Oral administration of leaf extracts to rumen liquid donor lambs modifies in vitro gas production of other tree leaves

Abstract

This study was conducted to determine if adaptation of lambs to ingestion of tree leaf extracts of Salix babylonica and Leucaena leucocephala can modify in vitro gas production of Celtis ehrenbergiana, Ficus trigonata, Fraxinus excelsior and Prunus domestica. Samples of leaves were collected in triplicate (i.e., three individual samples of each tree leaf). Rumen inoculum was collected from 8 growing lambs fed a total mixed ration ad libitum (control; RC). Incubations were repeated with the rumen fluid collected from another 8 growing lambs of the same breed fed the same ration, but fed a daily dose of 30 ml/d of S. babylonica and L. leucocephala extracts in a 1:1 (v:v) mixture (treatment; RX). Leaf samples were incubated with each rumen fluid (i.e., RC and RX inoculums) in 3 runs on different weeks. Data of each of the three runs within sample replicate were averaged and used as the mean value of each individual sample within tree species for statistical analysis in a 4 (tree species) × 2 (rumen inoculum) factorial design. In vitro gas production was recorded at 2, 4, 6, 8, 10, 12, 24, 48 and 72 h of incubation. After 72 h, the incubation was stopped and supernatant pH was determined, and then filtered to determine apparent degraded substrate (ADS). Fermentation parameters, such as the 72 h partitioning factor (PF72), 24 h gas yield (GY24), in vitro organic matter digestibility (IVOMD), metabolizable energy (ME), short chain fatty acids concentration (SCFA), and microbial protein production (MP) were estimated. The crude protein content of the leaves ranged from 147 (F. trigonata) to 241 (C. ehrenbergiana) g/kg dry matter. The lowest fiber fraction values was in P. domestica, while F. excelsior had the highest, and C. ehrenbergiana and F. trigonata were intermediate. Secondary metabolites (i.e., total phenolics, saponins, aqueous fraction) were lowest in P. domestica and highest in F. trigonata. Accumulated gas production was highest (P<0.05) in F. excelsior during the first 24 h of incubation. All fermentation parameters (i.e., ADS, SCFA, GY24, PF72, IVOMD, ME, MP) varied (P<0.01) among tree leaves. The ADS, SCFA and MP were highest (P<0.01) in F. excelsior, lowest (P<0.01) in F. trigonata, and intermediate in P. domestica and C. ehrenbergiana. Incubation of tree leaves with RX inoculum did not affect gas production in the first 6 h, but it was lower (P<0.05) at 24–72 h, except for F. trigonata. C. ehrenbergiana had the highest (P<0.05) potential gas production, but rate of gas production and the discrete lag time did not differ among leaves. As incubation of tree leaves with RX inoculum lowered (P<0.05) all fermentation parameters, oral administrated extracts of S. babylonica and L. leucocephala did not seem to adapt the rumen microbial population to better utilize these tree leaves.