Abstract

Dairy cows that are being cared for in family businesses were used to compare the pregnancy rates by applying different time periods, using progesterone devices, and using fixed-time artificial inseminations. The cows were randomly divided into 3 groups. Group 1(n = 56); On day 0, GnRH (IM) (10mg Buserelin acetate, Ovarelin, CEVA DIF) + Progesterone implants (PRID®) (1,55 g progesterone CEVA), Day 8 PGF2α (Dinoprost tromethamine, 25 mg, Dinolytic, Pfizer), Day 9 Progesterone implants removal + PGF2α, insemination was performed at 56^th hours insemination after the second PGF2α injection. Group 2 (n = 50); on day 0, GnRH (IM) + Progesterone implants, PGF2α (IM) on the 8th day, Progesterone implants removal + PGF2α on the 9th day, insemination was performed at 48^th and 72th hour after the second PGF2α injection. Group 3 (n = 53); on day 0 GnRH (IM) + Progesterone implants, on the 5^th day PGF2α injection, day 6 PGF2α (IM) and remove progesterone implant and insemination at 56 hours after the second PGF2α. The average milk yield was recorded Group 1 16.66 ± 5.28 kg, Group 2 13.46 ± 3.05 kg. and Group 3 was recorded as 15.35 ± 4.60 kg. Pregnancy diagnoses were performed 35 days after the artificial insemination. The pregnancy rate was 41.07% in Group 1, 42% in Group 2, and 52.83% in Group 3. As a result; pregnancy rates were similar in all three groups. It has been concluded that synchronization with progesterone can solve many reproductive problems.

Keywords:
cow; progesterone; family business; synchronization; artificial insemination

HIGHLIGHTS

HIGHLIGHTS

INTRODUCTION

Increasing the success of artificial insemination in cows and various applications to obtain a calf per year are performed regularly. Systematic synchronization programs are needed for a sustainable farm due to the constantly increasing herd sizes [¹1 Pursley JR, Mee MO, Wiltbank MC. Synchronization of ovulation in dairy cows using PGF2a and GnRH. Theriogenology 1995;44,915. doi: 10.1016/0093-691x(95)00279-h
https://doi.org/10.1016/0093-691x(95)002... ]

CIDR^® (Controlled Internal Drug Releasing) and PRID^® (Progesterone Releasing Intravaginal Device) are inserted intravaginally for 7-10 days, both mimicking luteal phase progesterone secretion. One day before CIDR or PRID is removed from cows, prostaglandin F2 alpha (PGF2α) is administered to eliminate the potential source of endogenous progesterone. This provides the proper endocrinological order for the development and maturation of the dominant follicle. It is observed that most of the animals show estrus and insemination can be made within the next 3 - 5 days. In addition, fixed-time artificial insemination can be performed 48-64 hours after the removal of these implants. Progesterone therapy using implants can be used for hormonal manipulation of the estrus cycle and resynchronization of animals [²2 Roelofs J, López-Gatius F, Hunter RHF, Van Eerdenburg FJCM, Hanzen CH. When is a cow in estrus? Clinical and practical aspects. Theriogenology 2010;74,327-344. doi: 10.1016/theriogenology.2010.02.016
https://doi.org/10.1016/theriogenology.2... ].

The success of synchronization is attributed to the absence of corpus luteum (CL) at the end of the application and the presence of a new dominant follicle selected [³3 Mihm M. Delayed resumption of cyclicity in postpartum dairy and beef cows. Reprod. Domest. Anim. 1999;34,277-84. doi: 10.1111/j.1439-0531.1999.tb01252.x
https://doi.org/10.1111/j.1439-0531.1999... ]. The duration of progesterone therapy depends on the time interval for the development of the new dominant follicle and the hormone used. If the hormone selected for the beginning of the application is Gonadotrophin releasing hormone (GnRH), the duration of the PRID is 5-7 days, however; If the selected hormone is estradiol benzoate, it has been reported that the application time of PRID should be 7-12 days [³3 Mihm M. Delayed resumption of cyclicity in postpartum dairy and beef cows. Reprod. Domest. Anim. 1999;34,277-84. doi: 10.1111/j.1439-0531.1999.tb01252.x
https://doi.org/10.1111/j.1439-0531.1999... ].

In recent years, many studies have investigated the addition of progesterone to Ovsynch or modified Ovsynch protocols. In studies using progesterone (PRID, CIDR) with the Ovysnch protocol, an increase in the number of pregnancies in cows was observed [⁴4 Lane EA, Austin EJ, Roche JF, Crowe MA. The effect of estradiol benzoate or a synthetic gonadotrophin-releasing hormone used at the start of a progesterone treatment on estrous response in cattle. Theriogenology 2001;56,79-90. doi: 10.1016/s0093-691x(01)00544-1
https://doi.org/10.1016/s0093-691x(01)00...

5 Lane EA, Austin EJ, Roche JF, Crowe MA. The effect of estradiol benzoate on synchrony of estrus and fertility in cattle after removal of a progesterone-releasing intravaginal device. Theriogenology 2001;55,1807-18. doi: 10.1016/s0093-691x(01)00523-4
https://doi.org/10.1016/s0093-691x(01)00... -⁶6 El - Zarkouny SZ, Cartmill JA, Hensley BA, Stevenson JS. Pregnancy in dairy cows after synchronized ovulation regimens with or without presynchronization and progesterone. Journal of Dairy Science 2004;87,1024-37. doi: 10.3168/jds.S0022-0302(04)73248-8
https://doi.org/10.3168/jds.S0022-0302(0... ]. Pregnancy rates were 59% (Progesterone + Ovsynch) and 36% (Ovsynch), respectively [⁶6 El - Zarkouny SZ, Cartmill JA, Hensley BA, Stevenson JS. Pregnancy in dairy cows after synchronized ovulation regimens with or without presynchronization and progesterone. Journal of Dairy Science 2004;87,1024-37. doi: 10.3168/jds.S0022-0302(04)73248-8
https://doi.org/10.3168/jds.S0022-0302(0... ].

In this study, it was aimed to apply intravaginal progesterone-secreting preparations at different times and to determine the effect of one and two inseminations on fertilization in a certain period of time in multipourus cows raised in small family farms in Amasya.

MATERIAL AND METHODS

Animals

This study; was carried out in family farms (with a maximum of 20 cattle) located in Merzifon District of Amasya Province. Working time is from March to December 2018.

The animals used in the study gave at least one birth and formed cows between the ages of 36-72 months (Total, 159) (in Holstein, Brown Swiss, and Simmental breeds), dairy cows. When animals were examined, it was observed that at least 90 days postpartum, no true anestrus, PGF2α, and Ovsynch were applied, but estrus did not occur and problems were not resolved.

The animals were thoroughly examined for genital organs, and care was taken to ensure that there was no cystic structure and abnormal vaginal discharge. It was determined by the anamnesis finding that the last births of the animals to be included in the study were problem-free, and the phenomenon of retention secundinarum was not experienced.

Since they were animals in the same region, the conditions of care and feeding were the same. They were fed with high quality hay consisting of dry clover grass and sainfoin, corn silage and concentrated feed (3-4 kg/day) daily. Water ad libitium was given.

Age, Body Condition Scores (BCS), and milk yields of cows

The number of animals used in Group 1 was 56. 31 of these animals were Simmental, 19 were Holstein, and 6 were Brown Swisses. The average age was 57.05 ± 27.40 months, the BCS average was recorded as 2.75 ± 0.43, and the average milk yield was recorded as 16.66 ± 5.28 kg.

The number of animals used in Group 2 was 50. 31 of these animals are Simmental, 14 were Holstein, and 5 were Brown Swiss. The average age was 45.48 ± 26.81 months, the mean BCS was 2.74 ± 0.37, and the average milk yield was 13.46 ± 3.05 kg.

The number of animals used in Group 3 was 53. 26 of these animals were Simmental, 19 were Holstein, and 8 were Brown Swisses. The average age was 44.73 ± 20.25 months, the BCS average was recorded as 2.70 ± 0.34, and the average milk yield was recorded as 15.35 ± 4.60 kg.

Determination of animal groups

Milk yields of the cows included in the study were recorded and for the BCS of the animals, the scoring determined by Çitil and Uzlu [⁷7 Çitil M, Uzlu E. Sigirlarin dogum sonrasi hastaliklarinin erken tanisinda ultrasonografik yöntemle vücut kondisyon skor tayininin önemi. Kafkas Üniversitesi Veteriner Fakültesi Dergisi 2005;11,2,201-6. https://vetdergikafkas.org/uploads/pdf/pdf_KVFD_330.pdf
https://vetdergikafkas.org/uploads/pdf/p... ] was used.

BCS; 1.0 Extremely bad, 1.5 Very bad, 2.0 Bad, 2.5 Medium, 3.0 Good, 3.5 Very good, 4.0 Fat, 4.5 Very fat, and 5.0 Too much fat was scored as Çitil and Uzlu [⁷7 Çitil M, Uzlu E. Sigirlarin dogum sonrasi hastaliklarinin erken tanisinda ultrasonografik yöntemle vücut kondisyon skor tayininin önemi. Kafkas Üniversitesi Veteriner Fakültesi Dergisi 2005;11,2,201-6. https://vetdergikafkas.org/uploads/pdf/pdf_KVFD_330.pdf
https://vetdergikafkas.org/uploads/pdf/p... ].

Group 1 (n = 56): In the cows included in this group, Day 0 GnRH (IM) (10 mg Buserelin acetate, Ovarelin, CEVA DİF) + Progesterone implants PRID® (1.55 g progesterone CEVA), Day 8 PGF2α (Dinoprost tromethamine, 25 mg, Dinolytic, Pfizer), Day 9 Progesterone implants removal + PGF2α, insemination was performed at 56th hours insemination after the second PGF2α injection (Figure 1).

Group 2 (n = 50): on day 0, GnRH (IM) + Progesterone implants, PGF2α (IM) on the 8th day, Progesterone implants removal + PGF2α on the 9th day, insemination was performed at 48th and 72th hour after the second PGF2α injection.

Group 3 (n=53): on day 0 GnRH (IM) + Progesterone implants, PGF2α (IM) on the 5th-day insert of Progesterone implants, day 6 Progesterone implants removal + PGF2α (IM), and insemination at 56th hour after the second PGF2α injection (Figure 3).

Pregnancy diagnoses were made with an ultrasonography device (Welld® WED-3000 Shenzhen WELLD Medical Electronics Co.) 35 days after the artificial insemination of all cows.

Oestrus monitoring and artificial insemination

The most important symptoms of estrus are do let it jump on it and uterine tone is graded with 3 points and it was decided that cows with at least 4 points were successfully synchronized.

Statistical analysis

Before performing the statistical analysis, data were examined with the Kolmogorov-Smirnov test for normality and the Levene test for homogeneity of variances as parametric test assumptions. The relationship between groups, race, animal owners’ complaints, BCS, and pregnancy rates were determined using the Chi-square test. Relationship coefficients were calculated with Cramer’s V coefficient. The differences between age, estrus signs, and milk yields in pregnant-no-pregnant groups were determined using the Student t-test. P < 0.05 was considered significant in all analyses. All statistical analysis was performed by using SPSS 14.01 package program for Windows.

The data obtained were analyzed in the SPSS package program according to their variability and continuity with different statistical methods. Pregnancy rates by groups, Chi-square test was used to determine the differences between pregnancies and races, the complaints of animal owners and pregnancies, BCS, and pregnancies. Independent Sample T-Test was used to determine the difference between age and pregnancy, to determine the difference between estrus findings and pregnancies, and to determine the relationship between milk yields and pregnancy.

Ethics committee permission

Ethics Committee approval was not obtained because our study was evaluated within the scope of "Good Clinical Practices".

RESULTS

In Table 2; It is shown which applications the animals in the groups have been exposed to before.

In Table 3; The scores given according to the estrus scoring and whether they were pregnant at the end of the study were shown.

The mean score of the animals used in group 1 (n = 56) was recorded as 5.39 ± 1.56 according to the scoring system prepared. The pregnancy rate was 41.07%. (Table 3).

The average score of the animals used in group 2 (n = 50) was recorded as 5.6 ± 1.38 according to the scoring system prepared. The pregnancy rate was 42%. (Table 3).

The mean score of the animals used in group 3 (n = 53) was recorded as 5.49 ± 1.52 according to the scoring system prepared. The pregnancy rate was 52.83%. (Table 3).

No difference was found between the groups in terms of pregnancy rates (P > 0.05).

There is no difference in whether or not pregnancies differ by race (P > 0.05).

There was a statistically low relationship between the complaints of the cattle participating in the study and their pregnancies (P = 0.000, Cramer's V = 0.317). It was also determined that there was a difference between their anger complaints and their pregnancy.

In the examination on whether there is a relationship between BCS and pregnancies, it was determined that there was a significant (P < 0.05) pregnancy in the group above BCS 3.5 (P < 0.05).

DISCUSSION

It has been reported that in cows and heifers, vaginal hyperemia, uterine tone, and vaginal discharge increase during the estrus period, which is the appropriate insemination time, and with these findings, the cow that is in heat when jumped on does not escape, and that it can become pregnant when artificial insemination is performed [⁸8 Dobson H, Kamonpatana M. A review of female cattle reproduction with special reference to a comparison between buffaloes, cows and zebu. Journal of Reproduction and Fertility 1986;77,1,1-36. doi: 10.1530/jrf.0.0770001
https://doi.org/10.1530/jrf.0.0770001... ]. In the presented study, the above estrus findings during artificial insemination were scored and followed with the estrus scoring system, but all cows were applied fixed-time artificial insemination regardless of whether there were any estrus findings after the progesterone implant synchronization protocol.

Additional applications are made to increase the synchronization rate in estrus synchronizations with CIDR. In a study on 2077 heifers, Mihm [³3 Mihm M. Delayed resumption of cyclicity in postpartum dairy and beef cows. Reprod. Domest. Anim. 1999;34,277-84. doi: 10.1111/j.1439-0531.1999.tb01252.x
https://doi.org/10.1111/j.1439-0531.1999... ] divided heifers into 4 groups, applied CIDR to the heifers (n = 517) in Group 1 for 7 days, and injected 25 mg PGF2α on the day of removal of the CIDR, followed by the estrus for 84 hours. They were inseminated. The heifers that did not show estrus for eighty-four hours were inseminated by applying 100 μg of GnRH. The heifers in Group 2 (n = 504) were also applied to those in Group 1, but the only difference was the application of 100 μg of GnRH on the day the CIDR application started. The heifers in group 3 (n = 531) were treated with GnRH on the day of CIDR application, and PGF2α on the day of removal, followed by the second GnRH application at 60th hour, and artificial insemination was performed without looking at the signs of estrus. The heifers in group 4 (n = 525), on the day of removal of CIDR, were treated with PGF2α, followed by GnRH at 60th hour, and artificial insemination was performed regardless of estrus symptoms. As a result, there was no difference in pregnancy rates between Group 1 (54.5%) and Group 2 (57.3%), but a higher pregnancy rate was obtained than those inseminated without estrus [³3 Mihm M. Delayed resumption of cyclicity in postpartum dairy and beef cows. Reprod. Domest. Anim. 1999;34,277-84. doi: 10.1111/j.1439-0531.1999.tb01252.x
https://doi.org/10.1111/j.1439-0531.1999... ]. In this study, artificial insemination was performed in three different groups without synchronization, and the pregnancy rate of animals used in group 1 (n = 56) was determined as 41.07%, and the pregnancy rate of animals used in group 2 (n = 50) was 42%. The pregnancy rate of the animals used in the third group (n = 53) was determined as 52.83% and was found consistent with the mentioned study.

The researchers (9) report that 66.7-90% of estrus can be seen as a result of PRID applications for 6-12 days. Xue et al. [¹⁰10 Xue L, Arbeiter K, Breitenfellner N. Die repetierte transvaginale Progesteron medikation zur Zyklusprovakation und Fertilitätsüberwachung beim Rind. Wiener Tierärztliche Monatsschrift 1984;81:380-388] reported that the rates of estrus obtained with PRID applied in different periods are different, accordingly, 80-100% of cyclic cows and 75% of animals in anestrus are observed. Grunert [¹¹11 Grunert E. Zyklus und brunststörungen. In: E Grunert, M Berchtold editor. Fertilitätsstörungen beim weiblichen Rind, Verlag Parey, 1982, Berlin, Hamburg.] reports that 74% of estrus was seen with 12 days of PRID applications in postpartum 40 and 80 days to induce ovaries in cows with symptoms of subestrus. In this study, according to Table 1, the most important symptoms of estrus are grading permitting, and uterine tone is graded with 3 points and it is decided that the cows with at least 4 points are successfully synchronized [¹⁰10 Xue L, Arbeiter K, Breitenfellner N. Die repetierte transvaginale Progesteron medikation zur Zyklusprovakation und Fertilitätsüberwachung beim Rind. Wiener Tierärztliche Monatsschrift 1984;81:380-388]. The average score of the animals used in group 1 (n = 56) was recorded as 5.39 according to the scoring system prepared. The average score of the animals used in group 2 (n = 50) was recorded as 5.6 according to the scoring system prepared. The average score of the animals used in group 3 (n = 53) was recorded as 5.49 according to the scoring system prepared.

It has been reported that a single PGF2α application is not very effective in regressing the newly shaped CL using the fixed-time artificial insemination protocol [¹²12 Tsai SJ, Wiltbank MC. Prostaglandin F2 regulates distinct physiological changes in early and mid-cycle bovina corpora lutea. Biology of Reproduction 1988;58,346-352.doi: 10.1095/biolreprod58.2.346
https://doi.org/10.1095/biolreprod58.2.3... ]. Various investigators have been reported on which day and interval of synchronization of the second PGF2α injection [¹³13 Santos JEP, Narciso CD, Rivera F, Thatcher WW, Chebel RC. Effect of reducing the period of follicle dominance in a timed artificial insemination protocol on reproduction of dairy cows. J. Dairy Sci. 2010;93,7,2976-2988. doi: 10.3168/jds.2009-2870
https://doi.org/10.3168/jds.2009-2870... , ¹⁴14 Ribeiro ES, Bisinotto RS, Favoreto MG, Martins LT, Cerri RLA, Silvestre FT, Greco LF, Thatcher WW, Santos JEP. Fertility in dairy cows following resynchronization and administering twice the luteolytic dose of prostaglandin F2a as one or two injections in the 5-day timed artificial insemination protocol. Theriogenology 2012;78,273-284. doi: 10.1016/j.theriogenology.2012.01.012
https://doi.org/10.1016/j.theriogenology... ]. In another study, no difference was reported between the pregnancy rates in the fattening cows subjected to the 5-day Cosynch + CIDR program with the removal of the CIDR applicator 2 doses at 8-hour intervals or 2 doses in a single treatment [¹⁵15 Bridges GA, Ahola JK, Brauner C, Cruppe LH, Currin JC, Day ML, Gunn PJ, Jaeger JR, Lake SL, Lamb GC, Marquezini GHL, Peel RK, Radunz AE, Stevenson JS, Whittier WD. Determination of the appropriate delivery of prostaglandin F2a in the five-day CO-Synch + controlled intravaginal drug release protocol in suckled beef cows. J. Anim. Sci. 2012;90,4814-22. doi: 10.2527/jas.2011-4880
https://doi.org/10.2527/jas.2011-4880... ].

CL's early regression deficiency is an interesting biological condition that is not yet fully understood [¹⁶16 Nascimento AB, Souza AH, Keskin A, Sartori R, Wiltbank MC. Lack of complete regression of the Day 5 corpus luteum after one or two doses of PGF2a in nonlactating Holstein cows. Theriogenology 2014;81,3,389-95. doi: 10.1016/j.theriogenology.2013.10.009
https://doi.org/10.1016/j.theriogenology... ]. However, the inability to fully activate intracellular signal transduction pathways has been suggested and supported by various researchers [¹⁷17 Mondal M, Schilling B, Folger J, Steibel JP, Buchnick H, Zalman Y, Ireland JJ, Meidan R, Smith GW. Deciphering the luteal transcriptome: Potential mechanisms mediating stage-specific luteolytic response of the corpus luteum to prostaglandin F-2 alpha. Physiological Genomics 2011;43,447-456. doi: 10.1152/physiolgenomics.00155.2010
https://doi.org/10.1152/physiolgenomics.... ,¹⁸18 Diaz FJ, Luo W, Wiltbank MC. Prostaglandin F2alpha regulation of mRNA for activating protein 1 transcriptional factors in porcine corpora lutea (CL): Lack of induction of JUN and JUND in CL without luteolytic capacity. Domestic Anim. Endocrinol. 2013;44,98-108. doi: 10.1016/j.domaniend.2012.09.005
https://doi.org/10.1016/j.domaniend.2012... ].

Some studies have reported statistical differences between pregnancy and in multiparous cows as a result of fixed-time artificial insemination. Others did not report any significant differences in conception rates between primiparous and multiparous cows [¹⁹19 Carvalho PD, Guenther JN, Fuenzalida MJ, Amundson MC, Wiltbank MC, Fricke PM. Presynchronization using a modified Ovsynch protocol or a single gonadotropin-releasing hormone injection 7 d before an Ovsynch-56 protocol for submission of lactating dairy cows to first timed artificial insemination. J. Dairy Sci. 2014;97,6305-6315. doi: 10.3168/jds.2014-8222
https://doi.org/10.3168/jds.2014-8222...

20 Carvalho PD, Fuenzalida MJ, Ricci A, Souza AH, Barletta RV, Wiltbank MC, Fricke PM. Modifications of Ovsynch improve fertility during resynchronization: Evaluation of resynchronization with gonadotropin-releasing hormone 6 d before initiation of Ovsynch and addition of a second prostaglandin F2a treatment. J. Dairy Sci. 2015;98,8741-52. doi: 10.3168/jds.2015-9719
https://doi.org/10.3168/jds.2015-9719... -²¹21 Giordano JO, Wiltbank MC, Guenther JN, Pawlisch R, Bas S, Cunha AP, Fricke PM. Increased fertility in lactating dairy cows resynchronized with Double-Ovsynch compared with Ovsynch initiated 32 d after timed artificial insemination. J. Dairy Sci. 2012;95,639-653. doi: 10.3168/jds.2011-4418
https://doi.org/10.3168/jds.2011-4418... ]. In the study presented as a result of the aforementioned studies, a PGF2α injection was made in each of the three groups that were synchronized with an interval of 24 hours.

The initiation of new ovulation at the beginning of the synchronization protocol has been reported to increase plasma Progesterone concentrations during PGF2α injection [²²22 Colazo MG, Dourey A, Rajamahendran R, Ambrose DJ. Progesterone supplementation before timed AI increased ovulation synchrony and pregnancy per AI, and supplementation after timed AI reduced pregnancy losses in lactating dairy cows. Theriogenology 2013;79,833-841. doi: 10.1016/j.theriogenology.2012.12.011
https://doi.org/10.1016/j.theriogenology... ]. In the early stage induced by exogenous GnRH application, it is noted that the ovulation of a dominant follicle will be ovulated as a result of the second follicular wave and decrease the luteal function and conception in beef breed cattle [²³23 Mussard ML, Burke CR, Behlke EJ, Gasser CL, Day ML. Influence of prematüre induction of a luteinizing hormone surge with gonadotropin-releasing hormone on ovulation, luteal function, and fertility in cattle. J. Anim. Sci. 2007;85:937-943. doi: 10.2527/jas.2006-592
https://doi.org/10.2527/jas.2006-592... ]. However, in a previous study, it was reported that there was no significant relationship between the diameter of follicles to be ovulated in dairy cows and pregnancy rates [²⁴24 Colazo MG, Gordon MB, Rajamahendran R, Mapletoft RJ, Ambrose DJ. Pregnancy rates to timed-AI in dairy cows treated with gonadotropin-releasing hormone or porcine luteinizing hormone. Theriogenology 2009;72,262-70. doi: 10.1016/j.theriogenology.2009.02.017
https://doi.org/10.1016/j.theriogenology... ].

It is reported that in animals with inactive and active ovarium, estrus mostly occurs within 2-3 days with PRID application for 7-12 days for the treatment of estrus synchronization or functional disorders [²⁵25 Arbeiter K, Pohl W. Über die anwendung der PRID-spirale beim ovariellen funktionsstörungen des rindes (Feldversuch 2). Tierärztliche Umschau 1986;41,664-668.]. The GnRH hormone used in the treatment of inactive ovaries causes the release of LH, thus contributing to the maturation and ovulation of the dominant follicle [²⁶26 Noakes DE, Parkinson TJ, England GCW. Infertility in the cow 383-472. In: Arthur's Veterinary Reproduction and Obstetrics. 2009; W. B. Saunders, London.]. In some studies, it has been suggested that a high progesterone environment with long-term progesterone administration creates follicular dominance, and as a result, an aged oocyte may be produced [²⁷27 Townson DH, Tsang PC, Butler WR, Frajblat M, Griel LC Jr, Johnson CJ, et al. Relationship of fertility to ovarian follicular waves before breeding in dairy cows. J Anim Sci. 2002;80:1053- 1058. doi: 10.2527/2002.8041053x.
https://doi.org/10.2527/2002.8041053x... ,²⁸28 Austin EJ, Mihm M, Ryan MP, Williams DH, Roche JF. Effect of duration of dominance of the ovulatory follicle on onset of estrus and fertility in heifers. J Anim Sci. 1999;77:2219 -26. doi: 10.2527/1999.7782219x
https://doi.org/10.2527/1999.7782219x... ]. In this study, which was presented by making use of the researches reported above, GnRH was applied together with short- time PRID.

CONCLUSIONS

As a result; as the yield of cows increases, it becomes harder for them to become pregnant. For sustainable livestock, it is necessary to obtain one cub per year from a cow. Many hormonal applications and many formulas have been developed to achieve this. In various studies conducted in the world and our country and the field study presented, it is tried to ensure that the cows are conceived at any time with the tools containing progesterone and fixed-time artificial insemination protocols. As it is known, it is very difficult to carry out a study with hundreds of business owners in field conditions. In this study, which was carried out in animals fed the same ration in a certain area and kept under the same care conditions, it was seen that the highest pregnancy rate with 52.83% (statistical analysis did not show the superiority) was in the 3^rd group implanted with Progesterone for 6 days and artificially inseminated at 56 hours by injecting PGF2 alpha on the 5^th and 6^th days. In this group, a better pregnancy result was obtained than the group applied for 9 days (Group 2). It is thought that oocyte aging that may occur with the prolonged application of progesterone implants leads to such a result. Besides, it is more economical because of single insemination in terms of cost. The study should be done in more detail in more animals in the future and question marks should be removed.

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