Impact of subclinical mastitis on milk yield and economic return of dairy cows
Notice bibliographique
Résumé
The general objectives of the present thesis were to evaluate: (i) the effects of subclinical mastitis (SM) caused by major pathogens on SCC, milk leukocyte differentials (MLD) and milk yield; (ii) milk yield losses caused by SM at the cow and quarter level; and (iii) the economic impact of SM caused by major pathogens. The thesis was structured in four studies. In study 1, quarter milk samples (n = 302) from 78 cows with SCC gt;200,000 cells/mL were analyzed by milk leukocyte differential (MLD) methodology and by microbiological culture (MC). Quarters with positive-culture results were obtained from 102/156 (65.4%) of MLD-positive milk samples, while 28/135 (20.7%) of MLD-negative milk samples were MC-positive. When MC was considered the gold standard for mastitis diagnosis, the sensitivity (Se) of the MLD was 65.4% (IC95% = 57.4 to 72.8%) and the specificity (Sp) was 79.3% (IC95% = 71.4% to 85.7%). In conclusion, the use of the MLD on cows with monthly composite SCC > 200×103 cells/mL for screening at quarter level identified quarters more likely to be culture-positive. In study 2, the effect of different pathogens was evaluated by comparison of contralateral (healthy and infected) mammary quarters of 146 lactating cows. The impact of SM on economic return (quarter milk yield × milk price) was determined by applying milk payment estimates on milk collected from healthy versus infected glands. The milk losses ranged from 0.07 Kg/quarter.milking to 2.9 Kg/quarter.milking, and varied according to the pathogen causing SM. Economic losses were higher for SM caused by Enterococcus spp. (US$0.43/quarter.milking), Strep. Dysgalactiae (US$ 0.74/quarter.milking) and E. coli (US$0.98/quarter.milking). Additionally, there was a trend for Staph. aureus and Citrobacter spp. To induce economic losses of US$ 0.26 and 0.29/quarter.milking, respectively. In general, the economic return was lower in quarters with SM caused by environmental and contagious pathogens (US$ 0.18 and 0.22/quarter.milking, respectively) when compared to their healthy contralateral quarters. In study 3, a total of 146 out of 650 lactating cows were selected from seven dairy herds for having composite milk SCC > 200,000 cells/mL in combination with the isolation of a major mastitis pathogen. From these selected cows, 1,436 quarter milk samples were collected during three successive sampling occasions at intervals of 15-20 days. Quarter milk yield was measured by milking the mammary quarters individually using three successive milk samplings over time. Bacterial isolates were identified by microbiological culture, MALDI-TOF MS and partial sequencing of the 16S rRNA gene. Milk losses and economic returns varied according to the type of mastitis-causing pathogen: 0.24 to -0.87 kg/quarter.milking for environmental streptococci, and -1.57 to -1.69 kg/quarter.milking for Staph. aureus. Overall, mammary quarters that were cured from SM caused by Staph. aureus and environmental streptococci exhibited an increase in economic return of approximately 0.47 and 0.69 US$/quarter.milking, respectively. In study 4, test day records (n = 1,200,002) were obtained from the Paraná State Holstein Association, which included data from 92,560 lactating cows, from 781 herds, from January 2010 to December 2015. A segmented regression was fitted to estimate the cut-off point of Log10SCC scale where milk yield started to be affected by mastitis: 0.90 (~7,963 cells/mL). In conclusion, first lactation cows have a reduction of 1.37 to 2.28 kg/cow/d of milk yield for each increase of one unit of Log10SCC over the cutoff point, whereas second and later lactation cows are expected to have milk yield losses of 2.36 to 4.20 kg/cow/d for each unit increase of Log10SCC over the cutoff point. Overall, the results of this thesis indicated that milk losses depend on the type of pathogen causing SM. Major pathogens have showed greater effects on milk quality than when it was observed using the approach of culture results of negative or positive. The methodology for evaluation of subclinical mastitis effect on milk yield interferes in the estimation of milk losses, and should include factors such as DIM and number of parity.
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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 | 0,000 | 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 | 0,000 |
| 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 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 ».