The Effects of a GnRH Antagonist, Cetrorelix, on Ovarian Function in Cattle
Notice bibliographique
Résumé
Estradiol-based ovulation synchronization protocol are effective for breeding management in cattle, however, political pressure from the European Union has resulted in many countries enacting similar bans on the use of estradiol in livestock animals. Our long-term goal is to engineer an alternative protocol for fixed-time artificial insemination that is simple, steroid-free, and effective during different stages of the estrus cycle. Two studies were conducted to determine the effects of a GnRH antagonist, cetrorelix, on the follicular dynamics in cattle during different stages of follicular growth and in different endocrine milieus. The specific objective was to test the hypothesis that cetrorelix would induce regression of the dominant follicle and induce a new follicular wave emergence at a predictable time after treatment. In the first study (Chapter 4, two experiments), we explored the effects of cetrorelix at three stages of dominant follicle development and synchrony of subsequent follicular wave emergence and ovulation in cattle. In this study, ovaries of sexually mature heifers (>13 months of age, n=8 per group) were examined daily by transrectal ultrasonography to detect ovulation (Day 0 = wave emergence) and record the number, location, and diameter of follicles. In Experiment 1 of Study 1, heifers were given two doses of cetrorelix (1.5mg x2; 0.5 mg/ml in 5% D-Mannitol) 24 hr apart im starting on Day 1 (Cetro1-2; early-growing/pre-selection phase dominant follicle), Day 3 (Cetro3-4; mid-growing phase dominant follicle), and Day 6 (Cetro6-7; static phase dominant follicle), or normal saline (Control). Jugular venipuncture plasma samples were collected 0, 2, 4, and 6 days after cetrorelix treatment to assess luteal function. In all cetrorelix-treated heifers, dominant follicle regression occurred, and a new follicular wave emerged consistently 5.8 ± 0.3 days after treatment. There was a tendency for cetrorelix to reduce the diameter of the corpus luteum (CL), but there was no difference in the luteal function or lifespan between Control and treatment groups. In Experiment 2 of Study 1, heifers were given a single bolus of 3 mg cetrorelix im on Day 1, 3, or 6 of the wave; prostaglandin 9 days after cetrorelix treatment; and then heifers were artificially inseminated 12 hr after estrus detection. A single bolus of cetrorelix induced similar follicular regression as in Experiment 1 and a new follicular wave emerged consistently 3.6 ± 0.3 days after treatment. Artificial inseminations resulted in a 56.5% pregnancy rate (n=13/23) in all cetrorelix-treated heifers versus 42.9% (n=3/7) in Control, indicating no adverse effects of cetrorelix on oocyte competence. In the second study (Chapter 5), we examined the effects of cetrorelix on the ability to induce a new follicular wave by inhibiting ovulation during the preovulatory phase (Experiment 1) and determined the effect of cetrorelix on the ovulatory ability of the dominant follicle to exogenous challenge of hCG (Experiment 2). In Experiment 1 of Study 2, heifers (n=6 per group) were given either a luteolytic dose of cloprostenol on Day 4 and 4.5 (PreOv group) or heifers were allowed to maintain a functional CL (Luteal group). All heifers were given 3 mg cetrorelix im on Day 5 and the ovaries were examined daily until the next ovulation or wave emergence. Cetrorelix prevented the dominant follicle from ovulating and induced follicular regression in the Luteal and PreOv groups, resulting in a consistent follicular wave emergence 3.1 ± 0.3 days after cetrorelix treatment. In Experiment 2 of Study 2, heifers were synchronized by ultrasound-guided follicular ablation in combination with an intravaginal progesterone-releasing device for 5 days and PGF at the time of removal. Heifers were given either cetrorelix (Cetro groups) or normal saline (Control groups) on Day 5 (2x2 factorial; n=6 heifers per group) and all groups were treated with 1500 IU of hCG im on Day 7. Jugular venipuncture plasma samples were collected from all animals for progesterone analysis (-24 hr, 24 hr, and 48 hr from cetrorelix treatment). Cetrorelix did not prevent the dominant follicle from ovulating in response to exogenous hCG 48 hr after treatment. Combined between the two experiments, cetrorelix does not affect the diameter, vascularity, and progesterone secretion of the CL. In summary, a single bolus or split doses of cetrorelix given during the pre-selection, growing, or static phase of dominant follicle development and during the preovulatory phase induced follicular regression, resulting in the emergence of a new follicular wave at a predictable interval post-treatment. CL function and subsequent oocyte competence were not affected. Finally, cetrorelix treatment is an effective method to synchronize wave emergence and ovulation for reproductive management in cattle.
Récupéré en direct depuis OpenAlex et désinversé. Les résumés ne sont pas conservés dans cette base de données : les index inversés représentent 8,6 Go des 9,3 Go de texte de la base, et le serveur dispose de 13 Go libres.
Comment cette classification a été obtenuedéplier
Prédiction machine sur la base complète
Imitation des enseignantsNi prévalence calibrée, ni vérité terrain. Validation humaine à venir. Le volet Gemma est une étiquette directe du modèle pour chaque travail de la base, lue sur la notice réduite au titre. Le volet Codex est un classifieur appris des 10 348 étiquettes directes de Codex et calibré sur les taux pondérés de l'échantillon; les champs sans appui suffisant ne portent aucun appel Codex. Le mode candidate est l'union des deux volets; le consensus est leur intersection. Ces sorties portent le statut machine_predicted_unvalidated et ne sont pas des étiquettes humaines.
Scores du classifieur distillé par catégorie (deux têtes)
| Catégorie | Codex | Gemma |
|---|---|---|
| Métarecherche | 0,000 | 0,000 |
| Méta-épidémiologie (sens strict) | 0,000 | 0,000 |
| Méta-épidémiologie (sens large) | 0,000 | 0,000 |
| Bibliométrie | 0,000 | 0,000 |
| Études des sciences et des technologies | 0,000 | 0,000 |
| Communication savante | 0,000 | 0,000 |
| Science ouverte | 0,000 | 0,000 |
| Intégrité de la recherche | 0,000 | 0,001 |
| Charge utile insuffisante (le modèle a refusé de juger) | 0,001 | 0,000 |
Scores machine (provisoires)
Les deux têtes enseignantes du modèle étudiant, lues sur ce travail. Un score ordonne la base pour la relecture; il n'affirme jamais une catégorie, et le statut de validation accompagne chaque rangée tel quel.
Scores de référence d'un modèle non mature (critères de maturité non atteints, 7 itérations). Un score ordonne; il n'affirme jamais une catégorie.
score_only:v0-immature-baseline · tel quel depuis la passe de notation : score_only signifie que le nombre peut ordonner les travaux, et qu'aucune étiquette de catégorie n'en découleClassification
machine, non validéePrédiction automatique; un appel candidat d’une seule source (Gemma direct ou Codex distillé), pas un consensus.
Le détail, modèle par modèle et score par score, se trouve en fin de page sous « Comment cette classification a été obtenue ».