Use of medroxyprogesterone acetate (MAP) in lactating Holstein cows within an Ovsynch protocol: follicular growth and hormonal patterns

To evaluate the effects of incorporating medroxyprogesterone acetate (MAP) in an Ovsynch protocol, cyclic lactating dairy cows were assigned randomly to two groups (control and MAP, n=8 each). Ovsynch treatment (Day 0: GnRH, Day 7: PG, Day 9: GnRH) was initiated at random stages of the estrous cycle (control) and an intravaginal polyurethane sponge impregnated with 300mg of MAP was inserted intravaginally in the MAP group at Day 0 and removed at Day 7 of the Ovsynch protocol (MAP treatment). Ovaries were scanned daily from Day 0 until the second GnRH treatment on Day 9 and from then every 6h for 36 h. Milk samples were collected three times weekly starting 17 days before the initiation of treatment to determine the stage of the cycle at the beginning of the Ovsynch protocol. Blood samples were collected to monitor estradiol (E2), progesterone (P4), LH, and 15-ketodihydro-PGF(2alpha) (PGFM) by RIA. Response to the first GnRH treatment varied with the stage of the cycle at the time of initiation of treatment, as cows in metestrous and late diestrous did not ovulate. In cows ovulating, growth rate of the new follicle was not affected by the addition of MAP. No treatment differences were found in E2 concentrations which reached a maximum at Day 9, consistent with the maximum follicular size. At Day 7, cows with luteal concentrations of P4 had increased concentrations of PGFM, but cows with basal P4 did not show an active release of prostaglandins. There were no treatment differences in the ovulatory response to the second GnRH-induced ovulation, with 11 of the 16 cows ovulating between 16 and 32 h. The addition of MAP to the Ovsynch protocol could not mimic the normal high progesterone levels needed to prevent premature ovulations in those cows with premature CL regression.     

Strategic treatment of anovular dairy cows with GnRH

The primary objective was to evaluate fertility of anovular dairy cows given GnRH 4 d after first postpartum timed AI (TAI). Secondary objectives were to determine ovulatory response to treatment, effect of treatment on serum progesterone (P(4)) concentrations, and the proportion with a short luteal phase. Lactating Holstein cows (n=1047) were submitted for first postpartum TAI using a Presynch+Ovsynch protocol. Anovular cows were identified from an initial 1047 lactating Holstein cows using transrectal ultrasonography, based on the absence of a CL at the first GnRH injection of a Presynch+Ovsynch protocol, and anovular cows were randomly assigned to receive either no further treatment (Control, n=85), or 100 microg of GnRH 4 d after TAI (GnRH treated; n=71). For GnRH treated cows, 51% responded by ovulating a follicle in response to GnRH treatment 4 d after TAI; however, pregnancies per AI (P/AI) did not differ between GnRH treated cows that ovulated (36%) compared to GnRH treated cows that did not ovulate (21%). There was a quadratic effect of P(4) at the PGF(2 alpha) injection of Ovsynch on P/AI, and cows with P(4)>or=1 ng/mL at the PGF(2 alpha) injection of Ovsynch had greater P/AI (41%) than cows with P(4)<1 ng/mL (12%); however, no treatment difference was detected. Overall, P/AI did not differ between control (30.1%) and GnRH treated (29.6%) treatments for synchronized cows. Although treatment of anovular cows with GnRH 4 d after TAI failed to improve fertility, variation among cows in serum P(4) at the PGF(2 alpha) injection of Ovsynch dramatically affected fertility of anovular dairy cows.     

Strategies to optimize reproductive efficiency by regulation of ovarian function in yak (Poephagus grunniens L.)

Ovulatory response to the first GnRH of Ovsynch is the critical determinant for successful synchronization of ovulation in animals. An attempt was made in this study to design a pre-Ovsynch hormonal strategy in yaks to increase the ovulatory response to the first GnRH injection of Ovsynch so that overall synchronization rate to Ovsynch could be improved. Non-lactating cyclic yak cows (n=33) were assigned to receive either no treatment before Ovsynch (control) or 0.375 mg of PGF2alpha (PreP) followed 2 d later by 10 microg of GnRH (PreG), administered 4 (G4G), 5 (G5G), or 6 (G6G) d before initiating the Ovsynch protocol. Rectal palpation was performed to assess ovulation and blood samples were collected to measure progesterone concentrations during pre-treatment, treatment and post-treatment periods. All the animals received timed AI 12 and 24h after the final GnRH of Ovsynch. Diagnoses for pregnancy were performed by rectal palpation and profiles of plasma progesterone 35 d after AI. Percentage of yak cows that ovulated in response to the first GnRH injection of Ovsynch, synchronized to Ovsynch treatment, had a functional CL at PGF2alpha of Ovsynch, had circulating concentrations of P4 at PGF2alpha of Ovsynch and likely to be pregnant after 35 d after AI, were greater in G6G and G5G compared with control, whereas G4G did not differ from controls. In addition, animals that ovulated in response to first GnRH of Ovsynch had greater response to PGF2alpha of Ovsynch and greater synchronization rate to the overall protocol than those that did not ovulate. In summary, PGF2alpha-and-GnRH-based pre-Ovsynch strategies consisting of 5 or 6-d interval between PreG and first GnRH of Ovsynch resulted in a greater ovulatory and luteolytic response to first GnRH andPGF2alpha of Ovsynch, respectively, compared with control animals. These, in turn, optimized synchronization rate to Ovsynch in yaks.     

Reduction in size of the ovulatory follicle reduces subsequent luteal size and pregnancy rate

We hypothesized that reducing the size of the ovulatory follicle using aspiration and GnRH would reduce the size of the resulting CL, reduce circulating progesterone concentrations, and alter conception rates. Lactating dairy cows (n=52) had synchronized ovulation and AI by treating with GnRH and PGF2alpha as follows: Day -9, GnRH (100 microg); Day -2, PGF2alpha (25 mg); Day 0, GnRH (100 microg); Day 1, AI. Treated cows (aspirated group; n=29) had all follicles > 4 mm in diameter aspirated on Days -5 or -6 in order to start a new follicular wave. Control cows (nonaspirated group: n=23) had no follicle aspiration. The size of follicles and CL were monitored by ultrasonography. The synchronized ovulation rate (ovulation rate to second GnRH injection: 42/52=80.8%) and double ovulation rate of synchronized cows (6/42=14.3%) did not differ (P > 0.05) between groups. Aspiration reduced the size of the ovulatory follicle (P < 0.0001; 11.5 +/- 0.2 vs 14.5 +/- 0.4 mm), and serum estradiol concentrations at second GnRH treatment (P < 0.0002; 2.5 +/- 0.4 vs 5.7 +/- 0.6 pg/mL). The volume of CL was less (P < 0.05) for aspirated than nonaspirated cows on Day 7 (2,862 +/- 228 vs 5,363 +/- 342 mm3) or Day 14 (4,652 +/- 283 vs 6,526 +/- 373 mm3). Similarly, serum progesterone concentrations were less on Day 7 (P < 0.05) and Day 14 (P < 0.10) for aspirated cows. Pregnancy rate per AI for synchronized cows was lower (P < 0.05) for aspirated (3/21=14.3%) than nonaspirated (10/21=47.6%) cows. In conclusion, ovulation of smaller follicles produced lowered fertility possibly because development of smaller CL decreased circulating progesterone concentrations.     

Effect of presynchronization using prostaglandin F2alpha and a milk-ejection test on pregnancy rate after the timed artificial insemination protocol, Ovsynch

The objective of this research was to determine if PGF2alpha-induced milk letdown (ML) is an accurate indicator of luteolysis, allowing cows to be synchronized to begin the Ovsynch protocol (GnRH-7d-PGF2alpha-2d-GnRH-24h-AI) at the most beneficial time of the estrous cycle (days 5-9), and determine if this would improve pregnancy rate (PR). Lactating Holstein cows between 55 and 70 days in milk were used to evaluate the ML test and PR after the Ovsynch protocol, when initiated on the basis of the test result (PROSYNCH). PROSYNCH cows (n = 60) had one teat cannulated to test for ML and were treated with 500 microg cloprostenol, PGF2alpha analogue (PG). Cows with ML were started on Ovsynch 10 days later, and those without started 3 days later. Cows in the control group (OVSYNCH, n = 64) were injected with physiological saline and observed for ML. This group was started on Ovsynch 10 days after saline treatment. Milk samples were collected thrice weekly to determine progesterone concentrations. ML indicated luteolysis with a sensitivity of 98% and a specificity of 60%. The positive and negative predictive values were 83 and 92%, respectively. Pregnancy rates were 48% for PROSYNCH and 52% for OVSYNCH (P = 0.72). When data from both groups were combined, PR was greater in cows that started the Ovsynch protocol in stage 2 of the estrous cycle (days 5-9, 67%) than all other stages (stage 1: days 1-4, 35%; stage 3: days 10-16, 45%; stage 4: days 17-21, 42%; P < 0.01). The proportion of animals with ovulation after GnRH#1, luteolysis after PGF2alpha, and ovulation after GnRH#2 were all greater in the PROSYNCH group (77% versus 55%, P < 0.02; 83% versus 66%, P < 0.03; 97% versus 84%, P < 0.03, respectively). Therefore, the ML test indicated luteolysis with sufficient precision to time the initiation of the Ovsynch protocol between days 5 and 9 of the cycle, however, this did not alter PR compared to starting the protocol randomly throughout the cycle. Initiating the Ovsynch protocol between days 5 and 9 of the cycle increased PR, and improved the efficacy of each injection.     

Synchronization of ovulation in dairy cows using PGF2alpha and GnRH

This paper reports a new method for synchronizing the time of ovulation in cattle using GnRH and PGF(2alpha). In Experiments 1 and 2, lactating dairy cows (n=20) ranging from 36 to 280 d postpartum and dairy heifers (n=24) 14 to 16 mo old were treated with an intramuscular injection of 100 mug GnRH at a random stage of the estrous cycle. Seven d later the cattle received PGF(2alpha) to regress corpora lutea (CL). Lactating cows and heifers received a second injection of 100 mug GnRH 48 and 24 h later, respectively. Lactating cows were artificially inseminated 24 h after the second GnRH injection. Ovarian morphology was monitored daily by trans-rectal ultrasonography from 5 d prior to treatment until ovulation. In Experiment 3, the flexibility in the timing of hormonal injections with this synchronization protocol was evaluated by randomly assigning 66 lactating dairy cows to 3 different treatment groups. Lactating cows received the injection of PGF(2alpha) 48 (Group 1), 24 (Group 2), and 0 h (Group 3) prior to the second injection of GnRH, which was administered at the same time in each group to ensure the second injection of GnRH was given when follicles were at a similar stage of growth. In Experiments 1 and 2, the first injection of GnRH caused ovulation and formation of a new or accessory CL in 18 20 cows and 13 24 heifers. In addition, this injection of GnRH initiated or was coincident with initiation of a new follicular wave in 20 20 lactating cows and 18 24 heifers. Corpora lutea regressed after PGF(2alpha) in 20 20 cows and in 18 24 heifers. All cows and 18 24 heifers ovulated a newly formed dominant follicle between 24 and 32 h after the second injection of GnRH. Ten of 20 cows conceived to the timed artificial insemination. In Experiment 3, the conception rate in Groups 1 and 2 were greater than in Group 3, (55 and 46 % vs 11%, respectively). In summary, this protocol could have a major impact on managing reproduction in lactating dairy cows, because it allows for AI to occur at a known time of ovulation and eliminates the need for detection of estrus.     

Effect of hCG vs. GnRH at the beginning of the Ovsynch on first ovulation and conception rates in cyclic lactating dairy cows

Ovulatory response to the first GnRH of Ovsynch is a very important factor for determining the outcome of a successful synchronization. The aim of the present study was to develop a protocol to increase the percentage of cows that ovulated in response to the first administration of Ovsynch. This study was designed to compare ovulation rates in response to GnRH or hCG at the beginning of Ovsynch and to evaluate the effects of this manipulation on pregnancy. Cows (n = 371) with corpus luteum (CL) and at least one follicle greater than 10 mm diameter size on either ovary were included in the study. Cows were divided into two groups. The Ovsynch protocol began with GnRH (10 μg) in the GPG group (n = 161; GnRH-7d-PGF2α-56h-GnRH-18h-AI), whereas in the HPG group, the first GnRH of the Ovsynch was replaced with 1500 IU hCG (n = 210; hCG-7d-PGF2α-56h-GnRH-18h-AI). Ovarian ultrasonography was performed at the times of GnRH or hCG and of PGF2α administration, at the time of artificial insemination (AI) and seven days after AI, to determine ovulation. Maximal follicle size at the beginning of the Ovsynch did not affect on response to the first GnRH/hCG treatment. Conception rate (31 d) was 0.6 times more likely to be higher (P < 0.001) in cows that responded to the first hormonal administration of Ovsynch than in those that did not respond (95% CI = 0.29-0.71). Conception rate was found to be different between the HPG (37.6%, 79/210) and the GPG groups (48.4%, 78/161). Thus, beginning of the Ovsynch protocol with hCG did not increase ovulation and conception rate in lactating dairy cows, suggesting that hCG is not a suitable replacement of the first GnRH of Ovsynch. However, our results do show that increasing the ovulation rate in response to the first hormonal administration of Ovsynch can have a significant effect on conception rate.     

The effect of a GnRH analogue on the dynamics of follicular development and synchronization of estrus in lactating cyclic dairy cows

A GnRH analogue was used to synchronize ovarian follicular development prior to an injection of PGF(2alpha) for the synchronization of estrus in lactating Holstein cows. On Day 12 (estrus = Day 0) of the experimental cycle, cows (n = 8) were injected with 8 mug Buserelin (BUS group), followed by 25 mg PGF(2alpha) 7 d later (Day 19). Control cows (n = 7) received PGF(2alpha) on Day 12 (PGF group). Ovaries were scanned daily via ultrasonography, and plasma progesterone and estradiol concentrations were determined. Sizes of all visible follicles were recorded. Follicles were classified as small (3 to 5 mm), medium (6 to 9 mm), or large (>/= 10 mm). Between Days 12 and 16 of the cycle, the number of large follicles in PGF cows remained unchanged (1.2), whereas in the BUS group, the number of large follicles decreased from 1.3 on Day 12 to 0.5 on Day 15. Only 4 of 7 PGF cows ovulated a second-wave dominant follicle. In the BUS group, 7 of 8 cows ovulated a GnRH analogue induced dominant follicle that was first identified on Day 15. During the follicular phase (last 5 d prior to estrus), plasma progesterone declined in association with CL regression in both groups, and estradiol concentrations increased, reaching higher (P<.0.05) preovulatory peak concentration in BUS cows than in PGF cows (14.0 +/- 1.0 vs 10.4 +/- 1.1 pg/ml). The number of medium-size follicles was smaller and the number of small-size follicles tended to be higher in BUS cows than in the PGF-treated group. On the day of estrus, the size of the ovulatory follicle (16.1 vs 13.3 mm) and the size difference between the ovulatory and second largest follicle (11.4 vs 6.2 mm) were both larger in BUS cows than in PGF-treated cows, suggesting a more potent dominance effect of the ovulatory follicle in the BUS cows. This study suggests that a GnRH analogue can alter follicular development prior to synchronization of estrus with an injection of PGF(2alpha) in lactating dairy cows.     

Persistent ovarian follicles in dairy cows: a therapeutic approach

Anestrus is common during the postpartum period in high-producing dairy cows. In a previous investigation, we were able to diagnose persistent follicles of 8 to 12 mm in anestrous cows. This report describes 2 consecutive studies. The objectives of the first were to 1) assess the association of persistent follicles with anestrus; and 2) evaluate 2 therapeutic treatments. In the second study, we compared the effectiveness of the best treatment established in Study 1 with the Ovsynch protocol. For Study 1, anestrous cows were considered to have a persistent follicle if it was possible to observe a single follicular structure > 8 mm in the absence of a corpus luteum or a cyst in 2 ultrasonographic examinations performed at an interval of 7 d. At diagnosis (Day 0), cows were assigned to 1 of 3 treatment groups. Cows in Group GnRH/PGF (n=17) were treated with 100 microg GnRH i.m., and 25 mg PGF2alpha i.m. on Day 14. Cows in Group PRID (n=18) were fitted with a progesterone releasing intravaginal device (PRID, containing 1.55 g of progesterone) for 9 d and were given 100 microg GnRH i.m. at the time of PRID insertion, and 25 mg PGF2alpha i.m. on Day 7. Cows in Group Control (n=18) received no treatment. The animals were inseminated at observed estrus and were monitored weekly by ultrasonography until AI or 5 weeks from diagnosis. Blood samples were also collected on a weekly basis for progesterone determination. The mean size of persistent follicles on Day 0 was 9.4 +/- 0.04 mm. Progesterone levels were < 0.2 ng/mL during the first 35 d in 16 of 18 Control cows. Cows in the PRID group showed a lower persistent follicle rate (16.7% < 70.6% < 88.9%; P < 0.0001; PRID vs GnRH/PGF vs Control, respectively); a higher estrus detection rate (83.3% > 29.4% > 11.1%; P < 0.0001) and a higher pregnancy rate (27.8% > 5.9% > 0%; P = 0.02). For the second study, 145 cows with persistent follicles were randomly assigned to 1 of 2 treatment groups: cows in Group Ovsynch (n=73) were treated with 100 microg GnRH i.m. on Day 0, 25 mg PGF2alpha i.m. on Day 7, and 100 microm GnRH i.m. 32 h later. Cows in this group were inseminated 16 to 20 h after the second GnRH dose (Ovsynch protocol). Cows in Group PRID (n=72) were treated as those in the PRID group of Study 1, and were inseminated 56 h after PRID removal. Cows in the PRID group showed a higher ovulation rate (84.8% > 8.2%: P < 0.0001); a higher pregnancy rate (34.2% > 4.1%; P < 0.0001) and lower follicular persistence rate (22.2% < 63%; P < 0.0001) than those in Ovsynch. Our results indicate that persistent follicles affect cyclic ovarian function in lactating dairy cows. Cows with persistent follicles can be successfully synchronized and time inseminated using progesterone, GnRH and PGF2alpha but show a limited response to treatment with GnRH plus PGF2alpha.     

Follicular wave emergence, luteal function and synchrony of ovulation following GnRH or estradiol benzoate in a CIDR-treated, lactating Holstein cows

This study evaluated the effect of GnRH or estradiol benzoate (EB) on follicular wave emergence and progesterone concentrations, and following a second injection of GnRH, synchrony of ovulation, and pregnancy rates in a controlled internal drug release (CIDR)-based timed AI (TAI) protocol in lactating Holstein cows. Cows received a CIDR device without hormone (controls), with an injection of 100 microg GnRH or with an injection of 4 mg EB. Thereafter, all received PGF(2 alpha) at the time of CIDR removal on Day 7, GnRH on Day 9, and TAI 16 h later. Follicular wave emergence occurred within 7 days in 19/20 GnRH-treated, 14/20 EB-treated and 5/20 control cows (P < 0.05). The interval to wave emergence was the shorter and less variable (P < 0.01) in the GnRH group (2.9 +/- 0.2 days) than in the EB (4.7 +/- 0.5 days) or control (4.8 +/- 1.0 days) groups. Serum progesterone concentrations from Days 4 to 7 were higher (P < 0.01) in the GnRH-treated cows that ovulated than in those that did not ovulate, or in control and EB-treated cows. The diameters of dominant follicle on Day 7 differed among groups (P < 0.01), and the diameters of the preovulatory follicle on Day 9 were larger (P < 0.01) in the control and GnRH groups than in the EB group. The proportion of cows with synchronized ovulations did not differ among groups, but pregnancy rate to TAI was higher (P < 0.05) in the GnRH group (65%; 13/20) than in the control (30%; 6/20) or EB (35%; 7/20) groups. Results suggest that GnRH treatment of CIDR-treated lactating Holstein cows will result in synchronous follicular wave emergence, large preovulatory follicles and synchronous ovulation, resulting in an acceptable pregnancy rates to TAI.     

Ultrasonographic evaluation of endometrial thickness near timed AI as a predictor of fertility in high-producing dairy cows

The objectives were to evaluate changes in endometrial thickness (ET) near the time of a synchronized ovulation and to assess the relationship of ET and fertility in lactating Holstein cows, with or without estrogen supplementation near timed ovulation. In Experiment 1, eight cows were examined with transrectal ultrasonography, once daily for 5 d, starting concurrent with PGF_2α (PGF) treatment during an Ovsynch protocol (GnRH - 7d - PGF - 72h - GnRH). The ET increased rapidly after PGF (from ∼7 to ∼9.5 mm), remained > 9 mm for the next 2 d, then decreased to ∼8 and 7.4 mm, 1 and 2 d, respectively, after the second GnRH. In Experiment 2,642 cows (total of 758 breedings) were subjected to an Ovsynch protocol (GnRH - 7d - PGF - 56h - GnRH - 16h - timed AI); cows received either no further treatment (Ovsynch) or 1 mg of estradiol-17β im 8 h before the second GnRH (Ovsynch + E2). For both uterine horns, ET was measured (∼2 cm from the internal uterine body bifurcation) before E2 treatment (48 h after PGF). In cows with ET ≤ 8 mm vs > 8 mm, rates of ovulation were 86.0% (n = 136) vs 98.1% (n = 472; P < 0.01), respectively, and percentage pregnant per AI (P/AI) were 26.7% (n = 146) vs 42.7% (n = 524; P < 0.01). Treatment with E2 increased P/AI in cows with lower ET (Ovsynch + E2 = 37.0% vs Ovsynch = 23.3%; P = 0.07), but did not significantly improve P/AI in cows with ET > 8 mm (Ovsynch + E2 = 43.4% vs Ovsynch = 42.1%). In conclusion, a single ultrasonographic evaluation of ET in Holstein cows 48 h after PGF treatment in an Ovsynch program was a good predictor of ovulation failure and pregnancy success. Perhaps poor fertility in cows with reduced ET was low peripheral E2 concentrations near AI, poor P4 priming, or luteolysis failure during timed AI procedures.     

Synchronization of ovulation in beef cows (Bos indicus) using GnRH, PGF2alpha and estradiol benzoate

The objective of this study was to evaluate protocols for synchronizing ovulation in beef cattle. In Experiment 1, Nelore cows (Bos indicus) at random stages of the estrous cycle were assigned to 1 of the following treatments: Group GP controls (nonlactating, n=7) received GnRH agonist (Day 0) and PGF2alpha (Day 7); while Groups GPG (nonlactating, n=8) and GPG-L (lactating, n=9) cows were given GnRH (Day 0), PGF2alpha (Day 7) and GnRH again (Day 8, 30 h after PGF2alpha). A new follicular wave was observed 1.79+/-0.34 d after GnRH in 19/24 cows. After PGF2alpha, ovulation occurred in 19/24 cows (6/7 GP, 6/8 GPG, 7/9 GPG-L). Most cows (83.3%) exhibited a dominant follicle just before PGF2alpha, and 17/19 ovulatory follicles were from a new follicular wave. There was a more precise synchrony of ovulation (within 12 h) in cows that received a second dose of GnRH (GPG and GPG-L) than controls (GP, ovulation within 48 h; P<0.01). In Experiment 2, lactating Nelore cows with a visible corpus luteum (CL) by ultrasonography were allocated to 2 treatments: Group GPE (n=10) received GnRH agonist (Day 0), PGF2alpha (Day 7) and estradiol benzoate (EB; Day 8, 24 h after PGF2alpha); while Group EPE (n=11), received EB (Day 0), PGF2alpha (Day 9) and EB (Day 10, 24 h after PGF2alpha). Emergence of a new follicular wave was observed 1.6+/-0.31 d after GnRH (Group GPE). After EB injection (Day 8) ovulation was observed at 45.38+/-2.03 h in 7/10 cows within 12 h. In Group EPE the emergence of a new follicular wave was observed later (4.36+/-0.31 d) than in Group GEP (1.6+/-0.31 d; P<0.001). After the second EB injection (Day 10) ovulation was observed at 44.16+/-2.21 h within 12 (7/11 cows) or 18 h (8/11 cows). All 3 treatments were effective in synchronizing ovulation in beef cows. However, GPE and, particularly, EPE treatments offer a promising alternative to the GPG protocol in timed artificial insemination of beef cattle, due to the low cost of EB compared with GnRH agonists.     

Associations between the manipulation of patterns of follicular development and fertility in cattle

The wave-like patterns of ovarian follicular development in cattle can be manipulated by shortening the luteal phase with prostaglandin F2alpha (PGF), lengthening the period of follicle dominance with progesterone or curtailing follicle development with GnRH or oestradiol as 17beta, benzoate or cypionate. These hormones can also be used to synchronise ovulation allowing timed inseminations without detected oestrus. Progesterone, PGF, GnRH and oestradiol benzoate have each been used to increase conception rates in some situations, but their use has reduced them in others. For example, inseminations made within 96 h of a single injection of PGF administered during the luteal phase were associated with increased conception rates in dairy cows whereas double injection protocols reduced conception rates. The three forms of oestradiol and GnRH have greater effects on follicular development following divergence and dominance than following wave emergence. This can mean that follicles of differing maturity will be present about 7 days later and can result in varied intervals to the onset of oestrus following a PGF injection. The consequent variation in ovulation time can be reduced by injecting GnRH or an oestradiol during pro-oestrus. This means that some less mature follicles will ovulate, forming corpus luteum (CL) associated with a slower rise in plasma progesterone and lower mid-luteal concentrations. The lower conception rates recorded with single timed inseminations with synchronised ovulations have been associated with increased prevalences of short cycles in lactating dairy cows (with GnRH), with long luteal phases in cows and heifers (with oestradiol benzoate) and with embryo loss following positive pregnancy diagnosis (as with Ovsynch in lactating Holstein cows). Extensive Canadian studies have demonstrated that these same hormones can be successfully used without these limitations and reliably obtaining conception rates over 50% and up to 70% in beef cattle that have been supplemented with a progestin during the period of ovarian follicle synchronisation. The inherently lower fertility of Holstein cows during early lactation may be contributing to the reduced effectiveness of hormonal treatments for synchronised follicle development and ovulation. The role of reduced dose rates of GnRH in compromising this effectiveness needs to be determined if the potential of these treatments realised with beef cattle is to be achieved with lactating Holstein cows.     

Ovulation rate after GnRH or PGF2alpha administration in early postpartum dairy cows

The objectives of this study evaluating induction of ovulation in early postpartum dairy cows were to: compare two methods of GnRH (100 mcg) administration (i.m. route and s.c. implant), and determine if prostaglandin F(2alpha) (PGF) causes release of LH or ovulation similar to that reported for GnRH. In trial #1, serum LH peaked at 2h after i.m. administration of GnRH and was declining at 4h. The s.c. GnRH implant also caused an elevation in serum LH at 2 and 4h after treatment, with LH declining at 6h. Serum LH was unchanged in control cows. Experimental treatment caused ovulation in 4 of 14 GnRH i.m. treated cows, 4 of 12 GnRH implanted cows and 0 of 13 control cows. Parity had no effect on LH response but did affect resulting ovulation rate as multiparous cows were more likely to ovulate than were primiparous cows in response to either GnRH treatment. All cows that ovulated had a follicle larger than 12 mm at the time of treatment. In trial #2, serum LH increased as before after i.m. administration of GnRH, however, serum LH was unchanged in cows treated with PGF or saline. Gonadotropin releasing hormone caused more cows to ovulate than did PGF or saline treatments, and GnRH shortened the interval from treatment to the onset of CL function over the PGF treatment; 13.9+/-2.6, 28.2+/-4.1 and 22.3+/-4.1 days for GnRH, PGF and saline, respectively. In summary, there was no difference in the ability of s.c. implantation and i.m. administration of GnRH to cause ovulation. Prostaglandin F(2alpha) did not cause release of LH or ovulation. In 22 early postpartum dairy cows treated with 100 mcg GnRH i.m. in these two trials, nearly all cows (95%) responded with a release of LH but only 45% (10/22) responded with an ovulation and subsequent formation of a CL.     

Modifications of the G6G timed-AI protocol improved pregnancy per AI and reduced pregnancy loss in lactating dairy cows

In dairy cows, subjected to a G6G protocol, objectives were to determine effects of (1) extending the interval from prostaglandin F2α (PGF2α) to gonadotropin-releasing hormone (GnRH) during presynchronization; and (2) adding a second PGF2α treatment before artificial insemination (AI), on ovarian response, plasma progesterone (P4) concentrations and pregnancy per AI (P/AI). In a 2×2 factorial design, lactating cows were randomly assigned to one of four timed AI (TAI) protocols: (1) G6G (n=149), one injection of PGF2α, GnRH 2 days later and a 7-day Ovsynch (GnRH, 7 days, PGF2α, 56 h, GnRH, 16 h, TAI) was initiated 6 days later; (2) G6GP (n=144), an additional PGF2α treatment (24 h after the first) during Ovsynch of the G6G protocol; (3) MG6G, one injection of PGF2α, GnRH 4 days later before initiation of the G6G protocol; and (4) MG6GP, an additional PGF2α treatment (24 h after the first) during Ovsynch of the MG6G protocol. Blood samples were collected (subset of 200 cows) at first GnRH and PGF2α of the Ovsynch, and at TAI to measure P4. Ultrasound examinations were performed in a subset of 406 cows to evaluate ovarian response at various times of Ovsynch, and in all cattle to determine pregnancy status at 32 and 60 days after TAI. Extending the interval by 2 days between PGF2α and GnRH during presynchronization increased (P<0.01) ovulatory response to first GnRH of Ovsynch, circulating P4 during Ovsynch, and P/AI at 32 and 60 days after TAI. Adding a second PGF2α treatment before AI increased the proportion of cows with luteal regression (P=0.04), improved P/AI at 60 days after TAI (P=0.05), and reduced pregnancy loss between 30 and 60 days after TAI (P=0.04). In summary, extending the interval from PGF2α to GnRH during presynchronization increased response to first GnRH of Ovsynch and P4 concentrations during Ovsynch, whereas adding a second PGF2α treatment before AI enhanced luteal regression. Both modifications of the G6G protocol improved fertility in lactating dairy cows.     

Neither duration of progesterone insert nor initial GnRH treatment affected pregnancy per timed-insemination in dairy heifers subjected to a Co-synch protocol

Our objectives were to: 1) compare response to cloprostenol, synchrony of ovulation, and pregnancy per timed-AI (P/TAI) in a 5 d versus a 7 d Co-synch + PRID protocol (Experiment 1); and 2) investigate whether the initial GnRH is necessary to achieve acceptable P/TAI in a 5 d Co-synch + PRID protocol (Experiment 2) in dairy heifers. In Experiment 1, 64 Holstein heifers, 15 to 17 mo, were assigned by age to receive 100 μg of GnRH and a PRID for 5 or 7 d (PRID5 and PRID7, respectively). At PRID removal 500 μg of cloprostenol (PGF) was given i.m. Heifers received the second GnRH treatment concurrently with TAI at 72 (PRID5) or 56 (PRID7) h after PRID removal. Transrectal ultrasonography monitored ovarian dynamics, ovulation synchrony, and pregnancy status (28 and 45 d after TAI). Plasma progesterone concentrations were determined at PRID removal and TAI. Five of seven heifers that ovulated before TAI became pregnant, and only two heifers did not respond to PGF treatment in the PRID5 group. Five PRID5 and 2 PRID7 heifers failed to ovulate after the second GnRH. However, P/TAI did not differ between PRID5 (59.4%) and PRID7 (58.1%). Overall ovulation response to first GnRH treatment was only 31.7%, and a larger proportion of heifers that did not ovulate became pregnant (65.1 versus 45.0%). In Experiment 2, 56 Holstein heifers, assigned as in Experiment 1, were subjected to a PRID5 protocol with (PRID5G) or without (PRID5NoG) GnRH at PRID insertion; all heifers were TAI 72 h after PRID removal. Transrectal ultrasonography and progesterone determinations were performed as in Experiment 1. Pregnancy per TAI did not differ whether or not heifers received GnRH at PRID insertion (67.9 versus 71.4%). Consistent with our previous findings, seven of nine heifers that ovulated before TAI became pregnant, and only two heifers did not respond to PGF treatment. Combining both experiments, length of proestrus but not ovulatory follicle diameter was identified as a significant predictor of probability of pregnancy 28 d after TAI, with a maximum predicted probability of 80.1% when the length of proestrus was 3 d. In summary, a PRID5 protocol resulted in comparable P/TAI to a PRID7 protocol. Most of the heifers that ovulated before TAI in the PRID5, PRID5G, and PRID5NoG protocols became pregnant. More than one PGF or a GnRH treatment at PRID insertion in a 5 d Co-synch + PRID protocol was not required to achieve acceptable P/TAI in dairy heifers.     

Effect of timing of Cosynch on fertility of lactating Holstein cows after first postpartum and Resynch timed-AI services

To compare two intervals from the PGF(2alpha) injection to the second GnRH injection+timed artificial insemination (TAI) of Ovsynch, lactating Holstein cows received their first postpartum TAI after Presynch + Ovsynch (n=352) and second and greater postpartum TAI after resynchronization of ovulation using Ovsynch (Resynch; n=458). Each week, cows housed in each of four breeding pens were randomized by breeding pen to receive the second GnRH injection of Presynch + Ovsynch or Resynch and TAI either 48 h (Cosynch 48; n=382) or 72 h (Cosynch 72; n=428) after the PGF(2alpha) injection of Ovsynch or Resynch. Overall, pregnancies per AI (P/AI) did not differ for cows receiving Cosynch 48 (29%) versus Cosynch 72 (33%). Furthermore, treatment did not affect P/AI for cows receiving first postpartum TAI after Presynch + Ovsynch, for cows receiving second and greater TAI after Resynch, or the proportion of female calves born. In conclusion, delaying the second GnRH injection and TAI from 48 to 72 h after the PGF(2alpha) injection of Ovsynch did not affect P/AI or calf sex ratio. The lack of a difference in fertility between these Cosynch protocols may offer more flexibility for implementing a systematic synchronization protocol when a Cosynch strategy is used.     

Effect of presynchronization strategy before Ovsynch on fertility at first service in lactating dairy cows

The aim of this study was to evaluate the effect of presynchronization with or without the detection of estrus on first service pregnancy per artificial insemination (P/AI) and on Ovsynch outcome in lactating dairy cows. A total of 511 cows were divided randomly but unevenly into 3 treatment groups at 44 to 50 days in milk (DIM). Ovsynch was started at the same time (69 to 75 DIM) in all three groups. Cows in the Ovsynch group (CON, N = 126) received no presynchronization before Ovsynch, and all cows were bred by timed AI (TAI). Cows in the presynchronization with estrus detection (PED) and the presynchronization with only TAI (PTAI) groups received two doses of prostaglandin F_2α (PGF) 14 days apart, starting at 44 to 50 DIM. Ovsynch was initiated 11 days after the second PGF treatment. Cows in the PED group (N = 267) received AI if estrus was detected after either PGF injection. Cows that were not determined to be in estrus after PGF injection received Ovsynch and TAI. Cows in the PTAI group (N = 118) were not inseminated to estrus, with all cows receiving TAI after Ovsynch. The ovulatory response to the first GnRH injection administered as part of Ovsynch differed (P = 0.002) among treatment groups (83.1% in PTAI, 72.6% in PED, and 62.7% in CON). However, the ovulatory response to the second injection of GnRH during Ovsynch did not differ among treatment groups. Of the 267 PED cows, a total of 132 (49.4%) exhibited estrus and were inseminated. The P/AI at the 31-day pregnancy diagnosis was similar between the cows in the PED group with AI after estrus detection (37.9%; 50/132) and those bred with TAI (34.1%; 46/135). The P/AI in the CON group (46.8%; 59/126) was greater (P < 0.05) than that in the PED group (36.0%; 96/267). In addition, the P/AI in the CON group was greater (P = 0.04) than that in the PED cows receiving TAI (34.1%; 46/135) but less than that in the PED cows bred to estrus (37.9%; 50/132) (P = 0.16). At the 31-day pregnancy diagnosis, the cows in the PTAI group had greater P/AI (55.9%; 66/118) than both those in the PED group (P < 0.01; either estrus or TAI) and those in the CON group (P = 0.08). Thus, presynchronization with PGF (PTAI) increased the ovulatory response to Ovsynch and improved P/AI in dairy cows. Interestingly, the breeding of cows to estrus during presynchronization reduced fertility to the TAI and overall fertility, including cows bred to estrus and TAI. These results indicate that maximal fertility is obtained when all cows receive TAI after the presynchronization protocol.     

Efficacy of PGF(2alpha) to synchronize estrus in water buffalo cows (Bubalus bubalis) is dependent upon plasma progesterone concentration,corpus luteum size and ovarian follicular status before treatment

This study was conducted to identify factors affecting PGF(2alpha) efficacy to synchronize estrus in water buffalo cows. After detection of a corpus luteum (CL) by rectal palpation, cows were treated (im) with dinoprost (12.5, 25 or 50mg) or D(+) cloprostenol (75, 150 or 300 microg) in a total of 66 treatments. Blood samples were collected 0, 24 and 48 h after treatment and ultrasound examinations and observations for estrus were performed daily to the day of ovulation or to 6 days after treatment. No PGF(2alpha) dose-response pattern was observed and overall rates of luteal regression (progesterone <1.0 ng/ml at 48 h), estrus, no detected behavioral estrus with ovulation occurring, and ovulation were 71.2, 36.4, 19.7 and 54.5%, respectively. To analyze plasma progesterone concentrations and ovarian dynamics, cows were divided in three groups according to their response to treatment. Cows that failed to have ovulations from a follicle after treatment (Group A, n = 30) had (P < 0.05) a lower plasma progesterone concentration (2.98 ng/ml) and smaller CL area (CLA; 187.3 mm(2)) before treatment as compared with cows that had an ovulation from a follicle (4.43 ng/ml and 223.7 mm(2), respectively; Groups B and C, n = 36). In cows that failed to ovulate, plasma progesterone concentration decreased in the first 24 h, but did not decline further and was >1.0 ng/ml 48 h after treatment. Moreover, no significant change in CLA after treatment was detected, indicating that treatment induced only partial luteolysis. In cows that ovulated, plasma progesterone concentration and CLA decreased continuously from treatment to ovulation (consistent with complete luteolysis). Threshold values of 2.8 ng/ml for plasma progesterone concentration and 189 mm(2) for CLA were identified as the best predictors of ovulation before treatment (83.3 and 80.6% sensitivity and 58.6 and 65.5% specificity, respectively, with positive and negative predictive values around 71%). When the origin of the ovulatory follicle was investigated, the interval from treatment to ovulation was shorter (91.9 versus 113.3 h; P < 0.05), and the ovulatory follicle had a slower growth rate (1.02 versus 1.55 mm per day; P < 0.005), a lesser increase in diameter from treatment to ovulation (4.7 versus 8.0 mm; P < 0.001), and a greater maximum diameter (13.2 versus 12.1 mm; P < 0.05) in cows that ovulated from the largest follicle present in the ovary before treatment (Group B, n = 27) compared with cows that ovulated from the second largest follicle present in the ovary before treatment (Group C, n = 9). In summary, the efficacy of PGF(2alpha) for causing luteolysis and synchronizing estrus and ovulation in buffalo cows was dependent upon plasma progesterone concentration, CL size and ovarian follicular status before treatment.     

Timing of final GnRH of the Ovsynch protocol affects ovulatory follicle size,subsequent luteal function,and fertility in dairy cows

Synchronization of ovulation (Ovsynch) is an effective method for controlling time of first and subsequent AI in lactating dairy cows. However, validation of the original Ovsynch program did not include testing the optimal time to deliver the final treatment of GnRH. In Experiment 1, the effect of administering the final dose of GnRH on the same day as prostaglandin F2alpha (PGF2alpha) administration was tested. Lactating dairy cows (n = 218) were randomly assigned to receive either Ovsynch (OV; cows were given 100 microg GnRH, then 7 days later cows were administered 25mg PGF2alpha followed by a subsequent treatment of 100 microg GnRH 2 days after the PGF2alpha or the modified version of Ovsynch (MOV; cows were given 100 microg GnRH, then 7 days later cows were administered 25mg PGF2alpha followed immediately with 100 microg GnRH). In both treatment groups, AI took place 16 h after the final administration of GnRH. In Experiment 2, cows (n = 457) were randomly divided into four treatment groups that were administered GnRH 0, 12, 24 and 36 h following PGF(2alpha). The 36 h treatment group served as control. Pregnancy diagnoses were performed by palpation per rectum 36 days post-AI in Experiment 1 and by ultrasonography on Day 28 in Experiment 2. In Experiment 1, pregnancy rate/AI (PR/AI) was greater (P<0.025) in OV versus MOV. In a subset (n = 85), percentage of cows with both synchronized ovulations and regressed CL following administration of PGF2alpha were similar (P>0.1) between OV and MOV, respectively. All cows that became pregnant in the MOV subset group showed regression of the CL in response to the PGF2alpha. Diameter of the ovulatory follicle at the time of final GnRH administration was greater (P<0.05) in OV versus MOV. In Experiment 2, the synchronization rate was once again similar among treatments (P>0.28). There was a linear effect of treatment on follicle size (P<0.05) and PR/AI (P<0.0001) as time increased between administration of PGF2alpha and GnRH, with the greatest PR/AI at 36 h. There was a trend for a greater percentage of cows with short luteal phases in the 0 h group (P<0.10). In summary, delivering the final treatment of GnRH of the Ovsynch program at the same time as PGF2alpha, or in the 24h following PGF2alpha, resulted in lower fertility compared to controls.