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Prediction of ruminal starch degradability of maize forage
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Edité par CCSD ; Wageningen Academic Publishers -
Session 62. Free communications animal nutrition. International audience. Maize silage is the main source of energy in the diet of high-yielding ruminants. The current French system to evaluate its energetic value provides knowledge on energetic value of the whole plant. However, there is no indication on the nature of its available energy for animals resulting in rate and extent of ruminal degradation of starch and cell-wall fraction. In this study, we investigated different parameters of maize whole plant chemical composition in order to predict ruminal starch degradability. Nineteen degradability trials with fistulated cows (from 1996 to 2013) were selected to build up the database. The data of the 115 samples of ensiled forage maize were collected from samples initially dried during 72 h at 60 °C and ground at 4 mm. The methodology involved measuring ruminal starch degradability at different incubation times using nylon bags. Effective starch degradability (ED6) was calculated with a step by step model and assuming a particulate passage rate of 0.06 h-1. Models were fitted by taking into account within-hybrid and within-harvest year effects. Starch ED6 is closely related to the association between dry matter (DM) at harvest and starch content (g/kg DM) with the equation: ED6starch = 118.9 – 0.125×DM + 0.022×starch (R2adjusted=0.89; RSD=4.7; Ntotal=175; Nexp=19). Other chemical composition parameters did not significantly improve the prediction model of effective starch degradability (P>0.05). A validation step is planned before use with forage maize harvested in 2015 (n=28). These results indicate that the use of criteria characterizing whole plant maturity stage and chemical composition could be relevant to estimate starch ED6. The prediction model of starch ED6 will be included in the future French feed evaluation system of nutritive and integrated in the future infrared laboratory calibration.
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