Dynamic model of milk production responses to grass-based diet variations during grazing and indoor housing
Jacquot, Anne-Lise | Delaby, Luc | Pomiès, Dominique | Brunschwig, Gilles | Baumont, René | Physiologie, Environnement et Génétique pour l'Animal et les Systèmes d'Elevage [Rennes] (PEGASE) ; Institut National de la Recherche Agronomique (INRA)-AGROCAMPUS OUEST | Unité Mixte de Recherche sur les Herbivores - UMR 1213 (UMRH) ; Institut National de la Recherche Agronomique (INRA)-VetAgro Sup - Institut national d'enseignement supérieur et de recherche en alimentation, santé animale, sciences agronomiques et de l'environnement (VAS)
Dairy cow systems based on grassland utilization are characterized by a variation of harvested forage quality from1 year to another and a fluctuation of grass availability and quality during the pastureseason. Consequently, theenergy supplied by the diet–i.e., concentrates plus hay or silage in winter and grazing in summer, may notalways match animal requirements. A modelling approach enables a representation of the complex relationshipsbetween the cow and pasture as they interact. A dynamic model of intake and milk production, focused on grasslandutilization by the dairy cow, has been developed. The model operates in a deterministic fashion with a daily time stepand is capable of dealing with a day-to-day variation in grass availability and quality at grazing as well as a constantfeeding regime during the winter. The model has been built based on the theory that milk production is a result of(i) the energy requirements defined by the potential milk production and physiological status of dairy cows; (ii) thevariation of energy supply by the diet; (iii) the ability ofdairy cows to mobilize or store body reserves. The model wasvalidated by comparing milk production predictions with experimental data (two groups of dairy cows in the wintertime and one group at grazing). The model demonstrates a satisfactory range of accuracy (root-mean-square devi-ation equal to 1·8, 2·1 and 1·4 kg/cow/day). Model validations indicate that milk production predictions are sensitiveto the diet offered (forage, grass and concentrate supply) and depend on dairy cowcharacteristics and their require-ments (pMP). This model can be connected to a grass growth model in order to develop whole farm simulations.
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