Nutritional properties and <i>in vitro</i> gas production in cactus pear (<i>Opuntia stricta</i>) and cassava (<i>Manihot esculenta</i>) shoot silages

Abstract

This study evaluated the effects of different inclusion levels of cactus pear (Opuntia stricta) (at 0%, 15%, 30% or 45% on fresh matter basis) ensiled with shoots of cassava (Manihot esculenta) on the mineral nutrients, carbohydrates fractionation, nitrogen compounds and in vitro gas production, using a completely randomised design consisting of four treatments and five replicates per treatment, totalling 20 experimental units. There were significant increases (p < 0.05) in the concentrations of Mg, B, Fe, total carbohydrates and fraction A+B1 (non-fibre carbohydrates) with increased cactus pear inclusion, whereas nitrogen and fractions B2 (available fibre) and C (insoluble protein, indigestible in rumen and intestine) significantly decreased (p < 0.05) with the inclusion. The inclusion of cactus pear significantly (p < 0.05) reduced crude protein content and the fractions A (non-protein nitrogen) and B3 (insoluble protein with a slow degradation rate in the rumen) in the silages. Fraction B1+B2 (rapidly degraded true protein + insoluble protein with an intermediate degradation rate in the rumen) significantly increased (p < 0.05) with increasing levels of cactus pear inclusion. Gas production parameters showed a quadratic effect for Ca, Mn, observed gas volume, estimated gas volume by the bicompartmental model, rate of degradation of fibre carbohydrates, and rate of degradation of non-fibre carbohydrates (p < 0.05). The use of cactus pear increased the content of soluble sugars in mixed silages made with the aerial part of cassava plants. However, gas production was low with the inclusion of 45% cactus pear. Based on the overall results, the combination of 45% cactus pear with 55% of the aerial part of cassava in mixed silages is recommended.