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 · d−1) for average high-producing dairy cows.