Genetic parameters of the fatty acid composition of milk of Canadian holsteins and genetic associations between feed intake and type traits in Canadian holsteins
Notice bibliographique
Résumé
The first part of the thesis discusses about the fatty acid composition of bovine milk fat. One morning milk sample was collected from each of 3185 dairy cows between February and June 2010 from 52 commercial herds enrolled in the Quebec Dairy Production Centre of Expertise, Valacta. Individual fatty acid percentages (g/100g of total fatty acids) were determined for each sample by gas chromatography. After necessary editing, final data included 2573 cows representing 46 herds. The objectives of the first study were to study the effects of parity, age at calving and stage of lactation on fatty acid composition of milk of Canadian Holsteins. The model included the fixed effects of parity, age at calving and stage of lactation nested within parity and random effects of herd-year-season of calving and residual. The mixed model was fitted using restricted maximum likelihood (REML) methodology. Parity of cow was significantly (P < 0.05) related to the variation in most fatty acids in milk fat. First parity cows had relatively higher proportions of some beneficial fatty acids and lower proportions of potentially harmful saturated fatty acids as compared to later parity cows. Stage of lactation significantly affected fatty acid composition of cows. The short and medium chain fatty acids were low in the beginning of lactation and increased during the early part of lactation, whereas, an opposite trend was observed for long chain fatty acids. The objective of the second study was to estimate heritabilities of and genetic and phenotypic correlations among fatty acids in milk of Canadian Holsteins using fatty acid data from the first study. Genetic parameters were estimated using multitrait animal models fitted under REML. The estimates of heritability ranged from 0.01 to 0.39 with standard errors ranging from 0.01 to 0.06. Generally, monounsaturated (0.20 to 0.39) and saturated fatty acids (0.02 to 0.34) showed higher heritability estimates than polyunsaturated fatty acids (0.01 to 0.21) and trans fatty acids (0.01 to 0.05). Overall, saturated fatty acids were negatively genetically correlated with monounsaturated and polyunsaturated fatty acids. Most of the genetic correlation estimates between monounsaturated and polyunsaturated fatty acids were positive. In order to change milk fat composition in a desirable direction, selection for one or more monounsaturated fatty acids may be more effective than selection against saturated fatty acids.The objective of the third study (Part 2 of thesis) was to estimate genetic correlations between feed intake and type traits with a view to considering the potential of indirect genetic selection for feed intake using type traits in dairy cattle. Feed intake data on 119388 first lactation Holstein cows were obtained from the Quebec Dairy Production Centre of Expertise, Valacta. The two trait animal models were fitted under restricted maximum likelihood (REML). Estimates of heritabilities ± standard errors for DMI, NELI and CPI were 0.12 ± 0.01, 0.13 ± 0.01 and 0.13 ± 0.01, respectively. Estimates of heritabilities ± standard errors of dairy strength, angularity, body depth, stature and final score were 0.31 ± 0.01, 0.24 ± 0.01, 0.30 ± 0.01, 0.50 ± 0.01 and 0.22 ± 0.01, respectively. All phenotypic and genetic correlation estimates between feed intake and type traits were positive. Angularity showed the highest genetic correlation estimates with feed intake traits (0.60 to 0.65) followed by dairy strength (0.48 to 0.54), stature and body depth (0.29 to 0.36) with all three feed intake traits. Angularity, dairy strength, stature and body depth may be useful for indirect selection of feed intake traits in dairy cattle.
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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 | 0,001 | 0,001 |
| Méta-épidémiologie (sens strict) | 0,000 | 0,000 |
| Méta-épidémiologie (sens large) | 0,001 | 0,001 |
| Bibliométrie | 0,002 | 0,002 |
| Études des sciences et des technologies | 0,002 | 0,001 |
| Communication savante | 0,001 | 0,000 |
| Science ouverte | 0,001 | 0,000 |
| Intégrité de la recherche | 0,000 | 0,000 |
| Charge utile insuffisante (le modèle a refusé de juger) | 0,002 | 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 ».