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Aptitude des vaches laitières à se reproduire en systèmes pâturants contrastés : Quelle vache pour quel système ?

Abstract : Reproductive performance of dairy cows has been declining while their milk production was improving. The strong genetic selection that was applied on milk production is considered to be responsible for this. Each step of the reproductive process has been impacted: abnormal ovarian activity is more common in the current population, the duration and intensity of oestrus has dramatically decreased and the occurrence of pregnancy failures has increased. The consensus in the literature is that reproduction is impaired because dairy cows are investing most of their resources in milk production. The aim of this Ph.D. thesis is to explore the effect of alternative selection strategies based on milk fat and protein content on robustness of dairy cows. Our hypotheses were that at similar genetic merit for milk solids yield, compared to cows with high genetic merit for milk yield,dairy cows with high genetic merit for fat and protein contents (i) are exporting less energy in milk and are consequently safeguarding their body reserve; (ii) have better reproductive performance (earlier resumption of ovarian activity, more intense oestrus, better ability to ensure pregnancy). Our results suggest that cows selected for production through high fat and protein content instead of high milk yield would resume ovarian activity earlier, have similar oestrus intensity but more pregnancy failures. These intriguing results suggest that the steps of the reproductive process are genetically partly disentangled. Selecting dairy cows for fat and protein content is not a promising way to improve repro
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Submitted on : Wednesday, June 14, 2017 - 9:45:07 AM
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Nicolas Bedere. Aptitude des vaches laitières à se reproduire en systèmes pâturants contrastés : Quelle vache pour quel système ?. Génétique animale. Agrocampus Ouest, 2016. Français. ⟨NNT : 2016NSARB286⟩. ⟨tel-01496897v2⟩

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