Comparing the in vitro digestibility of leaves from tropical trees when using the rumen liquor from cattle, sheep or goats

Abstract

This study compared the effect of ruminal inoculum from different donor species (goat vs. cattle and sheep vs. cattle) on the in vitro dry matter digestibility (IVDMD) and in vitro organic matter digestibility (IVOMD) of leaves from tropical plant species. Comparisons were performed with and without the addition of N and polyethylene glycol (PEG). Leaves from six tropical trees with different condensed tannin content were used (Caesalpinia gaumeri, Cordia alliodora, Gymnopodium floribundum, Neomillspaughia emarginata, Piscidia piscipula and Senegalia gaumeri). Donors of ruminal liquor included a ruminal cannulated adult cow (500 kg live weight [LW]), two growing Criollo goats (22 ± 3 kg LW, study one) and two growing Pelibuey lambs (24.8 ± 0.28 LW, study two). Donors were maintained in individual pens and received a basal diet with concentrate feed and Pennisetum purpureum grass. The IVDMD and IVOMD using sheep or goat vs. cow rumen liquor were determined from dry samples of a commercial concentrate feed, P. purpureum grass, and the leaves from experimental plants with a 2 × 2 factorial arrangement: with or without N-enriched media (+N and -N), and with or without polyethylene glycol (+PEG and -PEG). Respective standard linear regressions and orthogonal regressions were used to compare equivalence of IVDMD and IVOMD results between ruminal inoculum from different donor species (cattle vs. goat in study one and cattle vs. sheep in study two). The standard linear regressions suggested strong associations between the ruminal inocula compared, in both IVDMD and IVOMD with the four treatments (R2 > 87 % for study one and R2 > 89 % for study two, P < 0.001). However, orthogonal regressions showed differences between inocula of cattle and goats on IVDMD, when using + PEG media, and on IVDMD and IVOMD when using + N media (P < 0.05). Differences between inocula of cattle and sheep were only evident in the absence of PEG (P < 0.05). The standard linear and orthogonal regressions suggested that the IVDMD and IVOMD of leaves from tropical trees obtained with sheep or goats’ ruminal liquors, within the evaluated range of digestibilities (c. 0.2 to 0.65), can be predicted from the IVDMD and IVOMD obtained with the cattle ruminal liquor. However, when evaluating digestibilities of leaves from tropical trees it is important to evaluate the specific incubation conditions using the donor species of interest to improve accuracy of results.