Fermentation in the rumen of sheep fed Atriplex nummularia cv. De Kock supplemented with incremental levels of barley and maize grain

 

 

C.J.L. du Toit^I; W.A. van Niekerk^I,; Abubeker Hassen^I; N.F.G. Rethman^II; R.J. Coertze^I

^IDepartment of Animal & Wildlife Sciences, University of Pretoria, Pretoria 0002, South Africa
^IIDepartment of Plant Production & Soil Science, University of Pretoria, Pretoria 0002, South Africa

 

 

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ABSTRACT

The aim of this study was to investigate the effect of two carbohydrate sources, barley and maize, on the ruminal fermentation of Atriplex nummularia cv. De Kock fed to sheep. Barley was used as a source of rapid fermentable carbohydrates while maize was used as a moderately fermentable source. Ten rumen cannulated Merino wethers were fed different increments of ground maize and barley supplements (0%, 15%, 30%, and 45% of the ration dry matter to a basal diet of A. nummularia over four different periods. Supplementation of A. nummularia with energy tended to increase ruminal fermentation. Rumen ammonia nitrogen (NH3-N) decreased at the 30% level of supplementation, though an increase in rumen NH3-N concentration was observed for maize at the 45% level. This decrease might have been due to an improvement in microbial protein synthesis. Total rumen volatile fatty acids increased with increasing levels of both barley and maize supplementation. Evidence of the increase in volatile fatty acid production was supported by a decrease in ruminal pH values, with the barley at 45% level of supplementation yielding the lowest rumen pH values. Supplementing sheep with barely and maize at 30% level increased fermentation in the rumen of sheep fed on A. nummularia and enhanced utilisation of degradable protein available in the rumen.

Keywords: Atriplex, carbohydrates, fermentability, foliage, leaves

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Introduction

Atriplex nummularia has shown promise for reclamation of degraded rangelands. This species has proven to be particularly well adapted to areas that receive low annual rainfalls (Van Niekerk et al., 2004). In terms of nutritive value, A. nummularia leaves have an energy concentration of ca. 6.1 MJ ME/kg dry matter (DM) and a crude protein (CP) concentration of 176 - 234 g/kg DM (Van Niekerk et al, 2004). The high CP content of A. nummularia could be misleading since its CP is extensively degraded to ammonia in the rumen (Weston et al., 1970). Consequently, the available energy from A. nummularia is insufficient for the efficient utilization of the ammonia by rumen microorganisms. Increasing nutrient availability for higher levels of microbial growth, digestion and subsequently ruminant production can be achieved by one or more of the following strategies: Increasing the quantity of dry matter intake, improving the ratio of rumen fermentation end-products or supplementing by-pass nutrients for subsequent absorption in the small intestine (McCarthy et al., 1989). Generally carbohydrates and proteins are the major nutrients supporting microbial growth, and the possible energy deficiency in A. nummularia would likely be manifested in terms of inefficient rumen fermentation and subsequent poor animal production (Hoover & Stokes, 1991). Supplementing Atriplex material with carbohydrate sources may rectify this. However, digestion of fibre decreases when the amount and proportion of readily fermentable carbohydrate sources in the rumen increase beyond an optimal level (Hoover, 1986). The aim of this study was to quantify the influence of source (high and medium fermentability) and level of carbohydrate supplementation on ruminal fermentation of sheep fed A. nummularia cv. De Kock diets.

 

Materials and Methods

Ten adult Merino wethers (43 ± 14.3 kg body weight) fitted with ruminal cannulae were randomly allocated to two groups of five animals. Each group received a diet consisting of sun-dried A. nummularia supplemented with one of the two carbohydrate sources, maize (moderate fermentability) or barley (high fermentability), each at four levels (0%, 15%, 30% and 45%/kg DM of the diet) of supplementation. The carbohydrate sources were finely ground through a 1 mm sieve and fed with A. nummularia as a total mixed ration on an ad libitum basis. The sheep were housed in individual metabolism cages. The experimental animals were adapted to their diets for 14 days prior to a 10 day collection period. The experiment was carried out in four sequential periods. Diets were allocated randomly to each of the four experimental periods. Within each period five animals received the same diet in the following order of supplementation: 0%, 30%, 15% and 45%. Between two consecutive experimental periods animals were fed a lucerne diet for a period of 15 days to avoid residual effects from the preceding diet.

At the end of a collection period individual rumen fermentation parameters were determined on eight rumen fluid samples collected over a 24 h period at 5:00, 7:00, 10:00, 14:00, 16:00, 22:00, 2:00 and 5:00 the following day. Rumen fluid samples were collected as described by De Visser et al. (1992). Immediately after collection the pH was measured, using an electronic pH meter. Samples for ammonia nitrogen (NH3-N) analysis (10 mL rumen fluid) were preserved with 2 mL of a 0.5 M H₂SO₄ solution and stored at -10°C. Samples for volatile fatty acid (VFA) analysis (10 mL rumen fluid) were preserved with a 1 mL 10% NaOH solution and stored at -10 °C. The NH₃-N concentration of rumen fluid was determined using a Technicon autoanalyser, according to the AOAC (2000). A modified derivatization technique of Puttman et al. (1993) for high performance liquid chromatography (HPLC) and a UV detector were used for the analysis of VFA in the fluid.

All parameters measured were analysed using one-way analysis of variance by the PROC GLM of SAS (2001). It is assumed that there will be no difference between the experimental periods (except treatment effect) due to simultaneous harvesting and drying of the A. nummularia used in the experimental diet. Where treatment effect was significant, differences between means were determined by using Bonferrani's test (Samuels, 1989).

 

Results and Discussion

The supplementation of A. nummularia with maize appeared to have increased the DM intake compared to the control, but the difference was statistically significant (P < 0.05) only at the 45% supplementation level (Table 1). In the barley supplemented groups, intakes did not differ significantly from that of the control. The effect of carbohydrate source (barley vs. maize) on rumen pH value was not significant (P > 0.05), while with both sources rumen pH values decreased with increasing levels of supplementation above the 15% level (Table 1). This agrees with Overton et al. (1995) who reported a decrease in pH as the amount of readily fermentable carbohydrate in the diet increased. According to Hoover & Stokes (1991) pH greatly modifies microbial growth efficiency and nutrient digestion. Overton et al. (1995) reported a decrease in fibre degradation because of a decrease in pH. Similarly, Du Toit et al. (2004) reported a lower level of neutral detergent fibre digestibility of A. nummularia with an increasing level of supplementation of maize and barley due to negative associative effects. It is likely that the low ruminal fluid pH decreased cellulolytic activity of the bacteria and depressed ruminal fibre degradation of the diets (Ben-Ghedalia et al., 1989). However, the extent to which rumen cellulolysis is inhibited varies with the type and level of carbohydrate and nitrogen sources (Hoover & Stokes, 1991). Furthermore, the inhibition of fibre degradation could be partially alleviated if rumen pH was maintained at a level of 6.7, normally associated with the fermentation of an all roughage diet (Mould et al., 1983). In the present study the pH decreased from 6.98 to 6.10 for the maize and from 7.05 to 5.94 for the barley supplement. Except for 45% barley supplemented treatment, the pH values recorded were higher than the pH optima for protozoan proteases (3 to 4.5), but it was within the range of pH optima for bacteria (6.0 and 7.0) (Kopecny & Wallace, 1982; Ben-Ghedalia et al., 1989). The lack of significant differences between barley and maize, in terms of rumen pH values, contradicts with De Visser et al. (1992), who reported higher rates of degradability (%/h) of barley starch compared to that of maize starch (25.8 vs. 8.7%).

Rumen NH₃-N concentration of the control sheep ranged between 7.23 - 7.28 mg/100 mL (Table 1). This is relatively higher than rumen NH3-N concentrations of 5 mg/100 mL reported by Satter & Slyter (1974) as a minimal concentration for optimum microbial protein synthesis. The relatively higher level was probably due to the high proportion of non-protein nitrogen (NPN) in Atriplex (470 g/kg) (Benjamin et al., 1995), which is highly soluble in the rumen (Weston et al., 1970). The high level of rumen NH₃-N concentration (8.12 and 7.90 mg/100 mL) recorded at the 15% supplementation level suggested that this level did not supply enough fermentable energy to the rumen microorganisms to make sufficient use of the available NH₃-N (McDonald et al., 2002). Compared to the rumen NH₃-N concentration of at 15% supplementation level, lower levels of 4.68 and 5.24 mg/100 mL were recorded at the 30% supplementation level for maize and barley, respectively. These reduced ammonia levels could be due to a more efficient N-utilization by rumen microbes when more fermentable energy was available (Casper et al., 1999). These authors also reported that increased rumen liquid volumes could play a role in the reduction of NH3-N concentrations. The significant difference in rumen NH3-N concentration between maize and barley at the 45% level of supplementation cannot be explained and this could be due to an error.

Significant differences were found in terms of total VFA concentrations between the non-supplemented and carbohydrate supplementation groups (Table 1). In all supplemented diets total VFA concentration increased with increasing levels of supplementation. In this study, the differences between barley and maize in terms of total VFA concentration were not significant (P > 0.05). This is contrary to previous findings that reported higher VFA concentrations for cows fed a barley-based diet, which correlated well with the higher ruminal starch digestibility of barley compared to cows fed a maize-based diet (McCarthy et al., 1989). One possible reason for this could be higher ruminal liquid volumes in the barley-fed animals that would have a diluting effect on VFA concentrations (Casper et al., 1999). The reason for the increase in ruminal fluid volumes when barley supplemented diets were fed is not clear, but it could possibly be related to non-structural carbohydrate solubility or the degradability of barley compared to maize. The lower VFA concentration for barley supplemented animals (Casper et al., 1999) could possibly be as a result of increased absorption from the rumen due to the lower ruminal pH of the barley supplemented animals (Lana et al., 1998).

 

Conclusions

Supplementing animals with barely and maize at 30% level enhanced the ruminal fermentation environment of sheep fed on A. nummularia without decreasing the rumen pH below the critical level that sustains optimum fibre digestion. Higher grain supplementation levels improve rumen fermentation and the utilisation of degradable protein in the rumen as indicated by the increase in total fatty acids and reduction of NH3-N concentrations in the rumen.

 

Acknowledgement

This research project was supported in part under the Grant No. TA-MOU-99-C16-091 funded by the U.S.-Israel Cooperative Development Research Program, Bureau for Economic Growth, Agriculture and Trade, U.S. Agency for International Development.

 

References

AOAC, 2000. Official Methods of Analysis (15^th ed.). Association of Official Analytical Chemists, Inc., Washington D.C., USA.         [ Links ]

Benjamin, R.W., Lavie, L., Forti, M., Barkai, D., Yonatan, R. & Hefetz, Y., 1995. Annual regrowth and edible biomass of two species of Atriplex and of Cassia sturtii after browsing. J. Arid Environ. 29, 63-84.         [ Links ]

Ben-Ghedalia, D., Yosef, E., Miron, J. & Est, Y., 1989. The effects of starch- and pectin-rich diets on quantitative aspects of digestion in sheep. Anim. Feed Sci. Technol. 24, 289-298.         [ Links ]

Casper, D.P., Maiga, H.A., Brouk, M.J. & Schingoethe, D.J., 1999. Synchronization of carbohydrate and protein sources on fermentation and passage rates in dairy cows. J. Dairy Sci. 82, 1779-1790.         [ Links ]

De Visser, H., Van der Togt, P.L., Huisert, H. & Tamminga, S., 1992. Structural and non-structural carbohydrates in concentrate supplements of silage-based dairy cow rations. 2. Rumen degradation, fermentation and kinetics. Nether. J. Agric. Sci. 40, 431-445.         [ Links ]

Du Toit, C.J.L., Van Niekerk, W.A., Rethman, N.F.G. & Coertze, R.J., 2004. The effect of type and level of carbohydrate supplementation on intake and digestibility of Atriplex nummularia cv. De Kock. S.Afr. J. Anim. Sci. 34, 35-37.         [ Links ]

Hoover, W.H., 1986. Chemical factors involved in ruminal fibre digestion. J. Dairy Sci. 69, 2755-2766.         [ Links ]

Hoover, W.H. & Stokes, S.R., 1991. Balancing carbohydrates and proteins for optimum rumen microbial yield. J. Dairy Sci. 74, 3630-3644.         [ Links ]

Lana, R.P., Russel, J.B. & Van Amburgh, E.M., 1998. The role of pH in regulating ruminal methane and ammonia production. J. Anim. Sci. 76, 2190-2196.         [ Links ]

Kopecny, J. & Wallace, R.J., 1982. Cellular location and some properties of proteolytic enzymes of rumen bacteria. Appl. Environ. Microbiol. 43, 1026-1033.         [ Links ]

McCarthy, R.D., Klusmeyer, T.H., Vicini, L.J. & Clark, J.H., 1989. Effect of source of protein and carbohydrate on ruminal fermentation and passage of nutrients to the small intestine of lactating cows. J. Dairy Sci. 72, 2002-2016.         [ Links ]

McDonald, P., Edwards, R.A., Greenhalgh, J.F.D. & Morgan, C.A., 2002. Animal Nutrition. (6^th ed.) Adison Wesley. Publ. Longman, Singapore Ltd.         [ Links ]

Mould, F.L., Ørskov, E.R. & Gauld, S.A., 1983. Associative effects of mixed feeds. II. The effect of dietary addition of bicarbonate salts on the voluntary intake and digestibility of diets containing various proportions of hay and barley. Anim. Feed Sci. Technol. 10, 31-47.         [ Links ]

Overton, T.R., Cameron, M.R., Elliot, J.P. & Clark, J.H., 1995. Ruminal fermentation and passage of nutrients to the duodenum of lactating cows fed mixtures of corn and barley. J. Dairy Sci. 78, 1981-1998.         [ Links ]

Puttman, M., Krug, H., Von Ochsenstein, E. & Kattermann, R., 1993. Fast HPLC determination of serum free fatty acids in the picomole range. Clin. Chem. 39, 825-832.         [ Links ]

Samuels, M.L., 1989. Statistics for the Life Sciences. Collier MacMillan Publishers, London. pp 597.         [ Links ]

SAS, 2001. Statistical Analysis Systems User's Guide (Version 8.2). SAS Institute Inc., Cary, NC, USA.         [ Links ]

Satter, L.D. & Slyter, L.L., 1974. Effect of ammonia concentration on rumen microbial protein production in vitro. Br. J. Nutr. 32, 199-205.         [ Links ]

Van Niekerk, W.A., Sparks, C.F., Rethman, N.F.G. & Coertze, R.J., 2004. Qualitative characteristics of some Atriplex species and Cassia sturtii at two sites in South Africa. S. Afr. J. Anim. Sci. 34, 108-110.         [ Links ]

Weston, R.H., Hogan, J.P. & Hemsley, J.A., 1970. Some aspects of the digestion of Atriplex nummularia by sheep. Proc. Aust. Soc. Anim. Prod. 8, 507-512.         [ Links ]

Williams, A.G., 1988. Metabolic activities of rumen protozoa. In: The Role of Protozoa and Fungi in Ruminant Digestion. Eds. Nolan, J., Leng, R. & Demeyer, D., Publ. Penambul Books, Armidale, New South Wales, Australia.         [ Links ]

 

 

# Corresponding author. E-mail: willem.vanniekerk@up.ac.za