Dynamic model of milk production responses to grass-based diet variations during grazing and indoor housing
Résumé
Dairy cow systems based on grassland utilization are char
acterized by a variation of harvested forage quality from
1 year to another and a fluctuation of grass availability an
d quality during the pasture
season. Consequently, the
energy supplied by the diet
–
i.e., concentrates plus hay or silage in winter and grazing in summer, may not
always match animal requirements. A m
odelling approach enables a represent
ation of the complex relationships
between the cow and pasture as they interact. A dynamic m
odel of intake and milk production, focused on grassland
utilization by the dairy cow, has been developed. The model o
perates in a deterministic fa
shion with a daily time step
and is capable of dealing with a day-to
-day variation in grass availability an
d quality at grazing as well as a constant
feeding regime during the winter. The model has been bu
ilt based on the theory that milk production is a result of
(i) the energy requirements d
efined by the potential milk production and ph
ysiological status of dairy cows; (ii) the
variation of energy supply by the diet; (iii) the ability of
dairy cows to mobilize or store body reserves. The model was
validated by comparing milk production predictions with ex
perimental data (two groups of dairy cows in the winter
time and one group at grazing). The model demonstrates a sa
tisfactory range of accuracy (root-mean-square devi-
ation equal to 1·8, 2·1 and 1·4 kg/cow/day). Model validatio
ns indicate that milk production predictions are sensitive
to the diet offered (forage, grass and con
centrate supply) and depend on dairy cow
characteristics and their require-
ments (pMP). This model can be connected to a grass growth model in order to develop whole farm simulations.
Domaines
Sciences du Vivant [q-bio]Origine | Fichiers produits par l'(les) auteur(s) |
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