The hypothesis that South African game animals that use browse containing condensed tannins (CT) could have rumen microbial populations better able to ferment tanniniferous forages was explored. Rumen fluid (RF) from a range of browsing ruminants was used to ferment tanniniferous forages in vitro and the results were compared with the values obtained with rumen fluid from sheep. Leaves of the shrub legumes Leucaena leucocephala, L. pallida, L. trichandra, Calliandra calothyrsus,Gliricidia sepium, and Acacia boliviana were used as substrates. In vitro digestibility of dry matter (IVDMD) and nitrogen (IVND) was measured in the presence or absence of polyethylene glycol (PEG) 4000 to assess the adverse effects of the CT in the feeds. Rumen fluid from giraffe, greater kudu, eland, duiker, impala, nyala, goat, and gnu was compared with that from sheep. Ability to metabolise or block the adverse effects of CT was expected to result in only a small or no response to PEG in terms of IVDMD and IVND with rumen fluid from browsers, and therefore to result in a significant animal feed and animal PEG interaction. There were no significant (P > 0.05) animal feed interactions. For every animal species there was a response to PEG in terms of IVND, and this response was linearly related to the CT in the feed as measured by PEG binding using 14C-labelled PEG. Rumen fluid from browsers had a lower pH (5.78 0.060 v. 6.68 0.052) and a higher dry matter content (1473 102 mg v. 415 4.3 mg/100 mL RF) than that of grazers (sheep and gnu). However, when measured at 2 pH levels (6.7 and 5.8), IVDMD and IVND of the feeds were not improved at the lower pH with rumen fluid from the browsers. Rather, digestibility was depressed at the lower pH with rumen fluid from all animal species. We conclude from these in vitro studies that rumen microbial populations from browsers are not able to ferment tanniniferous forages better than rumen microbial populations from grazers. It seems likely that these browsers do not have rumen bacteria capable of degrading the CT in these shrub legumes. Production on such tanniniferous feeds may well depend on tannin binding with proline-rich saliva rather than on metabolism of or tolerance to CT by rumen bacteria.
An experiment was conducted to investigate the influence of stage of growth at harvest on fermentative characteristics of Panicum maximum silage. The treatments were three different growth stages (early vegetative, boot and full bloom stage) that were ensiled directly or wilted prior to ensiling. Directly ensiled and wilted forage material were mixed prior to ensiling with molasses at 12 and 8 kg/ton dry matter, respectively. Thereafter, each treatment was ensiled in 12 one litre glass jars (bottles). From each treatment, samples of the silage were taken from three bottles at 0, 7, 21 and 120 d post-ensiling for analysis of fermentative characteristics. Growth stage in directly cut silage had no effect on silage pH between days 0 and 21. In contrast, within the wilted groups, a lower pH was observed at day 7 when the plants were harvested at the boot stage than at an early vegetative or full bloom stage. In both directly cut as well as prior wilted silage, a higher lactic acid concentration was recorded on day 7 in the boot stage silage compared to the full bloom stage silage, but on day 21 the boot stage had a lower lactic acid concentration than that of the full bloom stage silage. Growth stage had no effect on the acetic acid concentration on day 7. However, on days 21 and 120 the full bloom stage had a higher acetic acid concentration when the material was directly ensiled. In contrast, in prior wilted silage a higher acetic acid concentration was found in the early vegetative stage silage than in the full bloom stage silage at 120 days post-ensiling. Total nitrogen was lower in the full bloom stage silage than in the early vegetative and boot stage silages. A higher level of ammonia nitrogen was recorded at days 7 and 21 for the early vegetative stage silage as compared to the boot stage silage. A similar trend was revealed in the prior wilted groups between days 0 and 21. Harvesting at the boot growth stage consistently resulted in a good fermentation process with desirable fermentation end products (low pH and higher lactic acid concentration) up to a period of 21 days, but when compared at 120 days post-ensiling the differences between boot and bloom stages were not clearly observed in terms of fermentative attributes, probably due to the confounding effect of undesirable fermentation by entrobacteria or yeast.
Conservation of surplus forage is important to alleviate feed shortages during periods of feed deficits. The storage of An experiment was conducted to investigate the influence of stage of growth at harvest on fermentative characteristics of Digitaria eriantha subsp. eriantha silage. The treatment included three different growth stages (early vegetative, boot stage and full-bloom stage). The materials were ensiled either directly (unwilted) or after wilting for a period of 5-6 h prior to the ensiling. Samples of silage were taken from three bottles at 0, 7, 21 and 120 d for analysis of fermentative characteristics. Within the directly cut silage, stage of harvesting had no effect on pH on day 7, but on days 21 and 120 there were differences. Lower pH was recorded consistently for the boot stage silage. Within the prior-wilted groups, lower pH was recorded on day 7 for the boot growth stage while the difference between the growth stages in terms of pH was not significant on day 21. Within the directly cut silage, lactic acid concentration was consistently higher for the boot stage as compared to the early or full-bloom stage. Similarly, within the prior-wilted group, silages harvested at the boot growth stage resulted in higher lactic acid concentration on days 7 and 21, but on day 120 lactic acid concentration was higher for the early vegetative stage. In directly cut silages, harvesting at the boot growth stage resulted in a higher acetic acid concentration than that of the early vegetative growth stage or the full-bloom growth stage. For wilted silage, however, lower acetic acid concentration was recorded for the boot stage silage. In directly cut silage, the total nitrogen (N) concentration of boot-stage silage on day 120 was higher compared to the rest, but within the wilted silage the N value for boot-stage silage was not significantly different compared to the early vegetative stage. At day 120 the ammonianitrogen concentration increased for the early vegetative growth stage and full-bloom growth stage, while it was either reduced or remained similar for the boot-stage harvest when compared to the control. Under the current set of experiments, harvesting at the boot growth stage seems beneficial as the silage is lower in pH, higher in lactic acid concentration and able to retain most of the nitrogen in the silage for later use by the target animal.
The aim of this study was to compare two tropical grass species, Panicum maximum and Digitaria eriantha, in terms of silage fermentation attributes and certain rumen fermentation characteristics of silage made either at the boot or full bloom stages of growth. A lower silage pH was recorded for the D. eriantha than for the P. maximum silage. Neither species nor maturity stage had a significant effect on silage ammonia nitrogen, or lactic, acetic and butyric acid concentrations. For P. maximum silage total N was higher at full bloom than at the boot stage. D. eriantha had a higher total nitrogen content than P. maximum silage at the boot stage. Rumen pH was lower in sheep fed D. eriantha than P. maximum silage. In P. maximum fed sheep, a higher rumen NH 3 -N concentration was recorded when silage from the full bloom stage was fed compared to silage from the boot stage. In sheep fed D. eriantha silage, higher concentrations of acetic, propionic, butyric and total volatile fatty acids in the rumen were recorded from full bloom than from the boot stage. Neither species nor stage of maturity had significantly influenced the acetic : propionic acid ratio. The results suggested no significant difference between the species, but the full bloom stage showed a higher nutritive value and better preservation compared to the boot stage silage in both D. eriantha and P. maximum silage.
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