Gonadotropin-releasing Hormone Injection Research Articles

The effect of Pregnant Mare Serum Gonadotrophin (PMSG) and GnRH injection on weaning to oestrus interval and litter size of artificially inseminated sows

This experiment was carried out to investigate the effect of exogenous pregnant mare serum Gonadotrophin (PMSG) and Gonadotrophin-releasing hormone (GnRH) on weaned sows bred by artificial insemination. Chilled semen at 24 hours after the onset of standing heat was used for the experiment. In the treatment group (experiment 1), sows (n = 32) were injected with 500 IU of PMSG at weaning and 50 μg of GnRH injection was given at the time of insemination. As the control, sows (n = 33) were inseminated without giving any hormones. Weaning to estrus interval, conception rate and litter size were recorded. Results were analyzed using the Minitab Statistical Software version 14, 2010. The means were compared using the Student’s t-test. Results revealed that in group 1, the PMSG treated sows had significantly (p Tropical Agricultural Research Vol. 24 (3): 270-278 (2013

Risk factors for and reproductive outcomes of phantom cows on New Zealand dairy farms

AIMS: To determine some of the risk factors for cows not observed in oestrus within 35–42 days of an unsuccessful artificial insemination (AI; phantom cows), and the reproductive outcomes and effect of treatment of phantom cows.MATERIALS AND METHODS: Over 2 years, in dairy herds from the Waikato (n=10) and Canterbury (n=4) regions of New Zealand, pregnancy diagnosis was carried out 35–42 days after AI on cows that had been inseminated in the first 3 weeks after the start of mating (PSM) but had not been seen returning to oestrus. Risk factors for phantom cows were analysed using a generalised linear mixed effect model.In Year 1, all phantom cows were left untreated. In Year 2, phantom cows were categorised as having a corpus luteum (CL) (CL+ n=120), or having ovarian follicles ≥10 (n=101) or <10 (n=40) mm in diameter. Cows with a CL were treated with cloprostenol or untreated and placed with bulls. Cows with no CL received intravaginal progesterone (P4) for 7 days, with injection of gonadotrophin-releasing hormone (GnRH) on Days 0 and 9, and cloprostenol on Day 7 followed by AI. Pregnancy diagnosis of all cows took place 100–120 days after PSM and interval to conception and final pregnancy rate determined.RESULTS: Overall, of cows inseminated in the first 3 weeks after PSM that did not return to oestrus, 610/6,734 (9.1%) were phantom cows. From the final multivariable analysis, treatment for anoestrus, BCS ≤4.0 at mating, being 2 or >6 years of age, and pure-bred, and decreasing interval between calving and mating, until 98 days post calving, were associated with increased odds of being a phantom cow. Compared to all other groups of cows, phantom cows had a longer interval to conception (p<0.001) and a lower final pregnancy rate (p<0.001).Treatment of CL+ cows or cows with follicles ≥10 mm did not affect reproductive outcomes (p>0.3). For cows with follicles <10 mm treatment decreased the final percentage not pregnant (3/27; 11%; p=0.01) and interval to conception (21 days; p=0.02) compared with controls (7/13; 54% and 37 days, respectively).CONCLUSIONS AND CLINICAL RELEVANCE: Risk factors for phantom cows were identified that could be manipulated to reduce the number of phantom cows in a herd, in particular increasing BCS. Treatment of the majority of phantom cows did not improve reproductive performance.

Synchronization of ovulation with human chorionic gonadotropin in lactating dairy cows with ovarian cysts during heat stress.

A study was conducted during hot season to determine the effect of synchronization of ovulation with human chorionic gonadotropin (hCG) on fertility of lactating dairy cows with ovarian cysts. Non cyclic Holstein dairy cows (n = 80) were stratified by parity and diagnosed as having an ovarian cyst. The cows were further identified as follicular or luteal cysts according to the plasma progesterone (P4) concentration and the cystic image of ultrasonography. Cystic cows were randomly assigned to receive treatments (Ovsynch as the control or Ovsynch plus 3000IU hCG). All cows were artificially inseminated at 16-18h after the second gonadotropin releasing hormone injection. Cows supplemented with hCG had a greater number of corpus luteum (1.8 ± 0.2 and 0.8 ± 0.3; P < 0.05) and had greater P4 concentration on day 12 than those control cows (6.3 ± 0.3 and 3.9 ± 0.4ng/ml; P < 0.05). Concentration of cortisol did not differ between groups of cystic cows. No significant differences were found in overall conception rates between the treatments; however, significantly greater conception rate (P = 0.03) was observed in cows with luteal cysts receiving Ovsynch plus hCG. This study highlights that administration of hCG following the Ovsynch-based timed artificial insemination (AI) is more effective than the control Ovsynch by which the hCG affects corpus luteum (CL) development, P4 concentration, and thus improves conception rate in dairy cows with luteal cysts.

Comparative efficacy of E-17β and GnRH administration on day 0 of a controlled internal drug release (CIDR) based protocol on synchrony of wave emergence, ovulation and conception rates in Murrah buffalos (Bubalus bubalis).

The study was undertaken to compare the efficacy of an estradiol-17β + CIDR based protocol with the conventional ovsynch + CIDR based protocol for synchrony of wave emergence and ovulation in Murrah buffalos. In group I (n=25), on day 0 (beginning of experiment), buffaloes were administered a CIDR device (1.38 g P4) and concurrently received 1.5 mg E-17β. On day 9, the CIDR was removed and a prostaglandin (PG) F2α analogue (500 µg) was administered. On day 11, buffaloes were administered a gonadotropin releasing hormone (GnRH) analogue (20 µg) and inseminated twice at 12 h and 24 h following GnRH injections. Group II (n=25) protocol was based on an ovsynch regimen plus CIDR for 7 days followed by double insemination at induced estrus. Group III (n=10) served as control and was not given any hormone on day 0 of the protocol. In groups I, II and III, the duration of new follicular wave emergences were observed on days 4.22 ± 0.12, 3.12 ± 0.33 and 5.14 ± 0.42, respectively. In group I, synchrony of wave emergence was more and the diameter of pre-ovulatory follicles was larger (P<0.05) compared to groups II and III. The first service conception rate (FSCR) was higher (P<0.05) in group I while ovulation rates were not different between groups I and II. In conclusion, more synchrony of wave emergence, larger diameter of dominant follicles and higher first service conception rate was observed following the E-17β + CIDR based protocol in buffalos.

Conception rates to fixed-time artificial insemination of two oestrus synchronisation programmes in dairy heifers

AIM: To evaluate the conception rate to fixed-time artificial insemination (FTAI) of two oestrus synchronisation programmes in dairy heifers on eight farms over 2 years.METHODS: The study was conducted in 2008 and 2010 on eight farms near Palmerston North, New Zealand. Nulliparous Friesian and Friesian×Jersey heifers (13–15 months of age) were randomly allocated to one of two oestrus synchronisation programmes. Group 1 (GPG+P4; n=330), received gonadotrophin-releasing hormone (GnRH) I/M on Day 0, a progesterone (P4)-releasing intravaginal device from Days 0–7, prostaglandin F2α (PGF) I/M on Day 7 and a second dose of GnRH at the time of FTAI on Day 9. The second group (P4+PGF; n=343) received a P4-releasing intravaginal device from Days 0–7, PGF on Day 6 and FTAI on Day 9. Pregnancy was diagnosed from Days 42–52 by transrectal ultrasonography.RESULTS: The overall conception rate was 52.4% and 54.8% for the GPG+P4 and P4+PGF groups, respectively. The odds of conception for the two treatments were not different (OR=0.90; 95% CI=0.67–1.23), nor was there any difference between groups in different years (p=0.58). Farm affected conception rate (p=0.002), but there was no interaction with treatment (p=0.92) .CONCLUSIONS: This study has shown that an alternative synchronisation programme can produce similar results in terms of conception rate to the GPG+P4 treatment, currently commonly used in heifers. More research is required to establish whether other modifications to the GPG+P4 programme can produce similar results at lower costs, and to identify and quantify farm factors which affect the economic benefit of heifer synchronisation.CLINICAL RELEVANCE: This study indicated that synchronising heifers with P4 and PGF resulted in conception rates equivalent to those resulting from a GPG+P4 treatment, but with reduced drug costs. However, because heifers in the GPG+P4 group received the second GnRH injection at the time of AI, they needed only three yardings as opposed to the four required for the heifers treated with P4 and PGF. Thus, the choice of programme for an individual farm will depend on that farm's circumstances, in particular the cost of yarding the heifers.

Effect of a single injection of gonadotropin-releasing hormone (GnRH) and human chorionic gonadotropin (hCG) on testicular blood flow measured by color doppler ultrasonography in male Shiba goats.

Although color Doppler ultrasonography has been used to evaluate testicular blood flow in many species, very little has been done in goat. Eight male Shiba goats were exposed to a single intramuscular injection of either gonadotropin-releasing hormone (GnRH group; 1 µg/kg BW) or human chorionic gonadotropin (hCG group; 25 IU/kg BW). Plasma testosterone (T), estradiol (E2) and inhibin (INH) were measured just before (0 hr) and at different intervals post injection by radioimmunoassay. Testis volume (TV) and Doppler indices, such as resistive index (RI) and pulsatility index (PI) of the supratesticular artery, were measured by B-mode and color Doppler ultrasonography, respectively. The results indicated an increase in testicular blood flow in both groups, as RI and PI decreased significantly (P<0.05), but this increase was significant higher and earlier in hCG group (1 hr) than in the GnRH group (2 hr). A high correlation was found for RI and PI with both T (RI, r= −0.862; PI, r= −0.707) and INH in the GnRH group (RI, r=0.661; PI, r=0.701). However, a significant (P<0.05) correlation was found between E2 and both RI (r= −0.610) and PI (r= −0.763) in hCG group. In addition, TV significantly increased and was highly correlated with RI in both groups (GnRH, r= −0.718; hCG, r= −0.779). In conclusion, hCG and GnRH may improve testicular blood flow and TV in Shiba goats.

Central estrogen action sites involved in prepubertal restraint of pulsatile luteinizing hormone release in female rats

The present study aimed to determine estrogen feedback action sites to mediate prepubertal restraint of gonadotropin-releasing hormone (GnRH)/luteinizing hormone (LH) release in female rats. Wistar-Imamichi strain rats were ovariectomized (OVX) and received a local estradiol-17β (estradiol) or cholesterol microimplant in several brain areas, such as the medial preoptic area (mPOA), paraventricular nucleus, ventromedial nucleus and arcuate nucleus (ARC), at 20 or 35 days of age. Six days after receiving the estradiol microimplant, animals were bled to detect LH pulses at 26 or 41 days of age, representing the pre- or postpubertal period, respectively. Estradiol microimplants in the mPOA or ARC, but not in other brain regions, suppressed LH pulses in prepubertal OVX rats. Apparent LH pulses were found in the postpubertal period in all animals bearing estradiol or cholesterol implants. It is unlikely that pubertal changes in responsiveness to estrogen are due to a change in estrogen receptor (ER) expression, because the number of ERα-immunoreactive cells and mRNA levels of Esr1, Esr2 and Gpr30 in the mPOA and ARC were comparable between the pre- and postpubertal periods. In addition, kisspeptin or GnRH injection overrode estradiol-dependent prepubertal LH suppression, suggesting that estrogen inhibits the kisspeptin-GnRH cascade during the prepubertal period. Thus, estrogen-responsive neurons located in the mPOA and ARC may play key roles in estrogen-dependent prepubertal restraint of GnRH/LH secretion in female rats.

Pregnancy outcomes after change in dose delivery of prostaglandin F2α and time of gonadotropin-releasing hormone injection in a 5-day timed artificial insemination program in lactating dairy cows

We demonstrated that 50mg of PGF2α on d 6 successfully induced luteolysis in lactating dairy cows enrolled in a traditional 5-d Ovsynch-72 program [GnRH injection 5 d before (d 0; GnRH-1) and 56 (p.m. on d 7; GnRH-2) or 72h (d 8; GnRH-2) after a 25-mg injection of PGF2α (d 5 and 6 after GnRH injection); timed artificial insemination (AI) on d 8]. Our current objective was to determine pregnancy outcomes in lactating dairy cows after a 50-mg injection of PGF2α on d 6 or a 25-mg injection of PGF2α on d 5 and 6 in a 5-d Ovsynch program. Cows in herd 1 diagnosed not pregnant between 30 and 36 d since last AI were enrolled to receive either a 50-mg injection of PGF2α on d 6 (1×50; n=134) or a 25-mg injection of PGF2α on d 5 and 6 (2×25; n=139) after GnRH-1 (d 0), with GnRH-2 at 72h after PGF2α injection (d 5), concurrent with timed AI (d 8). Cows in herd 2 diagnosed not pregnant between 34 and 40 d were treated similarly: even-tagged cows received the 2×25 (n=422) treatment, and odd-tagged cows received the 1×50 (n=450) treatment, except that GnRH-2 was administered at 56h. Blood collected from cows in herd 1 at d 0, 5, 6, and 8 was assayed for progesterone. Luteolysis was defined to occur when progesterone concentration was ≥1ng/mL on d 5, and 72h later (d 8) was either <0.5ng/mL or <1ng/mL. Progesterone concentrations did not differ between treatments on pretreatment d 0 and 5, but were greater in 1×50 than 2×25 cows on d 6 (4.7±0.2 vs. 1.1±0.2ng/mL) and d 8 (0.43±0.04 vs. 0.19±0.04ng/mL), respectively. Luteolysis was greater in the 2×25 versus 1×50 treatment when the cut point was 0.5ng/mL, whereas no difference was detected when the cut point was <1ng/mL on d 8. Lack of complete luteolysis was greater in cows classified as early cycle on d 0 or having a new corpus luteum after d 0 because progesterone concentration was greater on d 5 and 6 than for cows classified as late cycle on d 0 or cows having low progesterone on d 0 and 5. Pregnancy per AI at 30 to 40 d did not differ between 2×25 and 1×50 cows having luteolysis by d 8 or in all cows (37.2 vs. 33.3%) in herd 1, respectively, but differed in herd 2 (24.7 vs. 19.5%; no treatment by herd interaction). We conclude that incomplete luteolysis by d 8 was greater in 1×50 cows using a cut point of <0.5ng/mL at AI. The difference in pregnancy outcome in herd 2 may have resulted from insufficient time for complete luteolysis before GnRH-2 at 56h compared with GnRH-2 at 72h (at AI) in herd 1.

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

Presynchronization strategies, such as Presynch-Ovsynch and Double-Ovsynch, increase fertility to timed artificial insemination (TAI) compared with Ovsynch alone; however, simpler presynchronization strategies could reduce costs and simplify reproductive management. Lactating Holstein cows (n=601) were randomly assigned to 1 of 2 presynchronization treatments before beginning an Ovsynch-56 protocol (GnRH at 70±3 DIM, PGF2α 7 d later, GnRH 56h after PGF2α, and TAI 16h later at 80±3 DIM) for first TAI. Cows (n=306) in the first treatment (Double-Ovsynch; DO) were presynchronized using a modified Ovsynch protocol (GnRH at 53±3 DIM, 7 d later PGF2α, and GnRH 3 d later) ending 7 d before the first GnRH injection (G1) of an Ovsynch-56 protocol. Cows (n=295) in the second treatment (GGPG) were presynchronized using a single injection of GnRH 7 d before G1 of an Ovsynch-56 protocol at 63±3 DIM. Blood samples were collected at G1 and the PGF2α injections of the Ovsynch-56 protocol to determine progesterone (P4) concentrations. Pregnancy diagnosis was performed using ultrasonography 32 d after TAI, and pregnant cows were reexamined 46 and 70 d after TAI. Overall, DO cows had more pregnancies per artificial insemination (P/AI) compared with GGPG cows 32 d after TAI (53 vs. 43%). Overall, P/AI did not differ by parity (primiparous vs. multiparous), and pregnancy loss did not differ between treatments or parities. More DO cows had P4 in a medium range (>0.5 to <4ng/mL) at G1 of the Ovsynch-56 protocol compared with GGPG cows (82 vs. 50%), and more DO cows had high P4 (>4ng/mL) at the PGF2α injection of the Ovsynch-56 protocol compared with GGPG cows (67 vs. 36%). Thus, presynchronization with a modified Ovsynch protocol increased P/AI after TAI at first AI by increasing synchrony to the Ovsynch-56 protocol compared with presynchronization using a single injection of GnRH.

The number of life-history stages does not influence the androgen responsiveness to male–male interactions: Sedentary and migratory black redstarts (Phoenicurus ochruros) do not elevate testosterone in response to simulated territorial intrusions

High plasma levels of testosterone at the beginning of the breeding season adjust male physiology for mating and promote territorial behavior in birds. Conversely intra-sexual competition may elicit a temporary increase in circulating testosterone. Male black redstarts (Phoenicurus ochruros) from migratory populations show the expected increase in baseline testosterone during early breeding, but circulating testosterone levels do not change in response to male–male interactions. Because sedentary populations express fewer life-history stages they may be more flexible in timing of life-history stages and more responsive to environmental modulation of hormone concentrations. Therefore, we tested whether the androgen responsiveness to male–male interactions differs between migratory (6 life-history stages) and sedentary black redstarts (3 life-history stages) during early breeding, predicting that in contrast to migratory birds, sedentary birds would modulate testosterone in response to simulated territorial intrusions (STI). In contrast to our prediction, sedentary males did not modulate post-capture testosterone levels in response to simulated territorial intrusions. Males of both populations increased testosterone after an injection of gonadotropin releasing hormone (GnRH), demonstrating that they were capable of increasing testosterone. Interestingly, in sedentary males the GnRH injection elicited a higher testosterone response in STI males than in control males. The two populations did not differ in their behavioral response to the STIs, except that sedentary males spent less time close to the decoy. In combination with previous data from black redstarts and other socially monogamous and biparental birds our current study adds to the growing evidence that current theory regarding hormone-behavior relationship needs to be refined.

The effects of intramuscular or intravenous injections of gonadotropin releasing hormone at fixed-time artificial insemination on pregnancy rates of Bos indicus beef cows

The effect of an intramuscular versus intravenous administration of gonadotropin releasing hormone (GnRH) at fixed-time AI (FTAI) on the pregnancy rates of crossbred Bos indicus beef cows was evaluated. Pluriparous nursing calv cows (n=120) were synchronized as follows: d 0 cows received a 2.0 mg injection of estradiol benzoate (EB) and insertion of a controlled intravaginal progesterone releasing device containing 0.558 g of progesterone, d 8 removal of the progesterone device , a 0.15 mg injection of prostaglandin F2α (PGF), a 1.0 mg injection of EB, and 400 IU injection of equine chorionic gonadotropin. Fifty-four hr after PGF, all cows were exposed to FTAI and a 0.084 mg injection of GnRH was administered either via Vena caudalis (n=60), or via Longissimus dorsi (n=60). Cows were inseminated with the same sire and by a single AI technician. Pregnancy was determined by the transrectal ultrasonography on d 40 after AI. Cows receiving the intravenous administration of GnRH had higher (P = 0.04) pregnancy rates than the cows receiving the intramuscular injection of GnRH (65 vs 46.6%, respectively). It was concluded that the intravenous administration of GnRH at the time of AI improved the pregnancy rates of crossbred Bos indicus beef cows submitted to FTAI.

Effect of an Ovsynch56 protocol initiated at different intervals after insemination with or without a presynchronizing injection of gonadotropin-releasing hormone on fertility in lactating dairy cows

The objectives of this study were to evaluate effects of 2 resynchronization protocols beginning at different intervals after artificial insemination (AI) on the pattern of return to estrus, ovarian responses, and pregnancy per AI (P/AI) to reinsemination. Lactating cows from 2 dairies, located in Texas (n=2,233) and Minnesota (n=3,077), were assigned to 1 of 4 timed AI (TAI) protocols 17±3d after AI. All cows were examined for pregnancy 31±3d after previous AI. Cows assigned to early Ovsynch56 (E-OV56) or OV56 received the Ovsynch56 protocol starting 24 or 31d after AI, respectively. Cows assigned to early GnRH-GnRH-PGF2α-GnRH (E-GGPG) or GGPG received a presynchronizing GnRH injection 17 or 24d after AI, respectively, 7d before the start of the Ovsynch56 protocol. Cows observed in estrus after enrollment were inseminated on the same day. Ovaries were examined and blood was sampled for progesterone concentration on the day of first GnRH and PGF2α injection of the Ovsynch56 protocol. Pregnancy was diagnosed at 31 and 66d after resynchronized AI. On the day of the first GnRH injection of the TAI, a higher percentage of cows on E-GGPG and GGPG protocols had a corpus luteum (E-GGPG=83.8, GGPG=91.2, E-OV56=80.4, and OV56=75.5%) and progesterone concentration >1ng/mL (E-GGPG=62.5, GGPG=76.0, E-OV56=53.6, and OV56=60.8%) than cows assigned to other protocols. However, the percentage of cows ovulating to the first GnRH injection of TAI was not affected by treatment. Fewer E-GGPG and more OV56 cows were reinseminated in estrus (E-GGPG=23.7, GGPG=49.0, E-OV56=41.6, and OV56=57.6%). Treatment did not affect P/AI at 31 or 66d for cows reinseminated in estrus. However, cows reinseminated in estrus had greater P/AI at 31 (40.0 vs. 27.5%) and 66d (36.0 vs. 23.9%) than cows completing the TAI protocols. Among cows completing the TAI protocols, initiation of GGPG at 24d after AI increased, whereas initiation of Ovsynch56 at 24d after AI decreased P/AI at 31d after reinsemination (E-GGPG=30.6, GGPG=28.3.0, E-OV56=22.3, and OV56=28.7%). Pregnancy per AI did not differ across treatment at 66d after TAI (E-GGPG=26.6, GGPG=24.4, E-OV56=20.0, and OV56=24.1%). Overall, type of resynchronization protocol and protocol initiation time did not affect P/AI 66d after reinsemination (E-GGPG=29.7, GGPG=30.5, E-OV56=26.1, and OV56=30.4%). In conclusion, GGPG resynchronization protocols and initiation of resynchronization protocol 24d after AI reduced the number of cows reinseminated in estrus but neither the timing of initiation of resynchronization nor presynchronization with GnRH affected overall P/AI.

Individual variation in testosterone and parental care in a female songbird; The dark-eyed junco (Junco hyemalis)

When competition for sex-specific resources overlaps in time with offspring production and care, trade-offs can occur. Steroid hormones, particularly testosterone (T), play a crucial role in mediating such trade-offs in males, often increasing competitive behaviors while decreasing paternal behavior. Recent research has shown that females also face such trade-offs; however, we know little about the role of T in mediating female phenotypes in general, and the role of T in mediating trade-offs in females in particular. Here we examine the relationship between individual variation in maternal effort and endogenous T in the dark-eyed junco, a common songbird. Specifically, we measure circulating T before and after a physiological challenge (injection of gonadotropin releasing hormone, GnRH), and determine whether either measure is related to provisioning, brooding, or the amount of T sequestered in egg yolk. We found that females producing more T in response to a challenge spent less time brooding nestlings, but provisioned nestlings more frequently, and deposited more T in their eggs. These findings suggest that, while T is likely important in mediating maternal phenotypes and female life history tradeoffs, the direction of the relationships between T and phenotype may differ from what is generally observed in males, and that high levels of endogenous T are not necessarily as costly as previous work might suggest.

Natural variation in circulating testosterone does not predict nestling provisioning rates in the northern cardinal, Cardinalis cardinalis

Behavioural transitions between territoriality and parental care are necessary for many seasonally breeding vertebrates. Among birds, such transitions can be mediated by the steroid hormone testosterone (T), resulting in a T-mediated behavioural trade-off. This theory is supported by many implantation studies with birds demonstrating that the administration of exogenous T during parental phases can negatively affect offspring care. However, little is known about relationships between naturally circulating levels of T and parental behaviour in wild bird populations. We examined covariation in circulating levels of T (before and after injection of gonadotropin-releasing hormone (GnRH)) and nestling provisioning rates in male and female northern cardinals, Cardinalis cardinalis, a highly aggressive, biparental resident songbird. Results indicate that both sexes had detectable levels of initial T when providing parental care, but only males produced significantly higher elevations of T following GnRH injections. Furthermore, T levels (both initial and following GnRH injections) and nestling provisioning rates did not covary for either sex, and these measures were not correlated between members of breeding pairs. When results of this study are considered with prior work indicating that elevations in T might not be necessary to support male or female aggression in this species, it appears that relationships between circulating T and reproductive behaviour could be more complex for the cardinal than for many others birds similarly examined. Such findings warrant additional examination of interrelationships between T, aggression and other forms of parental care to assess whether this species engages in T-mediated behavioural trade-offs. Possible alternative mechanisms influencing behaviour in the cardinal and future directions for research are discussed.

Presynchronizing PGF2α and GnRH injections before timed artificial insemination CO-Synch + CIDR program (2013)

Fixed-time artificial insemination is an effective management tool that reduces the labor associated with more conventional artificial insemination programs requiring detection of estrus. The 7-day CO-Synch + controlled internal drug release (CIDR) insert protocol has been shown to effectively initiate estrus and ovulation in cycling and non-cycling suckled beef cows, producing pregnancy rates at or greater than 50% in beef cows. The gonadotropin-releasing hormone (GnRH) injection that begins the CO-Synch + CIDR program initiates ovulation in a large proportion of cows, particularly anestrous cows. The CIDR, which releases progesterone intravaginally, prevents short estrous cycles that usually follow the first postpartum ovulation in beef cows. Our hypothesis was that inducing estrus with a prostaglandin injection followed 3 days later with a GnRH injection, 7 days before applying the 7-day CO-Synch + CIDR protocol, might increase the percentage of cycling cows that would exhibit synchronous follicular waves after the onset of the CO-Synch + CIDR protocol. We also hypothesized that the additional GnRH injection would increase the percentage of anestrous cows that would ovulate, thereby increasing pregnancy outcomes.

The use of progesterone-supplemented Co-synch and Ovsynch for estrus synchronization and fixed-time insemination in nulliparous Saanen goat

The effect of Chronogest-supplemented Ovsynch and Co-synch protocols on estrus synchronization, follicular development, and fertility after fixed-time insemination was investigated in goats during the breeding season. Co-synch (n = 24) and Ovsynch (n = 25) protocols were applied to nulliparous does with a body weight of more than 30 kg. The onset and duration of estrus were determined with teaser bucks. The does were laparoscopically inseminated with 11.5 × 10^6 motile spermatozoa/straw at the second gonadotropin-releasing hormone (GnRH) injection for Co-synch and 8 h after the second GnRH injection for Ovsynch. The rates of estrus exhibited in the does were 92% and 84% and the times from sponge removal to the onset of estrus were 31.1 h and 30.9 h; the duration times were 34.4 h and 29.4 h for Co-synch and Ovsynch, respectively (P > 0.05). The follicle diameters at the second GnRH injection were 0.72 cm and 0.68 cm, and the number of ovulations was 2.6 and 2.8 for Co-synch and Ovsynch, respectively. There were no significant differences between the Co-synch and Ovsynch groups for the nonreturn rate within 30 days (NRR_{30}) (62% and 40%) and the pregnancy rates (38% and 24%) determined on day 30. The kidding and prolificacy rates were 38% and 1.4 for the Co-synch-treated goats and 24% and 1.2 for the Ovsynch-treated goats (P > 0.05). The Co-synch protocol could yield better results compared to the Ovsynch protocol, which was related to the variation in ovulation time during the onset of puberty and the breeding season. Further studies should be done to determine the best time for fixed-time insemination and the acceptable insemination dose to improve the fertility results after timed artificial insemination in does.

Concentrations of luteinizing hormone and ovulatory responses in dairy cows before timed artificial insemination (2013)

The objective of this study was to determine the incidence of spontaneous and gonadotropinreleasing hormone (GnRH)-induced surges of luteinizing hormone (LH) and ovulatory responses in lactating dairy cows enrolled in a timed artificial insemination (TAI) protocol. Cows (n = 70) in a single herd were assigned to one of two presynchronization protocols: Pre- 10 or PG-3-G. Cows assigned to the Pre-10 treatment received 2 injections of prostaglandin F2α(PGF2α) 14 days apart (Presynch), with the second injection administered 10 days before the onset of a TAI protocol. Cows assigned to the PG-3-G treatment received an injection of prostaglandin F2α(PGF2α), then 3 days later an injection of GnRH (GnRH-1) 7 days before the onset of a TAI protocol. All cows received the first GnRH injection (GnRH-2) of the Ovsynch protocol and a PGF2αinjection 7 days later, then cows received the breeding injection of GnRH (GnRH-3) at either 56 or 72 hours after PGF2α, with insemination occurring 12 to 16 hours after the second GnRH injection. Blood samples were collected during the study to monitor serum changes in LH, progesterone, and estradiol to determine why ovulatory responses to GnRH-induced LH release did not approach 100% when follicle dominance and adequate follicle size was achieved. Presynchronization administration of GnRH-1 increased the incidence of LH surges and ovulation rates in cows presynchronized with PG-3-G compared with Pre-10. Incidence of ovulation and occurrence of LH surges did not differ after GnRH-2, but more LH was released in Pre-10 than PG-3-G cows. Luteolysis, LH surge incidence, and ovulation rates were similar among the 4 treatment-time combinations after GnRH-3. Pregnancy per TAI was decreased in Pre-10 at 56 hours compared with Pre-10 at 72 hours and PG-3-G at 56 and 72 hours. We concluded that administration of GnRH 56 hours before breeding decreased pregnancy per TAI compared with administration of GnRH at 72 hours when cows were presynchronized with Pre-10. Presynchronization with PG-3-G resulted in acceptable pregnancy per TAI with GnRH administration occurring at either 56 or 72 hours before TAI. The flexibility of GnRH timing with the PG-3-G presynchronization protocol may be an advantage compared with the Pre-10 protocol for dairy cattle when programmed for a TAI at first service.; Dairy Day, 2013, Kansas State University, Manhattan, KS, 2013; Dairy Research, 2013 is known as Dairy Day, 2013

Five-day resynch programs in dairy cows including controlled internal drug release at two stages post-artificial insemination (2013)

Two experiments were conducted to assess pregnancy outcomes after a 5-day Ovsynch-56 Resynch (RES; gonadotropin-releasing hormone injection 5 days before [GnRH-1; d 0] and 56 hours (GnRH-2) after PGF2α [PG] injections on day 5 and 6, timed artificial insemination [TAI] on day 8) with and without a progesterone-releasing intravaginal controlled internal drug release (CIDR) 5-day insert. In Exp. 1, nonpregnant cows were enrolled on day 34 postAI: day 34 RES-CON (n = 528) or day 34 RES-CIDR (n = 503). Blood was collected for progesterone assay. Pregnancy per AI (P/AI) was diagnosed by uterine palpation per rectum at 34 and 62 days post-TAI. Only 76% of 1,031 cows had high progesterone (≥1 ng/mL) on day 34 at the nonpregnant diagnosis. No differences in P/AI were detected between treatments. The day-34 RES-CIDR cows with low (<1 ng/mL) progesterone, however, had greater (P = 0.036) P/AI than day-34 RES-CON cows (37.7 vs. 29.4%), whereas day-34 RES-CIDR cows with high progesterone had lesser P/AI than day-34 RES-CON (27.4 vs. 34.3%). In Exp. 2, cows were enrolled on day 31 post-AI after a nonpregnant diagnosis: (1) day 31 PG-3-G (n = 102): Pre-PG on day 31, Pre-GnRH on day 34, and RES on day 41 (n = 102); (2) day 41 RES-CON (n = 108) as Exp. 1, but on day 41; and (3) day 41 RES-CIDR (n = 101) as Exp. 2, but on day 41. Blood was collected for progesterone assay and ovarian structures were mapped by ultrasonography on days 31, 34, 41, 46, and 48. Pregnancy was diagnosed by ultrasonography on days 31 and 59 post-TAI. The proportion of cows with high progesterone on day 31 was 70.6%. More (P < 0.001) cows ovulated after Pre-GnRH on day 31 PG-3-G (60.4%) than for day 41 RES-CON (12.5%) or day 41 RES-CIDR (17.1%). More (P < 0.001) PG-3-G cows had luteolysis after Pre-PG on day 31 than other treatments (73.7 vs. < 11%). The proportion of cows with high progesterone on day 41 at GnRH-1 tended (P = 0.10) to be greater for PG-3-G (75.6%) than for other treatments (65 to 70%). The P/AI was greater in cows starting RES on day 41 when progesterone was low (44%) than when it was high (33%), but no treatment differences were detected 31 days after TAI (PG-3-G = 33.3%; d 41 RES-CON = 38.9%; d 41 RES-CIDR = 35.6%). We concluded that improved P/AI for cows initiating the 5-day RES on day 34 without a corpus luteum is progesterone-dependent because addition of the CIDR insert to the RES treatment improved P/AI in cows with low progesterone (Exp. 1). Although day-31 PG-3-G increased luteolysis and produced greater ovulation rates before the onset of RES, no increase in P/AI was detected compared with RES started on day 41 with or without a CIDR insert.

Evidence of estrus before CIDR insertion does not influence pregnancy rate to fixed-timed artificial insemination in beef heifers

Protocols used for fixed-timed artificial insemination strive to synchronize growth of follicular waves and commonly do so by administration of gonadotropin-releasing hormone (GnRH) at the beginning of the treatment. The stage of the cycle at the time of GnRH injection influences the proportion of animals that respond, and cows respond more consistently than heifers. Variability in response to GnRH has been offered as an explanation for why why short-term fixed-timed insemination protocols tend to be less effective in heifers than cows. The dairy industry has used prostaglandin (PG) to "pre-synchronize" cow ovulation before a protocol to improve the proportion of cows that initiate a new wave of follicular growth. Because of the additional cost in time and product, the beef industry has been reluctant to explore this approach. South Dakota State University research has indicated that variability in onset of estrus was reduced when PG was given 3 days before a controlled internal drug release (CIDR) protocol. A reduction in variability of the onset of estrus may improve response to fixed-time artificial insemination. The objective of this study was to determine if the onset of estrus prior to a PG 6-day CIDR protocol would improve pregnancy rates to fixed-time artificial insemination in beef heifers.

Between-female variation in house sparrow yolk testosterone concentration is negatively associated with CYP19A1 (aromatase) mRNA expression in ovarian follicles

Maternally-derived yolk androgens influence the development and long-term phenotype of offspring in oviparous species. Between-female variation in the amounts of these yolk androgens has been associated with a number of social and environmental factors, suggesting that the variation is adaptive, but the mechanisms behind it are unknown. Using two different approaches, we tested the hypothesis that variation in yolk androgen levels across individuals is associated with variation in their capacity to synthesize androgens. First, we injected female house sparrows with exogenous gonadotropin-releasing hormone (GnRH) to maximally stimulate ovarian steroidogenesis. Second, we collected pre-ovulatory follicle tissue and quantified the mRNA expression of four key enzymes of the steroid synthesis pathway: steroidogenic acute regulatory protein (StAR), cytochrome P450-side chain cleavage enzyme (CYP11A1), 17β-hydroxysteroid dehydrogenase (HSD17B1), and aromatase (CYP19A1). Thirty minutes after GnRH injection, androgen concentrations in both the plasma and in the yolks of pre-ovulatory follicles were significantly elevated compared to controls. However, this measure of steroidogenic capacity did not explain variation in yolk testosterone levels, although physiological differences between house sparrows and more widely studied poultry models were revealed by this approach. Steroidogenic enzyme mRNA levels were detectable in all samples and were significantly lower in the most mature pre-ovulatory follicles. Of the four measured genes, CYP19A1 expression exhibited a significant negative relationship with yolk testosterone concentrations in laid eggs, revealing a key mechanism for between-female variation in yolk testosterone. Furthermore, this suggests that any factors which alter the expression of CYP19A1 within an individual female could have dramatic effects on offspring phenotype.