Design and evaluation of a non-steady state rumen model

Abstract

The effects of the length of allowed grazing time (Experiment 1) and length of starvation period before grazing (Experiment 2) on dry-matter (DM) intake, ingestive behaviour and changes in DM rumen pool sizes during the first grazing bout were investigated in lactating Holstein-Friesian dairy cows. In Experiment 1, four lengths of allowed grazing time (1, 1·75, 2·50 and 3·25 h) after overnight starvation were compared. Increasing the length of the allowed grazing time significantly increased DM intake (P < 0·01), the proportion of time spent actively eating (P < 0·01) and DM rumen pool size after grazing (P < 0·05). However, DM rumen pool size after grazing was smaller than that measured immediately before the start of starvation (P < 0·01). Bite mass during the first hour of grazing was greater than in the following grazing time. Experiment 2 consisted of a factorial combination of two durations of starvation before grazing (16·5 h and 2·5 h) and the presence or absence in the rumen of 12·5 kg of a synthetic indigestible material. DM intake, as well as grazing time, were greater after a starvation period of 16·5 h and were reduced by the presence in the rumen of indigestible material (P < 0·01). The interaction between factors on grazing time, although not significant (P < 0·06), supports the idea of a combination of signals controlling meal size under grazing conditions. Bite mass was not significantly modified by the period of starvation. DM rumen pool size after grazing was reduced by the placement in the rumen of synthetic indigestible material (P < 0·05) and tended to be lower in cows with the larger period of starvation (P < 0·058). In both experiments, bite rate declined as the grazing session progressed, but bite rate was not affected by treatments.

A dynamic mechanistic model of lactic acid metabolism in the rumen

“…Although the simulation of a steady state within the rumen during continuous feeding has proved effective for the simulation of many aspects of rumen fermentation, the objectives of this investigation require pulsed model inputs, thus simulating rumen function in the cow fed a limited number of meals during the day. France et al (1982), Baldwin, (1995), and Chilibroste et al (2001Chilibroste et al ( , 2008 describe models of whole-rumen function for which inputs were either continuous or pulsed to represent discontinuous feeding schedules. Due to the objectives of the present model, the approach taken by France et al (1982) is used to simulate discontinuous feeding where instantaneous values for nutrient inputs (D x ) are represented as follows:…”

Improving the prediction of methane production and representation of rumen fermentation for finishing beef cattle within a mechanistic model

“…It is also possible that the equations developed for V ru are not applicable to these data for some reason, but this is difficult to determine without observed V ru values to compare against. An empirical representation of V ru was taken for this exercise, which allowed consideration of the RP% of the diet DMI and BW, but other approaches such as that of Chilibroste et al (2001) may be valid as well, where discontinuous feeding is represented and V ru is described mechanistically over time based on the DM% of rumen contents. As discontinuous feeding pattern data were not available for the independent beef database, an empirical approach was logical, although further investigation of whether the Chilibroste et al (2001) approach results in better predictions could be warranted.…”

Recent advances in modeling nutrient utilization in ruminants1

“…The authors were satisfied that the model predictions were close to observed values and, based on simulations, recommended supplementing the basal diet with Leucaena and rice bran to increase milk production. Subsequently, Chilibroste et al (2001) and Rodrigues et al (2002) adapted the model to evaluate supplements to enhance the nutrient supply and milk production of cattle fed diets based on ryegrass and elephant grass, respectively. Behera et al (2005) also used the model to simulate milk production by dairy cows fed sugarcane top-based diets and other local supplements in India.…”