Abstract :
The aim of this work was to develop an index describing the relative intake of the total diet by dairy cows, and hence the ability
to predict intake responses to changes in both forage and concentrate variables. An evaluation of concentrate factors affecting
silage dry matter (DM) intake of dairy cows was conducted based on dietary treatment means from milk production experiments.
The data were divided into four subsets according to concentrate treatments used within the experiments: the amount of
concentrate supplementation (n5217), protein supplementation (n5336), carbohydrate composition (n5114) and fat
concentration of the concentrate (n529). The data were subjected to mixed-model regression analysis. Increased concentrate DM
intake (CDMI) decreased silage DM intake (SDMI) quadratically. The substitution rate (substitution of silage DM for concentrate
DM) increased with improved silage intake potential. SDMI increased quadratically with concentrate protein intake, the response
being negatively related to the effective protein degradability (EPD) of concentrates. Replacement of starchy concentrate
ingredients with fibrous supplements had a small positive effect on silage intake, whereas increased concentrate fat concentration
slightly decreased SDMI. The outcome of concentrate factors influencing total DM intake (TDMI) was used to create a relative
CDMI index as follows: CDMI index51001103[(CDMI20.16293CDMI20.018823CDMI225.49)1((0.94743CCPI2
0.49653CCPI2)22.0173(CEPD20.74))10.002253(CNDF2250)20.01033(402Cfat)20.000583(CDMI28.0)3
(SDMI index2100)], where CDMI5concentrate DM intake (kg/day), CCPI5supplementary concentrate CP intake (kg/day;
CP.170 g/kg DM), CEPD5concentrate EPD (g/g), CNDF5concentrate NDF concentration (g/kg DM), Cfat5concentrate fat
concentration (g/kg DM) and SDMI index is the relative intake potential of silage (Huhtanen, Rinne and Nousiainen 2007. Animal 1,
758–770). TDMI index was calculated as SDMI index1CDMI index2100 to describe the relative intake potential of the total diet.
For the whole data set (n5943), one TDMI index unit was equivalent to 0.095 kg/day DM intake, i.e. close to the default value of
0.100 kg. The CDMI index explained proportionally 0.88 of the variation in TDMI within a study with a 0.27 kg/day residual meansquare
error (n5616). The corresponding values for the TDMI index were 0.81 and 0.37 kg/day (n5943), respectively. The residual
mean-square errors in cross-validation were marginally higher. The developed TDMI index can be used to estimate the intake
responses to diet changes. It provides an improved basis for practical dairy cow ration formulation and economic evaluation.
Keywords :
concentrate , Forage , protein , silage intake potential , intake regulation
