12 Ovulation Timing Following an Aromatase Inhibitor-Based Synchronization Protocol in Beef Heifers and Cows
Notice bibliographique
Résumé
The study was conducted to determine the effects of parity/lactation and the timing of gonadotropin-releasing hormone (GnRH) treatment on the efficacy of a non-steroidal aromatase inhibitor-based synchronization protocol in cattle. Results from previous studies confirmed drug-release from a new letrozole-impregnated intravaginal silicone device, which was used in the present study. Hereford-cross cows with suckling calves (41 to 65 days postpartum; n = 30) and sexually mature heifers (n = 30), at random stages of the oestrous cycle, were given a letrozole intravaginal device for 4 days followed by a luteolytic dose of prostaglandin F2a (PGF2a). Following PGF2a treatment, animals were assigned randomly to 3 groups and given GnRH (100 µg of gonadorelin) intramuscularly at 48 or 60 h, or no GnRH (n = 10 cows and 10 heifers per group). Ovaries were examined by transrectal ultrasonography every 8 h starting at the time of PGF2a treatment to record follicle diameter and ovulation. After ovulation, ultrasonography was done every 24 h until Day 10 (Day 0 = ovulation) to assess the corpus luteum (CL) diameter profile. The timing of ovulation, diameter of the preovulatory follicle, synchrony of ovulation, and Day-7 CL diameter were compared using two-way ANOVA, and CL diameter profiles were compared by two-way ANOVA for repeated measures. There was no treatment × parity/lactation status interaction for any endpoint. The ovulation rate within 96 h of PGF2a treatment was not different between heifers and cows (24/30 v. 27/30; P = 0.14) or treatment group (18/20, 18/20, and 15/20 in the 48 h, 60 h, and no GnRH groups, respectively; P = 0.18). The interval from PGF2a treatment to ovulation was not influenced by parity/lactation (83.1 ± 2.4 h) but was shortest in the GnRH 48 h group (mean ± SEM; 74.2 ± 2.7 h, 85.6 ± 4.8 and 89.2 ± 4.1, respectively; P < 0.05). Similarly, the variation in the interval to ovulation (mean ± s.e.M of residuals) was not influenced by parity/lactation (16.0 ± 2.0 h), but was lower in the GnRH groups than the no-GnRH group (P < 0.01), and tended to be lower (P = 0.1) in the GnRH 48-h v. 60-h group (10.0 ± 2.8, 14.2 ± 3.5, and 24.1 ± 3.1 h, respectively). The maximum diameter of the ovulatory follicle was larger for cows than heifers (17.0 ± 0.4 v. 15.1 ± 0.5; P < 0.01), and was smaller in the GnRH groups than the no-GnRH group (15.3 ± 0.3, 15.4 ± 0.7 and 17.3 ± 0.5 mm, respectively; P < 0.01). The diameter of the CL on Day 7 was larger for cows than heifers (22.3 ± 0.8 v. 20.2 ± 0.6 mm; P < 0.05) and was influenced by treatment (21.9 ± 0.5, 19.5 ± 0.7, 22.3 ± 1.1 mm, respectively; P = 0.05). A tendency for a treatment effect on CL diameter profile (P = 0.1) was attributed to a smaller profile in the GnRH 60-h group. In conclusion, GnRH treatment 48 h after PGF2a treatment increased synchrony of ovulation without adverse effects on ovulating follicle diameter or resulting CL growth, and may be incorporated into a novel steroid-free oestrous synchronization protocol for use in beef heifers and lactating cows. Research was supported by the Alberta Livestock and Meat Agency and Vencofarma, Brazil.
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Comment cette classification a été obtenuedéplier
Prédiction distillée sur la base complète
Imitation des enseignantsNi prévalence calibrée, ni vérité terrain. Validation humaine à venir. Apprise à partir de 10 348 étiquettes directes de Codex et de 10 348 étiquettes directes de Gemma. Le mode candidate est l'union des têtes enseignantes seuillées; le consensus est leur intersection. Ces sorties portent le statut machine_predicted_unvalidated et ne sont ni des étiquettes humaines ni des étiquettes directes de modèles de pointe.
Scores Codex et Gemma par catégorie
| Catégorie | Codex | Gemma |
|---|---|---|
| Métarecherche | 0,001 | 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 | 0,001 | 0,000 |
| Communication savante | 0,000 | 0,001 |
| Science ouverte | 0,000 | 0,000 |
| Intégrité de la recherche | 0,000 | 0,000 |
| Charge utile insuffisante (le modèle a refusé de juger) | 0,000 | 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 tête enseignante, 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 ».