Comparative Veterinary Reproduction and Obstetrics, Lecture 4
Patrick J. Hemming DVM
Hormone Therapy and Estrus Cycle Control
Hormones used for estrus
control:
A) Progesterone
Progesterone
is a steroidal hormone produced by the ovary (corpus luteum) and is responsible
for maintaining pregnancy.; Progesterone
is also produced by the corpus luteum (CL) during diestrus (the period between
estrus) in the non-pregnant animal. During diestrus or pregnancy progesterone suppresses ovulation and
expression of estrus when a dominant follicle is present on the ovary.
Progesterone
compounds are used pharmacologically to suppress the pituitary release of
gonadotropins (FSH and LH), which effectively suppresses estrus. While the animal is being supplemented with the
progesterone compound estrus will not occur.
This can be of benefit when synchronizing estrus. Soon after withdrawing the progestogen, the
animal will come into heat in 2 to 5 days. In addition to natural progesterone there are several other progestogen compounds that have the same
physiological effect as progesterone. These synthetic progestogens are available commercially for
estrus control. Progestogens can be
administered by injection, orally, as a removable sub-cutaneous implant or in
an intravaginal drug releasing devices. Animals can be kept on progestogens for a short (7 to 16 days) period
for estrus synchronization. It is also
possible to achieve absolute estrus suppression or birth control by
administering a progestogen for an extended period of time, as with the use of
oral MGA in feeder heifers or oral Regu-Mate for mares in training or
competition)
1) Megestrol,
Ovaban tablets 5 and 20 mg tablets, are typically used for estrus suppression
or birth control in companion animals.
2) Norgestomet,
Syncro-Mate-B implants 6.0 mg/SQ implants. Syncro-Mate-B has been used for
estrus synchronization in cattle, but is not currently available in US,
although it is still an approved drug.
3) Melengestrol,
MGA feed additive. MGA is typically supplied
as a feed supplement and is fed at a rate of .5mg MGA per head per day. Usually MGA supplement is formulated to
contain .5mg MGA per pound of feed, and 1 pound of MGA supplement is fed per
head per day. MGA is typically used for
long-term estrus suppression in feeder heifers. It has also been used to synchronize estrus in various short-term
protocols.
4) Altrenogest,
Regu-Mate, oral solution. 2.2mg/ml. Used
in horses for estrus suppression or can be used to induce fertile estrus in
transitional mares. Regu-Mate is also
used in swine and experimentally in cattle.
5) Progesterone
releasing intravaginal device, The CIDR-B Vaginal Insert, with 1.38gm natural
progesterone, is now available in the U.S. The CIDR-B Vaginal Insert, with 1.9gm natural progesterone, is available
in the rest of the world. Either CIDR
appears to work fine. CIDRs are used in
cattle for estrus synchronization. They
are place in the vagina for 7 to 8 days, where the progesterone that they
release is readily absorbed. When removed
a prostaglandin injection is given and the rapid drop in progesterone levels in
the circulatory system allows the animal to come into heat in 2 to 4 days.
The
following progestogen releasing devices are not currently available in the
United States but may eventually be approved for use by the FDA
6) Medroxyprogesterone
acetate, MAP, Repromap sponge
7) Fluorogestone
acetate, FGA. Cronogest sponge
B) Estradiol
Estradiol
is the hormone produced by dominant follicles prior to and at estrus. In addition to causing a female to be
receptive to breeding, estradiol also prepares the reproductive tract for
breeding and sperm transport. Estradiol
is also responsible for positive feedback on the hypothalamus during proestrus,
stimulating the release of GnRH, and thus the LH surge, that is responsible for
ovulation. Many of the effects of
estradiol on the reproductive tract, endocrine system and on the brain
(receptivity) are only evident when progesterone levels are less than 1 ng/ml,
or in other words, when there is not an active CL present on the ovaries. In the presence of elevated progesterone, (an
active CL is present, or the animal is supplemented with a progestogen)
estradiol exerts negative feedback on the hypothalamus and the pituitary gland,
suppressing the release of GnRH and the gonadotropins FSH and LH. Without gonadotropin support of the growing
follicles, atresia (degeneration) of all growing follicles present on the
ovary, including the dominant follicle that is producing the estradiol, will
occur.
Estradiol
is used in estrus synchronization in two ways.
1. If given
during diestrus, when there is an active CL or during progesterone
supplementation, it will cause atresia of growing follicles and result in a new
follicular wave in 3 to 5 days. This
effect can be utilized to synchronize follicular development in groups of
cattle undergoing estrus synchronization.
2. If given 18
hours prior to the scheduled estrus in synchronized cattle, after progesterone
levels have decreased to a baseline level (progesterone supplementation is
removed and prostaglandin F2 alpha have been administered at least 24 hours
previously to lyse the CL), it will effectively synchronize ovulation by
stimulating a LH surge. This also
assumes of course that the follicular wave was synchronized 7 to 8 days earlier
so that all cattle have a dominant follicle that is capable of responding to
the LH surge.
Unfortunately
there are no FDA approved estradiol preparations available in the United States
that can be used to synchronize follicular waves or synchronize ovulation. Estradiol Cypionate (ECP, Upjohn) is FDA
approved but not currently available. ECP is not an ideal estradiol compound for follicular synchronization
though, since it is a long acting compound.
Estradiol Benzoate (E2-B) is a short acting estradiol compound that is
available throughout the rest of the world. E2-B has been used for many years to safely synchronize estrus and
ovulation in ruminants. Hopefully we
will have a short acting estradiol compound available in the U.S. some time,
but I am not holding my breath. Until
E2-B or another short acting estradiol is available, we must rely on GnRH to
synchronize the follicular cycle and ovulation (to be legal).
C) GnRH
GnRH is
gonadotropin releasing hormone. GnRH
is produced by the brain (hypothalamus) and is solely responsible for causing
the release of luteinizing hormone (LH) from the anterior pituitary gland. GnRH also stimulates increases in FSH release
from the anterior pituitary. LH and FSH
are gonadotropin hormones, which are responsible for follicular development
(FSH) and ovulation (LH). Without GnRH,
LH would not be released and ovulation would not occur.
Pharmacologically
GnRH is approved for treating cystic ovarian disease (LH deficiency) in cattle
by causing luteinization of follicular cysts. There have been several other uses for GnRH in cattle and horses. These include:
1. It may be use
in cows at 15 to 25 days postpartum to increase fertility and accelerate the
return to cyclicity.
2. In cattle GnRH
may be used to induce a new follicular cycle (also called a follicular wave). This is used in cattle estrus synchronization
to achieve tighter estrus synchrony of cattle that receive an injection of prostaglandin
F2 alpha.
3. In cattle superovulation
protocols GnRH can be used to initiate a new follicular cycle which may, if
timed correctly, result in higher embryo collection rates.
4. Again in
cattle superovulation protocols GnRH may be used in cattle, where the last heat
date is unknown, to begin the FSH injection concurrent with the beginning of a
new follicular cycle. This is done in
concurrently with the application of a CIDR device to prevent ovulation until
superovulation is completed.
5. GnRH injectable
can be used for the induction of a LH surge and ovulation in cattle. It is usually used in cattle that have undergone
an estrus synchronization protocol.
6. In mares
when the dominant follicle is larger than 30mm a GnRH analog implant (Ovuplant
SQ implants) can be used to initiate an LH surge and ovulation.
All
available GnRH products are synthetic analogs of natural GnRH.
1) Injectable GnRH preparations include: Cystorelin, Factrel and Fertagyl. All three preparations contain Gonadorelin 50 mg/ml. A typical dose is 2ml or 100mg for cattle.
2) Sub-cutaneous GnRH implants are used in mares: Ovuplant. Contains 2.1mg Deslorelin
D) Prostaglandin F2 alpha
Natural
prostaglandin F2 alpha (PGF) is produced by the uterus lining and targets
luteal tissue in the corpus luteum (CL) on the ovary. Starting about 15 to 17 days after estrus, if
the animal is not pregnant, the uterus will start to increase production of
PGF. Increased PGF will cause lysis
(luteolysis), or destruction, of the CL. This results in a rapid decrease in progesterone. As a result, if, or as soon as, a mature
dominant follicle is present on one of the ovaries, the cow or mare will come
into heat and ovulation can occur. In
the case of a pregnant animal, the embryo will secrete a substance that
suppresses the release of PGF from the uterine lining. This is called maternal recognition of
pregnancy, and prevents the cow or mare from coming back into heat.
Pharmaceutical
prostaglandin F2 alpha and its synthetic analogs are 20 carbon cyclic fatty
acids that have the same action on the ovary as naturally released uterine
prostaglandins. If an intramuscular
injection of PGF or one of its analogs is given to a cow or mare with a mature
CL, it will cause regression of that CL, allowing the cow or mare to come into
heat. The available preparation of
prostaglandin include:
1) Dinoprost tromethamine, Lutalyse 5000 mcg/ml, 5 mg/ml, (5ml cattle, 2ml equine, 1 ml / 20 Kg canine) approved for use in cattle and horses.
2) Cloprostenol,
Estrumate 250 mcg/ml (2ml) for use in cattle
There is
one very important point to remember for anyone using PGF for estrus synchronization
or as a treatment for mis-mating; the early CL that forms after ovulation is
refractory to the effects of prostaglandin F2 alpha for a period of about 5
days post-estrus. During this refractory
state of the CL, an injection PGF will not induce luteolysis.
E) Gonadotropins
FSH and LH are the two natural gonadotropins
produced by the pituitary gland. These
are available commercially. In addition
two other gonadotropins of embryonic or fetal placenta origin are also
available. These are equine chorionic
gonadotropin (eCG has FSH and LH activity) and human chorionic gonadotropin
(hCG has LH activity). FSH and eCG are
used to stimulate follicular development while LH and hCG are used to induce
ovulation or treat cystic ovarian disease.
1) Porcine FSH: Folltropin-V, (Bioniche Canada Inc),
2) Porcine FSH: Pluset (Serono, Italy / Calier, Spain)
3) Ovine FSH: Ovagen (ICP Bio, ICP, Auckland, New Zealand)
4) hCG 10,000 IU: Chorulon, Follutein
5) PMSG + hCG: PG600, 400 IU eCG and 200 IU hCG
The
following gonadotropin preparations are not currently available in the United
States
6) Porcine LH: Lutropin-V, 25mg Armour standard (Bioniche Canada Inc)
7) PMSG: Equinex, Folligon, 5000 IU per 10ml vial
Common Reasons for female
hormone therapy:
The goal of estrus control is
usually to: allow breeding to occur when it is convenient, synchronize estrus
in a group of animals for AI or ET, induce a fertile estrus for breeding in
pre-pubertal heifers, induce a fertile estrus for breeding in prost-partum
cows, induce superovulation, induce estrus in superovulated animals, suppress
estrus behavior in female athletes, show animals, feedlot heifers and pets, and
also for birth control.
Initiation of estrus cyclicity
Frequently when estrus synchronization
for breeding is scheduled, some of the animals to be bred are not cycling. This is particularly true with 15-month old
heifers, post-partum cows and non-lactating mares early in the breeding season. Many protocols have been used on these animals
to initiate cyclicity. The most
effective protocols utilize progestogens to mimic diestrus. The progestogen will suppress LH release and
estrus. When the progestogen is removed,
there is a rebound effect on FSH and LH release, which will stimulate follicular
maturation and the animals are thus induced (some of the time) to come into an
ovulatory estrus.
Induction of puberty
Inducing puberty requires that the animals are sufficiently
old enough for natural puberty, have sufficient weight, uterine development,
gonadal maturity and follicular development. Also important is that the animals are on an adequate
plain of nutrition for maintenance and growth. Hormonal induction of puberty is most effective if the animals are at or
near puberty
Induction of postpartum
cyclicity
It is often desirable to
synchronize dairy cattle or beef cows that are lactating heavy and have not yet
resumed cycling. It is particularly
beneficial for beef cows that have calved late in a calving season. Shortening the interval from calving to
breeding will cause the cow to calve earlier the following year, with the rest
of the herd. If a cow is not cycling
special procedure must be used to synchronize estrus.
The requirements for successful
initiation of cyclicity in postpartum cows include many management
factors. First of all it is important
for cows to calve with a good body condition score. If the animal has adequate fat reserves at
the time of parturition she will be better equipped to cope with the stresses
of parturition and the negative energy balance and weight loss that occurs in
peak lactation. A cow should still be in
moderate body condition at estrus synchronization for breeding to be
successful. See: http://ohioline.osu.edu/l292/
for body condition scoring of beef cattle and: http://ianrpubs.unl.edu/dairy/g997.htm
for body condition scoring of dairy cattle).
Nutrition at the time of estrus
synchronization and breeding must be adequate for maintenance of body condition
and lactation. Adequate protein and
mineral supplementation are also essential. It is important for cows that are in peak lactation to receive an
adequate quantity of feed or have access to a high quality pasture so they are
able to maintain their weight and body condition, or only loose weight
slowly.
A sufficient postpartum interval,
usually 45 days, is recommended before estrus synchronization is
initiated. It is amazing though, how some
cows may breed back as early as 30 days postpartum.
Induction of estrus during
seasonal anestrus
Sheep, goats and deer are seasonal
breeders with the normal breeding season occurring in the fall. It is possible with these species to breed
out of the normal breeding season if progesterone based estrus synchronization
methods are utilized. In sheep there are
distinct economic benefits if lambs can be born in the late summer or fall so
that they can be ready for slaughter in the spring for the Easter market. This requires that the ewes be bred outside
of the normal fall breeding season. In
some breeds of sheep it is possible to achieve 2 lamb crops per year with top
management, excellent nutrition and hormonal induction of estrus in the spring
when ewes are still nursing their lambs.
Initiation of cyclicity in
Transitional mares
Mares that are not pregnant will
normally not start cycling until after the 1st of March in the
northern hemisphere. The time from
February 1st, until a mare ovulates and resumes cycling, is called
the transitional period. This is the
transition from winter anestrus to the normal cyclicity that occurs during the
spring and summer breeding season. With
the use of artificial lighting and progestogen therapy many mares will commence
normal cycling as early as January 1st.
Detection of silent heat or
breeding with no estrus detection
Sometimes it is necessary to
utilize an estrus synchronization program where estrus detection is not
required. This can be due to labor constraints
(inadequate manpower to properly heat check) or in individual animals estrus
may not be displayed due to psychological reasons. Utilizing progestogens to synchronize estrus,
in combination with estradiol or GnRH to synchronize follicular waves, estrus
and ovulation can be synchronized so tightly in cattle that it is not necessary
to check the cows for heat. Cows can
simply be bred at the prescribed time after completion of the hormonal therapy. This type of procedure is also effective in
other ruminants. Unfortunately it is not
yet practical to attempt synchronization of ovulation in mares.
Induction of estrus during
anestrus in monestrous animals
Monestrous animals are species
(canine) that only have a single estrus interspersed with long periods of
anestrus. Utilizing progestogen and
gonadotropin therapy, some success has been achieved in achieving estrus in
dogs that were in the anestrus state.
Some of the protocols used (in
general terms)
Progestogen therapy
(Syncro-Mate-B, MGA, Progesterone, etc.)
These modes of estrus
synchronization, cyclicity induction, estrus suppression and birth control are
uses in all species. Many of the
progestogen protocols include the use of other hormone drugs to achieve their
goal. With regards to estrus
synchronization and cyclicity induction, these methods tend to be the most
complex, but frequently they will result in higher estrus response rates and
tighter synchrony of the animals than natural methods or treatments based
primarily on prostaglandins.
A) Treatment
of heifers with Syncro-Mate-B implants. Norgestomet is a potent Progestogen.
1) Norgestomet
silastic implant containing 6mg norgestomet is implanted SQ on the back of the
ear,
2) 2ml
Norgestomet and Estradiol is injected at time of implant
3) The
estradiol induces a rapid decrease in FSH and LH, resulting in follicular
atresia, initiating a new follicular wave
4) Induction
of endometrial oxytocin receptors
5) PGF2 alpha
production
6) Regression
of CL, if present, due to estradiol inducing oxytocin receptors and PGF release
(not 100%)
7) FSH rebound
in 4 to 5 days initiates a new follicular wave
8) Endometrial
glandular development
9) Removal of
implant at 9 days
10) Estrus at 24
to 48 hours after implant removal
11) Low
fertility of first pubertal heats
12) Possibly
poor oocyte maturation
13) Pregnancy
rate about 50% with timed AI
14) Can be used
in sheep and goats, 1/2 of an implant (3mg)
B) Treatment
of heifers with Melengestrol acetate (MGA) + Lutalyse
1) MGA .5mg
per head per day, added to feed
2) Feed MGA
for 14 days
3) There may
be a transient decrease in FSH and LH release, but follicular atresia may not
occur. There is a rebound increase in LH
release
4) Follicular
recruitment and follicular waves may be prolonged and the dominant follicle
tends to persist for an extended period. The persistent dominant follicles oocyte is less likely to be
fertilized and develop normally, adversely affecting fertility if the animal is
bred at the 1st heat after MGA withdrawal
5) Endometrial
glandular development
6) Removal of
MGA from feed after 14 days
7) Estrus at 3
to 7 days after last MGA feeding
8) The heifers
are NOT bred on this heat due to oocyte age, poor oocyte quality and low
fertility of the MGA heat.
10) Poor
fertility if overcome by breeding on the second heat after MGA treatment
11) PGF2 alpha
is administered at 17 to 19 days after the last MGA feeding, Approx. 10 to 14
days after the MGA estrus
11) Pregnancy
rates are about 65% after breeding at the PGF2 alpha induced heat.
12) This program
works best with observation of heifers for heat and breeding each heifer 12 to
24 hours after she is observed in estrus.
C) Treatment
of cattle, sheep, goats and deer with progestogen impregnated sponges or
progesterone releasing intravaginal devices such as the CIDR-B device.
1) Natural or
synthetic progesterone impregnated sponge containing 30 to 60 mg progesterone
analog or the CIDR device containing 1.38 or 1.9 gram of natural progesterone
is placed in the vagina
2) Estradiol
capsule can be attached to the intravaginal device or an injection of estradiol
can be administered at the time of vaginal insert placement. GnRH can be used instead of estradiol. GnRH may also initiate a new follicular wave
by causing luteinization of a dominant follicle
3) Estradiol
causes a rapid decrease in FSH and LH, causing follicular atresia
4) Induction
of endometrial oxytocin receptors and PGF2 alpha production and CL regression
if estradiol is administered
5) FSH rebound
in 4 to 5 days initiates a new follicular wave
6) Endometrial
glandular development
7) Administration
of a prostaglandin 12 to 24 hours prior to vaginal insert removal (or at the
time of insert removal) assures regression of the corpus luteum
8) Removal of
device at 7 days if estrogen or GnRH is given at device insertion, (cattle)
9) Removal of
device at 8 days (cattle), 14 days (ewes), or 16 days (does) if only
progesterone is used
10) In sheep and
goats eCG (PMSG) or eCG / hCG (PG600) can be given to induce follicular
development and ovulation; this improves fertility and contributes to twinning
11) Bull, buck
or ram exposure may also increase fertility
12) Estrus
occurs at 36 to 72 hours after implant removal, depending on supplemental
treatments
13) Pregnancy
rate vary depending on species and season
D) Treatment
of mares with the oral progestogen Altrenogest (Regu-Mate)
1) Label
indication is suppression of estrus with a predictable occurrence of estrus
following drug withdrawal,
2) Used in
transitional mares (mares with good follicular activity - follicles of 25mm or
greater), mares with anovulation, prolonged estrus, or weak estrus
3) Can be used
to suppress estrus prior to scheduled breeding
4) If breeding
during January and February, mares should have been maintained under lights, usually
initiated in November
5) Treatment
continues for 15 days
6) Estrus
behavior will usually begin in 48 to 72 hours after the last dose of
progestogen
7) Pregnancy
rate vary depending on season, typically very good
GnRH therapy (Cystorelin,
Fertagyl, Factrel)
GnRH will cause ovulation or
luteinization of dominant or large follicles with LH receptors. It accomplishes this by causing the release
of LH from the anterior pituitary gland. GnRH is not used by itself to synchronize estrus, but rather it is used
as an adjunct to estrus synchronization. The two primary reasons for using GnRH in an estrus synchronization
program are to synchronize follicular development or induce ovulation.
When GnRH is used to synchronize
follicular development it is given 7 days prior to the time of progestogen
removal and/or prostaglandin injection. At this time GnRH causes ovulation or luteinization of large
follicles. This will causes a new group
of follicles to begin development (a new follicular wave) at approximately 2
days after GnRH injection. If large
follicles are not present or are atretic, small follicle will continue to grow
and be ready to ovulate at the scheduled heat. The goal is to have as many animals as possible with a new dominant
follicle that is ready to ovulate at the time of progestogen removal and/or
prostaglandin injection. In other words
GnRH is not used to synchronize estrus, but it is used to synchronize follicle
development, hopefully causing more synchronous ovulation.
GnRH can also be used to induce of
ovulation at the time a heifer, cow, or mare is in heat or due to be in heat,
further increasing the chance for synchronizing ovulation with
insemination.
There are
several prostaglandin/GnRH based estrus synchronization programs for cattle.
Select-Synch, Ov-Synch, Co-Synch, Modified
Co-Synch, and a few others
The basic protocol for these is:
1) Day 0
inject 100mcg (2ml) GnRH, inducing a LH surge and luteinization of the dominant
follicle(s) and atresia of the subordinate follicles. Progesterone levels rise.
2) A new
follicular wave is initiated in about 2 days
3) On day 7
inject prostaglandin; luteolysis of the original CL and the luteinized
follicles allow estrus to occur
4) There are
then 4 options
A. Breed 12 to
18 hours after observed heat, estrus usually occurs at about 48 hours after
prostaglandin injection (referred to as Select-Synch).
B. Inject a
second dose of GnRH 48 hours after the prostaglandin injection and breed 18
hours after the second GnRH injection, no heat detection required (referred to
as Ov-Synch).
C. Inject a
second dose of GnRH at 60 hours (timing varies by practitioner) after the
prostaglandin injection and breed at the same time as the second GnRH
injection, no heat detection required (referred to as Co-Synch). (Not recommended by A.R.T., as the pregnancy
rate is lower than the other protocols)
D. Breed cows
12 to 18 hours after observed heat, then at 60 hours after the prostaglandin
injection and inject all cows not observe in heat with GnRH and breed at the same
time (referred to as modified Co-Synch)
5) GnRH /
Prostaglandin synchronization methods do have the potential to initiate
postpartum cyclicity in cows if there is adequate follicular activity and a
dominant or large follicle.
6) GnRH /
Prostaglandin synchronization methods are not a good choice in peri-pubertal
heifers unless a progestogen is added to the protocol, such as using a CIDR-B
insert at the time of the first GnRH injection and pulling the CIDR at the time
of the prostaglandin injection (referred to as CIDR-Synch). Other methods that utilize progesterone
compounds and do not rely on GnRH to synchronize follicular waves, probably
work better in heifers.
Induction of ovulation in animals with a mature dominant
follicle is possible with GnRH.
1) In cattle
an injectable GnRH is effective in inducing a LH surge that should cause
ovulation if the GnRH is administered at the time of expected estrus. As long as progesterone levels are low
(baseline < 1 ng/ml), and a healthy dominant follicle is present, pregnancy
may be achievable even in animals that are not displaying estrus. GnRH should be given at the very start of
estrus for maximum effectiveness in animals displaying heat.
2) In mares
injectable GnRH has not been effective in inducing ovulation of large
(>=30mm) follicles. Therefore an
implant has been developed, Ovuplant
that releases GnRH continually over several days. The resulting increase in circulating LH
will cause ovulation in 86% of implanted mares within 48 hours. Ovuplant contains 2.1 mg of GnRH analog that
is released over 4 to 5 days.
All of
the above methods of estrus induction can be used to synchronize the heat
period of large numbers of animals for efficient artificial insemination.
Prostaglandin Therapy, Short Cycling and estrus synchronization
with prostaglandin F2 alpha
The normal estrus cycle in most farm animals is 18 to 21 days. By causing early CL regression with prostaglandin F2 alpha (PGF), the length of the estrus cycle can be shortened in mares, cows, ewes and does. There are a few important points to consider when using prostaglandin preparations: The CL of the mare and ruminants is refractory to PGF2 alpha treatment for about 5 days after ovulation. Animals that had a heat only 5 days ago will probably not respond. Also, since prostaglandins exert their effect on a mature and functional CL they are only effective in a cycling animal. Animals that are pre-pubertal, and those in post-partum anestrus or seasonal anestrus will not respond. Due to these factors the response rate to a single PGF injection will vary from 0% to 75% maximum. It is rare, except in a small group, to ever get a response rate that exceeds 75%. Prostaglandins are not very effective in swine since their CL is only responsive to PGF2 alpha very late in the estrus cycle when natural PGF2 alpha is released from the uterus anyway.
After administration of a prostaglandin preparation, CL regression is complete within 48 hours for a responsive CL. If a dominant (estrogen active) follicle, of ovulatory size, is present, the animal will exhibit estrus, typically within 48 to 72 hours after injection. Earlier estrus occurs if CL regression was already occurring, in spite of the PGF injection (0 to 36 hours). A longer interval to estrus will occur if there is not a dominant follicle present (84 hours to 9 days). If the CL was refractory to PGF treatment, estrus will occur at the normal interval for that animal (10 to 21 days after PGF injection).
Prostaglandin F2 alpha analogs are
used extensively as an inexpensive and effective method to synchronize estrus
for AI in cycling ruminants. Since
simple PGF injection protocols (utilizing only PGF) do nothing to synchronize
the follicular cycle, heat detection is usually done. Numerous protocols have been used in cattle including:
A) Single injection methods: The following methods will reduce material and semen costs but usually require labor for heat detection.
1) Inject a
single dose in all cattle, observe for estrus, and breed 12 hours after
standing heat is observed. This method
is used when minimization of materials and semen costs is necessary. All animals not bred by day 10 or 11
post-injection can be injected with a second dose of PGF and heat detection and
breeding can continue.
2) The best (my opinion) single injection method includes observing the cattle for estrus for 5 or 6 days prior to PGF injection. Breed all cattle at 12 hours after seen in heat. On day 6 or 7 inject PGF into all cattle not yet observed in heat. Continue to breed at 12 hours after observed heat. This protocol effectively deals with refractory CLs, since all animals that are to be injected with PGF would have had a heat over 6 days prior to injection. By 5 days post injection 100% of all cycling cattle should have had a heat. Timed AI at 75 to 80 hours post injection, of all animals not yet observed in heat, has been utilized with this protocol, but it is not recommended. Perhaps a few animals will become pregnant as a result of the timed AI, but many animals that have not responded by 80 hours may be anestrous or maybe just not yet in heat. A better way to deal with animals that have not responded is to treat them with a CIDR-B protocol.
3) If timed AI must be used for labor saving reasons, inject a single dose of PGF in all cattle, use timed AI at 75 to 80 hours post injection (no estrus detection). This method is used when semen cost is of no concern, minimization of labor is necessary and conception rate to the timed AI is not critical. Only expect about 65 to 70% of the animals to actually respond and exhibit estrus. Timing of the AI will be poor for many of the animals bred. Overall conception rates of 35 to 50% are expected. Clean-up bulls should be used to breed the balance of the cattle.
B) Double injection methods:
1) Inject first dose of prostaglandin. Expect about 65% to 70% of the animals to respond and exhibit estrus in 2 to 5 days. The animals are not bred at this time.
2) Inject a second dose of prostaglandin 11 days after the first dose. All animals that had a heat after the first dose should respond and exhibit estrus after the second dose. Animals that did not respond after the first dose due to refractory CLs (too soon after the previous estrus) should also respond to the second dose of prostaglandin and exhibit estrus. The only animals that will not respond to the second dose are anestrous. Heat detect after the second dose of PGF and breed 12 hours after standing heat is observed. Timed AI at 75 to 80 hours post injection (no estrus detection) can be employed if desired.
3) If desired, animals seen in heat after the first dose can be inseminated. Obviously these animals would be excluded from the second injection of prostaglandin.
C) Estrus synchronization using GnRH in combination with Prostaglandin, Ov-Synch, Select-Synch, etc. are discussed above.
D) In mares
PGF is used to induce a fertile heat but it will not synchronize ovulation due
to the long and variable length of estrus.
E) Prostaglandins
have some other uses:
1) Early
abortion of mis-mated farm animals. In
cattle and horses the PGF treatment should be delayed for 6 or 7 days to
account for the CLs refractory period. In swine treatment should be delayed for 14 post-ovulation. Usually a single luteolytic dose of PGF is all
that is required. Sometimes heifer
calves are treated at weaning time with PGF to assure that there are no
pregnancies in early maturing individuals.
2) Early
abortion of mis-mated bitches (although with much greater difficulty than in
farm animals). Requires twice a day
(BID) treatment for at least 4 days. There are many side effects.
3) Synchronization
of farrowing in swine
4) Treatment
of uterine infections associated with a functional CL
5) Treatment
of canine pyometra
Gonadotropin therapy
Although gonadotropins (FSH, LH,
eCG or hCG) are not used extensively in estrus synchronization, there are some
gonadotropin applications, related to estrus control, that are worth
mentioning.
PG600 from Intervet is a
commercial preparation of eCG (also called PMSG) in combination with hCG. PG600 is used in postpartum sows, pubertal gilts,
and anestrous sheep. The eCG part of
this product has very potent FSH activity and will stimulate follicular
development if given during diestrus or the proestrus parts of the estrus
cycle. Follicular development is also
stimulated by eCG during the transition from anestrus to proestrus in
non-cycling animals. The hCG part of
this product has LH activity and promotes final maturation of large graafian
follicles. Using this product may hasten
or stimulate an estrus.
PG600 is used in pre-pubertal and
pubertal gilts at 6 to 8 months of age to initiate an estrus. This will shorten the time to puberty in
later maturing gilts and can be used to synchronize gilts for AI. Response to treatment is usually over
65%. PG600 is given to sows at the time of
weaning pigs to induce estrus, reduce the number of anestrus sows post-weaning,
and shorten the time interval from weaning to first estrus. Most gilts and sows treated with PG600 will
be in heat within 4 days.
During progesterone-based
synchronization procedures in small ruminants PG600, given at the time of
progesterone removal and prostaglandin administration may induce twins or even
triplets, which is particularly desirable in sheep.
FSH and PMSG have been used in
embryo recipient cows at sub-superovulation dosage to induce 2 or 3 ovulations,
thus boosting progesterone levels and theoretically pregnancy rates. There has been some success using this
technique.
FSH or PMSG (not PG600) are used
for superovulation in cattle, sheep and goats. PMSG has a longer duration of action (half-life of about 2 days) than
FSH (half-life of 30 to 60 minutes). PMSG is effective with a single injection. FSH based superovulation requires several
injections, usually twice a day for up to 5 days.
Postpartum induction of estrus
using natural methods:
A) Nutrition;
Increasing the level of energy in the diet 30 to 45 days prior to expected
breeding will hasten the onset of estrus cyclicity at puberty and after
parturition. This is referred to as a
nutritional flush.
B) Weaning;
Weaning the offspring early will initiate estrus cyclicity in several
species. This is particularly valuable
in swine where weaning will initiate the first post-partum estrus within 5 to
10 days.
C) Exposure to
males; this is referred to as the "Ram Effect" in sheep. Exposure to males will increase the percent
of post-partum females that cycle early. This effect is also effective in early breeding of seasonally polyestrus
species and increasing the percent of females that respond to estrus
synchronization. Sterile teaser males
can be used in artificial insemination programs.
Inducing estrus during seasonal
anestrus using natural methods:
A) Mares and
Lights; by manipulating the hours of daylight using artificial lighting, mares
can be made to cycle earlier in the year than normal. The transition from anestrus to estrus in
mares typically occurs in February or March. In December and January, in the Northern Hemisphere, there are only
about 8 to 10 hours of daylight. The
long hours of darkness result in long periods of melatonin secretion that
suppress the hypothalamus and pituitary glands. By exposing mares (and stallions) to 14 to 16 hours of light, using
artificial light in the morning and evening, the onset of the breeding season can
be hastened by 30 or more days. It is
recommended that the lighting be increased incrementally by about 30 minutes
per week, but abrupt transition to 15 hours of light is also effective. Typically artificial lighting is initiated
around the first day of December in order to commence fertile estrus activity
in mid January.
B) Felines and
Lights; Felines such as the domestic cat, are spring breeders, and like mares,
will also respond to artificial lengthening of daytime. 12hr / 12hr light / dark stimulation, during
seasonal anestrus should be effective although 15 hours of light may be
better. If maintained under artificial
light queens will start to exhibit estrus within 2 to 6 weeks.
C) Small
ruminants and Dark; In fall breeding species such as sheep, goats and deer,
decreasing daylight hours and the resulting increase in melatonin secretion has
the opposite effect and stimulates hypothalamic GnRH secretion. I am not aware of the commercial application
of artificial shortening of exposure to daylight as a means of hastening the
breeding season or inducing out of season breeding. If year around breeding is desired, it may be
advisable to maintain a constant 12hr/12hr light / dark cycle in conjunction
with hormonal therapy. Instead of
relying exclusively on photo period control, typically progestogens are used in
fall breeding species to induce out of season breeding.
Suppression of estrus cycles,
Contraception and Population control
A) Ovariectomy and Ovario-hysterectomy
B) Birth control: Primarily progestogen
therapy in one form or another is used:
1) Megestrol (Ovaban) in dogs, 5mg and 20
mg tablets.
a. Proestrus regimen is begun as soon as
blood spotting is noticed. Administer 1
mg/pound BW daily for 8 days. Will stop
follicular development, prevent ovulation and prevent functional CL
development. Suppresses the
hypothalamic-pituitary axis, via negative steroidal hormone feedback on the
hypothalamus, preventing FSH and LH release by the pituitary gland.
b. Treatment with low dose Megestrol during
anestrus will prevent the onset of estrus. Daily treatment with .25 mg/pound BW for 32 days is effective. Once again, moderate elevation in this
progestogens blood level will suppress FSH and LH release from the pituitary
and prevent or delay the onset of proestrus and estrus.
c. Bitches will return to estrus in 4 to 6 months after either treatment regimen. The nearly normal anestrus period length after megestrol therapy indicates that therapy will mimic diestrus.
2) Megestrol (Ovaban) in cats:
a. Like canines a proestrus regimen is begun as soon as sexual behavior is noticed. Daily treatment with 1 mg/pound BW (.5mg is effective for most queens) for 3 days will stop follicular development, prevent sexual behavior, and prevent mating. Since queens are induced ovulators it is wise to isolate the queen from the tom in case therapy is started too late.
b. Treatment with low dose Megestrol
during anestrus will prevent the onset of estrus. Once weekly treatment with 2.5 to 5 mg is
effective. Treatment should be limited
to 10 weeks maximum.
c. Return to estrus is quite variable and
depends on the time of year, due to the seasonality of the feline reproductive
cycle.
3) Repository Progesterone (Reprogest) injections can be used in the feline instead of Ovaban. Use a dose of 3mg/lb on a weekly basis as needed to prevent estrus. Other injectable and oral progestogens are available and can be used if an effective dosage regimen is available. Progesterone, like all gonadal steroid hormones, will suppresses the hypothalamic-pituitary axis, via negative steroidal hormone feedback on the hypothalamus, preventing FSH and LH release by the pituitary gland. As a rule of thumb, therapy with any progestogens should never be extended beyond 10 weeks or approximately the length of gestation in any species.
4) Norgestimate and estradiol and other
progestogen / estrogen combinations are used in humans. The result of therapy is similar to megestrol
in preventing follicular development and ovulation by suppressing the
hypothalamic-pituitary axis. The cycle
of progestogen / estrogen allows normal menstrual cycles to occur.
5) Altrenogest (Regu-Mate) therapy in
Mares
6) MGA treatment of heifers or ewe lambs in the feedlot
Treatment can be extended throughout the entire feeding period. Results in increased feed consumption, increased rate of weight gain and reduced injury due elimination or decrease in sexual activity.
C. Anti-progesterone therapy: RU486 is a progesterone receptor antagonist (mimics progesterone by binding to receptors but has no biological activity). Prevents attachment and implantation due to decreased progesterone effects in the uterus.
Induction of ovulation
A) hCG and LH therapy
1) Direct
action on the LH receptors in the follicular thecal cells and granulosa cells
2) Only
mature, dominant follicles will respond by ovulating
3) If
administered prior to a new follicle achieving dominance, it will cause atresia
of the growing follicles
4) A
regressing dominant follicle may luteinize without ovulation if atresia is not
advanced
5) A growing
dominant follicle that is not mature (no LH receptors on granulosa cells, may
partially luteinize without ovulation
B) GnRH therapy
1) Binds to
GnRH receptors on gonadotrope cells (cells that secrete the gonadotropin LH
& FSH) in the anterior pituitary gland
2) Strong
stimulation of LH Secretion and LH production
3) Non-pulsatile,
prolonged LH release (over 1-2 hours) causes an elevation in circulating LH
levels that resembles the normal LH surge
4) GnRH should
always be administered as a single injection. Even a single injection causes gonadotrope depletion. Repeated injections are not effective.
5) The
resulting LH level may cause ovulation if a mature dominant follicle(s) is
present.
C) Estrogen therapy
1) If used
alone, an estrogen injection to induce estrus and ovulation is an antiquated
mode of therapy.
2) Is
occasionally effective due to late follicular phase positive feedback of
estrogen on GnRH secretion (LH surge). If a mature follicle is present it may induce a fertile estrus and
ovulation.
3) Also
effective in inducing signs of heat
4) Proper
timing of therapy is difficult without constant ultrasound monitoring of
follicular growth or without synchronizing the follicular wave cycle. Should be used as an adjunct to follicular
wave and estrus synchronization with GnRH/PGF or Progestogen therapy such as
Syncro-Mate-B.
5) Estrogen
should be given just prior to expected estrus to induce an LH surge and
ovulation.
Induction of superovulation
Brute force methods,
circumventing the negative feedback of estrogen and inhibin on gonadotropin
secretion by direct administration of gonadotropins
A) FSH
1) Administered
for 3 to 5 days using twice a day injections (BID) starting during mid diestrus
day 9 to 11 post-estrus. It is best to
start injections at the initiation of a new follicular wave.
2) Prostaglandins
are administered with the FSH on the 3rd or 4th day of therapy to induce
estrus. Progestogen therapy can also be
used to induce or synchronize estrus during FSH treatment.
3) FSH
preparations are partially purified extracts of pituitary glands
4) Most FSH
preparations are contaminated with LH
5) FSH:LH
ratio appears to be important in superovulation success
a. Too much LH
will lower embryo recovery and / or lower embryo quality
b. FSH:LH
ratios of 5:1 to 10:1 appear to be effective in most British and Continental
breeds of cattle. FSH-P (Schering),
FSH-P (Sioux Biochemical)
c. Preparations
with very high FSH:LH ratios, i.e. >= 100:1, are available, Folltropin
(Vetrepharm, Canada), Ovagen (ICP, New Zealand), Super Ov (AUSA)
d. Very high
FSH:LH ratios may lower overall embryo yield but will increase embryo quality.
e. Some LH is
required for follicular and oocyte maturation but it probably does not need to
be supplied with the FSH injections
f. Too high
of a LH content will cause pre-mature luteinization of follicles, which may
lower oocyte quality and fertility.
g. Too high of
a LH content may also cause premature rise in progesterone which may prevent
the normal estrus LH surge or cause a premature LH surge.
h. NOTE: it
appears that some cattle will only respond to FSH preparations with higher LH
content.
6) Usual dose
in cattle is 25 to 50 mg of FSH Armour Units, (1AU = ~1mg) or 200 to 400 mg of
NIH FSH P1 (Folltropin) divided into 8 injections administered BID for 4
days. Start cattle on day 9 to 11
post-estrus.
7) Usual dose
in sheep and goats is 15 to 25 mg of FSH Armour Units divided into 6 to 8
injections administered BID for 3 to 4 days. Start sheep on day 11 to 13 and goats on day 13 to 15 post-estrus.
8) Variability
in response is the rule with FSH superovulation. There is significant variability between
breeds, between animals, and even between consecutive superovulation procedures
performed on an individual animal.
d. Breeds and
individuals that are prone to twinning tend to yield more embryos
B) Human Menopausal Gonadotropin
(Pergonal, Serono)
1) FSH and LH
purified from the urine of menopausal women.
2) FSH:LH
ratio of 1:1
3) Can be used
in livestock but tends to be expensive.
4) Pergovet
(Serono) is available in Europe for superovulation of livestock.
5) FSH-P is
probably more appropriate for most animals
6) Can be
tried in animals that have not responded to higher FSH:LH ratio products.
7) Can be
tried in animals that have been superovulated numerous times and a suspected
immunity to porcine FSH is preventing a good response to FSH-P
C) ECG (PMSG) in conjunction with
anti-PMSG antibody
1) Administered as a single injection on
day 9 to 11 days post estrus
2) Prostaglandins are administered 48
hours after PMSG injection
3) Anti-PMSG antibody is given with the
PGF injection
4) Progestogen therapy can also be used to
induce or synchronize estrus
5) PMSG has a high LH activity
Subtle methods of superovulation
are used to overcome the negative feedback of estrogen and inhibin on
gonadotropin (FSH) secretion
D) Anti-estrogen antibodies, Fecundin, is
used to induce twins or triplets in ewes
E) Anti-Inhibin antibodies are in
development
F) Anti-estrogen
therapy, using clomiphene citrate, has been tried in livestock with moderate
success. Can result in superovulation in
women.
1) Clomiphene citrate is the most commonly used anti-estrogen drug.
2) Used
primarily in humans as a fertility drug
3) Clomiphene
has affinity for estrogen receptors in the hypothalamus, anterior pituitary and
elsewhere, but very weak estrogen activity.
4) Inactivation
of estrogen receptors in the hypothalamus via competitive binding results in a
marked decrease in estrogen activity, releasing GnRH secreting neurons and the
anterior pituitary gonadotropes from the negative feedback action of estrogen.
5) Removal of
negative estrogen feedback on the hypothalamus results in an increase of
pulsatile GnRH secretion and a resulting increase in production and secretion
of LH and FSH. Does not remove the
negative influence of inhibin on FSH secretion from the pituitary. FSH increase is usually moderate.
6) Removal of
negative estrogen feedback on the pituitary results in an increase in secretion
of FSH, which is the main desirable effect.
7) Clomiphene
is administered for 5 days during the follicular stage of the cycle to
stimulate follicular development. hCG
may be administered after cessation of clomiphene to induce ovulation.
8) Follicle
development is followed with ultrasound to assess development and coordinate
the timing of clomiphene withdrawal and hCG administration.
9) Can produce
ovarian over-stimulation or superovulation.
Induction of abortion
A) Prostaglandins
are used during the first trimester in cattle sheep, horses and dogs
B) Various
combinations of estradiol, corticosteroids, oxytocin and prostaglandins are
used during late pregnancy.
Induction of parturition
Estradiol, prostaglandin, oxytocin
and dexamethasone are all hormones that are used to induce parturition at or
near term in domestic animals. It is
best if current methods are referred to for the specific species to be
induced. Methods vary tremendously
between species.
Induction of lactation
Chronic administration of
progesterone and estrogen over a 2-week period is effective (sometimes) in
cattle. The hormones can be given as
injections or as implants.
Treatment of pathologic
conditions
A) Cystic ovaries in cattle
1) LH
deficiency is usually a post-partum problem at the time of re-initiation of
cyclicity.
2) A dominant
follicle matures, but absence of a normal LH surge prevents ovulation
a. Complete
lack of a LH surge results in a follicular cyst, which may be estrogen active
and cause nymphomania
b. A deficient
LH surge may result in partial luteinization of a pre-ovulatory follicle and a
luteal cyst may form. A normal cycle may
follow if the luteal cyst is capable of responding to uterine PGF release.
c. Cystic CLs
are normal CLs with a cystic cavity. They can form from an ovulated follicle or an un-ovulated follicle. Cystic CLs respond to uterine PGF release and
normal cyclicity occurs.
3) Continued
FSH stimulation may cause the follicle to continue to grow
4) Cysts are
not necessarily static, cysts may regress and new cysts develop.
5) Multiple
cysts are common
6) Genetic
predisposition
7) Nutritional
(energy) deficiency may predispose to this condition, i.e. a lactational
catabolic state.
8) Therapy for
follicular cysts:
a. hCG or LH,
direct effect upon the cystic follicle, causing luteinization of the cyst
b. GnRH
injection inducing an endogenous LH surge like release of LH from the anterior
pituitary, causing luteinization of the cyst
c. Manual
rupture of the cyst is possible with a thin walled follicular cyst, this is not
recommended as it may cause hemorrhage, scarring, and does not cause
luteinization of the cyst.
d. Luteal
cysts and cystic CLs by definition are already luteinized and should respond to
prostaglandin therapy. If in doubt about
the degree of luteinization of a cyst, it is best to first administer GnRH or
hCG, and then follow that with prostaglandin 6 or 7 days later, to induce
estrus.
B) Male
Hormone Therapy; There are few indications for hormone therapy in the male.
1) Administration
of GnRH to newborn males with cryptorchidism
a. Testicular
descent is influenced by testosterone
b. GnRH will
increase testosterone production in a newborn calf at a time when testosterone
production is decreasing.
c. The
continued testosterone stimulation may cause final descent of the retained
testicle.
d. Only
occasionally effective but worth trying.
2) Testosterone
injections to increase libido (Don't use
this therapy)
a. Effective
in increasing libido if animal is truly deficient in testosterone.
b. Decreased
libido is frequently associated with injury or chronic pain.
c. Testosterone
injections will inhibit gonadotropin secretion and result in decreased
spermatogenesis.
3) FSH or PMSG
for treatment of oligospermia or azoospermia (decreased numbers or complete
lack of sperm cells in the ejaculate)
a. May be effective if the cause of decreased spermatogenesis is truly a deficiency in hypothalamic or pituitary function. Usually oligospermia or azoospermia have predisposing causes such as genital or gonadal infection, injury, endocrine pathology or a genetic basis.
b. Treatment
must be continued for longer than the full length of the spermatogenesis cycle,
or at least 60 days to 90 days before evaluation of therapy can be made.
c. Weekly injections
of PMSG are typically used. FSH must be
injected daily.
Non-Reproductive Hormone
Therapy
A) Growth
promotants, used in feeder cattle.
B) Anabolic
steroids in debilitation of all species
C) Antineoplastic
therapy
1) Treatment
of breast cancer and other estrogen responsive neoplasia (human)
a. Selective
antiestrogen or selective estrogen receptor modulator drugs such as Tamoxifen
can allow remission of breast cancers that are stimulated by estrogen. Tamoxifen is a non-steroidal estrogen receptor-binding
agents that block estrogen from binding and activating the receptor in mammary
gland cells. (Although non-steroidal the
molecule resembles the estrogen molecule).
b. These drugs
are primarily used as adjuncts to surgery or chemotherapy to prevent metastasis
or recurrence.
c. Obviously
cannot be used in breeding animals or pregnant animals.
d. Not
approved for animal use.
2) Treatment
of benign prostatic hyperplasia and prostatic neoplasia
a. Castration
is therapy of choice, not desirable in some animals or humans
b. Estrogen
therapy is sometimes effective but results in decreased spermatogenesis and has
other side effects such as prostatic metaplasia and further enlargement of the
prostate
c. Anti-androgen
drugs would be an ideal treatment but are only experimental at this time. (Flutamide is an anti-androgen drug that
competitively inhibits testosterone activity.
d. GnRH agonists can be used to down
regulate or paralyze the pituitary gonadotrope cells and inhibit LH
secretion. Without adequate LH the
testicles will stop testosterone production, which allows hormone responsive
prostatic hyperplasia and/or cancer to undergo remission. Lupron is a brand name for leuprolide, which
is a potent GnRH agonist, available for use in men. Lupron is available as a depot injection.
