11 Conception rate of high-producing dairy cows at first service using prostaglandin F2α and oestradiol benzoate

2019 ◽  
Vol 31 (1) ◽  
pp. 131
Author(s):  
M. Yamaguchi ◽  
M. Takayama ◽  
H. López ◽  
O. Dochi
Keyword(s):  
New York ◽  
Dairy Cows ◽  
Corpus Luteum ◽  
Animal Health ◽  
Prostaglandin F2α ◽  
Conception Rate ◽  
Chi Square ◽  
Average Interval ◽  
Oestradiol Benzoate ◽  
Days Open

We have shown that a simplified oestrus synchronization protocol using prostaglandin F2α (PG) and oestradiol benzoate (EB) resulted in a satisfactory conception rate, similar to that obtained in high-producing dairy cows with natural oestrus (Yamaguchi et al. 2018 Reprod. Fertil. Dev. 30, 147 abstr). However, we found no significant effect of PG+EB protocols on the first-service conception rates (CR) of dairy cows. This study investigated the effect of the first-service CR by using PG+EB protocols in the high-producing dairy cows that had not exhibited oestrus expression after calving. Data concerning the first-service CR were obtained for 481 Holstein cows from 4 commercial dairy herds in Hokkaido and Ibaraki, Japan, from 2014 to 2017. The average number of parity, average interval between calving and the first service, and average milk yield (at 305 days) of the cows were 2.2±1.3, 89.7±26.1 days, and 10314±1994kg, respectively. We carried out the PG+EB protocols on cows not showing evident standing heat from Days 50 to 150 postpartum regardless of the presence of a corpus luteum in the ovary. The statuses of ovaries of cows were confirmed using ultrasonography before starting the treatment. Prostaglandin F2α (25 mg; Lutalyse, Pfizer, New York, NY, USA) was injected into cows with a >20mm cutoff for functional corpus luteum diameter at a random stage of oestrus, and EB (1 mg; Ovahormon®, Aska Animal Health Co., Tokyo, Japan) was injected 24h later, and AI was carried out 24 to 48h after EB injection. Cows with a natural oestrus service from Days 50 to 150 postpartum were used as control. All the cows were inseminated after the onset of standing heat or removal of the tail chalk. Pregnancy diagnoses were performed using ultrasonography 30 to 45 days after AI. The CR and intervals of partum to conception were analysed using a chi-square test and ANOVA. The first-service CR (i.e. the number of pregnant cows/total number of cows in the treatment group) of the natural oestrus (n=330) and PG+EB (n=151) groups were 42.7 and 41.1%, respectively, and there were no significant differences between these 2 groups (P=0.7). The average interval between calving and the first service of the PG+EB groups was significantly longer than that of the natural oestrus groups (86.4±1.5 days v. 96.9±1.9 days; P<0.01). The average days open of the natural oestrus and PG+EB groups were 88.5±3.2 days and 98.1±2.3 days, respectively (P<0.05). These results confirmed that the first-service CR in the PG+EB and natural oestrus groups of high-producing dairy cows were similar. We suggest that conducting PG+EB protocols was effective in the high-producing dairy cows that had not exhibited oestrus expression after calving. Moreover, using PG+EB protocols could prevent the further increase in the number of days open.

8 RESPONSE OF COMMUNAL COWS TO OESTRUS SYNCHRONIZATION AND TIMED ARTIFICIAL INSEMINATION

2016 ◽  
Vol 28 (2) ◽  
pp. 133
Author(s):  
Z. C. Raphalalani ◽  
K. A. Nephawe ◽  
M. L. Mphaphathi ◽  
F. V. Ramukhithi ◽  
M. M. Seshoka ◽  
...  
Keyword(s):  
New York ◽  
Body Condition Score ◽  
Animal Health ◽  
Age Groups ◽  
Reproductive Technologies ◽  
Conception Rate ◽  
Bull Semen ◽  
Significant Difference ◽  
Oestradiol Benzoate ◽  
Condition Score

Reproductive technologies such as oestrus synchronization and AI have been tested in controlled environments in the commercial farms in South Africa but not in an uncontrolled communal setup. The aims of the study were to evaluate the response of communal cows to oestrus synchronization and timed AI. The effects of age and body condition score (BCS) on oestrus response and conception rate were also studied. A total of 96 cows were selected from the communal villages. Cows with the BCS of 2.5 to 4.5 (on a scale of 1–5) and age between 3 and 10 years were used. Cows were grouped into 2 BCS groups (<3 and = 3) and 2 age groups (<6 and = 6). All groups were subjected to a 9-day Ovsynch + CIDR (CIDR®; Pfizer Laboratories, New York, NY, USA) protocol. A CIDR® was inserted into the vagina on Day 0 (random days of the cycle), and 2 mg of oestradiol benzoate (Ciderol®; Pfizer Laboratories) was administered. On Day 8, the CIDR® was removed, and the cows were administered with 500 μg of cloprostenol (PGF; Estrumate®, Schering-Plough Animal Health). In addition, on Day 9, cows were given 1 mg of oestradiol benzoate, and a heat mount detector (Karma®; Four Lakes) was placed on the tail head of the cows to detect oestrus response (standing heat). All the synchronized cows were then inseminated at 36 and 42 h with frozen-thawed Nguni bull semen following oestradiol benzoate injection. Pregnancy diagnosis was performed 90 days following timed AI using ultrasound scanner and transrectal palpation. Data were analysed using ANOVA. An overall 73% oestrus response and 45% conception rate were achieved in this study. There was no significant difference in oestrus response in cows with a BCS <3 (67%) and = 3 (83%) or age <6 (77%) and = 6 (72%). There was no significant difference in conception rate between those <6 (41%) and = 6 (47%) years of age. However, cows with a BCS of = 3 had greater (P < 0.05) conception rate (55%) compared with those with a BCS <3 (35%). In conclusion, communal cows responded to an oestrus synchronization program involving timed AI. The BCS and age did not alter the oestrus response, but conception rate was higher in communal cows with BCS of = 3.

8 EFFECT OF SUPPLEMENTATION WITH ESTRADIOL OR ESTRADIOL PLUS GONADOTROPIN-RELEASING HORMONE AFTER PROSTAGLANDIN F2α ADMINISTRATION ON THE PREGNANCY RATES FOLLOWING TIMED ARTIFICIAL INSEMINATION IN DAIRY COWS

2012 ◽  
Vol 24 (1) ◽  
pp. 115
Author(s):  
J. K. Jeong ◽  
H. G. Kang ◽  
I. H. Kim
Keyword(s):  
Dairy Cows ◽  
Pregnancy Rate ◽  
Artificial Insemination ◽  
Animal Health ◽  
Prostaglandin F2α ◽  
Pregnancy Rates ◽  
Gnrh Analogue ◽  
Chi Square ◽  
Array Transducer ◽  
Timed Artificial Insemination

This study determined the effect of supplementation with oestradiol or oestradiol plus GnRH after PGF2α administration on pregnancy rates after timed artificial insemination (TAI) in dairy cows. Three hundred and six Holstein dairy cows with corpus luteum confirmed by ultrasonography (Tringa Linear with 5.0 MHz array transducer; Esaote Pie Medical, Maastricht, the Netherlands) were randomly allocated to three treatments: a single injection of 500 μg of cloprostenol, PGF2α analogue (Estrumate, Schering-Plough Animal Health, Friesoythe, Germany; PGF2α group, n = 115) designated as 0 h, an injection of 500 μg of cloprostenol and an injection of 1 mg of oestradiol benzoate (EB, SY Esrone; Samyang, Seoul, Korea) 56 h later (PGF2α + EB group, n = 114), or the same treatment as in the PGF2α + EB group and an additional injection of 100 μg of gonadorelin, GnRH analogue (Godorel, Uni-Biotech Co., Ltd., Korea) 24 h later (PGF2α + EB + GnRH group, n = 77). All cows in each group received TAI 80 h after the PGF2α injection. Pregnancy was determined at 40 to 50 days after TAI by using both ultrasonography and rectal palpation. Pregnancy rate among groups were compared by the chi-square test using the SAS program (version 9.1: SAS Institute Inc., Cary, NC, USA). Pregnancy rate following TAI were higher (P < 0.05) in the PGF2α + EB + GnRH group (34/77, 44.2%) than in the PGF2α group (31/115, 27.0%), with the PGF2α + EB group intermediate (39/114, 34.2%). In conclusion, the supplementation with oestradiol plus GnRH after PGF2α administration improved pregnancy rate after TAI in dairy cows. This work was supported by the research grant of the Chungbuk National University in 2011.

Comparison of reproductive responses after PGF2α and GnRH-PGF2α oestrous synchronisation schemes in Holstein cows

2001 ◽  
Vol 26 (2) ◽  
pp. 467-470
Author(s):  
J.F. Cox ◽  
F. Saravia ◽  
O. Torrealba ◽  
A. Zavala ◽  
A. Lobos
Keyword(s):  
Dairy Cows ◽  
Corpus Luteum ◽  
Detection Efficiency ◽  
Post Partum ◽  
Conception Rate ◽  
Milk Samples ◽  
Reproductive Response ◽  
Holstein Friesian ◽  
Breeding Schemes ◽  
Friesian Cows

AbstractControlled breeding schemes for oestrous detection constitutes a proactive technical response that balances the infrastructural requirement for a profitable dairy operation and the demands for optimal animal performance. The present study compared (a) the reproductive response of a treatment based on a short vs longer-acting PGF2α analogue (tiaprost vs luprostiol), and (b) the reproductive response after a treatment of GnRH-PGF2α vs PGF2α alone for synchronizing dairy cows. Holstein-Friesian cows averaging 9000 kg milk/lactation and fed according to their requirements were used in the study. Cows were cyclic, at least 60 days post partum and were clinically sound before being considered for the experiments. In Experiment 1, animals were synchronised using an i.m. injection of either 15 mg of luprostiol or 0.75 mg of tiaprost, based on ultrasonic diagnosis of a corpus luteum. Animals were inseminated at observed oestrus. In Experiment 2, cows were synchronised, at random, by either an injection of 10pg ofbuserelin (day 0) followed by 0.75 mg of tiaprost at day 7 (GnRH-PGF2α) orjust 0.75 mg of tiaprost (PGF2α). For both treatments only cows with an ultrasonically detected corpus luteum were treated. Animals were inseminated at oestrus. At the time of treatment and again 3 days later, milk samples were collected and assayed for progesterone by RIA. Cows with progesterone concentrations >1 ng/ml were considered to have corpus luteum. Luteolysis was considered to have occurred when concentrations of progesterone were > 1 ng/ml at day 0 and <0.8 ng/ml at day 3. In Experiment 1, both analogues gave similar results in terms of induced luteolysis [luprostiol: 36/39 (92.3%) vs tiaprost: 36/41 (87.8%)], oestrous detection efficiency [luprostiol: 26/36 (72.2%) vs tiaprost: 30/36 (83.3%], oestrous distribution [day 2, 3 and 4, respectively: luprostiol: 26.9%, 50.0%, 19.2% vs tiaprost: 36.7%, 50.0%, 13.3%], and conception rates [luprostiol: 12/25 (48.0%) vs tiaprost: 14/28 (50.0%); P>0.05]. In Experiment 2, oestrous detection efficiency, interval to oestrus and conception rate were similar between treatments [97/149 (65.1%), 71.1 h, 43/95 (45.3%) for PGF2α vs 130/188 (69.1%), 68.2h, 65/126 (51.6%) for GnRH-PGF2α, respectively]. However the oestrous distribution was more concentrated in GnRH-PGF2α treated animals (P<0.01).

23 EFFECTS OF THE NUMBER OF SERVICES FERTILITY IN DAIRY COWS

2011 ◽  
Vol 23 (1) ◽  
pp. 118 ◽  
Author(s):  
M. Yamaguchi ◽  
M. Tanisawa ◽  
H. Koyama ◽  
S. Takahashi ◽  
O. Dochi
Keyword(s):  
Dairy Cows ◽  
Conception Rate ◽  
Low Fertility ◽  
Chi Square ◽  
The Third ◽  
Total Percentage ◽  
Conception Rates ◽  
Service Conception ◽  
Chi Square Test ◽  
Rectal Palpation

In recent years, reproductive performance of dairy cows has been declining worldwide, especially among cows of high genetic merit for milk production. The cause of the low fertility may considerably vary across countries and is probably multifactorial. This problem remains unsolved. Further, the first-service conception rate of dairy cows has remarkably decreased worldwide. The number of services required for conception has increased due to the low fertility in dairy cows. However, there are few reports about the relationship between conception rates and the number of services in the current dairy cows. The objective of this study was to investigate whether the number of services affects the conception rates of dairy cows. Data concerning the conception rates was obtained for 8386 Holstein cows from 40 commercial dairy herds in eastern Hokkaido, Japan, from 2006 to 2009. The diagnosis of pregnancy was confirmed by rectal palpation between 30 and 45 days after insemination. The average interval between calving and the first-service was 87.3 days. The average milk yield was 8500 kg. Number of conducting services was from the first to the seventh service. The conception rate was analysed using chi-square test. The results are presented in Table1. The conception rate from the first to the seventh service was 40.2 to 54.0%. The conception rate at the first service was significantly low (40.2%); however, the conception rates did not significantly differ after the second-service. A similar tendency was observed during each year. Moreover, the total percentage of conceptions from the first to the third service was 83.8%. The average number of services per conception was 2.2. The results of this study indicate that the first service yielded the lowest conception rates. The conception rates after the second service did not significantly differ. Moreover, ∼84% of the dairy cows became pregnant between the first service and the third service. However, this result shows that ∼16% of the dairy cows in the herds were repeat breeding. In order to improve fertility, it is necessary to study the factors that affect the first-service conception rates of dairy cows. Moreover, to improve the conception rate of dairy cows, it is important to elucidate the cause of these problems. Table 1.The number and percentage of dairy cows conceiving at each of the services for consecutive services

43 COSTS RELATED TO ESTRUS SYNCHRONIZATION AND AI PROTOCOLS IN CROSSBRED HOLSTEIN-ZEBU DAIRY COWS

2010 ◽  
Vol 22 (1) ◽  
pp. 179
Author(s):  
L. D. P. Sinedino ◽  
B. T. Gerhardt ◽  
A. P. Dourado ◽  
L. A. G. Nogueira
Keyword(s):  
New York ◽  
Dairy Cows ◽  
Pregnancy Rate ◽  
Animal Health ◽  
Cost Benefit ◽  
Estradiol Benzoate ◽  
Estrus Synchronization ◽  
Labor Costs ◽  
Estrus Detection ◽  
The Cost

The objective of this paper was to compare 3 bovine AI protocols, evaluating the cost of each treatment and the pregnancy rates obtained, to demonstrate the importance of routine utilization of estrus synchronization techniques. The experiment was conducted in the Farm School of Cachoeiras de Macacu of the Federal Fluminense University, in the state of Rio de Janeiro, during the period from 2006 to 2007 (August to June). One hundred sixteen crossbred female Holstein-Zebu dairy cows in cycle, with body condition between 2.5 to 4 (on a scale from 1 to 5), were selected and divided randomly in 3 groups (G). Animals in G1 [n = 60; 21 heifers (H), 13 primiparous (P), and 26 multiparous (M)], with palpable corpus luteum, received 25 mg of prostaglandin F2 intravulvar, and AI was done 12 h after estrus detection. For animals in G2 (n = 30; 11 H, 6 P, and 13 M) an intravaginal progesterone device (CIDR®, Pfizer Animal Health, New York, NY, USA) was inserted and 2 mg of estradiol benzoate (EB) was administered i.m. on Day 0. On Day 8 the device was removed and 25 mg of prostaglandin was administered i.m. on Day 9, 2 mg of EB was administered, and 30 h later, timed AI of all animals was performed. For G3 (n = 26; 9 H, 5 P, and 12 M), the protocol used was similar to that for G2, except that on Day 8 400 IU of eCG was administered (in addition to the removal of the device) and on Day 9 the dose of EB was reduced to 1 mg and timed AI was done 27 h later. AI was done with semen from 2 sires with proven fertility, by the same technician. The pregnancy diagnoses were done on Day 45 by palpation per rectum and transrectal ultrasonography. The cost-benefit relation was calculated according to the cost of pharmaceuticals multiplied by the number of animals in each experimental group divided by the number of pregnancies obtained in each one, without considering the manual labor costs in all the groups and considering 3 uses of the CIDR. The statistical analyses were done using chi-square test. The pregnancy rate obtained in G2 (60%, 18/30) was superior to that in G1 (30%, 18/60) (P < 0.05), demonstrating the efficiency of the treatment that utilized progesterone. G3 (53.85%, 14/26) was similar (P > 0.05) to G2, despite the fact that the eCG was added in this group. In reference to cost-benefit, considering only the pharmaceuticals costs and the value for pregnancy obtained in each group, the costs found, respectively, were G1 U$7.02 and U$23.66; G2 U$28.57 and U$47.59; and G3 U$47.96 and U$89.05. The lowest cost in the estrus synchronization was based on the use of prostaglandins alone; the use of progesterone increased the synchronization cost, but also increased the pregnancy rate and eliminated the need for estrus observation. The addition of eCG in cows that are cycling does not necessarily demand a increase in pregnancy rate. Failure in estrus detection, using prostaglandin alone, increased the interval from calving, causing a daily loss in milk production, which justified the investment in protocols of estrus and ovulation synchronization, contributing to increase the reproductive efficiency of a dairy cow herd.

320 INFLUENCE OF PROGESTERONE AND MOMENT OF ESTRADIOL BENZOATE INJECTION ON MULTIPLE-OVULATION EMBRYO TRANSFER RESULTS

2013 ◽  
Vol 25 (1) ◽  
pp. 307
Author(s):  
S. Kmaid ◽  
J. M. Saldaña
Keyword(s):  
Negative Binomial ◽  
Body Condition Score ◽  
Animal Health ◽  
Prostaglandin F2α ◽  
Control Group ◽  
Negative Binomial Regression Model ◽  
Embryo Production ◽  
Oestradiol Benzoate ◽  
The Moment ◽  
Universal Laboratory

Current superovulatory treatment combines progesterone as well as oestradiol injection at the moment of CIDR insertion to improve synchronization of follicular wave emergence [reviewed by Bo et al. 2002 Theriogenology 57, 53–172; and Mapletoft et al. 2003 J. Anim. Sci. 81 (E. Suppl.), E28–E36] The aim of the present work was to study if delaying oestradiol benzoate (EB) injection 24 or 48 h from CIDR insertion would have the same outcome on embryo production after superovulatory treatment as additional progesterone administered at CIDR insertion. One hundred and eleven superovulatory treatments conducted during the same period (5 consecutive collection days) at random stages of the oestrus cycle at the same location were retrospectively evaluated. Holstein cycling heifers of 18 months of age (body condition score 3.2 ± 0.28, 1–5 range; weighing 357 ± 28 kg) were divided according to the following treatments: control group (n = 24): Day 0: CIDR insertion (Pfizer Animal Health, New York, NY, USA), 50 mg of progesterone, and 2 mg of oestradiol benzoate (Benzadiol, Universal Laboratory, Montevideo, Uruguay); Group BE24 (n = 47): Day –1: CIDR insertion and Day 0: 2 mg of oestradiol benzoate; Group BE48 (n = 40): Day –2: CIDR insertion and Day 0: 2 mg of oestradiol benzoate. All heifers were superstimulated on Day 3.5 (Day 0 = EB injection) with 290 NIH units of FSH (Folltropin, BionicheAnimal Health, Belleville, ON, Canada) in twice-daily decreasing doses over 4.5 days. On Day 6, all cows received 2 doses (a.m. and p.m.) of a prostaglandin F2α analogue (800 µg, Delprostenate, Glandinex, Universal Laboratory), and CIDR were removed on the morning of Day 7. Cows were injected with 10 µg of GnRH (Receptal, Intervet, Boxmeer, the Netherlands) on Day 8 a.m. and were inseminated 12 and 24 h later with semen of 3 bulls of proven fertility. On Day 15, ova/embryos were collected nonsurgically and evaluated in accordance with IETS guidelines. Data were analysed with a negative binomial regression model (Table 1). Administration of EB 24 or 48 h after CIDR insertion produced similar numbers of transferable and freezable embryos as well as total ova/embryos compared with addition of progesterone and EB at the moment of CIDR insertion. According to these results, EB could be administrated without progesterone injection either 24 or 48 h after CIDR insertion without compromising embryo production. Table 1.Embryo production of heifers superstimulated after additional progesterone (P4) and different times (24 or 48 h after CIDR insertion) of oestradiol benzoate administration (results are mean ± SE)

153 EFFECT OF DIFFERENT HOLDING AND TRANSPORT MEDIA ON CONCEPTION RATES FOLLOWING TRANSFER OF IN VIVO AND IN VITRO FERTILIZATION-DERIVED BOVINE EMBRYOS

2011 ◽  
Vol 23 (1) ◽  
pp. 180
Author(s):  
C. A. Zanenga ◽  
C. M. Martins ◽  
N. C. Rodovalho ◽  
F. Aidar ◽  
J. F. Hasler ◽  
...  
Keyword(s):  
Animal Health ◽  
Conception Rate ◽  
Bovine Embryos ◽  
Chi Square ◽  
Mato Grosso ◽  
Conception Rates ◽  
Chi Square Test ◽  
Donor Cows

Two experiments were conducted to compare conception rates following embryo transfer (ET) of bovine embryos held and transported in Syngro® holding medium (Bioniche, Belleville, Ontario, Canada) with other 2 holding media: Emcare® (ICPbio, Auckland, New Zealand) for in vivo-derived embryos and HEPES-buffered synthetic oviduct fluid (H-SOF) for IVF-derived embryos. The first trial was performed in the period from October through December 2006 at the Curitiba farm in Poços de Caldas, Minas Gerais, Brazil. A total of 140 in vivo-derived embryos were produced from 20 Nelore donor cows and transferred fresh at the same farm. After each donor recovery, embryos were equally separated per stage (morula or blastocyst) and classification (grades 1, 2, and 3) into 2 Petri dishes, each containing either Syngro or Emcare. The embryos were held for an average of 3 h after recovery, loaded into 0.25-mL straws, and transferred fresh into recipients heifers, which were all previously synchronized with the same hormonal protocol treatment and presented a corpus luteum on the day of transference. Conception rate was checked at approximately 60 days of conception by rectal palpation. The chi-square test was used for statistical analysis. The conception rate of embryos maintained in Syngro was significantly higher than those in Emcare: 64.2% (43/67) v. 47.9% (35/73; P < 0.05). A second experiment was performed between September and December 2008 at Embriza Biotechnology Laboratory, Campo Grande, Mato Grosso do Sul, Brazil. A total of 1689 IVF-derived embryos (stage = 7, quality = 1), produced from Nelore donor cows, were randomly assigned to be held and transported in either Syngro (769) or H-SOF transport medium (920). Transportation time ranged from 1 to 9 h, and the recipient farms ranged from 100 to 1200 km in distance from the Embriza Laboratory. Crossbred recipient heifers (Bos taurus × Bos indicus) were synchronized with prostaglandin or vaginal progesterone device protocols. Pregnancy diagnosis was performed by ultrasonography approximately 60 days after ET. Statistical comparisons were performed using the chi-square test. Conception rates resulting from embryos transported in Syngro (45.1%, 347/769) and in H-SOF (42.0%, 386/920) were not different (P = 0.19). Financial support from Embriza Biotecnology, Tecnopec LTDA, and Bioniche Animal Health

7 COMPARISON OF TIMED ARTIFICIAL INSEMINATION PROTOCOLS USING PROSTAGLANDIN F2α+ESTRADIOL OR PROSTAGLANDIN F2α+ESTRADIOL+GONADOTROPIN-RELEASING HORMONE IN DAIRY COWS

2012 ◽  
Vol 24 (1) ◽  
pp. 115
Author(s):  
J. K. Jeong ◽  
H. G. Kang ◽  
I. H. Kim
Keyword(s):  
Dairy Cows ◽  
Pregnancy Rate ◽  
Artificial Insemination ◽  
Prostaglandin F2α ◽  
Pregnancy Rates ◽  
Gnrh Analogue ◽  
Chi Square ◽  
Array Transducer ◽  
Chi Square Test ◽  
Timed Artificial Insemination

This study compared pregnancy rates following 2 timed artificial insemination (TAI) protocols using PGF2α + oestradiol or PGF2α + oestradiol + GnRH in dairy cows. Four hundred fifty-five Holstein dairy cows, 2.2 ± 0.1 in parity, 148.3 ± 3.6 days in milk, with corpus luteum of greater than 20 mm diameter confirmed by ultrasonography (Tringa Linear with 5.0 MHz array transducer; Esaote Pie Medical, Maastricht, the Netherlands) were randomly divided into two treatments: an injection of 500 μg of cloprostenol, PGF2α analogue (Iliren cycle BP®, Intervet International GmbH, Unterschleissheim, Germany) and an injection of 2 mg of oestradiol benzoate (EB, SY Esrone, Samyang, Seoul, Korea) 36 h later (PGF2α + EB group, n = 257), or an injection of 500 μg of cloprostenol, an injection of 2 mg of EB 36 h later and an additional injection of 100 μg of gonadorelin, GnRH analogue (Godorel, Uni-Biotech Co., Ltd., Korea) 24 h later (PGF2α + EB + GnRH group, n = 198). All cows in the two groups received TAI 24 h after the EB injection. Pregnancy was determined at 40 to 50 days after TAI by using both ultrasonography and rectal palpation. Pregnancy rates between the PGF2α + EB and PGF2α + EB + GnRH groups were compared by the chi-square test using the SAS program (version 9.1: SAS Institute Inc., Cary, NC, USA). Pregnancy rate following TAI did not differ between the PGF2α + EB (32.7%) and PGF2α + EB + GnRH groups (34.9%; P > 0.05). In conclusion, addition of GnRH for TAI protocol using PGF2α + oestradiol did not improve pregnancy rate in dairy cows.

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