title: A model to optimise the requirements of lactating dairy cows for physically effective neutral detergent fibre.
abstract: This study modelled multiple physiological responses of dairy cows to physical and chemical characteristics of a diet aiming to optimise their requirements for physically effective neutral detergent fibre, expressed inclusive of particles-dry matter > 8 mm (peNDF > 8). Extensive research data, comprising a wide range of feeding conditions (n = 64 studies and 257 different dietary treatments), were used to parameterise the model, while statistical modelling was used to account for the inter- and intra-experiment variation as well as to derive the model estimates. Physiological thresholds and 'safety limits' of peNDF > 8 for maintaining different physiological variables were derived using non-linear statistical modelling. Results showed that peNDF > 8 content in the diet is a key factor stimulating rumination activity, maintaining optimal ruminal pH and promoting fibre digestion. Modelling data with regard to the association of fibre digestion and time duration of ruminal pH < 5.8 and dietary peNDF > 8 suggests that feeding of less than 13.7% peNDF > 8 (the lower 'safety limit') is critical to prevent depression of fibre digestion in dairy cows. The study also indicated that the beneficial effects of peNDF > 8 on ruminal pH and fibre digestion can be at the expense of the dry matter intake (DMI) level of high-producing cows when the peNDF > 8 threshold of 14.9% in the diet is exceeded. In terms of the optimisation of peNDF > 8 requirements, the modelling data suggest that feeding of 17-18.5% peNDF > 8 can be beneficial in maintaining ruminal pH, while allowing a relatively high DMI (22.3-22.7 kg x d(-1)) for average high-producing dairy cows.
authors: Institute of Animal Nutrition, University of Hohenheim, Stuttgart, Germany. zebeli@ualberta.ca
authors: Qendrim
authors: Q
authors: Zebeli
authors: Dominik
authors: D
authors: Mansmann
authors: Burim N
authors: BN
authors: Ametaj
authors: Herbert
authors: H
authors: Steingass
authors: Winfried
authors: W
authors: Drochner
mesh_terms: D000821:Animal Feed / Q000032:analysis*; D000822:Animal Husbandry; D000824:Animal Nutritional Physiological Phenomena; D000818:Animals; D002417:Cattle / Q000502:physiology*; D003612:Dairying; D016208:Databases, Factual; D004043:Dietary Fiber / Q000032:analysis*; D004063:Digestion / Q000502:physiology; D005260:Female; D006863:Hydrogen-Ion Concentration; D007774:Lactation / Q000502:physiology*; D008409:Mastication; D008954:Models, Biological; D015233:Models, Statistical; D009751:Nutritional Requirements; D012417:Rumen / Q000737:chemistry / Q000502:physiology