PERTE DE COMPOSÉS VOLATILS LORS DE LA DÉTERMINATION A L'ÉTUVE DE LA TENEUR EN MATIÈRE SÈCHE DES ENSILAGES

Open Access
Publisher Website
Google Scholar
Abstract
A method for correcting the dry matter content of silages determined after oven-drying was developed, taking into account the various volatile components of these silages and the level of their losses during oven-drying. The dry matter contents determined after drying in 2 different ovens adjusted to the same temperature (80.degree. C) were compared. The difference between the dry matter contents was very small (on a average 0.11, i.e., 0.52%) and negligeable as compared to the accuracy of the determination of silage digestibility and voluntary intake in sheep. Losses of different volatiles were very similar for the 2 ovens. A more detailed study was made on the losses observed during drying in the oven (A) used at the laboratory. Losses of ammonia represented, on an average, 50.8%, but they varied widely according to plant species and silage characteristics. Ammonia was more volatile with increasing pH levels (grasses and lucerne). Drying caused losses of lactic acid in grass and maize silages only. In the latter, the average losses of this acid represented 12.4%. This percentage, although widely variable, could not be related to silage characteristics. The average losses of acetic acid was 78.7%. For grass and lucerne samples, these losses mainly varied with silage pH and ammonia content. With the maize, they varied with the acetic content itself. The losses of alcohol was always 100%. For 65 silages the amounts lost of known volatiles represented, on an average, 50.8 g/kg non-corrected dry matter. To correct the dry matter content (determined at 80.degree. C), a quantity Y (volatile components lossed at oven-drying) should be added to 1000 g of oven dry matter. The values of Y are given by these relationships: grass Y = 0.616 x1 + 0.142 x2 + 0.830 x3 + 1.000 x4; lucerne Y = 0.534 x1 + 0.732 x3 + 1.000 x4; and maize Y = 0.382 x1 + 0.106 x2 + 0.782 x3 + 1.000 x4, in which Y is the amount of volatile dry matter lossed during oven-drying in g/kg non-corrected dry matter and x1, x2, x3 and x4 the contents of ammonia, lactic acid, volatile fatty acids and alcohols, respectively, expressed in g per kg non-corrected dry matter. This correction method agrees with the dry matter contents corrected for losses at oven-drying and the dry matter contents determined by toluene distillation, except for silages containing formic acid. For the latter, the value of Y determined by these formulae is about 10 g lower than the real losses estimated by comparing the dry matters determined after oven-drying with those obtained after toluene distillation. This difference is probably largely due to the presence of volatile, but non-determined, formic acid.

This publication has 1 reference indexed in Scilit: