A simulation model to evaluate the risk of subacute ruminal acidosis in high-yielding dairy cows fed total mixed rations ad-libitum (Abstract)

Publication Type

Contribution to conference

Authors

Zebeli Q. and W. Drochner

Year of publication

2007

Published in

Proceedings: 13th Int. Conference

Editor

M. Fürll (Ed.)

Page (from - to)

160

Conference name

Production Diseases in Farm Animals

Conference location

Leipzig

Conference date

29.07.-04.08.2007

Keywords

acidosis, high-yielding dairy cow, simulation, Simulationsmodell, TMR-Fütterung

Subacute ruminal acidosis (SARA) is a common and economically important metabolic disorder in dairy cattle, which occurs when ruminal pH drops below an optimum for fiber digestion, due to excessive consumption of fermentable carbohydrates and low dietary fiber. In this study, we defined the response of ruminal pH to chemical and physical characteristics of the diet to develop a physiologically-based, easy-to-use, simulation model to assess the risk of SARA occurrence in high-yielding dairy cows. To model the variation of ruminal pH throughout the day, a database from 77 published studies (n = 316 dietary treatments) was generated. Further, a second database from 58 (n = 238 dietary treatments) recently published studies with high-yielding dairy cows (in average: 95 days in milk and 34.9 kg milk/d) fed total mixed rations (TMR) was compiled including information on ration composition, DM intake (23.1 ±2.1 kg DM/d) and ruminal pH measured over 24h. The average content of physically effective NDF, estimated by the proportion of diet DM retained on sieve 1.18 mm (peNDF), using dry-sieving methods, was 23.7 ±7.2%. The amount of ruminally degradable starch of concentrates (RDSC) and forages (RDSF) composing TMR averaged 14.8 ±4.9% and 5.99 ±5.2%, respectively. The model was developed in SAS (2001) using mixed modelling procedure to account for random effect of experiment, within-study covariance and unequal variances among studies. The model simulations were performed using a stochastic Monte-Carlo algorithm with Beta-PERT probability distribution using computer software RiskAMP (Structured Data, LLC). The model revealed that high-yielding dairy cows are not at risk of SARA (0% risk), if duration of time in which ruminal pH is below 5.8 does not exceed 1h per day. This study showed that daily mean ruminal pH or time of ruminal pH < 5.8 can be accurately predicted (R2 > 50%) accounting for dietary peNDF, RDSC and total DM intake. The model ... the risk of SARA with30-40%