| Livestock Research for Rural Development 32 (7) 2020 | LRRD Search | LRRD Misssion | Guide for preparation of papers | LRRD Newsletter | Citation of this paper |
The aim of this experiment was to compare the efficacy of Ovsynch and select synch protocols on reproductive performance in dairy cows in Algerian farms (altitude 1080 m). 30 Holsteins and 40 Montbeliardes postpartum cows with ovarian activity were assigned randomly to two groups of oestrous synchronization protocols of 35 cows each. Group 1 (Ovsynch protocol) selected cows were treated with inj GnRH 100 μg of cystoréline at day 0, inj PGF2α 25 mg per cow of Dinoprost at day 7 and inj GnRH 100 μg at day 9 intramuscularly. The cows of group 2 (Synch protocol) were treated with inj GnRH 100 μg of cystoréline at day 0 and inj PGF2α 25 mg Dinoprost at day 7 intramuscularly. Cows that exhibited estrus were inseminated 8 to 12h later in Select Synch and 12 to 18h after PGF2α injection in Ovsynch. Pregnancy was diagnosed by ultrasonography at 30 days after AI and confirmed by rectal palpation on day 45.
The estrus responses for cows were 48.6% and 40.0% respectively in Ovsynch and Select Synch cows without a significative difference. Pregnancy rates at day 30 post insemination were 31.4% and 28.5% and conception rates were 64.7% and 71.4% in the Ovsynch and Select Synch groups, respectively.
No statistical differences were observed in pregnancy for first AI and conception rates for the two groups. The breed had also no significant effect on reproductive performance for the two protocols tested. Estrus Synchronization using Ovsynch protocols can provide a good way to manage reproduction in dairy cows by reducing the need for estrus detection. The Select Synch protocol can be recommended in farms where heat detection is not a problem to reduce the cost of heat synchronization, to reduce both the labour costs and the extra handling to daily estrus detection and AI. A systematic analysis of all the underlying factors of anestrus in the dairy cow is necessary with respective corrective measures.
Keywords: artificial insemination, conception rate, dairy cow, estrus response, Ovsynch, pregnancy rate, Select Synch
Le but de cette expérimentation est de déterminer l’efficacité comparative de 2 protocoles de synchronisation des chaleurs “Ovsynch et Select Synch” sur les performances reproductives de vaches dans des élevages laitiers Algériens (altitude 1080 m). 30 Holsteins et 40 Montbeliardes en activité ovarienne ont été réparties au hasard en deux groupes de 35 vaches chacun.
Dans premier groupe«Ovsynch» les vaches ont été traitées par une injection de GnRH 100 μg à base de cystoréline à J0, une injection de PGF2α 25 mg à base de Dinoprost à J7 suivie d’une seconde injection de GnRH 100 μg à J9 en intramusculaire. Dans le deuxième groupe «Select Synch» les vaches ont été traitées par une injection de GnRH 100 μg à base de cystoréline à J0 suivie d’une injection de PGF2α 25 mg à base de Dinoprost à J7 en intramusculaire. Les vaches ayant manifesté les signes de chaleurs ont été inséminées 8 à 12h plus tard pour le protocole Select Synch et 12 à 18h après la seconde injection de GnRH pour le protocole Ovsynch. Le diagnostic de gestation a été réalisé par échographie 30 jours après l’IA et confirmé par palpation rectale à J45.
Le taux de réponse à l’estrus a été de 48,6% et 40,0% respectivement chez les vaches des groupes d’Ovsynch et de Select Synch respectivement sans différence significative.
Les taux de gestation au jour 30 après l’insémination étaient 31,4% et 28,6% correspondant à des taux de conception de 64,7% et 71,4% respectivement pour les groupes Ovsynch et Select Synch (pas de différence significative). La race n’a pas eu également d’effet significatif sur les performances reproductives pour les deux protocoles testés. La synchronisation de l’œstrus à l’aide du protocole Ovsynch peut fournir un bon moyen de gérer la reproduction chez les vaches laitières en réduisant le besoin de détection des œstrus. Le protocole Select Synch peut être recommandé à la place du protocole Ovsynch dans les fermes où la détection des chaleurs n’est pas un problème afin de réduire le coût de la synchronisation, afin de réduire à la fois les coûts de main-d’œuvre et la manipulation supplémentaire à la détection quotidienne des œstrus de l’IA. Une analyse systématique de tous les facteurs sous-jacents de l’anoestrus chez la vache laitière est nécessaire avec des mesures correctives respectives.
Mots clefs : conception, gestation, insémination artificielle, Œstrus, Ovsynch, Select Synch, vache laitière
In Algeria, cattle farming has a population of 2 million head which represents only 6% of the total national herd of ruminants (MADRP, 2016). Reproductive efficiency is one of the key components of a profitable dairy system (Lucy et al 2001). A serious problem in reproductive management is the occurrence of diminished behavioural oestrous symptoms as productivity increases in dairy cows which the heat stress is a major cause of low fertility with pregnancies per artificial insemination decreasing of 40 to 60% in the summer (Udin et al 2017, Raphani et al 2020). This is increasingly challenging for breeding management of dairy particularly in larger herds. An oestrous synchronization is an important tool for increasing the rate of implementation of artificial insemination in cattle. It allows a quicker genetic improvement. Also, heat detection is done at a given time and is easier when heats are small and short. Oestrous synchronization allows grouped calving at a favourable season. Thus, in previous studies, several estrus detections have been developed by the administration of Ovsynch and Select Synch protocols (Caraba and Velicevici 2013, Khalil 2019).
To our knowledge, no comparative studies have been done in Algeria. The main objective of this study was to compare the effect of two estrus synchronization protocols (Ovsynch and Select Synch based programs) on the reproductive efficiency in dairy cows in Algerian farms.
This study was conducted on a private dairy farm in Setif area in Algeria located 217 km to Algiers at an altitude of 1080m, a latitude of 36°11'N and longitude from 5°24' E.
The research materiel consisted of 70 non-pregnant cyclic 30 Holstein and 40 Montbeliarde cows which the ages ranged between 2-5 and were between the intervals of 55-90 postpartum.
Montbéliarde is the most represented in the population (57%) followed by Prim’Holstein with 43%. The veterinarians performed a gynaecological examination and cows diagnosed by rectal palpation for ovarian activity before synchronization (as determined by the observation of corpus luteum in the ovaries in several ultrasound examinations). The cows selected and included in this study calved normally and were free from anatomical or reproductive disorders with a body condition score of 2-3 and above on a 1-5 scale according to Campanile et al (2010). They were randomly distributed to two treatment groups, as Ovsynch and Select Synch, consisting of 35 cows each and received the treatments during the period from June to September 2016.
The cows in Ovsynch group received inj GnRH (100 μg of cystoreline) at day 0, inj PGF2α (25 mg of Dinoprost) at day 7 and inj GnRH 100 μg at day 9 intramuscularly (Figure 1).
The cows in Select Synch group received inj GnRH (100 μg of cystoreline) at day 0 and inj PGF2α (25 mg Dinoprost) at day 7 intramuscularly (Figure 2).
|
|
| Figure 1. Schematic representation of the Ovsynch protocol |
|
| Figure 2. Schematic representation of the Select Synch protocol |
Estrus of cows (n = 70) was synchronized with gonadotropin-releasing hormone (GnRH) and prostaglandin F2α (PGF2α). The selected cows were monitored visually to observed twice daily for estrus signs (standing to be mounted, bellowing, redness and swelling of the vulva and clear mucous discharge). Cows also were confirmed by the permeability of the cervix of the pistol on the day of insemination. Artificial inseminations (AI) were applied to the cows in both of the groups. The cows that exhibited estrus were inseminated 8-12 h later in Select Synch and 12-18 h after PGF2α injection in Ovsynch.
Pregnancy was diagnosed by ultrasonography at 30 days after AI and confirmed by rectal palpation on day 45 after artificial insemination.
The reproductive performance variables recorded in this study were:
Data were analyzed with a statistical software program (SAS Version 9.12). The objectives of this analysis were to test the effect of the treatment on estrus response, pregnancy and conception rates for the two treatments. Significant differences in reproductive performance of the cows tested between treatments were determined by Chi-square. The level of significance was set at p < 0.05.
Rectal palpation was carried out in the cows both in Ovsynch and Select Synch groups before PGF2α Injection to control the luteal structures. The estrus responses, pregnancy and conception rates are shown at Table 1. Regardless of the estrus-synchronization protocol, an oestrous response was detected in 31 out of the 70 cows treated.
By treatment group, 17 cows (48.6%) that were subjected to Ovsynch synchronization protocol in our study showed estrus while 14 cows (40,0%) that were subjected to Select Synch synchronization protocol showed estrus (Table 1). There was no statistical difference (P>0.05) in the percentage of cows detected in estrus between Ovsynch and Select Synch programs.
| Table 1. Comparative efficacy of Ovsynch and Select Synch protocols observed in Algerian cattle (n=70) | ||
| Reproductive performance | Estrus- synchronization protocol | |
| Ovsynch protocol (35 dairy cows) |
Select Synch Protocol (35 dairy cows) |
|
| Synchronized estrus response: n (%) | 17 (48.6) | 14 (40,0) |
| Conception rate: n (%) | 11/17 (64.7) | 10/14 (71.4) |
| Pregnancy rate per IA by USG: n (%) | 11 (31.4) | 10 (28.6) |
However, synchronized pregnancy rates at 30 days post-AI (Figure 3) were 31.4% (11/35) and 28.6% (10/35) in the Ovsynch and Select Synch groups. The difference in the pregnancy rates among the groups (Table 1) was not statistically significant (p>0.05).
Our study recorded low pregnancy rates relative to conception rates. Highest synchronized conception rate was recorded in both protocols: 64.7% in Ovsynch protocol, lower than was 71.4% in Select Synch protocol (Figure 3), however a no significant difference (p>0.05).
 |
| Figure 3. Estrus responses, pregnancy and
conception rates observed in Algerian cattle subjected to Ovsynch and Select Synch protocols (n=70) |
The results of the effect of race on reproductive performance for the two protocols combined are shown at figure 4. 13/30 Holstein and 18/40 Montbéliarde cows were observed in heat with rates of 43.3% and 45.0% respectively. Conception rates of 69.0% and 72.2% were recorded respectively for Holstein (9/13) and Montbéliarde (13/18) cows. Concerning pregnancy rates, we noted a rate of 30% for (9/30) Holstein and (13/40) Montbéliarde cows.
 |
| Figure 4. Effect of breed on reproductive performance observed in Algerian cattle (n=70) |
Reproductive efficiency is the product of oestrous detection and conception rates (Rabiee et al 2005). For this purpose, new heat synchronization protocols based on GnRH and PGF2α are among the most studied treatment categories in recent years (Pursley et al 1995, 1997). However, these protocols are currently little used in Africa and Europe compared to those studied in North and South America (Kandiel et al 2012, Udin et al 2017). Ovsynch has been widely used in dairy cows and heifers (Pursley et al 1997, De Jarnette et al 2001, Tenhagen et al 2005).
Despite the applications of different Ovsynch protocols, low percentages of cows showed estrus and fertility was still low because there was a relatively lower estradiol concentration around AI (Lopez et al 2004). Santos et al (2004) stetted that asynchrony was determined in 13 – 16% of the cows in the Ovsynch program.
Cows that responded in the current study in Ovsynch protocol were 48%. This result is comparable to those reported in several studies estimating that ≤ 50% of the cows were detected in estrus in dairy herds (Stevenson et al 1999, Kandiel et al 2012). It is similar to that reported by Mesut Çevik et al (2010) and was lower than recorded in other studies (Wolfenson et al 2000, Caraba 2013, Udin et al 2017). According to Stevensen 1999, as few as 20% of Ovsynch treated cows showed estrus after the PGF2α injection associated with the Ovsynch protocol (Stevenson et al 1999). With exceptions, other rare works recorded better estrus responses although the periods of heat observation were somewhat different in these studies (Fricke et al 2003, Carab 2013). The stage of the oestrous cycle at which synchronization is initiated influences the reproductive responses based on Ovsynch protocol (Moreira et al 2000). Ovarian and estrous responses to the GnRH and PGF2α injections were dependent on day of the estrous cycle when the protocol was initiated.
With Select Synch treatment, 5 to 20% of the animals may show heat 1.5 to 2 days before PGF2α injection (Pusley 1997, Geary 2000). According to these authors, including the CIDR® is recommended when more cows are likely to be anestrous and/or when heat detection before to PGF is not feasible. Cows that responded in the current study in Select Synch protocol were 40%. This result was similar to that founded by Stevenson et al (1999) and was higher than that reported by the stated authors. The Select Synch treatment is capable of synchronizing estrus among the majority of cows in a herd with a low cost. There could be applied to the same group of cows with CIDR®s selectively placed in young thin or late calving cows (Twagiramungu et al 1995, Tenhagen et al 2005).
The pregnancy rates in the Ovsynch studies carried in dairy cows varied from 27 to 40% (Frike et al 2003, Neglia et al 2003, Taşal et al 2005, Çelik et al 2009). Pursley et al (1997) reported a pregnancy rate of 35.1% and 37.8% in heifers and cows respectively.
With the exception, Cartmill et al (2001) obtained a low rate of 20%. However, pregnancy rates in nulliparous heifers were also in the 40% range (Pursley et al 1997) much lower than what is normally achieved (60 to 70%) to AI at detected estrus in heifers. The present study recorded pregnancy rates in the Ovsynch group of 31.4% that is in the ranges of the authors stated. These were similar to those reported in recent reviews (Kasimanickam et al 2008, Gokhan Dogruer 2010, Kandiel 2012).
This result was better than the one found by Caraba and Velicevici (2013). Although this was lower than those obtained in other works (Rabie et al 2005, Ahmadi et al 2007).
Several authors indicated lower pregnancy rates per AI in heifers treated with Ovsynch than with Select Synch that varied from 38% to 70% (Pursley et al 1997, Stevenson et al 1999).
El-Zarkouny (2010) and Akbarabadi et al (2014) reported higher pregnancy rates in the Select Synch and Ovsynch protocols compared than in the control. The result recorded in our study was lower than reported in the bibliography.
Such low pregnancy rates relative to conception rates recorded in this study could perhaps be the consequence of the reduced fertility of an aged follicle/oocyte induced by estradiol injection (Pursley et al 1997). Tenhagen et al (2005) reported that a double-timed AI after synchronization with the Select Synch protocol was as effective in getting heifers pregnant as AI on observed estrus although more straws of semen are needed. Different protocols of estrus synchronization caused different conception rates in dairy cows and heifers after synchronized estrus ranging from 30% to 75% in Ovsynch program (Peters and Pursley 2003, Kandiel et al 2012, Udin et al 2017). This study showed a better conception rate for both groups, higher in Select Synch than in Ovsynch groups and is in accordance with previous reports. According to Vasconcelos et al 1999), conception rates were greatest in dairy cows that began the Ovsynch protocol between day 5 and 12 of the oestrous cycle.
Some reports indicated that the second injection of GnRH agonist caused ovulation of the dominant follicle recruited by the first injection of GnRH agonist (Pursley et al 1995, 1997). Those authors confirmed that ovulation occurred 24 to 32 h after the second GnRH agonist injection (given 24 or 48 h after PGF 2α in heifers and cows). Whereas in other studies conception rates were reduced (Stevenson et al 1999) but pregnancy rates were increased (Pursley et al 1997).
The good conception rate recorded in the Ovsynch program is in the ranges of the authors stated. It is similar to that reported in the bibliography (Alnimer et al 2011, Udin et al 2017, Akbarabadi et al, 2014). On the other hand, this result is higher to that found in other reviews (Stevenson et al 1999, Lean et al 2003, El-Zarkouny 2010). In the Select Synch program, conception rates after synchronized estrus ranging from 49.0 % to 66.0% (Tenhagen et al 2005). The conception rate found in this study (71.6%) was higher to that recorded in other works (Stevenson et al 1999, El-Zarkouny 2010).Burke et al (1996) obtained higher conception rate in cows undergoing AI at detected estrus without the second GnRH injection than in cows fixed-time inseminated (Ovsynch). Several factors affecting conception rate in dairy cows and heifers have been well documented in previous studies (Chebel et al 2007, Morris et al 2011). The variation of estrus response of cows caused the several factors such as cow age, body condition, management and the interval from calving to initiation of the timed AI (Wolfenson et al 2000, Chebel et al 2007). The correct management of dairy heifers to optimize their weight at the initiation of the breeding program could also improve oestrous detection rates. All these parameters provide valuable insight into the proportion of anestrous cows at the initiation of the synchronization program. On the other hand, the present study was conducted during summer and thus heat stress may have altered ovarian follicle development and steroidogenic capacity with a decrease in length and intensity of estrus (Udin et al 2017, Raphani et al 2020). A highly significant seasonal effect was observed, as a higher (p < 0.01) pregnancy rate was recorded for cows inseminated during cold months compared with that recorded for cows inseminated during the hot month (Khalil 2019). Kandiel et al (2012) reported a shorter heat observation time in the Ovsynch program compared to other protocols. According to the author, the use of estradiol ester in place of the second dose of GnRH induced an extension of heat duration on the one hand with recording satisfactory rates in the induction of ovulation and gestation.
A decline in fertility in dairy breeds and especially in Holstein breeds has been observed in many countries for several years (Lucy 2001, Barbat 2005). Thus, numerous physiological and pathological factors have been described such as the severe negative post-partum energy balance and the high milk yield which are often associated with a decrease in reproductive performance. Somewhat reproductive performance was recorded in the present study. Nevertheless, these results are in agreement with those reported in the various studies concerning dairy cows varying from 39.0% to 65.4% (Lucy 2001).
However, Tenhagen et al (2004) reported surprising results in recording a better pregnancy rate in cows with above-average milk production. The poor reproductive performance would, therefore, be more associated with a more discreet expression of heat leading to poor detection. Barbat (2005) reported a continuous and rapid deterioration of fertility in the Prim’Holstein breed, unlike the Montbéliarde breed. According to the author, the regular decrease of 1% per year in the success rate in 1st AI and the prolongation of the calving-1st AI interval are the main factors explaining this decrease in fertility in Prim'Holstein compared to other breeds. However, the success of the treatment varies greatly from one farm to another and from one animal to another and therefore is often not satisfactory and constitutes a solution to the problem.
These raw results are subject to numerous more or less confusing effects and require more in-depth analyzes to carry out a more elaborate diagnosis.
The implementation of the Ovsynch and Selectsynch protocols in Algerian breeding has led in our study to reproductive performance somewhat low but comparable for both protocols. The reproductive performance identified in our study corresponds to environmental factors and the breeding conduct carried out in our farms. The low body score, as well as the calving interval to initiation of the treatment applied in our study, may influence this reproductive performance also as a result of the seasonal effect on the duration and intensity of heats also knowing that this study was carried out in a season.
While these protocols theoretically reduce the breeder's working time, they do not improve breeding performance. But they synchronise the calvings. Thus, the Select Synch protocol gives as good results in design rates as the Ovsynch protocol. The Select Synch protocol can be recommended in farms where heat detection is not a problem in order to reduce the cost of heat synchronization, to reduce both the labour costs and the extra handling to daily estrus detection and AI. More detailed analyzes are necessary to understand the origin of the decline in reproductive performance of dairy breeds. Also, surveys should, therefore, be conducted on a larger scale with the Select Synch protocol to identify all existing problems. Other studies on a larger sample will have to be used in the future to determine the effects of the several factors on fertility to improve the results.
The authors thank Professor Daniel Tainturier, Head of the Department of Reproductive Pathology, ONIRIS, Nantes (France) for his collaboration in the improvement of this manuscript. The authors would also like to thank the participating veterinarians and the staff of the farm for their help and cooperation in carrying out this work.
Ahmadi M R, Nazifi S, Sajedianfard J and Moattari G 2007 Impact of oestrous synchronization methods on cellular proportions in cervical mucus and serum hormone concentrations. Theriogenology, 67, 598-604. https://doi.org/10.1016/j.theriogenology.2006.09.030
Akbarabadi M A, Shabankareh H K, Abdolmohammadi A and Shahsavari M H 2014 Effect of PGF2α and GnRH on the reproductive performance of postpartum dairy cows subjected to synchronization of ovulation and timed artificial insemination during the warm or cold periods of the year. Theriogenology, 82: 509-516.
Alnimer M A, Alfataftah A A and Ababneh M M 2011 A comparison of fertility with a cosynch protocol versus a modified ovsynch protocol which included estradiol in lactating dairy cows during the summer season in Jordan. Anim. Reprod., 8: 32-39.
Barbat A, Druet T, Bonatti B, Guillaume F, Colleau J J and Bouchard D 2005 Bilan phénotypique de la fertilité à l’insémination artificielle dans les trois principales races laitières françaises. INRA, Station de Génétique Quantitative et Appliquée, 78352 Jouy-en-Josas Renc. Rech. Ruminants 12, 137-140.
Burke J M, De LaSota R L, Risco C A, Staples C R, Schmitt E J P and Tacher W W 1996 Evaluation of timed insemination using a Gonadotropin-Releasing Hormone agonist in lactating dairy cows. Journal of dairy Science, 79, 1385-1393. https://doi.org/10.3168/jds.S0022-0302(96)76496-2
Campanile G, Baruselli P S, Vecchio D, Prandi A, Neglia G, Carvalho N A, Sales J N, Gasparrini B and D’Occhio M J 2010 Growth, metabolic status and ovarian function in buffalo (Bubalus bubalis) heifers fed a low energy or high energy diet. Animal Reproduction Science, 122 (1-2): 74-81. https://doi.org/10.1016/j.anireprosci.2010.07.005
Caraba I V and Velicevici S 2013. Using ovsynch protocol versus cosynch protocol in dairy cows. Anim. Sci. Biotechnol., 56: 63-65.
Cartmill J A, El-Zarkouny S Z, Hensley B A, Lamb G C and Stevenson J S 2001 Stage of cycle, incidence, and timing of ovulation, and pregnancy rates in dairy cattle after three timed breeding protocols. J Dairy Sci, 84, 1051-1059.
Çelik HA, Avc G, Ayd N İ, Bülbül A and Bülbül T 2009 Effect of beta-carotene on ovarium functions and Ovsynch success in repeat breeder cows. Kafkas Üniv Vet Fak Derg, 15, 87-94.
Çevik M., Selçuk M and Dogan S 2010 Comparison of Pregnancy Rates after Timed Artificial Insemination in Ovsynch, Heatsynch and CIDR-Based Synchronization Protocol in Dairy Cows. Kafkas Univ Vet Fak Derg16 (1): 85-89. KVFD-2009-451
Chebel R C, Santos J E P, Cerri R L A, Rutigliano H M and Bruno R G S 2006 Reproduction in dairy cows following progesterone inserts presychronizaion and resynchronization protocols. J Dairy Sci, 89, 4205-4219.
De Jarnette J M, Salverson R R and Marshall C E 2001 «Incidence of premature estrus in lactating dairy cows and conception rates to standing estrus or fixed-time inseminations after synchronisation using GnRH and PGF2α.» Animal Reproduction Sciences, 67, 27-35.
Dogruer G, M K Saribay, F Karaca and Ergun Y 2010 The comparison of the pregnant rates obtained after the Ovsynch and double dose PGF2+GnRH applications in lactating dairy cows. Journal of Animal and Veterinary Advances 9 (4): 809-913. ISSN: 1680-5593
El-Zarkouny S Z 2010 Conception rates for standing estrus and fixed-time insemination in dairy heifers synchronized with GnRH and PGF2α. Turk. J. Vet. Anim. Sci. 34(3): 243-248.
Fricke P M, Caraviello D Z, Weigel K A and Welle M L 2003 Fertility of dairy cows after presynchronization of ovulation at three intervals following first timed insemination. J. Dairy Sci.,86: 3941-3950.
Jobst S M, Nebel R L, McGiliard M Land Pelzert K D 2000 Evaluation of reproductive Performance in Lactating dairy Cows with Prostglandin F2alpha, Gonadotropin-Releasing Hormone, and Timed Artificial Insemination. Journal of Dairy Science, 83, 2366-2372.
Kandiel M. M M, Bassuoni L A , Sosa G A , Moustaf M A and Ghallab A M 2012 Comparative Efficacy of Ovsynch and Heatsynch Protocols Assessed by Transrectal Ultrasonography and Serum Progesterone in Egyptian Buffalo Heifers. Theriognology 2(3):173-183.
Kasimanickam R, Hall J B, Currin J F and Whittier W D 2008 Sire effect on the pregnancy outcome in beef cows synchronized with progesterone based Ovsynch and Co-synch protocols. Anim Reprod Sci, 104, 1-8,
Khalil A AY 2015 Fertility response of lactating dairy cows subjected to three different breeding programs under subtropical conditions. Beni-Suef University, Journal of Basic and Applied Sciences 2019, 8:6 doi.org/10.1186/s43088-019-0008-x
Kim I H, Suh G H and Son D S 2003 A progesterone-based timed AI protocol more effectively prevents premature estrus and incomplete luteal regression than ovsynch protocol in lactating Holstein cows. Theriogenology 60: 809-817.
Lean I J, Porte J A, Rabiee A R, Morgan W F, Tranter W P, Moss N and Rheinberger R J 2003 Comparison of effects of GnRH and prostaglandin in combination and prostaglandin on conception rates and time to conception in dairy cows. Austr. Vet. J., 81: 488-493.
Lopez H, SatterL D and Wiltbank M C 2004 Relationship between level of milk production and estrous behavior of lactating dairy cows. Anim. Reprod. Sci., 81: 209-223.
Lucy M C 2001 Reproductive lossinhigh-producing dairy cattle: wherewillit end? JDairy Sci.84:1277-1293.
MADRP 2016 Minister for Agriculture, Rural Development and Peach. Algiers, Algeria Moreira F, de la Sota R L, Diaz Tand Thatcher W 2000 Effect of day of the estrous cycle at the initiation of a timed artificial insemination protocol on reproductive responses in dairy heifers. J. Anim. Sci., 78,1568-76.
Morris M J, Kaneko K, Walker S L, Jones D N, Routly J E, Smith R F and Dobson H 2011 Influence of lameness on follicular growth, ovulation, reproductive hormone concentrations and estrus behavior in dairy cows. Theriogenology, 76: 658-668.
Neglia G, Gasparini B, Di Palo R, De Rosa C, Zicarelli L and Campanile G 2003 Comparison of pregnancy rates with two estrus synchronization protocols in Italian Mediterranean Buffalo cows. Theriogenology, 60, 125-133,
Peters M W and Pursley J R 2003 Timing of final GnRH of the Ovsynch protocol affects ovulatory follicle size, subsequent luteal function, and fertility in dairy cows. Theriogenology 60: 1197-1204.
Pursley J R , Mee M O and Wiltbank MC 1995 Synchronisation of ovulation in dairy cows using PGF2alpha and GnRH. Theriogenology, 44, 915-923.
Pursley J R , Wiltbank M C, Stevenson J S, Ottobre J S, Garverick H A and Anderson L L 1997 Pregnancy rates per artificial insemination for cows and heifers inseminated at a synchronized ovulation or synchronized estrus. J Dairy Sci, 80, 295-300.
Rabiee A R, Lean I J, Stevenson M A 2005 Efficacy of ovsynch program on reproductive performance in dairy cattle: A Meta analysis. J Dairy Sci, 88, 2754-2770.
Raphalalani Z C , Nedambale TL, Nengovhela N B and Nephawe K A 2020 An investigation of factors influencing synchronization response, conception and calving rate of communal cows in Limpopo Province, South Africa. Applied Animal Husbandry & Rural Development, Volume 13
Stevenson J S, Kobayashi Y and Thomson K E 1999 Reproductive performance of dairy cows in various programmed breeding systems including Ovsynch and combinations of Gonadotropin-releasing Hormone and prostaglandin F2alpha. Journal of Dairy Science, 82, 506-515.
Taşal I, Ataman M B, Aksoy M, Kaya A, Karaca Fand Tekeli T 2005 Estimation of early pregnancy by electrical resistance values of vaginal mucosa in cows and heifers. Rev Med Vet, 156, 91-94.
Tenhagen B-A, Surtholt R, Wititke M, Vogel C, Drillich M and Wolfgang H 2004 Use of Ovsynch in dairy herds - difference between primiparious and multiparious cows. Animal Reproduction Science, 81, 1-11.
Tenhagen B A, Kuchenbuch S and Heuwieser W 2005 Timing of ovulation and fertility of heifers after synchronization of oestrus with GnRH and Prostaglandin F2α. Reprod Dom Anim 40: 62-67.
Twagiramungu H, Guibault L A and Dufour J J 1995 Synchronization of ovarian follicular waves with a gonadotropin-releasing hormone agonist to increase the precision of estrus in cattle: A review. J. Anim. Sci., 73, 3141-3151.
Udin Z, Rahim F, H and Yellita Y 2017 Effect of Ovsynch and Co-synch on Follicle Size and Conception Rate Indifferent Postpartum of Simmental Cows Asian J. Anim. Vet. Adv 12 (2: 115-122) ISSN 1683-9919 DOI: 10.3923/ajava.2017.115.122
Vasconcelos J L M, Silcox R W, Rosa G J M, Pursley J R and Wiltbank M C 1999 Synchronization rate, size of the ovulatory follicle, and pregnancy rates after synchronization of ovulation beginning on different days of the oestrous cycle in lactating dairy cows. Theriogenology, 52:1067-78. https://doi.org/10.1016/S0093-691X(99)00195-8
Whittier JC 2000 Ovarian and Estrous Response of Suckled Beef Cows to the Select Synch Estrous Synchronization Protocol. DOI: 10.15232/S1080-7446(15)31653-3
Wolfenson D, Roth Z and Meidan R 2000 Impaired reproduction in heat-stressed cattle: Basic and applied aspects. Anim. Reprod. Sci., 60: 535-547
Received 13 April 2020; Accepted 18 May 2020; Published 1 July 2020