Effect of prepartum photoperiod and melatonin feeding on milk production and prolactin concentration in dairy heifers and cows
Notice bibliographique
Résumé
Holstein multiparous cows (n = 29) and primiparous heifers (n = 32) calving over a 1-yr period were subjected to photoperiod-melatonin treatments according to a 2 × 3 factorial design. Starting 8 wk before expected calving, all animals were subjected to 1 of the following treatments: 8h of light and 16 h of dark (8L:16D), 16 h of light and 8h of dark (16L:8D), or 16L:8D plus melatonin feeding (16L:8D-melatonin). Each day at 1355 h, the animals in the melatonin treatment received orally a gelatin capsule containing 25mg of melatonin. The treatments ended at calving, when the animals were moved to the lactation barn; all animals were then subjected to about 16 h of light per day. At the beginning and end of the treatment period before calving, blood samples were taken from 6 heifers and 6 cows through a jugular cannula for 24h at 30-min intervals to monitor serum melatonin and prolactin concentrations. Milk production in the heifers was not affected by the photoperiod treatments. Early-lactation milk production was higher in the cows exposed to the short-day photoperiod than in those exposed to a long-day photoperiod (16L:8D and 16L:8D-melatonin), with averages of 36.7 ± 0.9, 33.1 ± 0.8, and 34.1 ± 0.9 kg/d for 8L:16D, 16L:8D, and 16L:8D-melatonin, respectively. Photoperiod had no effect on late-lactation milk production in the cows. During lactation, the dry matter intake of heifers was not affected by the treatments, but dry matter intake of the cows exposed to a short-day photoperiod was greater than that of the cows exposed to a long-day photoperiod. Feed efficiency of heifers was improved by short-day photoperiod. During the treatment period, prolactin concentration was lower in the animals exposed to a short-day photoperiod than in those exposed to a long-day photoperiod, was lower with the 16L:8D-melatonin treatment than with the 16L:8D treatment, and tended to be lower with the 8L:16D treatment than with the 16L:8D-melatonin treatment, with averages of 3.5 ± 0.8, 9.9 ± 0.8, and 6.0 ± 0.8 ng/mL for 8L:16D, 16L:8D, and 16L:8D-melatonin, respectively. In early lactation, prolactin concentration was lower in the heifers exposed to the 16L:8D photoperiod during the dry period than in those exposed to the 8L:16D photoperiod or fed melatonin. In conclusion, a short-day photoperiod during the dry period transiently increases milk production of cows and the feed efficiency of heifers in the following lactation. However, melatonin cannot be used to mimic a short-day photoperiod during the dry period.
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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 | 0,002 | 0,001 |
| 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 | 0,001 |
| 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 ».