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Animal performances, pasture biodiversity and dairy product quality: how it works in contrasted mountain grazing systems
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International audience. The interactions between botanical composition of pasture, quality of herbage grazed, performances of dairy cows and sensory and nutritional properties of dairy products were investigated using an integrated system approach. Two contrasting grazing systems were evaluated from May to September in two years. The treatments included a continuous grazing system (DIV) managed at a lenient stocking rate (1.0 LU ha−1) on a botanically-rich permanent pasture, and a rotational grazing system (PROD) set up at a higher stocking rate (1.7 LU ha−1) on a former temporary grassland presenting moderate biodiversity. DIV aimed to maximize biodiversity and obtain high sensory and nutritional quality cheese, whereas PROD was oriented towards milk production and herbage quality. In each system, 12 non-feed-supplemented Montbéliarde cows were used. The DIV system led to higher milk production per cow in the early grazing season than the PROD system (22.2 vs. 19.9 kg d−1). At the beginning of summer, this milk production pattern was inverted following a decrease in grass nutritive value in the DIV system. In parallel, DIV cows showed a more marked loss of body condition than PROD cows over the season. In terms of milk fatty acid profile, the DIV system proved very interesting early in the grazing season but lost its value over time as the herbage matured. Cheese sensory properties differed between systems only after a long ripening period (6 months). Regarding the ecological performances, the DIV plot showed greater botanical and entomological biodiversity than the PROD plot. This study provides evidence that the balance between animal performances, dairy product quality and biodiversity in dairy systems is more complex than previously thought, since the expected benefits of each system vary markedly over periods. The evolution of herbage vegetation stage during the grazing season combined with the botanical composition of the pasture is a key component for understanding these variations.
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