The role of fodder trees in the utilization of roughage by sheep

The objective of this study was to offer reasons for responses attained in Menz sheep when given two fodder tree foliage supplements and a low quality roughage basal diet. In the first experiment, (Chapter 4), In vitro gas production, dry matter and nitrogen degradabilities of fresh and sun-dried foliages of four fodder trees (FTs) (Sesbania sesban, Leucaena leucocephala. Chamaecvtisus palmensis. Vernonia amygdalina) and of teff straw were estimated. In trial 1 of this study, feed samples were incubated in 3 different rumen environments (ecologies) created by feeding sheep the following: teff straw, teff straw + 250g/kg of sesbania and teff straw + 250g/kg of leucaena. In trial 2, different rumen ecologies were created by feeding teff straw supplemented with 119, 178 or 232 g/d of sesbania; or with 117, 175 or 232 g/d of leucaena. Gas production constants were estimated following the equation: GP=B(1-e-Ct) where B is gas production and C is the rate of gas production at time t. Rumen fluid was harvested at 3, 6. 9, 12 and 24 hours from sheep in experiment 2 and pit NH3-N, VFAs and minerals determined. Plasma urea nitrogen (PUN) concentrations were estimated in blood taken from the sheep at 3. 6. 9 and 12 hours. Drying relatively increased the neutral detergent fibre (NDF), acid detergent fibre (ADF) and NDF-nitrogen concentrations in all foliages except in leucaena. Drying decreased nitrogen in sesbania, tagasaste and vernonia but not in leucaena. Dry matter disappearance (DD) at incubation times of 3 to 48 hours and degradation constants differed among the 4 foliages (P<0.05). Compared to the other foliages, sesbania had lower fibre fractions and degraded faster. Fresh foliages degraded at a higher rate than dry ones. Supplementation did not affect (P>0.05) the DD of fresh foliages but enhanced (p<0.05) the rate of DD of dry foliages. There was no feed type x rumen ecology interaction (P>0.05) for either dry or fresh foliages. The rate of teff straw degradation in sheep fed supplemented diets was increased (P<0.06). Gas production was lower in fresh foliages than in dry. The extents of gas production (ml/200mg DM) for dry foliages were: sesbania (55.5). tagasaste (54.5), vernonia (49.5), leucaena (45), and for fresh foliages, tagasaste (81.8). sesbania (62.7). leucaena (51.1), vernonia (51). The rates of gas production C/h) were highest for dry tagasaste (0.0779), followed by sesbania (0.0718), leucaena (0.0563) and vernonia (0.0477). For fresh foliages, corresponding values were leucaena (0.0541). tagasaste (0.0528). sesbania (0.0478) and vernonia (0.0366). Supplementation increased levels of all rumen metabolites measured. Rumen NH3-N was highly correlated (r2=0.88; P<0.05) with PUN. Correlations among the other metabolites were either low or negative. The results are discussed in relation to the chemical composition, type and form of fodder tree and the rumen ecology resulting from these foliages. In experiment 2 (Chapter 5), 2 trials were conducted to investigate the effect of supplementation with fodder tree leaves on the utilization of teff straw. This was aimed at testing the hypothesis that forage supplements (eg. sesbania) that disappear faster from the rumen compared to slow disappearing ones (eg. leucaena) may elicit higher intakes of the basal diet. Experiment 1 investigated the effect of level (i .e. 0, 200, 300 and 400 g/kg dry matter (DM) intake) of leaves of Sesbania sesban or Leucaena leucocephala on the utilization of teff straw fed libitum. Seven sheep were fed the 7 diets in 4 periods following a partially balanced (7x4) cross-over design. In experiment 2, teff straw alone or supplemented with graded levels of sesbania (250. 350 and 450 /kg D.M intake), were fed to 16 sheep in a completely randomized blockdesign. Intake, degradability, nitrogen (N) utilization, particulate and liquid passage rates were estimated. In trial 1, protein source x protein level interaction was not significant. Supplementation increased intakes of total DM (P<0.05), organic matter (OM) (P<0.01) and N retention (P<0.01) but had no effect on the intake of teff straw. Supplementation with sesbania, but not with leucaena, increased (P<0.05) the digestibility of DM. Both supplements increased (P<0.05) the fractional rate of passage from the rumen. In trial 2, graded levels of sesbania increased DM intake (P<0.05), fractional rate of liquid outflow (P<0.05) and tended to increase the rate of degradation. It was concluded that the effect of fodder tree leaves on roughage intake is a function of their disappearance rate from the rumen. In experiment 3 (Chapter 6), twenty five rumen fistulated Ethiopian menz sheep were used in a randomised complete block design to determine roughage utilization when sheep were fed only a teff straw diet (control) or the control plus different types of supplements (sesbania. leucaena, cotton seed cake (CSC)) and forms (fresh and dry leucaena) were fed. The choice of these supplements was to observe how differences in the dry matter, nitrogen degradabilities and bulkiness between these supplements could influence the extent of roughage intake and utilization through improvement of rumen environment. The chemical composition, intake, digestibility, nitrogen balance and rumen degradability coefficients were determined. Rumen pH and ammonia-nitrogen (NH3-N) levels were estimated in samples taken at 1, 2, 3, and 6 hours after feeding. There was substitution of teff straw dry matter by the supplements. Fresh leucaena effected the highest substitution. Supplementation enhanced (p’<O.05) the dry matter degradation (DD) of teff straw at 6 and 12 hours of incubation but not (p>O.05) for the other incubation times. There were no significant differences (p>O.05) between treatments in the degradation constants: readily soluble component (a), slowly degradable fraction (b), potential degradability (PD=a+b) and rate of degradation (c). For rumen NH3-N concentration, the ranking was CSC > sesbania > dry leucaena > fresh leucaena > teff straw alone (p<0.05). The particularly high substitution rate observed for fresh leucaena might suggest that bulkiness may be a limiting factor in the control of the intake of low quality roughages supplemented with tree leaves. The lower DM and OM digestibilities of the supplemented diets were attributed to substrate preference by rumen cellulolytic bacteria. Excessively high levels of rumen NH3-N (328 mg/l) in the CSC diet resulted in high urinary nitrogen losses (r2=0.32; p<0.001) leading to low N retention. It was suggested that for the utilization of poor quality tropical roughages moderate levels of rumen NH3-N sustainedover a longer period may be needed. In the fourth experiment (Chapter 7), the treatments were similar to those described in experiment 3; the only exception was the elimination of the treatment with fresh leucaena. The remaining 3 supplemented diets had an additional 45 gDM/day of crushed maize supplement offered to the sheep. This study was aimed at determining the effects of an extra energy source on ammonia utilization by the microbes. Intake, digestibility, teff straw degradation, rumen pH and ammonia- nitrogen, nitrogen balance and purine derivatives were measured. Supplementation with crushed maize improved (P<0.05) the dry and organic matter intakes of teff straw, total feed intakes and digestibilities, nitrogen utilization, microbial protein synthesis, the rumen pH and ammonia -nitrogen as well as the readily soluble component of teff straw. While the intakes of teff straw and total feed were better (P<0.05) for sheep fed the foliages than cotton seed cake (CSC) diets, the opposite trend was recorded for nitrogen balance. Total PDs and Microbial N values were however similar (P>0.05). Cotton seed cake and sesbania seem to fit better with maize than with leucaena for roughage intake and nitrogen utilization respectively. It seems rate of degradation alone cannot be used to determine the extent of coupling between supplements. Growth kinetic and metabolism trials (Chapter 8) were conducted to study the effect of either nitrogen source or supply pattern on the growth, rumen fermentation pattern and utilization of straw by Ethiopian Menz sheep. All experimental sheep were given a teff straw basal diet. Irrespective of the trial, treatment sheep were offered either cottonseed cake. leucaena and sesbania in the morning prior to teff straw. Additional treatments with sesbania were offered either in the evening or morning and evening. Measurements included roughage intake, digestibility, kinetics, rumen fermentation patterns, nitrogen utilization, microbial protein supply and growth rate of sheep. Rate of degradation was highest (P<0.05) when sesbania was offered once a day compared to twice a day, while supplementation produced higher (P<0.05) liquid passage rates. Diets with sesbania produced higher (P<0.05) roughage intake compared to leucaena. Microbial protein supply as well as N economy were similar (P>0.05) among the foliage diets irrespective of source, time or frequency of feeding. Supplementation enhanced (P<0.001) growth rates in sheep while cottonseed cake (CSC) diet was superior (P<0.01) to the fodder trees. Growth rates declined across treatments during the second phase (6-10 weeks) compared to the initial period (1-6 weeks). These studies suggest that it is also possible for farmers to feed sesbania supplements in the morning or evening or twice daily without any detrimental effects. Generally, supplementing teff straw with sesbania significantly (P<0.05) influenced roughage intake more than leucaena. About 0.73 of the variation due to roughage intake was attributed to sesbania while 0.53 was due to leucaefla. The rapid degradation of sesbania and disappearance from the rumen were factors responsible for the variation. It was concluded that the superior rumen kinetic characteristic of sesbania, coupled with the high rumen fermentation compared to leucaena resulted in the overall better intake, digestibility, nitrogen utilization and growth performance.

Source: KNUST