via oxytocin, sympathetic controlled contraction of smooth muscle
- Seminal plasma expelled into urethra- Via sympathetic control
- Sperm and Seminal plasma mix
Expulsion:
- Contraction of muscles surrounding vas deferens, seminal vesicles and prostate
- Urethralis
- Sympathetic - Ischiocavernous
- Bulbospongiosus
- Somatic (pudendal)
- Urethralis
- Wave like/pulsatile contractions ejaculation
- Distal dilation of corpus spongiosum – enlarged glans
- Semen expelled
Ejaculation in stallion
Veyr forceful
Ejaculation in Bull
Single spurt (1 - 3 seconds)
Ejaculation in Boar
Extended process (5-20 mins)
Fractionated
Early fraction = gel acts as plug
Ejaculation in Camel
6 hours
Ejaculation in dogs
5-45 mins
Copulation in the dog
First stage coitus:
- Male mounts female
- First and second fraction of semen ejaculated
- 1-2 mins
The turn:
- Dog turns by lifting one leg over bitch
Second stage coitus:
- Third fraction of semen ejaculated (30ml)
- 5-45 mins
- Inter-uterine deposition
- Maintains high vaginal pressure
Erection in the dog penis
Male and female ‘tied
- Os penis
- Bulbus glandis fills with blood forming a ‘copulatory lock’
- Venous outflow restricted
- Muscles at base of penis contract
- Muscles in vulva of female
Semen deposition in Bull
Rapid (2 sec)
Single thrust
5-10 ml
Vaginal
Semen deposition in Ram
20 secs
Single thrust
0.5-1ml
Vaginal
Semen deposition in Tom
60 secs
Multiple thrusts
0.1ml
Vaginal
Semen deposition in Boar
10-15 min
Multiple thrusts until cervical contract
250-500ml
Uterine
Semen deposition in Stallion
3 min
Multiple forceful thrusts
30-60 ml
Vaginal but enters uterus under high pressure
Semen deposition in Dog
20 min
Multiple thrusts until tie
Turn and second stage coitus
10-20 ml
Uterine
Female repro tract - Pig
Wide uterus
Open cervix = uterine insemination/ semen deposition
Female repro tract - Ewe
Smaller uterus
Tight cervix = vaginal insemination / semen deposition
Semen deposition - Vaginal depositors
Animals that have high sperm concentration in ejaculate have a low volume of ejaculate and tend to be vaginal depositors - cant have high volume or it will just leak straight back out
Final stages of sperm maturation
= Capacitation and acrosome reaction
Occurs inside the female repro tract
Ejaculation has happened –> sperm is being transported through the tract (partly by swimming and partly by uterine contractions –> sperm go into the oviduct where they bind with oviduct epithelial cells and at some point they get a message from the female that the egg is there –> when the egg is there sperm capacitate – a chemical message which is sent through the female causes a change in the sperm causing remodeling on the sperm surface and it capacitates
When sperm capacitates it disengages from the oviduct epithelial cells and starts its final trip up the isthmus to the ampulla of the oviduct
In the ampulla sperm will meet the egg (if its lucky) and if it meets the egg and binds it will then undergo the acrosome reaction (if it has an acrosome)
Uses of AI
Widespread dissemination of superior male genetics
- Increase productivity of agriculture
Circumvent female pathology (wildlife)
Artificial ‘migration’ (wildlife) - don’t want to transport whole rhino etc. if you don’t have to
Spermatogenesis is under the control of…..
Under the control of the HPG axis
- LH acts on Leydig cells, FSH acts on sertoli cells
Reasons for control of oestrous & ovulation
- Limitation of reproduction
- Programming for management reasons
- Augmentation of fertility and fecundity
Reasons for control of oestrous & ovulation - Limitation of reproduction
- Companion animals (more manageable, docile when de-sexed)
- Horses for convenience in racing, shows, competition
- Production animals (e.g. feedlots or fattening of range cattle, don’t want to waste energy on reproduction)
- Methods may be permanent or temporary
Reasons for control of oestrous & ovulation - Programming reproduction
Convenience
Production
- Programmed mating & therefore parturition to suit market, environmental
- Facilitates AI
- Avoid weekend or holiday work
Reasons for control of oestrous & ovulation - Augmentation of fecundity and fertility
As part of reproductive management program e.g.
- Increased reproductive rate
- Proliferation of genes from superior females (MOET)
- Out of season breeding (including increased frequency of gestation)
To alleviate relative infertility
- Breeding juveniles or senescent animals
- Breeding subfertile individuals
Why do you have to do laproscopic AI with superovulated females?
Follicles produce oestrogen so with that many follicles there will be heaps of oestrogen –> oestrogen is responsible for cervical mucous so all sperm get washed away and cannot reach the egg
Follicular phase (hormones) - brief
Follicle makes lots of oestrogen
Follicle also makes inhibin which negatively feeds back on FSH
Oestrogen negatively feedsback on whole system
Preovulatory LH surge
LH surge occurs due to:
- Lots of oestrogen being produced because there is a huge follicle
- Lots of oestrogen means that instead of having negative feedback on the tonic centre of the hypothalamus there is positive feedback on the surge centre of the hypothalamus
- Surge center - makes GnRH pulse generator pulse more strongly and more rapidly –> more pulses of LH which builds up higher levels until it reaches a point of high enough levels that the luteinizing hormone is able to luteinize the follicle –> causes ovulation
Luteal phase (hormones) brief
Corpus luteum is making a lot of progesterone
Progesterone provide VERY STRONG negative feedback to the whole system –> reduces the pulsatility of the GnRH pulse generator –> less LH and less FSH
Control of reproduction - PGF2alpha
PGF2alpha can shorten oestrous cycles
Synchronisation of oestrous - Progestagen
To synchronize estrus give a progestagen (type of progesterone) –> tricks the animal into thinking her luteal phase is still happening even after she has received the signal to destroy corpus luteum –> once progesterone has been removed animal undergoes estrus and ovulation
Progestagens are also used as priming hormone in anoestrus
- Sheep require progesterone stimulation for oestrus behaviour, formation of CL; may or may not be required in cow, goat
How to shorten the luteal phase?
Administration of PGF2alpha to an animal with an active corpus luteum present, will destroy the corpus luteum –> results in earlier oestrus and ovulation
But if you administer prostaglandin early in luteal phase nothing will happen as it needs to have a CL to destroy
Best method is to:
- Administer 2 doses of prostaglandin 10 days apart - if first dose doesn’t have CL to act on it will have by the second dose - if first dose does have CL to destroy it will work but to synchronise whole flock you need to give second dose so all sheep have CL to destroy
Synchronisation of oestrus with prostaglandins
Numerous synthetic analogues
Administration via:
- Injection (2 x 10 days apart)
Simple
More expensive than progestagen
Not effective in non-breeding season
Not used as commonly
High degree of synchrony
- Timed insemination regardless of oestrus
Greater adverse effect on sperm transport through cervix than progestagen
- Not used with vaginal insemination
- No problem with intrauterine insemination
Comparison of progestogens with prostaglandins
Progestagen method is generally more successful
- Prostaglandins may interfere with sperm transport, trough progestagens may do also
- Progestagens not licensed for use in all countries
Prostaglandins are more expensive than progestogens
A combination of progestagen and luteolysin treatment is sometimes recommended
- E.g. Cattle (oestrogen as a luteolysin at start of relatively short progestagen treatment)
- E.g. Goats (Prostaglandins at progestagen withdrawal after relatively short treatment)
- Both enable shorter progestagen treatment than normal, an advantage as prolonged treatment in these species can sometimes lead to follicular cysts and reduced fertility
Pigs are relatively insensitive to prostaglandins until late in the cycle, close to normal luteolysis
Most progestagens cause cystic follicles in pigs
- Possibly not potent enough to cause full suppression of FSH
Allyltrenbolone (Regumate®), orally is effective but expensive and not used commercially
Regumate® is also the most effective progestagen in mares
Synchronisation of oestrous with progestagens
Administration via:
- Daily injection
- Subcutaneous implant
- Intravaginal passary
Cheap, simple, effective any time of year (even in non-breeding season can get ewes to cycle if combined with injection of PMSG at the end)
High degree of synchrony
- Timed insemination regardless of oestrus
Minor adverse effect on sperm transport through cervix
- Not used with vaginal insemination
- No problem with intrauterine insemination
Progestagens can artificially extend the luteal phase:
- Treatment is ended at will, followed by a natural (or induced) follicular phase, with oestrus and ovulation
Progestagens should, in theory, be administered for the length of one oestrus cycle
- Make sure all animals are synchronized
- Actually slightly shorter – if treatment starts early in the luteal phase CL fails to form
Progestagens are also used as priming hormone in anoestrus
- Sheep require progesterone stimulation for oestrus behaviour, formation of CL; may or may not be required in cow, goat
Must be rapidly absorbed, and rapidly cleared on withdrawal of treatment
- FGA, MAP are more potent than progesterone and are rapidly cleared on withdrawal of treatment
Synchronisation of ovulation
With synchronized oestrus, time of ovulation still variable
- Important for AI with limited sperm numbers or frozen semen
LH or hCG can trigger ovulation
GnRH can trigger endogenous LH surge
Synchronisation of ovulation with GnRH
In sheep give GnRH which causes endogenous LH surge (better than synthetic LH in most species)
In sheep give GnRH 24 hours after removal of sponges
If you give GnRH around the time LH surge would normally occur, it works a lot better – follicles will be more mature (much tighter ovulation window)
Use of LH, hCG or GnRH for ovulation control
Increase precision of time of ovulation
- Subsequent increase in fertility to timed AI
- Extra manipulation and cost of drug perhaps not worth it in commercial AI programs. Used in SOV in MOET in sheep
- Must be administered when follicles are mature otherwise luteinisation occurs without ovulation
- Time of administration depends on species – close to (just before) anticipated endogenous LH surge is best
Increasing ovulation rate
- Additional gonadotropins
- eCG
- FSH - Immunise vs ovarian steroids
- Knock out the effect of oestrogen in the body - Immunise vs inhibin
- knock out the effect of inhibin
Why doesn’t ovulation occur during luteal phase
Under influence of negative feedback of progesterone – even though there are follicular waves occurring during the luteal phase ovulations do not happen
Follicles that become dominant during luteal phase undergo atresia – because you don’t get big surge of oestrogen and LH needed for ovulation (strong negative feedback of progesterone)
Towards the end when there is no progesterone – follicle develops beyond dominant follicle, becomes a graffian follicle and then ovulation occurs
Increasing ovulation rate - FSH
If you add additional FSH around the end of luteal phase you will get more follicles growing and being recruited (rather than little follicles undergoing atresia they are rescued from that pathway and they become dominant as well – polyovulation)
This would be done with a synchronized oestrus, so you would know exactly when negative feedback of progesterone ends, to give additional FSH
Increasing ovulation rate - PMSG
Cheap, effective
Simple
- Single injection at pessary withdrawal - long half life
BUT:
- requires synchronisation
- Variable response triplets or more
AND high steroidogenic:
- Excess oestrogen
- LH as well as FSH activity
- Lutenised follicles (abnormal hormone production) - start producing oestrogen and progesterone at the same time = BAD
Administration of 400 units PMSG at time of sponge removal –> results in slight increase in ovulation (2 or 3 ovulations)
- Problems occur when you give more than 400 units for superovulation
Immunise vs Oestrogens
Can also increase ovulation rates slightly by immunizing vs oestrogens
Deliver a substance which binds to oestrogen and stops the effect of oestrogen in the body
As you have knocked out the effect of oestrogen (mostly) you have reduced negative feedback –> increases activity of HPG axis –> more FSH (pulses more) and LH –> moved from 1 to 2 follicles developing and ovulating
Does not require oestrus synchronization
Priming & booster injections
- Next season booster only
No excess response
- No triplets ovulation rate raised by ~0.5 per ewe
BUT may interfere with embryo survival
- Not used in Merinos
- Works well in British sheep breeds
Immunise vs inhibin
Reduced negative feedback acts on anterior pituitary increased FSH
Priming & Booster injections
High response
- Immunise vs whole molecule repeated superovulation
Moderate response
- Immunise vs subunits repeated twining
BUT there is no commercial product
MOET - use of PMSG
1200 units PMSG given 48 hours prior to pessary withdrawal will cause superovulation
Cheap
Long half life
Premature lutenization is very common when superovulating an animal using eCG
Developing follicles and embryos have been exposed to the wrong conditions
MOET - use of FSH
Relatively expensive
- Multiple injections start 48hr BEFORE pessary removal
- Short half life
Increased recruitment of follicles –> superovulation
NOT highly steroidogenic
- No premature luteinisation
- Few lutenised follicles
MOET - use of FSH
Relatively expensive
- Multiple injections start 48hr BEFORE pessary removal
- Short half life
Increased recruitment of follicles –> superovulation
NOT highly steroidogenic
- No premature luteinisation
- Few lutenised follicles
Additional FSH when dominant follicle IS present
Low superovulation
Additional FSH when dominant follicle IS present
Low superovulation
Effect of nutrition on ovulation rate
Increase ovulation rate by targeted 3 day feeding where you increase the plain of nutrition –> called flushing
Results in increased litter size
Cheap
Unreliable
How does nutrition work in increasing ovulation rate?
Nutrition effects the GNRH pulse generator
Nutritional supplement increased frequency of GnRH pulses –> increased LH levels –> increases ovulation rate
Unclear exactly how that happens but it is clear that some of the hormones that are involved in appetite are linked directly to the hypothalamus and the cells which secrete GnRH
- Insulin and Leptin involved
Ram effect
Females out of sight and smell (around 6 weeks) introduce male fires up GnRH pulse generator bring forwards season & synchronizes season as all females start cycling around the same time
Not precise enough for AI
Transcription of breeding season
Melatonin produced at night levels of melatonin influence the amount of pulsatility of the GnRH pulse generator
Long nights in sheep –> more melatonin –> increased pulsatility of GnRH
Regulin implant —> tricks animal into thinking it is long night –> brings on breeding season –> commonly used in sheep
Administration of melatonin
Implant in ear delivers melatonin for 6 weeks
Advances breeding season when applied 8-12 weeks before normal start (in conjunction with ram effect)
Increases twinning rate
No excess ovulations (triplets)
Only works in short day breeders
Regulin - used in sheep
High dose oestrogen - infertility
High dose blocks sperm transport, implantation (contraceptive)
