OvSynch Protocol and its Modifications in the Reproduction Management of Dairy Cattle Herds - an Update.

Current knowledge about the function of the reproductive tract and appropriate use of hormonal drugs affords control of the oestrus cycle of cows. One of the hormonal protocols is OvSynch, which enables artificial insemination (AI) to be performed at the precise optimum time without control of the ovaries and uterus. Use of such protocols in reproductive management allows oestrus cycles to be synchronised and cows to be effectively inseminated without oestrous detection, which is time-consuming and difficult in farms with numerous cows. Therefore, OvSynch has become the first management tool for AI and is an alternative method to heat detection. Over the 20 years since its first implementation, OvSynch has been modified many times to improve its reproduction outcomes and widen its use. Besides its original use for heat synchronisation, it is also used in many ovarian disorders as a therapeutic method. This review article describes the possibilities which OvSynch provides, its current modifications, various applications, and the advantages and disadvantages of its use in practice.

Introduction

A traditional method for noticing cows in heat is by observation, which is a time-consuming procedure (28). Unfortunately, many factors shorten the duration of heat and also weaken the behavioural signs of the phenomenon. Increasing milk yield, imbalanced feed ration, stress including heat stress, and welfare provision are the main factors influencing heat expression (38, 63). Additionally, the worldwide tendency to increase the number of animals in herds is leading to management problems for workers. To improve heat detection additional tools such as tail painting or pedometers are used (28, 39). However, even these methods cannot guarantee that every cow in heat will be found and inseminated. Generally, in recent decades oestrous rate detection has decreased to 60% (25). Thus there is still a need to improve heat detection and insemination success rate. To make oestrous detection more efficient and less time-consuming for staff, hormonal protocols have been invented and implemented into reproductive management (46, 57). Implementation of such protocols simultaneously improves quality of life for the farmers and minimises the costs of artificial insemination (AI). These hormonal schemes allow heat and ovulation to be synchronised, and in combination with timed AI (TAI) they render heat detection unnecessary. As a new trend in bovine reproduction and different impetus for hormonal protocols, there is a tendency to inseminate as many cows as possible until the 100th day after parturition. Early introduction of protocols about 30–40 days postpartum facilitates this, since many can be inseminated as early as possible (30, 36). One such protocol is OvSynch, which is used for the whole herd and allows shortening the days until opening and the successful insemination of numerous cows until the 100th day postpartum; this maximises milk production and improves operational economy. However, it must be remembered that if this protocol is used for all cows without each animal having undergone previous gynaecological examination, some animals will not respond due to undetected reproductive disorders such as true anoestrus, ovarian cysts, and endometritis (40, 43) Thus, an individual approach to animals in the herd is also preferred, including preliminary examination of the cows and their assignment on this basis either for hormonal synchronisation or treatment, if necessary. This review presents the opportunities for synchronisation of the oestrus cycles and treatment regimens by the use of the OvSynch protocol, and considers its limitations for veterinary practitioners.

Basic goal of the OvSynch protocol

The follicles, during their growth up to the size of around 9 mm, become sensitive to luteinising hormone (LH) and as a consequence it is possible to accelerate their maturation by injecting exogenous hormones (32, 67). They can be used case-by-case, according to the results of the gynaecological examination, or in blanket application, assuming a similar developmental stage of follicles in all cows. OvSynch (Fig. 1) is an example of such an injection protocol, and it leads to the equalisation of follicle development on the ovaries, causes ovulation, and enables AI (46). This programme assumes that the first gonadotropin-releasing hormone (GnRH) injection induces the ovarian follicle to ovulate, which leads to development of the corpus luteum (CL). The efficiency of ovulation induction by the first GnRH injection varies from 66% to 85% (44, 58) and depends on the maturation stage of the follicles (8) at the time of treatment. Ultrasound detection of the first developing follicles of a new wave is possible two days after GnRH injection (56) and one of these follicles will be used for TAI at the end of the OvSynch protocol. On the seventh day of OvSynch, prostaglandin F2α (PGF2α) is injected both to induce luteolysis and to allow the continuing development of the dominant follicle of the next wave.

Fig. 1

Scheme of OvSynch protocol

In turn, this follicle will be estimated to ovulate by the second GnRH injection on day 9 of the protocol. Insemination should be performed blindly 16–24 hours later.

OvSynch gives the best results when used for the whole herd. This strategy allows all the cows designated for AI to be inseminated at a similar time postpartum, and the pregnancy rate in the herd to be improved (45, 46). However, it does not improve the reproductive performance of the herd when used only for selected, problematic cows. The advantages and disadvantages of the OvSynch protocol are summarised in Table 1. The main benefit of hormonal programmes such as OvSynch is the reduction of the number of undetected oestrous cows which could be potentially inseminated and made pregnant (45). The first insemination rate (FIR) in the OvSynch protocol reaches about 35%, confirming that it is a good alternative to heat detection (45, 48). A higher percentage of pregnancies (47.7%) obtained with the use of the OvSynch protocol was reported by Vasconcelos et al. (60). The pregnancy rate after OvSynch was better when TAI was performed 16 hours after the second GnRH injection (45%), and a 41% rate was returned when performed 8 or 24 h after GnRH (47).

Table 1

Benefits and drawbacks of OvSynch protocol

Advantages	Disadvantages
Application possible in all cows	Possibility of AI in cows with reproductive disorders
Reduction of need for heat detection and gynaecological examination	Highest efficiency limited to start of protocol between 5th and 9th days of cycle
Shortening intercalving and voluntary waiting periods	Increased embryonic mortality rate
Synchronisation of work in herd	Cost of hormones
Possible therapeutic/cure effects	Different responses to hormonal treatment
Fertility comparable to other methods	Poor fertility in heifers

Dirandeh (24) synchronised cows on the 30th day after parturition and increased the efficiency of AI. The OvSynch protocol began six days after detecting heat signs, i.e. when follicles were able to respond to GnRH injection. In this group of cows the ovulation rate and pregnancy rate on the 60th day after AI were 82.5% and 28.9% respectively. After the second GnRH injection in the control group, in which the programme began at any moment of the cycle, only 75.8% of cows ovulated and 23.2% of cows were pregnant on the 60th day after AI. This observation shows that the time of the beginning of the OvSynch protocol influences its effectiveness, and the highest pregnancy rate was achieved when a follicle from the first wave was used for TAI. In view of this, some authors suggest that gynaecological examination or presynchronisation (e.g. Pre-Synch) may improve the fertilisation rate after OvSynch (3, 34). However, generally the OvSynch protocol was invented to eliminate heat detection. Nevertheless, the cited results contested this assumption. The weaknesses of the protocol which make it less effective are failure of the first ovulation or lack of luteolysis. The lower ovulation rate in numerous animals (only 54% of ovulation) was described by Pursley et al. (46, 48), showing poorer reproductive results of OvSynch in heifers. Studies performed by other authors also confirmed poor efficiency of the OvSynch protocol in heifers (55, 64). Pursley et al. (46) compared the percentage of pregnant cows and heifers after using the hormonal programme for ovulation synchronisation. The pregnancy rates in the groups of heifers differed starkly, with 35.1% in the OvSynch group and 74.4% when using PGF2α in the control group. In contrast, the rates in cows were quite similar, 37.8% – in the OvSynch group vs 38.9% – in control group (48). These differences were caused by a lower ovulation rate after the first GnRH injection in heifers. This phenomenon was in line with the lower concentration of progesterone in the blood on the day of PGF2α injection in heifers than in cows. The concentration of this hormone in 86.2% of cows was typical for the luteal phase (>1ng/mL), whereas in the group of heifers only 59.5% of animals reached this level (46, 48, 55). This fact suggests that in heifers reproductive performance could be better using another protocol, for example Double OvSynch (53, 55).

The second phenomenon that can reduce the efficiency of OvSynch is non-occurrence of luteolysis after PGF2α injection (15). As a consequence, the development of the second follicular wave will be suppressed, which makes the synchronisation of ovulation and TAI impossible. Many studies stress the detrimental effect of this phenomenon on fertility. A second PGF2α injection 24 h later has been proposed to overcome this problem and to improve the fertility in OvSynch-synchronised cows (12).

Other indications for OvSynch

Silent heat

Lack of oestrous signs is an increasing problem on many farms. Today this phenomenon affects 10%–40% of dairy farms (69), while over 25 years ago its prevalence was less than 5% (68). The reason for silent heat may be poor heat detection, but on the other hand, the shortening of oestrous duration and weakening of its signs have been confirmed in high-milk-yielding cows (61). As a main reason for this, negative energy balance and related endocrine alterations such as lower LH and oestrogen secretion have been considered (13, 61). Thus a reasonable solution for cows with silent or unobserved heat seems to be the use of hormonal protocols. These treatments allow precisely timed insemination of cows at the same optimum moment as TAI without heat detection. OvSynch applied to only such cows or as a part of reproduction management in the whole herd makes heat detection unnecessary. At the herd level, the decision must be taken how and when the postpartum OvSynch protocol should be administered in cows with silent heat. It can be started after gynaecological examination only in cows with active ovaries or without examination in cows known to have had silent heat in the past. The third possibility is blanket synchronisation of all cows after a voluntary waiting period. The total pregnancy rate after OvSynch can reach 35%–60% (26, 64). Such encouraging reproductive outcomes are the basis for recommendation of this method for cows with silent heat. However, independently of the hormonal protocols, heat detection should be improved and feed ration should be corrected as preventive measures.

Heat stress

Heat stress reduces reproductive performance but farms with animals suffering from it may mitigate this with OvSynch. As a synchronisation protocol, it can be also used as a treatment method during heat stress, and it has been shown that beginning the protocol on the sixth day of the second cycle after parturition improved the fertility rate during periods of consecutive hot days (24). Thus, the OvSynch protocol may be used successfully for this purpose during summer when oestrous behaviour is exhibited and the percentage of successful inseminations is lower due to high temperatures (2, 21). Heat stress disturbs the periodicity of the ovaries, reduces progesterone level in the blood (2), may cause cyst development (39), and decreases LH secretion in the peri-ovulation period by about half (54). During heat stress, lower follicular production of oestrogens and ovulation of lower quality oocytes were observed (21, 66). The negative consequence of such changes will be formation of a CL which produces a lower amount of progesterone during the next cycle (60, 65). These disturbances persist in cow fertility, so even for a longer period of up to a few months after hot days their negative effects can still be recognised in a lower fertility rate (52). It can be presumed that long-lasting hot days cause permanent changes in antral follicles, which will develop into dominant follicles in the following cycles (50). To minimise the negative effects of high temperatures on the secretion of hormones and maturation of oocytes, the use of hormonal protocols during this period has been proposed (50). Ullah et al. (58) compared the efficiency of insemination of cows treated and untreated with GnRH in oestrous during a high temperature period. In the group that received GnRH, 28.6% of the cows were pregnant after the first insemination, whereas in the control group only 17.7% were pregnant. Other studies (2, 19) also confirmed the hypothesis that administration of GnRH in oestrous during heat stress had a positive impact on the development of follicles and quality of oocytes. The comparison of three different hormonal methods (OvSynch protocol, two-fold PGF2α 14 days apart, and single PGF2α) in the summer and winter was performed by Alnimer et al. (1). The conception rates after the first insemination for the above mentioned methods were 36.7%, 22.7%, and 26.3%, respectively. It must also be noted that after the third insemination, 83% of cows in the OvSynch group were pregnant, compared to only 60% in both other groups. This outcome clearly shows the advantages of the OvSynch protocol over the other hormonal methods.

Cyst treatment

The OvSynch protocol mimics the combined treatment of ovarian cysts with GnRH-PGF2α-GnRH (67). Cysts are non-ovulating liquid-filled structures with a diameter of over 25 mm which persist on the ovary for over 10 days simultaneously with absence of the CL (27). Injection of GnRH causes higher LH secretion from the pituitary gland, which leads to luteinisation of cystic follicles or promotes other follicles to ovulate (9, 62). Occasionally, a rupture of the cyst may occur (31). The next important step in this hormonal therapy is PGF2α injection, to cause luteolysis of luteal tissue (41). The second GnRH injection should then stimulate the follicles of the last wave to ovulation, conditioning the animal for AI. Administering the same hormones as in the classic ovarian cyst treatment, the OvSynch protocol can be used for treatment of cysts, based on the similar hormonal changes it effects. Fricke and Wiltbank (29) proved that despite the presence of a cyst, after applying the above hormones, a follicle may develop and ovulate leading to fertilisation of the oocyte, and the follicle may be fully functional with no other impairment than the cyst. In their study, after performing the OvSynch protocol 71.3% of cows with cysts had a synchronised cycle and 36.8% of these cows became pregnant. Among the cows without cysts the treatment efficacy was only slightly better, since 48.8% of cows were pregnant on the 28th day after AI. These findings have also been confirmed in other studies (5, 31). De Rensis et al. (20) compared the effects of the OvSynch protocol and its modification (replacement of the second GnRH by hCG injection) in lactating cows with ovarian cysts. In cystic cows, which received hCG, cysts disappeared faster. Similar results were also obtained in other studies (4, 18), suggesting that injection of hCG instead of GnRH may be one way to improve the treatment effect of the OvSynch protocol on ovarian cysts in dairy cows (20). This improvement is probably based on the fact that hCG acts longer than GnRH and delivers a better clinical effect (37).

OvSynch modifications

Presynchronisation of ovaries with prostaglandin F2α

As was previously mentioned, presynchronisation with the use of PGF2α is able to equalise a cycle before the beginning of the OvSynch protocol (3, 34). The PreSynch protocol starts with a PGF2α injection given 12 days before OvSynch (17). This causes the synchronisation of the cyclic activity of the ovaries. There is, therefore, a much higher probability that during the first GnRH injection according to the OvSynch protocol, the follicles of the second wave present on the ovary will be able to develop (17). Other reasearch has suggested that presynchronisation with PGF2α should include two injections 14 days apart and the OvSynch protocol should begin 11 or 12 days after the second injection (26, 42) (Fig. 2). There is also the option of starting the OvSynch seven days after the second injection of PGF2α (23). El-Zarkouny et al. (26) used the PreSynch programme before OvSynch and obtained an increase of up to 48.8% in the pregnancy rate after the first AI but only obtained 37.5% using OvSynch alone. A similar study has been performed by Gumen et al. (35), who achieved an 8% insemination efficiency gain after the PreSynch protocol.

Fig. 2

Schemes of OvSynch modifications (PRID – Progesterone-releasing intra-vaginal device, CIDR – controlled internal drug release containing progesterone, TAI – timed artificial insemination)

Double OvSynch as a new presynchronisation schedule

Another modification of the basic OvSynch is Double OvSynch, which proceeds through two OvSynch protocols seven days apart and follows with TAI after the second protocol (Fig. 2) (53). The obtained results showed an even higher pregnancy rate compared to PreSynch outcomes (23, 53, 55). The final pregnancy rates showed the advantage of Double OvSynch compared to PreSynch: 49.7% vs 41.7%. The reason for this may be that cows with inactive ovaries after parturition did not respond to the PGF2α injection during PreSynch. In contrast, the two additional doses of GnRH in Double OvSynch stimulated the ovaries to return to activity. This treatment had no negative consequences in the cows with already active ovaries (35, 53). An interesting observation was that the Double OvSynch protocol was much more efficient in heifers (65.2%) than in cows (37.5%) (53). Souza et al. (53) therefore recommend Double OvSynch for heifers, whereas presynchronisation with PGF2α should be performed in cows because of its better efficiency in that group of animals (14, 50). Recent studies comparing these two methods showed worse outcomes, but still the advantageous effects of the Double OvSynch protocol over PreSynch have been confirmed (23).

Second injection of PGF2α during OvSynch protocol to improve luteolysis

As was previously mentioned, an important reason for the decreased pregnancy rate after OvSynch is lack of luteolysis after the PGF2α injection (Fig. 2). The most probable explanation for this phenomenon is the formation of a young corpus luteum after the first GnRH which is not sensitive to prostaglandin (15, 22).

Carvalho et al (15) have shown that a double PGF2α injection during the OvSynch protocol is able to boost luteolysis. In their study, the authors divided cows into four groups. Their 1st group’s regimen was OvSynch without any modification, the 2nd group received GnRH presynchronisation, the 3rd group was medicated with OvSynch with double PGF2α injection, and the 4th group was assigned a combination of the two previous protocols. The pregnancy rates per artificial insemination (P/AI) by group were 32%, 33%, 37%, and 40%, respectively. Cows treated with double PGF2α injections and with lower P4 concentration on the day of TAI had better reproductive outcomes than cows from the 3rd and 4th groups. The recommended time for the second PGF2α injection is 24 h after the first injection without any changes to the times of GnRH injection or TAI (12, 15).

Intravaginal devices for maintenance of CL function

Intravaginal inserts (PRID – progesterone-releasing intra-vaginal device or CIDR – controlled internal drug release) containing progesterone may also be included into the OvSynch protocol. This method of synchronisation was performed by Bisinotto et al. (10). Cows with detected CL on the ovaries were selected for this research and divided into two groups. In both groups a basic OvSynch protocol was applied. Additionally, cows from the experimental group received a progesterone device for seven days at the time of the first GnRH, while the control group was treated without any modification (Fig. 2). Unexpectedly, a slightly higher pregnancy rate was noticed in the control group (45%), than in the experimental group (40.5%). In the same study better results were obtained in heifers (40.5%) than in cows (35.7%) and better in cows which were inseminated for the first time after parturition (41.7%) than in reinseminated cows (34.7%). An explanation of these results is an increased level of progesterone, which reduces the LH pulse frequency. As a consequence, altered follicular growth and ovulation were possible (27). Another explanation is lower amplitude of secreted LH pulses after the GnRH injection (33).

On the other hand, some studies indicated the positive influence of progesterone-releasing devices on conception rate in OvSynch-synchronised cows. El-Zarkouny et al. (26) reached a conception rate of 59.3%, while Bisinotto et al. (11) noted 51.3%, after a protocol with a gestagen insert but also with a double injection of PGF2α on day 7 of OvSynch. Revah et al. (49) claimed that a high level of progesterone in the follicular phase causes the reduction of LH secretion, which improves the quality of oocytes. In consequence, and with reference to the studies cited above, there are difficulties in clearly defining the effects of progesterone supplementation during such an OvSynch protocol. These effects are caused by, inter alia, progesterone level’s subjection to many factors such as the level of dry matter intake, milk yield, and metabolic status (51, 59). As a consequence, application of an intravaginal device and the concentration of progesterone caused by this treatment can be insufficient in many cows, because of a very high turnover rate of this hormone.

Resynchronisation

Besides presynchronisation, there is also a possibility to resynchronise ovulation using the OvSynch protocol (5). This schedule assumes a consecutive AI if the cows were detected as not pregnant on days 30–32 after the first AI (6). The next OvSynch can be started at that moment, but it is also possible to shorten the time needed for the next AI by injecting the first GnRH dose seven days before the pregnancy check (22). This allows the injection of PGF2α at the time of the pregnancy check, and as a consequence three days later a cow can already be reinseminated, according to the basic OvSynch protocol. The efficacy of resynchronisation started on the 23rd–25th days varied from 23% to 50% (7, 16, 30) and when started on the day of the pregnancy check (30th–32nd days) it fell within 25.2% to 33.6% (5, 16). Bartolome et al. (5, 6, 7) compared the efficiency of resynchronisation using OvSynch started in different phases of the oestrus cycle. The highest pregnancy rate was achieved in the group in which OvSynch was begun in dioestrous (35.9%). In the group with ovarian cysts the pregnancy rate was the lowest (20.2%). To improve the effectiveness of resynchronisation, the use of progesterone devices, another GnRH injection, or shorter hormonal programmes are suggested; however, the results of these studies are inconsistent (7, 22).

Conclusions

Implementation of hormonal protocols, which are able to synchronise the oestrus cycle, provides many opportunities for reproductive management. A major advantage of some protocols is the possibility of timed AI, which makes work with the animals easier and less time-consuming. An additional effect is minimising the problem of unobserved heat. OvSynch, as one of the most popular hormonal protocols, can be used both for routine cycle synchronisation and for treatment of cystic ovarian disease, silent heat, or heat stress. This method is more effective when used for cows rather than heifers. To improve insemination and pregnancy rates after OvSynch, some modifications of its basic protocol are currently being tested. These modified hormonal protocols should overcome the problems with the development of follicles or corpora lutea not responding to GnRH or PGF2α. Another weakness to address is insufficiency of the corpus luteum, which may be ameliorated by the use of intravaginal progesterone devices.