Nutrient digestion and utilization in farm animals: modelling approaches.

Chapter 32 (Page no: 383)

The Nordic dairy cow model, Karoline - description.

The Karoline model described in this study is a whole-animal cow model intended to be used by the advisory services in the Nordic countries, i.e. Denmark, Finland, Iceland, Norway and Sweden. Karoline is a dynamic, deterministic and mechanistic simulation model of lactating dairy cows. It consists of two submodels: a digestion and a metabolism model. The first describes digestion in the forestomachs, the small intestine and the hindgut, while the second comprises portal-drained viscera (PDV), liver, extracellular fluid and mammary gland, as well as muscle, connective and adipose tissues. The model inputs are live weight (LW), week of lactation, rate of dry matter intake (DMI) and DM composition. Parameters describing the feed are crude protein (CP), crude fat, potentially degradable neutral detergent fibre (NDF), totally indigestible NDF, starch (St), fermentation products and a rest fraction (RF; sugars and other organic matter (OM) are not accounted for). The CP fraction is further divided into NH₃, amino acids (AA), peptides (PEP), soluble protein (SP), insoluble protein (ISP) and totally indigestible protein. Rate constants for ruminal degradation of NDF, protein and St also have to be provided. In the digestion submodel, ruminal degradation and passage of carbohydrates and protein is described by using two-compartment models. Rates of passage from the rumen are regulated by the NDF intake per kg LW. The rate of NDF degradation in the rumen is regulated by the ratio of non-structural carbohydrates to NDF. The fermentation pattern in the rumen is predicted by stoichiometric equations adjusted for feeding level and crude fat in concentrates. The efficiency of microbial protein synthesis (MPS) depends on the ruminal level of NH₃. In the metabolism submodel, nutrient partitioning between tissues as well as a number of intracellular transactions are regulated by the stage of lactation. The rates of nutrient oxidation are determined by the need of adenosine triphosphate (ATP) for tissue maintenance and product syntheses. The heat production (HP) in individual segments of the model is calculated according to the law of energy conservation. Animal performance is calculated from relevant nutrient and energy flows when the model has reached steady state. To the extent that the output from Karoline is reliable, the simulated animal performance (e.g. milk yield (MY), body weight (BW) change, faecal, urinary and gaseous wastes, HP) expresses the real value of a given feed in a given situation. Thus, Karoline is a tool of great potential value to advisory services .

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