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.

Effect of wheat hay particle size and replacement of wheat hay with wheat silage on rumen pH, rumination and digestibility in ruminally cannulated non-lactating cows

“…According to the results of the present study, it is suggested that Zebeli's rules are probably valid for the TMRs commonly used in the United States and Europe to feed lactating cows (500 g/kg forage and 500 g/kg concentrates, Zebeli et al, 2010), but the opposite trend might be present in concentrated TMR containing only 300 g/kg DM roughage with peNDF below 104 g/kg DM, as used in this study to feed nonlactating cows.…”

“…According to the literature, ruminal pH should not be <5.8 for >5 to 6 h/day, to minimize health disturbances due to SARA (Zebeli et al, 2012). A model based on 64 studies and 257 different dietary treatments found that content of NDF above the 8 mm sieve (physically effective NDF, peNDF) >18.5% of dietary DM prevents SARA (Zebeli et al, 2010 and. SARA may result from insufficient peNDF in dairy cow rations that reduces rumination and buffer secretion via saliva to the rumen to maintain pH, especially under massive volatile fatty acid (VFA) accumulation (Plaizier et al, 2008).…”

“…Using a model based on 64 studies and 257 different dietary treatments (without wheat forages), Zebeli et al (2010 and found that increasing the content of peNDF to over 149 g/kg TMR DM decreases DMI; on the other hand, decreasing peNDF content in the TMR below 185 g/kg DMI might reduce rumen pH below 5.8 and create SARA conditions (Zebeli et al, 2010 and. According to the results of the present study, it is suggested that Zebeli's rules are probably valid for the TMRs commonly used in the United States and Europe to feed lactating cows (500 g/kg forage and 500 g/kg concentrates, Zebeli et al, 2010), but the opposite trend might be present in concentrated TMR containing only 300 g/kg DM roughage with peNDF below 104 g/kg DM, as used in this study to feed nonlactating cows.…”

Characterisation of particle dynamics and turnover in the gastrointestinal tract of Holstein cows fed forage diets differing in fibre and protein contents

“…One of them is the limited dry matter (DM) forage intake capacity of cattle (Allen 2000;Zebeli et al 2010a), which would result in a limited energy and nutrient intake in lactating dairy cows, hence not reaching the requirements for high milk yields. Therefore, developing forage-based feeding strategies requires a better understanding on the effects of forages on digestive processes such as particle size kinetics, dynamics of particle change through the gastrointestinal tract (GIT) and turnover of nutrients including the water within the GIT, all of which have strong effects on ruminal degradation and regulation of the passage rate and feed intake capacity of cattle (Kennedy 2006;Zebeli et al 2006).…”

Effects of Supplemental Dietary Energy Source on Feed Intake, Lactation Performance, and Serum Indices of Early-Lactating Holstein Cows in a Positive Energy Balance

“…Concentrate contains high levels of rumen fermentable carbohydrates (RFC). Excess concentrate supplementation will decrease the rumen pH value, increase the risk of subclinical ruminal acidosis (SARA), and lower the rumen degradation rate of dietary fiber and feed conversion efficiency [5] (Zebeli et al 2010). The adverse effects of fat supplementation on rumen fermentation can be prevented with rumen inert fats, such as fatty acid calcium salts and saturated fat [6] (Bernard and Kertz 2009).…”