The objective of this work was to develop total dry matter intake (TDMI) prediction
models for growing cattle. The Finnish dataset of 1006 experimental period treatment
means from 17 feeding trials in growing bulls was collected for developing TDMI prediction
models. The diets were mainly based on grass silage or grass silage partly or completely
replaced by whole-crop silages or straw. The concentrate feeds consisted mainly of cereal
grains, fibrous by-products and various protein supplements. The following non-linear
equation for the relationship between TDMI and body weight (BW) (kg) was defined: TDMI
(kg/d)¼0.191 BW0.627 (Adj. RMSE¼0.451). The model was improved when both the
constant and exponent were adjusted for dietary variables. Dietary neutral detergent fibre
(NDF) concentration (kg/kg DM) generated a greater improvement in the model than other
variables investigated (dietary concentrations of forage NDF and ME, and the proportion of
concentrate). The constant decreased and the exponent increased with increasing dietary
NDF concentration. The following equation was defined: TDMI (kg/d)¼(0.209–
0.489 NDF) BW (0.614þ0.397 NDF) (Adj. RMSE¼0.438). In the model NDF concentration
was centred to the mean concentration of 0.40 kg/kg DM. The model was marginally
improved when the constant was adjusted for silage DMI (SDMI)-index that was centred to
100 units and dietary concentration of volatile fatty acids (VFA). The effects of SDMI-index
and VFA were highly significant (Po0.01): TDMI (kg/d)¼(0.199–0.380 NDFþ0.000348
SDMI-index0.00044 VFA) BW(0.624þ0.348 NDF) (Adj. RMSE¼0.433). A complete dataset
was used for the evaluation of models developed from the Finnish dataset. The complete
dataset was collected from growing cattle feeding experiments, in which total mixed rations
or forages were fed ad libitum. Overall, the complete dataset comprised 135 feeding
experiments and 687 treatment means. The following relationship between observed and
predicted TDMI was derived with a non-linear model including SDMI-index and dietary VFA
concentration as adjustment factors for the constant: Observed TDMI¼–0.35(70.40)þ1.01
(70.051) Predicted TDMI (n¼421; Adj. RMSE¼0.243). The developed models can be used
to estimate the intake responses to BW and diet changes. They provide an improved basis for
practical ration formulation systems and economic evaluation.
& 2013 Elsevier B.V. All rights reserved.
1. Intro