Dairy cows: GnRH or hCG given 5-7 days after AI vs no treatment for pregnancy rate — POSSIBLE

In dairy cows, does GnRH or hCG given 5–7 days after AI vs no treatment improve pregnancy rates?

Shelf #892 · gate-verified and approved by the developer

POSSIBLE: A single GnRH injection on day 5 after AI has not been shown to improve pregnancy rates, while hCG given 5-6 days after AI improves pregnancy rates in some populations (repeat breeders, heat-stressed or Heatsynch-bred cows) but not in unselected cows — so a benefit is possible, and population-dependent, rather than general. On GnRH: in Jeong 2016 (PMID: 27030200, Experiment 1; 569 dairy cows randomly allocated), pregnancy after timed AI was 34.4% with 100 micrograms gonadorelin on day 5 vs 31.6% in untreated controls (p > 0.05) — no benefit shown. On hCG in unselected cows: Schmitt 1996 (PMID: 8726740, Experiment 5; 201 lactating cows in summer heat stress) found pregnancy rates of 24.2% with hCG (3,000 IU) on day 5 or 6 after insemination vs 23.5% in controls, and Agarwal 2021 (PMID: 33751251; 50 crossbred cows, block-randomised, saline-controlled) found no significant difference in first-service conception rates for hCG on day 7 (or day 0 or day 14) vs saline, despite larger luteal dimensions. On hCG in selected populations: Alnimer 2015 (PMID: 25890835; 406 repeat-breeding cows) found pregnancies per AI on day 45 of 38.9% with 1,500 IU hCG on day 6 after timed AI vs 30.9% in untreated controls (absolute difference 8.0 percentage points; relative rate about 1.26), with pregnancy losses lower in the day-6 group (15.0%) and day-4 group (26.7%) than in controls (37.7%); and Shabankareh 2010 (PMID: 19309467; 667 cows, 3,000 IU hCG or saline on day 5 post-AI) found hCG significantly improved pregnancy rates in Heatsynch-bred cows (41.5% vs 24.8%, p < 0.01) and in the warm period overall (37.9% vs 23.6%, p < 0.001), with no hCG advantage reported for the Ovsynch subgroup. Design class (b): randomisation is established by records answering this shelf's own comparison and population (Jeong 2016 'randomly allocated'; Agarwal 2021 block randomisation with a saline control), but blinding is not established — no carded record states masked treatment or masked pregnancy assessment, and the largest positive trial (Alnimer 2015) used untreated rather than placebo controls. The stamp is POSSIBLE, not LIKELY, because the hCG benefits are confined to subgroups and selected populations, two directly-on-point records in unselected cows are null, and the GnRH arm of the question is null in its one large randomised test. Tier C reasoning, stated on the pack's face as required: Tier C is NOT engaged — a pregnancy-rate benefit as the primary claim is not a mortality, fetal-loss-as-primary or survival benefit claim (settled rulings, batches I/K); the pregnancy-loss differences in Alnimer 2015 are a component of its pregnancy-rate outcome, reported alongside pregnancies per AI, not a stand-alone fetal-loss benefit claim. One-home note: progesterone supplementation after AI (a different intervention) is topic #875, and post-AI GnRH/CIDR resynchronisation records are not re-carded here. Drafted Nov 10, 2026 (VetMed build, topic #892); figures from the abstracts, fetched and verified at drafting.

Jeong 2016 (Experiment 1): GnRH on day 5 after timed AI did not improve pregnancy rate (34.4% vs 31.6% untreated, p > 0.05) in 569 dairy cows

Randomised controlled trial (record states cows were randomly allocated; publication types: Journal Article, Randomized Controlled Trial)

Who: Dairy cattle: 569 dairy cows that underwent timed AI (day 0) following short-term synchronisation with prostaglandin F2alpha, randomly allocated to no further treatment (control, n = 307) or an injection of 100 micrograms gonadorelin on day 5 (GnRH, n = 262). The same record's Experiment 2 (279 cows, CIDR insert days 3.5-18 vs control) tests progesterone, not GnRH or hCG, and is not part of this card's claim.

Result: The probability of pregnancy following timed AI did not differ between the GnRH group (34.4%) and the control group (31.6%, p > 0.05) — an absolute difference of 2.8 percentage points (relative rate about 1.09), not significant. (For contrast within the same record, Experiment 2's CIDR insert treatment gave 51.1% vs 39.3% in controls, odds ratio 1.74, p < 0.05 — a progesterone result that belongs to the post-AI progesterone question, not to this shelf's GnRH/hCG claim, and is recorded here only so it is not mistaken for a GnRH effect.)

Watch out: This is the shelf's only large randomised test of post-AI GnRH, and it is null — do not let the same record's positive CIDR experiment (a different intervention, cross-pointed to the post-AI progesterone question) be quoted as support for GnRH. Synchronisation before AI was prostaglandin-only short-term synchronisation, and pregnancy-diagnosis timing is not stated in the abstract.

Jeong JK, Choi IS, Kang HG, Hur TY, Kim IH. Effects of gonadotropin-releasing hormone administration or a controlled internal drug-releasing insert after timed artificial insemination on pregnancy rates of dairy cows. J Vet Sci. 2016;17(4):577-582. PMID: 27030200. Registry ID: none in the record. MeSH: Animals · Cattle/physiology* · Cloprostenol/pharmacology* · Contraceptive Agents/administration & dosage · Estradiol/administration & dosage/analogs & derivatives · Female · Gonadotropin-Releasing Hormone/pharmacology* · Insemination, Artificial/veterinary · Luteolytic Agents/pharmacology* · Pregnancy · Pregnancy Rate* · Reproduction/drug effects

Alnimer 2015: in repeat-breeding cows, hCG on day 6 after timed AI raised pregnancies per AI (38.9% vs 30.9% untreated) and cut pregnancy losses (15.0% vs 37.7%)

Controlled trial in repeat breeders with untreated controls (publication types: Journal Article, Randomized Controlled Trial)

Who: Dairy cattle: repeat-breeding dairy cows, all synchronised with a Cosynch protocol before timed AI, then assigned to no hormonal treatment (control, n = 139), 1,500 IU human chorionic gonadotropin 4 days after timed AI (n = 136), or 1,500 IU hCG 6 days after timed AI (n = 131). Plasma progesterone was measured on the day of hCG treatment and 12 days after timed AI; pregnancies per AI were assessed on day 45.

Result: Pregnancies per AI on day 45 were greater for the day-6 group (38.9%) than controls (30.9%) — absolute difference 8.0 percentage points, relative rate about 1.26; the abstract does not report a day-45 pregnancies-per-AI figure for the day-4 group overall. Pregnancy losses were lower for day 6 (15.0%) and day 4 (26.7%) than controls (37.7%). In summer, pregnancies per AI were 30.3% (day 6) and 33.3% (day 4) vs 19.2% (control), with losses 18.2% and 31.0% vs 58.3%; in winter, pregnancies per AI were greater for day 6 (57.1%) than day 4 (30.6%) and controls (37.9%). In primiparous cows, pregnancies per AI were 46.4% (day 4) and 31.6% (day 6) vs 15.8% (control). Plasma progesterone on day 12 after timed AI was higher in treated than control groups. The authors concluded hCG 6 days after timed AI was beneficial, improving pregnancies per AI in summer and winter by reducing pregnancy loss and increasing progesterone.

Watch out: Repeat breeders only — a selected, subfertile population in which a luteal-support effect is most plausible; the result must not be generalised to first-service cows. The day-4 arm sits outside this shelf's 5-7 day window; only the day-6 arm is strictly on-window. Controls were untreated, not placebo-injected, and the abstract does not describe the allocation method or any masking, so this card alone does not establish blinding. Subgroup figures (season, parity) come from multiple comparisons within one trial.

Alnimer MA, Shamoun AI. Treatment with hCG 4 or 6 days after TAI to improve pregnancy outcomes in repeat-breeding dairy cows. Anim Reprod Sci. 2015;157:63-70. PMID: 25890835. Registry ID: none in the record. MeSH: Animals · Buserelin/administration & dosage/pharmacology · Cattle/physiology* · Chorionic Gonadotropin/administration & dosage/pharmacology* · Dinoprost/administration & dosage/pharmacology · Drug Administration Schedule · Estrus Synchronization/drug effects · Female · Humans · Insemination, Artificial/veterinary* · Parity · Pregnancy · Pregnancy Rate · Progesterone/blood · Seasons

Shabankareh 2010: hCG (3,000 IU) on day 5 post-AI improved pregnancy rates in Heatsynch-bred cows (41.5% vs 24.8% saline, p < 0.01) and in the warm period (37.9% vs 23.6%, p < 0.001)

Controlled trial with saline-controlled post-AI subgroups nested in three breeding programmes (publication types: Journal Article, Randomized Controlled Trial)

Who: Dairy cattle: 667 lactating dairy cows at random stages of the oestrous cycle, assigned to Ovsynch (n = 228), Heatsynch (n = 252) or natural-oestrus control breeding (n = 187), starting 44 ± 3 days in milk; on the day of AI, cows in every group were further assigned to receive 3,000 IU human chorionic gonadotropin intramuscularly or 10 ml saline on day 5 post-AI (subgroups of 94-129 cows). Pregnancy was assessed by rectal palpation at days 40-45 after AI.

Result: Treatment with hCG 5 days after AI significantly improved pregnancy rates in cows bred under the Heatsynch protocol compared with saline (41.5% vs 24.8%; p < 0.01; absolute difference 16.7 percentage points; relative rate about 1.67). Pregnancy rate was higher for hCG-treated cows than saline-treated cows during the warm period (37.9% vs 23.6%; p < 0.001). First-service pregnancy rates were higher in primiparous hCG-treated cows than pluriparous hCG-treated cows (57.9% vs 32.3%; p < 0.01). A clear negative effect of the warm period on first-service pregnancy rate was noted (p < 0.01), and the lowest pregnancy rate was in the Heatsynch protocol during the warm period. No significant hCG-vs-saline contrast is reported in the abstract for the Ovsynch or natural-oestrus subgroups.

Watch out: The hCG benefit is subgroup-specific: it is demonstrated for Heatsynch-bred cows and for the warm period, not as an overall main effect across all 667 cows, and the abstract's analysis is a main-effects logistic model in which the hCG effect interacts with programme and season. The record does not state that the day-5 subgroup allocation was randomised or that assessors were masked, despite the saline control.

Shabankareh HK, Zandi M, Ganjali M. First service pregnancy rates following post-AI use of HCG in Ovsynch and Heatsynch programmes in lactating dairy cows. Reprod Domest Anim. 2010;45(4):711-6. PMID: 19309467. Registry ID: none in the record. MeSH: Animals · Cattle · Chorionic Gonadotropin/pharmacology* · Dairying · Estrus Synchronization/methods* · Female · Fertility Agents, Female/pharmacology* · Parity · Pregnancy · Pregnancy Rate* · Pregnancy, Animal* · Seasons

Agarwal 2021: hCG on day 7 post-AI (1,500 IU) did not improve first-service conception vs saline in 50 healthy crossbred cows, despite larger luteal dimensions

Block-randomised, saline-controlled trial (record's own wording; publication types: Journal Article)

Who: Dairy cattle: 50 healthy lactating Indian crossbred dairy cows, allocated by block randomisation in equal numbers (n = 10 per group) to 5 ml normal saline (control) or 1,500 IU human chorionic gonadotropin on the day of AI, on day 7 post-AI, on day 14 post-AI, or on days 0, 7 and 14 post-AI. Cows were followed with sequential transrectal ultrasound for luteal parameters and accessory corpora lutea, serial plasma progesterone, and pregnancy.

Result: Mean primary luteal area, total luteal area and total luteal diameter were significantly greater in hCG-treated cows, and the day-14 group had a significantly higher percentage of cows with an accessory corpus luteum than controls. However, there were no significant differences in mean progesterone concentrations or in first-service conception rates between any of the groups. The authors conclude that hCG post-AI may enhance primary luteal dimensions or induce accessory corpora lutea but does not appear to have any beneficial effect on luteal function or pregnancy in these healthy cows. The abstract reports no conception-rate figures, only the non-significant comparison.

Watch out: Only 10 cows per group, so the null conception result is compatible with a wide range of true effects — this card shows 'no benefit demonstrated in healthy cows', not proof of no effect. Healthy, normal cyclic cows are the population least likely to show a luteal-support benefit; contrast Alnimer 2015's repeat breeders. Masking is not stated in the record.

Agarwal S, Gupta HP, Prasad S, Verma PK, Khanam A, Khan FA. Effect of various hCG treatment protocols on luteal characteristics, plasma progesterone concentration, and pregnancy in normal cyclic Indian crossbred dairy cows. Trop Anim Health Prod. 2021;53(2):220. PMID: 33751251. Registry ID: none in the record. MeSH: Animals · Cattle · Chorionic Gonadotropin/pharmacology · Clinical Protocols · Corpus Luteum* · Estrus Synchronization · Female · Gonadotropin-Releasing Hormone · Insemination, Artificial/veterinary · Lactation* · Plasma · Pregnancy · Progesterone

Schmitt 1996 (Experiment 5): hCG on day 5-6 after insemination did not increase pregnancy rates in lactating cows under summer heat stress (24.2% vs 23.5% control)

Multi-experiment controlled study; fertility experiments are controlled comparisons in heifers and lactating cows (publication types: Comparative Study, Journal Article)

Who: Dairy cattle and heifers: a five-experiment series in Holstein cattle testing induction of an accessory corpus luteum with a GnRH agonist (buserelin 8 micrograms) or human chorionic gonadotropin (3,000 IU) on day 5 after oestrus. Experiments 1-3 (heifers) established that both agents induced an accessory corpus luteum in 93% of treated animals, with a greater subsequent progesterone rise after hCG. Experiment 4 tested pregnancy rates in fertile heifers (n = 243) and Experiment 5 in lactating dairy cows during summer heat stress (n = 201), with hCG given on day 5 or 6 after insemination.

Result: Induction of an accessory corpus luteum with hCG on day 5 or 6 after insemination did not increase pregnancy rates in fertile heifers (Experiment 4: hCG 64.8% vs control 62.9%; n = 243) or in lactating dairy cows during summer heat stress (Experiment 5: hCG 24.2% vs control 23.5%; n = 201) — absolute differences under 2 percentage points in both. The record's fertility experiments tested hCG; the GnRH agonist was tested for accessory-corpus-luteum induction and progesterone response (Experiments 1-3), not for pregnancy rate.

Watch out: An older (1996) record whose fertility arms predate modern timed-AI programmes; Experiment 5's cows were under summer heat stress, the setting in which later trials (Alnimer 2015, Shabankareh 2010) did find hCG benefits in selected groups — the records conflict, and this shelf reports both rather than resolving them. The abstract does not state the allocation method for the fertility experiments. Heifer data (Experiment 4) are included only as the record's own companion experiment; the shelf's claim rests on the lactating-cow Experiment 5.

Schmitt EJ, Diaz T, Barros CM, de la Sota RL, Drost M, Fredriksson EW, Staples CR, Thorner R, Thatcher WW. Differential response of the luteal phase and fertility in cattle following ovulation of the first-wave follicle with human chorionic gonadotropin or an agonist of gonadotropin-releasing hormone. J Anim Sci. 1996;74(5):1074-83. PMID: 8726740. Registry ID: none in the record. MeSH: Animals · Buserelin/pharmacology* · Cattle/physiology* · Chorionic Gonadotropin/blood/pharmacology* · Corpus Luteum · Estrus/physiology · Female · Fertility/drug effects/physiology* · Gonadotropin-Releasing Hormone/agonists* · Humans · Luteal Phase/drug effects/physiology* · Ovarian Follicle/drug effects/physiology* · Ovulation/drug effects/physiology* · Ovulation Induction · Pregnancy · Pregnancy Rate · Progesterone/blood · Random Allocation

Synthesis: post-AI GnRH on day 5 not shown to help; post-AI hCG helps in selected populations only — POSSIBLE

Synthesis

Who: Synthesis of the five cards above (Jeong 2016, 569 cows; Alnimer 2015, 406 repeat breeders; Shabankareh 2010, 667 cows; Agarwal 2021, 50 cows; Schmitt 1996, 201 lactating cows plus 243 heifers) and of the near-miss records documented in the result, fetched at drafting and deliberately not carded as claim-carriers.

Result: (1) GnRH: the only large randomised post-AI test (Jeong, day 5: 34.4% vs 31.6%, p > 0.05) is null, and no carded record shows a pregnancy benefit for a single GnRH injection 5-7 days after AI. (2) hCG in unselected or healthy cows: null in Schmitt 1996 (24.2% vs 23.5%) and Agarwal 2021 (no significant conception difference). (3) hCG in selected populations: positive in repeat breeders at day 6 (Alnimer: 38.9% vs 30.9%, with losses 15.0% vs 37.7%) and in Heatsynch-bred and warm-period cows at day 5 (Shabankareh: 41.5% vs 24.8% and 37.9% vs 23.6%). All reported relative rates for the positive contrasts (about 1.26 to 1.67) lie inside the 0.5-2.0 band, so none would be solid evidence on its own; the POSSIBLE stamp rests on two independent trials finding benefits in biologically coherent selected populations against two nulls in unselected cows. (4) Near-misses not carded: Cunha 2021 (PMID: 34157566) randomised 564 Holstein and Jersey cows to GnRH or hCG on days 5-7 of the oestrous cycle, but treatment was given in the cycle BEFORE first AI and pregnancy per AI was measured at the subsequent service (Holstein: control 34.3%, GnRH 35.4%, hCG 31.5%, P = 0.93) — the timing is pre-AI, not 5-7 days after AI, so it cannot carry this shelf's claim. Pirokad 2022, a repeat-breeder heat-stress GnRH day-5 record (PMID: 36114327) reported higher pregnancy rates with GnRH on day 5 post-fixed-time AI (P < 0.01, n = 213) but its abstract reports no absolute pregnancy rates, so no figure from it is carded here. (5) Design class (b): randomisation established by Jeong 2016 and Agarwal 2021 for this shelf's own comparison; blinding not established in any carded record. Tier C is not engaged — the primary claim throughout is pregnancy rate, not mortality or survival.

Watch out: One-home check at drafting: none of PMIDs 27030200, 25890835, 19309467, 33751251, 8726740, 34157566 or 36114327 appears in any other pack on disk. Do not merge the two drugs into one claim: the GnRH evidence at day 5 is null and the hCG evidence is population-dependent. Do not quote Alnimer's pregnancy-loss figures as a stand-alone fetal-loss benefit — on this shelf they are reported only as a component of the pregnancy-rate outcome, and no Tier C claim is made.

Synthesis of Jeong JK et al. PMID: 27030200; Alnimer MA et al. PMID: 25890835; Shabankareh HK et al. PMID: 19309467; Agarwal S et al. PMID: 33751251; Schmitt EJ et al. PMID: 8726740; Cunha TO et al. PMID: 34157566; PMID: 36114327. Registry IDs as on the individual cards (none in the records).

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