Digestibility and degradability of silages from whole-plant pea–cereal mixtures

Requiring few inputs, protein plant–immature cereal mixtures can guarantee forage stocks in times of shortage. In order to test whether and how the principle of additivity predicts nutritional value, we conducted in vivo digestibility tests and in sacco degradability tests (crude protein degradability, CPD) to evaluate silages from two mixtures with different protein-plant (i.e., pea) contents. The mixture with low pea content, PEAS-l, contained 60 % triticale, 28 % oats and 13 % peas, whereas that with high pea content, PEAS-h, contained 35 % triticale, 24 % oats and 41 % peas). The same tests were conducted with the silages of the constituents (triticale, oats and forage peas). Of the two mixtures, PEAS-h had the highest digestibility figures (for organic matter: 76.5 vs. 61.9 %. The CPD was statistically similar between the mixtures. Furthermore, PEAS-h produced 6.4 MJ net energy content for lactation (NEL) per kg of dry matter (DM), whereas PEAS-l produced 4.9 MJ NEL/ kg DM. Mixtures reconstituted at the manger with the pure silages produced values similar to those of sown mixtures. The constituent additivity hypothesis correctly predicted the values for PEAS-l, the cereal-dominated mixture, but strongly underestimated those for PEAS-h.