Digestibility of forage in mixed rations

The digestibility of the organic matter (DOM) of a forage, whether estimated in vitro via modelling or determined in vivo via experimentation, is a nutritive value considered in isolation. A ration, however, generally consists of a mixture of different forages and concentrates. This trial – consisting of an in vivo study with wethers – studies the changes in DOM of different forages (herbage, grass silage, hay, and maize silage) distributed in different proportions (100–0, 80– 20, 50–50, 20–80, and 0–100 %, respectively) in two-component combinations. The DOM of the forage types changed (without statistically significant differences) as a function of the proportions in the mixture and the associated feed; the mean DOM deviation of the mixtures was 2.7 ± 1.1 percentage points. The greatest differences in DOM (4.3 percentage points) were found for mixtures of hay from different cuts or hay combined with maize silage. In 42 % of the cases the highest DOM was identified when the forage in question accounted for 80 % of a mixture. The DOM of the combinations obtained by adding the in vivo DMO of the individual components is slightly underestimated (r = 0.92). Taking into account the estimated DOM scores of the forages, the DOM scores of the combinations move further away from the in vivo values (r = 0.56). The experiment shows that each forage interacts differently in the combinations and as a function its proportions in the mixture.

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