New Trends For Estrus Synchronization Using A Combination Of Gonadotropins, Prostaglandin And Estradiol Cypionate In Dairy Cows
estrus, gnrh and estradiol cypionate, pgf2α, pregnancy, synchronization
H Amer. New Trends For Estrus Synchronization Using A Combination Of Gonadotropins, Prostaglandin And Estradiol Cypionate In Dairy Cows. The Internet Journal of Veterinary Medicine. 2006 Volume 3 Number 2.
This study was conducted to through the light on a recent method for estrus synchronization in lactating dairy cows using PGF2α, GnRH and estradiol cypionate (ECP). Four treatments were performed on sixty dairy cows. In treatment 1 (PP), cows received two injections of PGF2α on days 0 and 11 (n=14); while in treatment 2 (PGP), cows were injected twice PGF2α on days 0 and 11 and 100 ug of GnRH on day 3 after the 1st injection (n=14). In treatment 3 (PGPE-0), cows were treated with PGP and 1 mg of ECP at the same time of 2nd PGF2α injection (n=16). In treatment 4 (PGPE-1), cows were treated with PGP and 1 mg of ECP one day after 2nd PGF2α injection (n=16). The cows were examined rectally and ultrasonographically by B-mode Ultrasound System [Pie-Medical Scanner-240] with a 6-8 MHz linear rectal transducer. Every cow was blood sampled at selected intervals for progesterone and estradiol assay and inseminated at estrus.
The results showed a higher percentage of GnRH-treated cows (PGP) ovulated after 1st PGF2α injection than the non treated (PP) cows (64.3% vs 50%; P<0.05). The GnRH-treated cows tended to have a larger mature follicle present at 2nd PGF2α injection. Subsequently, the percentage of cows that ovulated after 2nd PGF2α injection was 71.4% vs 50% for GnRH-treated cows than none treated ones, respectively. Two days after 2nd PGF2α injection, cows treated with PGP had a higher peak preovulatory concentrations of estradiol compared to PP treated cows (3.2±0.48 vs 2.6±0.45 pg/ml). Additionally, cows treated with ECP (PGPE-0 and PGPE-1) had a higher peak preovulatory concentrations of estradiol (6.3±0.43 and 6.99±0.63 pg/ml; P<0.01); and a higher percentage ovulation (75.0% and 87.5%) than the other treated groups (PP or PGP). Thus, a higher percentage of ECP (especially PGPE-1 group) treated cows were observed in standing estrus and ovulated after 2nd PGF2α injection than the other treated groups. Submission rates (number of inseminated/totalX100), differed statistically across treatments, especially those treated with ECP, as well as; the conception and pregnancy rates were observed higher with the ECP treated cows than the other treatments. In conclusion, PGP protocol increased the number of cows that ovulated after 1st PGF2α injection and produced more mature follicles at the time of 2nd PGF2α injection. The combination of ECP and PGP (PGPE-1) enhanced the expression of estrus and increased ovulation percentage, thus it is potentially a new method to routinely synchronize estrus and ovulation in dairy cows.
Considerable research has focused on developing technologies to synchronize and efficiently detect estrus (Larson and Ball, 1992; Sterry et al., 2007), as lactating dairy cows have poor reproductive performance due to low fertility and low rates of estrus detection. Recently, a protocol has been developed (ovsynch) that synchronize the time of ovulation precisely using GnRH and PGF2α (Pursley et al., 1995). Ovsynch is based on the initiation of a new follicular wave with GnRH before inducing luteolysis by PGF2α. The emerging dominant follicle is forced to ovulate by a second treatment with GnRH allowing for timed artificial insemination (TAI). Ovsynch protocol utilizes 3 treatments; GnRH administered at a random stage of the estrus cycle, PGF2α given 7 days later, and a 2 nd GnRH treatment 2 days after PGF2α injection. In lactating dairy cows, this protocol synchronized follicular development, regression of the corpus luteum, and time of ovulation allowing effective TAI without the need for detection of estrus (Burke et al., 1996; Schmitt et al., 1996; Pursley et al., 1997). Combinations of PGF2α, steroids (E2 and P4) and GnRH are used to regulate the life span of the corpus luteum, control follicular wave emergence and ovulation, and synchronize estrus in cattle (Larson and Ball, 1992; Thatcher, 2001). Prostaglandins (PGF2α) or its analogues induce luteal regression, but interval to estrus is highly variable in randomly cycling cows (Lauderdale et al., 1974). Short-term pretreatment with P4 or multiple injections of PGF2α (at 11-14 day interval) reduced the proportion of cows that are in met estrus and increases the percentage of cows in estrus (Britt, 1979; Xu et al., 1997; Bicalho et al., 2007). A more precise expression of estrus (after PGF2α) can be achieved by synchronizing the follicular wave that gives rise to the preovulatory follicle. Estrogens and GnRH induce atresia or ovulation of dominant follicles and synchronize the emergence of a new follicular wave (Bo et al., 1994; Burke et al., 1999). Substituting oestradiol cypionate (ECP) for the second GnRH injection synchronizes ovulation and estrus and yields similar pregnancy rates to the original ovsynch program (Lopes et al., 2000; Pancarci et al., 2002). Oestradiol cypionate is the only form of estradiol registered for use in lactating dairy cows in the USA. Kojima et al. (2000) tested a GnRH-PGF2α protocol combined with P4 pretreatment in postpartum beef cows.
The objectives of the present study are, a) to evaluate an estrus synchronization protocol for dairy cows based on the 7-11 system, as the interval elapsed between the GnRH and 2 nd PGF2α injection was prolonged to 8 days (longer than the traditional 7 days interval, b) to improve the synchrony of estrus and ovulation, after placement of an ECP at the end of treatment.
Material and Methods
This study was conducted in a private dairy farm at Dakahlia Governorate. A total of sixty lactating Holstein cows those 64.5±4.6 days postpartum and eligible for first postpartum insemination were used. Cows were managed under routine conditions that included daily milking, free stall housing and twice daily feeding of total mixed ration (primary components are corn silage, alfa alfa hay and concentrates; balanced to NRC requirements). Milk production averaged 35.4±0.8 kg/day at the start of the experiment, and the rolling herd average was approximately 7500 kg milk per lactation period. Only healthy cows, with normal reproductive status and with history of normal parturition; were chosen for these experiments.
Cows were randomly assigned to each of four treatments (as described
Treatment 1 (PP)
The cows (n=14) were injected with PGF2α (2 ml Estrumate, Intervet) at day 0 and day 11.
Treatment 2 (PGP)
The cows (n=14) were injected with PGF2α (day 0), an injection of GnRH (100 ug; Cystorelin, Merial, Athens, GA) 3 days later and a 2 nd dose of PGF2α on day 11 (PGP treatment) was injected.
Treatment 3 (PGPE-0)
The cows (n=16) in this design were injected as in PGP as well as a 1 mg injection of ECP (Pharmacia Animal Health, Kalamazoo, MI) at the time of 2 nd PGF2α injection (PGPE-0). The 0 denoted that ECP was given 0 day after 2 nd PGF2α injection.
Treatment 4 (PGPE-1)
The cows (n=16) in this design were injected as in PGP with 1 mg of ECP given one day after the 2 nd PGF2α injection (PGPE-1).
Estrus detection and artificial insemination
Cows were observed for estrus 3 times daily and artificially inseminated approximately 12 hours after the observed estrus (a.m.-p.m. rules). All the cows were examined rectally and ultrasonographically by B-mode Ultrasound System [Pie-Medical Scanner-240] with a linear rectal transducer of 6-8 MHz] to record the corpora lutea and follicles (≥1.5 mm) at each observation in the 4 treatments.
Assay of plasma progesterone (P4) and estradiol (E2)
Coccygeal blood samples were collected on day 0 (1 st PGF2α injection), 3 and 5 and daily up to day 11 to ovulation or day 16 for cows that failed to ovulate after 2 nd PGF2α injection (examined per rectum) into EDTA-treated tubes and placed immediately on ice. Plasma was harvested by centrifugation (1500Xg for 15 minutes), within 4 h of collection and stored at –20°C until quantification of P4 and E2 by Radio-immunoassay (RIA). Plasma was harvested and assayed for progesterone and estradiol.
Plasma progesterone concentrations were determined using a commercial available RIA-kits (Coat-A-Count; Diagnostic Products Corporation, C.A), validated for bovine plasma (Kirby et al., 1997). Samples were analyzed across five assays and intra- and inter-assay coefficient of variation was 16.9 and 7.9%, respectively. Plasma estradiol concentrations were determined on day 11 through day 16 (in 4 treatments) with a validated RIA (Kirby et al., 1997). Samples were analyzed across 6 assays and intra- and inter-assay coefficient of variation was 7.5 and 14.7%, respectively.
Cows were checked for pregnancy by ultrasound scanning at 40 and confirmed by rectal palpation at 45 days after artificial insemination. The submission, conception and pregnancy rates were measured in the four groups of treated cows.
Submission rate=Number of cows inseminated within 4 days after 2 nd PGF2α injection/total number of cows.
Conception rate=Number of pregnant cows /number of inseminated cows.
Pregnancy rate=Number of pregnant cows /total number of treated cows.
Data were analyzed using the Statistical Analysis System (SAS, 1996). Plasma estradiol concentrations were analyzed as repeated measures using the General Linear Models Procedure (Proc. GLM). Proportion of cows ovulating after each PGF2α injection was tested using a
A greater percentage of GnRH-treated cows (PGP) ovulated after 1 st PGF2α injection than the non treated (PP) cows (64.3% vs 50%; P<0.05;
Cows treated with PGP had higher peak preovulatory concentrations of estradiol in plasma compared to PP treated cows (3.2±0.48 vs 2.6±0.45 pg/ml) following the 2 nd PGF2α injection (
After the 2 nd PGF2α injection, ovulation was defined as low P4 (<0.5 ng/ml) on day 13 and high P4 (≥0.5 ng/ml) on day 24. Cows not ovulated may had high P4 on day 13 and 24, low P4 on day 13 and 24, or high P4 on day 13 and low P4 on day 24. The development of accessory corpus luteum in the presence of a functional corpora lutea could not be determined because ovulation was based mainly on P4 concentration.
At the time of 2 nd PGF2α injection, the size of mature follicle was similar for all treatments after the ultrasound scanning. However, for cows treated with ECP (PGPE-0 and PGPE-1), mature follicles also determined within 3 days after 2 nd PGF2α injection (P<0.05). Addition of ECP to the PGP treatment increased the percentage of cows ovulating (50% and 71.4% for PP and PGP vs 75.0% and 87.5% for PGPE-0 and PGPE-1; P<0.05;
Treatment with ECP also increased plasma estradiol concentration after 2 nd PGF2α injection (
Thirty one of sixty cows (51.6%) were classified as anoestrus at the start of the trial (plasma P4 <0.5 ng/ml on days –8, 0 and 3). The percentage of cows that developed a corpus luteum (hereafter referred to as ovulation) after 1 st PGF2α injection was greater when cows received GnRH (75% and 81.2%; for PGPE-0 and PGPE-1 versus 50% and 64.3% for PP and PGP; P<0.001). A higher percentage of ECP treated cows were observed in standing oestrus and ovulated after 2 nd PGF2α injection and; 75% and 87.5%; P<0.05 for PGPE-0 and PGPE-1 vs 50% and71.4% for PP and PGP treated cows, respectively.
Plasma estradiol concentrations were similar across treatments at the time of 2 nd PGF2α injection. However, 2 days after 2 nd PGF2α, plasma estradiol concentrations were greater in cows that received ECP compared to PP or PGP (P<0.001;
Submission rates (number of inseminated cows/totalX100), the conception and pregnancy rates was observed to be higher with the ECP treated cows than the other treatments (
An estrus synchronization protocol (termed PGP) similar to 7-11 synch (Kojima et al., 2000; Kanitz et al., 2006) but without Melongesterol acetate was developed. The protocol consists of a PGF2α injection followed 3 days later by a GnRH injection and another PGF2α injection 8 days after the GnRH. The protocol is similar to the original PGF2α protocol consisting of 2 injections of PGF2α 11 days a part (Lucy et al., 1986; Sterry et al., 2007; Bicalho et al., 2007), but includes an injection of GnRH 3 days after the first PGF2α injection. The GnRH provides two-fold advantages. First, it forces a timely ovulation of the dominant follicle after 1 st PGF2α injection (Thatcher and Chenault, 1976). The timed ovulation prevents late ovulations that would potentially result in an immature and unresponsive corpus luteum at the time of 2 nd PGF2α injection. Second, the GnRH forces a percentage of anoestrus cows to ovulate (Britt et al., 1974) and induces cyclicity in cows that would otherwise not respond to PGF2α. The advantage of PGP was examined in the present experiments. In each case, the number of cows that ovulated after 1 st PGF2α injection was increased. For example, the percentage of cows that ovulated after 1 st PGF2α injection developed when GnRH was given on day 3 (PGP and PGPE-1 compared to PP).
In the present study, the cows treated with PGP had mature follicles that were larger at the time of 2 nd PGF2α injection. However, 2 days later, follicles were similar in size because the mature follicles of PP-treated cows continued to grow, whereas those of PGP-treated cows remained the same size. Treatment with GnRH appears to produce more mature follicles at the time of 2 nd PGF2α injection; supported by the fact that both PGP and PGPE-1-treated cows were in estrus before PP-treated cows. Luteal and follicular maturity may be an advantage of the PGP protocol over traditional GnRH- PGF2α protocols. The extra day between the GnRH and PGF2α injection (8 days for PGP versus 7 days for traditional protocols) may place more cows in diestrum (being responsive to PGF2α), and more mature follicle may lead to a more functional CL upon ovulation (Vasconcelos et al., 2001; Kanitz et al., 2006; Sterry et al., 2007).
Addition of ECP increased the number of cows that ovulated after 2 nd PGF2α injection (
One major goal for any new estrus synchronization protocol should be the implementation of timed AI. The interval to ovulation and interval to estrus were examined in this study. The results were promising, as a higher percentage of GnRH-treated cows ovulated after 1 st PGF2α injection (64.3% vs 50%; P<0.05). The GnRH-treated cows tended to have a larger mature follicle present at 2 nd PGF2α injection. The percentage of cows that ovulated after 2 nd PGF2α injection was 71.4% vs 50% for GnRH-treated cows than none treated ones, respectively. Cows treated with PGP had higher peak preovulatory concentrations of estradiol in plasma compared to PP treated cows (3.2±0.48 vs 2.6±0.45 pg/ml; following 2 nd PGF2α injection. Cows treated with ECP (PGPE-0 and PGPE-1) had a significant higher peak preovulatory concentrations of estradiol (6.3±0.43 and 6.99±0.63 pg/ml); and a significant higher percentage ovulation (75.0% and 87.5%) than the other treated groups (PP or PGP). The PGP protocols are similar to the other GnRH-PGF2α protocols because GnRH and PGF2α are given in a series. The primary difference is that PGF2α is given before 1 st GnRH injection. The first injection of PGF2α causes corpus luteum regression so that most cows are on day 8 of the estrus cycle when 2 nd PGF2α dose is injected. In late luteal phase, cows treated with GnRH and PGF2α at a 7 day interval tend to exhibit estrus around the time of PGF2α injection; i.e. before the time when most cows are in estrus, 2-3 days after PGF2α (Vasconcelos et al., 1999; Dejarnette et al., 2001). The present study did not compare PGP to GnRH and PGF2α given at a 7 day interval but with one day more (8 days). Nevertheless, estrus was not observed before 2 nd PGF2α injection in PGP cows. The possibility that relative to GnRH and PGF2α-alone, PGP increases the percentage of cows in estrus 2-3 days after the last PGF2α injection should be tested in larger experiment.
GnRH is an obvious substitution for ECP in the PGPE-1 protocol. The GnRH would be given 48 hours after 2 nd PGF2α injection but the timing of other injections would be similar (PGF2α day 0, GnRH day 3, PGF2α day 11, GnRH day 13; PGPG protocol). In a previous study, the PGPG protocol was tested in 45 postpartum dairy cows and 93% of the cows ovulated on day 14 (Sterry et al., 2007). Thus, the PGPG protocol may be an alternative to PGPE-1 that is highly suited for timed AI.
In conclusion, we can conclude that PGP protocol increased the number of ovulated cows after 1 st PGF2α injection and produced more mature follicles at the time of 2 nd PGF2α injection. Adding ECP to PGP (especially PGPE-1) enhanced the expression of estrus and increased ovulation percentage. Thus, a combination of PGP and ECP is potentially a new method to routinely synchronize estrus and ovulation in dairy cows.