Synchronization of Estrus in Cattle : A Review

Numbers of estrus synchronization programmes are available in cattle based on the use of various hormones like progesterone, prostaglandin F2a and their various combinations with other hormones like estrogen and Gonadotrophin Releasing hormone (GnRH). Selection of appropriate estrus synchronization protocol should be made on the basis of management capabilities and expectations of the farmer. Synchronization of oestrus can be accomplished with the injection of prostaglandin F2a alone, but it needs proper detection of the ovarian status of the cows as prostaglandin F2a is active in only functional corpus luteum in between 8 to 17 days of estrous cycle. Progesterone may reduce fertility up to 14 percent, but short time progesterone exposure (less than 14 days) is beneficial. Addition of GnRH in the Progesterone or Prostaglandin based synchronization programme is helpful for more synchrony in estrus as GnRH may be helpful to synchronize the oestrous cycle in delayed pubertal heifers and post partum cows (Post partum anoestrum) and further a single, timed artificial insemination is possible with this method. New methods of synchronizing estrus in which the GnRH-PG protocol is preceded by progesterone treatment offer effective synchronization of estrus with high


Introduction
breeding of the animals is possible with this technique.Estrus synchronization provides more economic Synchronization of estrus implies the returns by improving the production efficiency in manipulation of the estrous cycle or induction of estrus animals.to bring a large percentage of a group of females into Instead of females being bred over a 21-day estrus at a short, predetermined time (Odde, 1990).period, synchronization can shorten the breeding Synchronization of estrus is one of the advanced period to less than five days, depending on the managemental process through which the humane treatment regimen.Scientific management of cows errors and managemental costs could be minimized.It and calves is possible within the limited resources due is particularly beneficial in Sheep, where timely heat to the friendly environment.Production of uniform detection is difficult due to exhibitions of less external calf crop for the future replacement in the farm is heat symptoms and also in large cattle herd.Several another important advantage of this programme.In authors described the experiments that have been migratory herd of cattle maintained by nomads, conducted since the discovery of ovarian steroids and synchronization of oestrus may improve the which have lead to the effective control of the length of production potential by inseminating the animals with the bovine estrous cycle and the timing of estrus and superior germ plasm within a predefined short period ovulation (Hansel and Schechter, 1972; Hansel and at low altitudes before or after the animals reared in Beal 1979; Patterson et al., 1989;Odde, 1990; Larson summer grazing at alpine pastures available on the and Ball, 1992).Synchronization of estrus helps in great Himalaya.fixing the breeding time within a short predefined The current and future direction of estrous period and thereby scheduling the parturition time at synchronization is to focus on combining traditional the most favourable season, when the newborns can be methods of controlling cycle length with the reared in suitable environment with ample food for manipulation of follicular development.The immediate goal of controlling both CL function and enhancing their survivability.Fertility in farm animals follicular development is to devise a treatment that may be expected towards higher side as timely will synchronize estrus more precisely and to control 62% for untreated cows has been reported when cows were bred 12 h after estrus (Moody and Lauderdale, the time of ovulation more exactly to allow a single, timed insemination without the need for detection of 1977).Synchrony of estrus and fertility with these behavioral estrus.Combination of (GnRH) with the products is good with cyclic females, such as virgin Prostaglandin F2a (Prusley et al., 1994; Prusley et al., heifers, but can not induce estrous cycles in non-1995 a, b) and Progesterone (Patterson et al., 1999) cycling cows.based synchronization programme has shown a new (a) One Shot Prostaglandin : A single injection of direction in the estrus synchronization of cattle with prostaglandin is given to cyclic females, and then the manipulation of follicular development.these females are bred as they express estrus.The Knowledge on the hormonal profile and functional disadvantage of this program is that one-third of the structures present in the ovaries at various stages of females do not respond to the injection.The estrous cycle is very much important for the selection programme may be modified first with the detection of and successful implementation of the estrus estrus in the cows of the herd for 5 days and synchronization programme.
inseminated the cows showing estrus and only rest of the cows are given a single injection of Prostaglandin.

Basic approach for estrus synchronization
This represents the greatest savings in cost and labor Basic approach is to control the timing of the associated with treatments because only one injection onset of estrus by controlling the length of the estrous is given and not all the cows need it.cycle.The various approaches for controlling cycle (b) Two Shot Prostaglandin : Two injections of length are: prostaglandins are given at an interval of 10 to 14 days 1.
Administration of Prostaglandin to regress the (Wiltbank et al., 1967;Inskeep, 1973;Cooper, 1974) corpus luteum (CL) of the animal before the time of once stage of estrous cycle in the cows is unknown.natural luteolysis, or Crossbred and non descript cows in India were treated 2.
Administration of Progesterone or more with two injections of Lutalyse (Dinoprost commonly synthetic progestins to temporarily suppress thromithamine) 25 mg intramuscularly at 11 days the ovarian activity, or apart and reported 80.00 percent estrus rate in non 3.
A newer way of creating estrous synchrony is by descript and 100% in crossbred cows (Sahatpure and using gonadotropin-releasing hormone (GnRH) or an Patil, 2008).analogue, which causes ovulation of a large follicle.
Two injections of prostaglandin are given 10 to This help in synchronizing estrous cycle in anoestrous 12 days apart.Detection of estrus is not required female.
before or between injections.All cycling cows should respond to the second injection regardless of what

Methods of Estrus Synchronization
stage of the estrous cycle they were in when the first 1.Prostaglandin treatment injection was administered.The programme may be One of the oldest ways to synchronize estrus is modified with the breeding of all females exhibiting by using a luteolytic agent such as Prostaglandin F2a, estrus subsequent to the first PGF2a injection.Then or an analogue, which causes the regression of the the second injection is given only to the females that corpus luteum (Lauderdale, 1972;Louis et al., 1972; were not bred.This option lowers expense and Rowson et al., 1972;King and Robertson, 1974; handling, but results in two synchronized groups Roche, 1977).Prostaglandin F2a is only effective if instead of one and a longer breeding period.administered between days 8 to 17 of the estrous cycle 2. Progesterone treatment when functional corpus luteum is available in one of Synchronization of estrus with progestogens the ovaries.King et al. (1982) and others (Tanabe and (Nellore and Cole, 1956) maintains high levels of Hahn, 1984; Stevenson et al., 1984; Watts and Fuquay, progesterone in the female's system, even after the 1985) demonstrated that cattle injected with PGF2a regression of the corpus luteum.Synchrony of estrus between Days 5 and 9 of the cycle were less responsive occurs 2 to 5 days following progestin removal.than those injected later in the cycle.Fertility is high Commercial products that fall into this category are following prostaglandin synchronization.Most melengesterol acetate (oral feeding), Syncro-Mate-B studies indicate that conception rates are similar for (Ear Implant) and CIDR (Intra-vaginal device).Estrus beef cows or heifers synchronized with PGF2a and was synchronized in only 48% of the cows treated on d 3, but the synchronization was 100% when treatment those bred after a naturally-occurring heat.A conception rate of 59% for synchronized cows and began on d 9 of the estrous cycle (Pratt et al., 1991).In

Techniques of Progesterone treatment
general, the longer the progestin was administered to (a) Melengesterol Acetate (MGA) feeding :

cattle, the higher rate of estrous synchronization, but
Option I: MGA is added to feed such that females the lower the fertility of the synchronized animals.receive 0.5 mg per head per day for 14 days.Upon Simultaneously, Kaltenbach et al. (1964) and others removal of MGA from the feed, cyclic females begin (Loy et al., 1960;Wiltbank, 1966) demonstrated that to show estrus.This estrus is subfertile, and it is not estradiol was luteolytic when administered early in the recommended to breed.Females should be bred on the bovine estrous cycle.Hence, combining progestin second estrus following MGA removal.The treatment with the administration of estradiol at the administration of MGA at the recommended daily rate initiation of treatment enabled the period of progestin of 0.5 mg prevents the expression of behavioural treatment to be shortened (9-14 d)  was fed for 14 d and PGF2a was administered 16 to 18 marketed in Europe, Australia and New Zealand.The d after the last day of MGA feeding.This system was treatment of cyclic cows or heifers with exogenous designed to place cattle in the late luteal phase of the progestin preceded by an injection of estradiol is estrous cycle at the time of PGF2a administration.This usually followed by a high incidence (> 90%) of estrus system initially synchronizes estrus within the 7 d during the 5 days following progestin removal.
following the last MGA feeding (Patterson et al., 1989; Several workers successfully used ultrasono-Odde, 1990, King and Odde 1993).The administration graphy to demonstrate that progestin administration at of PGF2a 17 d after the last MGA feeding causes the "sub-luteal" levels inhibits estrus and ovulation and timing of PGF2a to occur after Day 10 of the estrous synchronizes estrus in cattle, but that a persistent, cycle in the majority of cattle and thus the estrous estrogen-secreting follicle develops when progestin response and fertility of cattle are expected to be treatment extends the estrous cycle (Lucy et al., 1990; maximized as PGF2a is more effective during the late Sirous and Fortune, 1990; Cupp et al., 1992).luteal phase (d 10 to 15) than during the early luteal Development of the persistent follicle is caused by phase (King et al., 1982;Tanabe and Hann, 1984; increased pulsatile secretion of gonadotropins during Watts and Fuquay, 1985).The rate of synchronization the period when the exogenous progestin is inhibiting of estrus following MGA-PGF2a is usually greater estrus, but the corpus luteum has regressed (Kojima et  silicon and progesterone mixture (10% w/w) around a Roche, 1976).In addition, short-term exposure to nylon spine under high temperature.The CIDR progestogens causes some anestrus (postpartum or pre contains 1.38 g progesterone and is designed to pubertal) cattle to begin cycling.However, for these maintain elevated blood concentrations of short-term progestogen systems to be effective in progesterone to at least 2 ng/ml for up to 10 days.synchronizing estrus, a luteolytic agent must be Being relatively thin, the CIDR is easily inserted into incorporated.
the vagina and has good retention capacity (2.5% loss following GnRH administration, however, ovulation rate is normal).A flexible nylon tail is attached to the of dominant follicles in the static or regressing phases device to allow for easy removal.The CIDR Cattle occurred 33% and 0% of the time, respectively.Insert provides an exogenous source of the hormone Pursley et al. (1995a) reported that the range in timing progesterone during the 7-day administration period. of ovulation in lactating dairy cows following GnRH-Removal of the CIDR Cattle Insert on treatment day 7 PGF2a treatment extended from 84 to 120 h postresults in a rapid fall in plasma progesterone levels, PGF2a.They demonstrated that the range in ovulation which results in synchronization of estrus in those time in cows could be reduced to 8 h (72 to 80 h postanimals responding to treatment. PGF2a) if a second GnRH injection was administered

CIDR and ProstaglandinF2a
48 h after PGF2a in the GnRH-PGF2a treatment The CIDR is inserted into the vagina of the (Ovsynch protocol).The four systems for synchrofemale for 7 days.An injection of PGF is to be given 1 nization of estrus with GnRH-PG combinations are day before the CIDR is removed.Females are OVSYNCH, COSYNCH, SELECT SYNCH and inseminated based upon detection of estrus during the HYBRID SYNCH. 3 to 6 day period after CIDR withdrawal.This system The initial GnRH injection (day 1; GnRH) is should effectively synchronize estrus in a large used to program follicle growth in cyclic females and proportion of cyclic females since treatment for 7 days to induce ovulation (to provide progestin prewith the CIDR prevents animals from being in the exposure) in anestrous females.The PGF2a (PGF; day 8) induces regression of CL that are present to cause a early stage of the cycle and not responsive to PGF2a decline in progesterone.The second GnRH given on induced regression of the CL.Some anestrous females day 10-11 induces ovulation of dominant follicles that will be induced to ovulate and show heat during the synchronization period.The advantage of CIDR plus have been pre-programmed by the first GnRH PGF treatment than the single PGF injection was that treatment.The major GnRH programs that do not involve use of the CIDR are described first in the CIDR plus PGF could increase the synchronization following section.rate by approximately 30%, and pregnancy rate by

GnRH -Based Synchronization Systems
for the GnRH -PGF system is "Select Synch".Synchrony of estrus and fertility with a Select-Synch combination of GnRH and Prostaglandin F2a are good Single dose of GnRH and Prostagalndin were for cyclic females and this combination may induce injected on day 1 and day 8, respectively.Some cows cyclicity in cows experiencing postpartum anoestrus (8%) exhibit estrus up to 48 hours before PGF (d 6).
The "early" heats are fertile and cows can be (Prusley et al., 1994; Prusley et al., 1995 a,b).This inseminated 12 hours after detection.The peak estrous most recently developed synchronization treatments combine traditional methods of controlling cycle response occurs 2-3 days after PGF with a range of length with the manipulation of follicular days 1 -5.With this system, a minimum of 5 days of development in order to "program" or "select" the estrus detection after PGF and 2 days preceding PGF is required to detect most heats.ovulatory follicle.The new methods synchronize (b) GnRH -PGF + GnRH System: This system is a estrus more precisely and control the time of ovulation GnRH -PGF system that includes a second GnRH more exactly in order to allow a single, timed injection (+GnRH) given to all, or some cows between insemination without the need for detection of 48 and 72 hours after PGF (day 2 to 3), with timed AI behavioral estrus.on all or a portion of the herd.Several variations of this Administration of GnRH during the bovine system are being used.

estrous cycle causes regression or ovulation of the Ovsynch dominant follicle and initiates the emergence of a new
The Ovsynch program is comprised of an wave of follicular growth an average of 2.  Twagiramungu et al., 1994).Ovulation of a pregnancy rates varied when cows were timed growing dominant follicle occurred 100% of the time inseminated at 0, 8, 16, 24 or 32 h after the second and given a second injection of GnRH.This program injection of GnRH in the Ovsynch program and the has a lower cost and less handling compared with highest pregnancy rate (45%) was achieved when Ovsynch and CO-Synch but more than Select-Synch.insemination was done 16 h after the second GnRH The primary advantage is that Hybrid-Synch appears injection.The first GnRH injection alters follicular to have the highest conception rates among all GnRHgrowth by inducing ovulation of the largest follicle prostaglandin programs.(dominant follicle) in the ovaries after the GnRH MGA-GnRH-PG protocol: MGA is administered to injection to form a new or additional CL (Pursley et al., the cows orally for 14 days.Ten days after the 1995).Thus, estrus usually does not occur until a withdrawal of MGA an injection of GnRH is given.PGF2a injection regresses the natural CL and the Seven days after the GnRH injection an injection of secondary CL (formed from the follicle induced to PGF2a is given.a CIDR to GnRH -based programs has the potential to after a second injection of GnRH.The GnRH reduce losses in each of these areas.The most common injections release pituitary luteinizing hormone (LH), use of the CIDR with GnRH -based systems involves the natural ovulation-inducing hormone of the estrous insertion of the CIDR on day 1, and withdrawal of the cycle.The stage of the estrous cycle when ovsynch CIDR on day 8.An injection of GnRH is given on day was initiated also affect synchronization and of CIDR insertion.The CIDR is kept in situ for seven conception rate (Vascon-celos et al., 1999).Higher days.On the day of CIDR withdrawal, an injection of conception rate was reported in subestrus buffaloes prostaglandin is given.The second GnRH injection is initiating the treatment with Ovsynch during the later given after two days of prostaglandin injection.stages of estrous cycle, but conception rate was 0 in The primary benefit of inclusion of the CIDR in anestrus buffaloes though incidence of cyclicity was GnRH-based programs is that it guarantees that observed due to the treatment (Ravikumar and females will be exposed to progesterone during the Asokan, 2008).Moreira et al., (2000) reported that period between day 1 and day 8.This progesterone initiating the ovsynch protocol in dairy heifers on day exposure will result in normal (21 days) rather than 15 of the estrous cycle exhibited estrus before the short (10 days) cycles in previously anestrous cows.second GnRH injection, whereas, no estrus behaviour Furthermore, since the withdrawal of a progestin has was observed when the protocol was initiated on d 2, 5, been demonstrated to induce onset of cycles in some 10 (or) 18 of the estrous cycle.Advantages of this anestrous females, the likelihood of an ovulation program are tight synchronization of estrus, most (either spontaneous or in response to second GnRH females respond to the program and it encourages injection) is enhanced.A second benefit to inclusion estrus in non-cycling cows that are at least 30 days of the CIDR in GnRH-based programs is that the early postpartum.
heats (days 6 to day 9) that are inherent to these CO-Synch: The CO-Synch program is comprised of systems are prevented.The progesterone released by an injection of GnRH on day 1, an injection of prostathe CIDR, will prevent estrus and ovulation between glandin on day 8 and then a second injection of GnRH days 1 and 9.The females that show early heats in with breeding on day 10.The advantages are tight GnRH -based programs would have conception rates synchronization of estrus, most females respond to the of near 0% if timed AI is performed on day 10 or 11. program and it encourages estrus in non-cycling cows Managemental intervention that are at least 30 days postpartum.Hybrid-Synch: The Hybrid-Synch program is Management in general has tremendous role in implemented with an injection of GnRH on day 1, an reproduction of animals.Appropriate nutritional injection of prostaglandin on day 8 and then estrous management of the herd is essential for successful detection and breeding from day 8 to 11. Females not implementation of several synchronization programs observed in estrus from day 8 to 11 are bred on day 11 in both cows and heifers.Managemental procedures (a) GnRH-PGF System: This combination represents approximately 20%, in both the anestrous and cyclic the simplest GnRH -based system.A common name females (Lucy et al., 2001).
5 d injection of GnRH on day 1, an injection of following treatment (Pursley et al., 1995 a).Atresia or prostaglandin on day 8, a second injection of GnRH on ovulation of the dominant follicle depends on the day 10 and then timed insemination on day 11 (Pursley status (growing, static or regressing) of the dominant et al., 1994; Pursley et al.,1995; Pursley et follicle at the time of GnRH injection (Silcox et al., al.,1997a,b).Pursley et al. (1995b) indicated that 1993;

( c )
Addition of progesterone in the GnRH-PG :

b) Syncro-Mate-B (Ear Implant)
(Sanchez et al., 1993;Savio et al., 1993ah and (Butler, 1996)92;Savio et al., 1993;Custer et al., 1994).The et al., 1995).lowfertility of cows bred at the synchronized estrus Option III: Two injections of prostaglandin are following long-term administration of progestin is due given; one at the time of MGA removal from the feed to premature resumption of meiosis of ova or and another 15 days following removal.This further abnormal development of embryos derived from ova reduces time spent in estrous detection and breeding of persistent follicles (Wishart and Young, 1974; and provides more concentrated synchrony.Mihm et al., 1994;Ahmad et al., 1995;Revah and (Butler, 1996).The pregnancy rate of cows bred SMB treatment late in the estrous cycle (> d 14) following progestin treatment that caused a persistent, in cow gives lower conception rates.The optimum dominant follicle to ovulate was reduced by 17 to 35% time for SMB treatment to begin is between d 8 and d(Sanchez et al., 1993;Savio et al., 1993; Wehrmann et 12 of the estrous cycle to maximize estrus response.