In Situ dry matter and nitrogen degradability of ammonium nitrate and urea treated dry veld grass and Zea mays stover in mature goats

E Chivandi, L Chipfupa* and S Ncube*

Department of Livestock and Wildlife Management, Faculty of Natural Resources Management and Agriculture,
Midlands State University, Private Bag 9055, Gweru, Zimbabwe
^*Matopos Research Station, Department of Research and Extension, Private Bag K5137, Bulawayo, Zimbabwe
emchivandi@yahoo.co.uk   or   chivandie@msu.ac.zw

Abstract

An in situ degradability study, in a factorial randomised complete block design, was carried out using three rumen-cannulated Kapaters (mature male castrate goats) to investigate the effects of ammonium nitrate treatment on poor quality roughages. The study was carried out in two phases: phase 1 had dry veld grass subjected to ammonium nitrate and urea treatment and phase 2 had maize stover similarly treated. Phase 1 treatments were: untreated dry veld grass only (DVG_, control), urea treated dry veld grass (UDVG) and ammonium nitrate treated dry veld grass (ANDVG). Phase 2 treatments were made up of untreated maize stover (MS, control), urea treated maize stover (UMS) and ammonium nitrate treated maize stover (ANMS).

Results indicated that treatment of dry veld grass with both ammonium nitrate and urea significantly (P<0.05) increased DM loss of the dry veld grass while the same treatment had no significant effect on DM loss of maize stover. ANDVG recorded 18.05 % actual DM loss which was significantly higher than that recorded for DVG and UDVG that had statistically similar (11.56 % and 15.42 % respectively) actual DM losses in the first 12 hours of incubation. In phase 2 of the trial all treatments recorded statistically similar actual DM losses that averaged 22.70 % during the first 12 hours of incubation. In both experimental phases length of incubation time had a significant effect (P<0.001) on DM loss with most of the DM loss occurring within the 12- to 24-hour incubation time bracket. Results also showed that in all trial phases both treatment and length of incubation time significantly (P<0.001) increased the actual N disappearance. ANDVG and ANMS (ammonium nitrated treated roughages) had the highest percentages of nitrogen disappearance, with 1.638 % and 1.1780 % respectively, whilst DVG and MS (raw roughages) had mean N-disappearance values of 0.1557 % and 0.308 respectively (the lowest) in 12 hours of incubation. In both phases of the trial most of the N was lost within the 12- to 24-hour incubation time.

Roughage treatment with ammonium nitrate increased effective degradability of DM and N across different ruminal fractional outflow rates. The study showed that ammonium nitrate could also be used in enhancing the in situ degradability of poor quality roughages particularly dry veld grass.

Key words: Chemical treatment, dry matter degradability, nitrogen disappearance, roughages

Introduction

Crop residues and dry veld grass are major supplementary roughages used by communal farmers in Zimbabwe particularly during the long dry season (Smith et al 1990) and Osuji et al 1993). Preston (1986) noted that crop residues form the principal feed of ruminant livestock during the dry season in semi-arid regions such as Zimbabwe. In Zimbabwe maize stover and dry veld grass are the main sources of roughage fed to ruminants as supplements or as whole feed in the dry and/or winter season (Smith et al 1990). However maize stover and dry veld grass used by communal farmers in Zimbabwe are of poor quality because they are invariably fibrous, low in nitrogen (N) and low in digestibility (Preston 1986; McDonald et al 1995). Besides low nutrient content and low voluntary feed intake, poor digestibility is one of the limiting factors in the utilization of low quality roughages for ruminant livestock production. However, Van Soest (1988) noted that low digestibility of poor quality roughages results from its failure to meet the rumen micro-flora and fauna nutrient requirements with N being the key limiting nutrient.

Ruminant production based on low quality roughages and non-protein nitrogen (NPN) is of interest to animal scientists because these materials are of little direct use as feedstuffs for non-ruminants (Males et al 1979) thus eliminate the possible competition. Wintering cattle on dry veld grass results in poor utilization of non-protein nitrogen (NPN) sources due to the lack of energy in the dry grass (Males et al 1979). Chemical treatment of poor quality roughages particularly with urea increases the amount of available N-content (Males et al 1979; Chivandi 2001). Urea treatment of crop residues and dry veld grass is widely practised by farmers in Zimbabwe particularly those in smallholder dairy projects (Reynolds 1984 and Chivandi 2001). However trials on the use of ammonium nitrate for improving N-content of stovers is still in its infancy. The objective of the study was to investigate the efficacy of ammonium nitrate (cheaper and readily available) as an alternative to urea in the treatment of poor quality roughages in terms of its effect on the nutritive value of resultant roughage and

Materials and methods

Research site

The research was done at Matopos Research Station (MRS) of Zimbabwe. The Station is situated 30 Km due South West to Bulawayo. It is in Natural Region IV (NR IV) (Magadzire 2002) characterized by limited and very variable rainfall averaging 600 mm per year (range 257-1376mm), a mean minimum daily temperature of 21⁰C (June) and a mean maximum daily (October) temperature of 29⁰C (Ward et al 1979). The trial was executed in-doors in order to minimize environmental fluctuations.

Chemical treatment of the roughages and proximate analyses

Samples of low quality dry veld grass and maize stover were each separately treated with urea and ammonium nitrate. The maize stover was harvested from a locally grown hybrid while the dry veld grass was cropped from the paddocks of the research station.

Urea treatment procedure of the roughages

Parcels of 2 kg of maize stover and dry veld grass were separately weighed followed by weighing of 2 separate units of urea each equivalent to 5 % of either the maize stover or dry veld grass. Water equivalent to 40 % of each of the test roughages was poured in two containers. Two equi-molar urea solutions were made. The solutions were used to urea treat the roughages (one on the maize stover and the other on the dry veld grass). The urea solution was sprinkled on the maize stover and dry veld grass respectively followed by ensiling in black polythene bags for five (5) weeks before the onset of the trial.

Ammonium nitrate treatment procedure of the roughages

Parcels of 2 kg of maize stover and dry veld grass were separately weighed followed by weighing of 2 separate units of ammonium nitrate each equivalent to 7 % either the maize stover or dry veld grass. Water equivalent to 40 % of each of the test roughages was poured in two containers. Two equi-molar ammonium nitrate solutions were made. The solutions were used to chemically treat the roughages (one on the maize stover and the other on the dry veld grass). The ammonium nitrate solution was sprinkled on the maize stover and dry veld grass respectively followed by ensiling in black polythene bags for five (5) weeks before the onset of the trial.

The use of different weights of urea and ammonium nitrate was calculated to ensure that the test roughages were exposed to similar levels of N regime from either chemical since the two have different concentrations of nitrogen.

Experimental treatments

There were six treatments split into three for phase 1 (dry veld grass based) of the trial and three for phase 2 of the trial (maize stover based). The treatments were as outlined below:

Phase 1 Treatments

• Raw Dry Veld Grass (Control, DVG)

• Urea Treated Dry Veld Grass (UDVG)

• Ammonium Nitrate Treated Dry Veld Grass (ANDVG)

Phase 2 Treatments

• Maize stover (Control, MS)

• Urea Treated maize stover (UMS)

• Ammonium nitrate Treated maize stover (ANMS)

Upon completion of the 5 weeks of incubation with the chemicals, proximate and fibre analyses were done on the test roughages, that is, treatment DVG through to ANMS. Samples were analysed for dry matter (DM), nitrogen (N) and crude protein (CP) as described by AOAC (1990). Neutral Detergent Fibre (NDF) and Acid Detergent Fibre (ADF) were determined as outlined by Van Soest et al (1991).

Animals and animal management

Three mature Matebele Kapaters (male castrate goats) with mean weight of 36.1kg (35-37 kg), each surgically fitted with a rumen cannula were used in both phases of the trial to determine the Dry Matter Degradability (DMD) and Nitrogen Degradability (ND) of the differently treated roughages (Ørskov et al 1980; Bhargava and Ørskov 1987). During phase 1 the kapaters were acclimatized to a dry veld grass-based diet (dry veld grass + 200 g goat meal) for 14 days and fed on the same diet for the rest of the experimental period. During phase 2 of the trial, the acclimatization period was 7 days with the kapaters being fed on a maize stover based diet (maize stover + 200 g goat meal) and continued on the same diet during the experimental period. Water was offered ad libitum.

Experimental design

Phases 1 and 2 of the trial had the same experimental design; a Factorial Randomized Complete Block Design (FRCBD) with treatment (chemical type) and incubation time as the two factors. The animal was the blocking factor. There were three animals and three incubation times. During each of the three incubation periods, there was one animal on a particular treatment such that by the end of each trial phase each animal had been subjected to all the treatments.

Incubation procedure

Three grammes (3 g) of each of the dried and milled (2-mm screen) test roughages were placed in nylon bags (measuring 140 x 90 mm and of pore size 46µm, Blutex No 150-Tripette et Renaud, France) made of synthetic polyester. The bags for each incubation period were tied using rubber bands on slits on a flexible vinyl tube (Bhargava and Ørskov 1987). Each of three kapaters had 6 bags, two bags for each incubation period. The bags were withdrawn at 12, 24, and 48 hours. Immediately after withdrawal of bags from the rumen, the bags were washed for 30 minutes under running tape water and squeezed gently until clear water came out of the bags. The washed bags with residue were then oven dried for 48 hours at 60^oC after which the dried bags and their residue were weighed. The residue was used for N-determination. Percent actual dry matter disappearance (% ADMD) at various incubation times, percent cumulative dry matter loss and percent nitrogen disappearance were determined. DMD and ND constants were determined using the equation described by Ørskov and McDonald (1979):

p = a + b (1 - e ^{- ct}) ……Equation 1

where:

p = degradability of DM and N at time (t),
a = rapidly degradable and soluble fraction (the zero time intercept),
b = the slowly degradable fraction (asymptote of the exponential),
t = time of incubation and
c = the rate of degradation.

Potential Degradability (PD) was estimated as (a + b). Effective Degradability (ED) of DM and N was calculated using outflow rates of 0.02, 0.05 and 0.08 per hour according to Ørskov and McDonald (1979) model:

ED = a + [bc / (c + k)]

where;

ED = Effective degradability and
a, b, and c are the constants as described in equation 1 and
k is the rumen fractional outflow rate.

Proximate analyses of the residues

Samples were bulked in terms of treatment and incubation times. Roughage residues retrieved after incubation, were analysed for N at 0, 12, 24 and 48 hours incubation times. This was used to determine N disappearance at different times. The semi-microkjeldahl method was used for N determination. The CP content of the residues was computed by multiplying the N-content with 6.25.

Statistical analysis

An analysis of variance was carried out on the chemical constituencies of the differently treated roughages and on the effect of treatment (effect of treatment chemical) and incubation duration on DM loss and ND using General Statistics Package (Genstat Release 6.1, 2002). Mean separation was done using the Least Significant Difference Procedure (LSD). Degradation constants were obtained by carrying out a non-linear regression using General Statistics (Genstat Release 6.1 2002).

Results

Chemical nutrient and fibre composition of the differently treated roughages are shown in Table 1.

Results for % ADMD for phases 1 and 2 are shown in Table 2.

Results for nitrogen disappearance (% ND) for both phases 1 and 2 are shown in Table 3.

Table 4 shows comparative results for the ED in terms of DM loss between dry veld grass based treatments and maize stover based treatments respectively.

Table 5 reflects comparative results for ED in terms of N disappearance between veld grass-based treatment and maize stover based treatments respectively.

Treatment (chemical) had a significant effect on the chemical nutrient and fibre content of the roughages (Table 1). Urea and AN treatment of roughages significantly (P<0.001) increased the CP content of the dry veld grass from 36.5 g /kg to 115.4 g/kg and 142 g/kg respectively. At the same time AN treatment of the dry veld grass decreased its ADF content from 501 g/kg to 494 g/kg (Table 1). A similar trend was observed when maize stover was treated with urea and AN (Table 1). Treatment (chemical type) and incubation time had a significant effect (p<0.001) on % ADMD particularly in the first 24-hour incubation period for phase 1 of the trial (Table 2). In phase 2 of the trial, treatment chemical (urea versus ammonium nitrate) did not have a significant effect on % ADMD during the first 24-hour incubation period. Significant differences were observed for phase 1 treatments only during the first 12 to 24 hours. Roughage treatment with ammonium nitrate (AN) effected high % ADMD in the first 12 hours of incubation (phase 1) with a mean % ADMD of 27.98 versus 18.38 for the urea treated dry veld grass. Chemical type had a significant (P<0.05) effect on % N-disappearance for both phases 1 and 2 of the trial (Table 3). The differences were sustained across the different incubation times. Roughage treatment with AN resulted in higher (P<0.05) % N-disappearance across the three incubation time frames (Table 3). Effective degradability (ED) in terms of DM loss increased with chemical treatment (Table 4). Treatment with AN effected an increase in ED in terms of DM loss across the different fractional outflow rates (Table 4) for both phases of the trial. A similar trend on ED in terms of N-disappearance was observed across treatments (Table 5) with treated roughages exhibiting higher (P<0.05) ED rates (Table 5).

Discussion

Chemical composition of roughages

Chemical treatment of low quality roughages (dry veld grass and maize stover) using either urea or ammonium nitrate fertilisers enhanced their CP levels (Table 1). Ammonium nitrate and urea treatment of roughages results in the ammonification of the roughages leading to the enhancement of N and hence CP. This is critical in the support of rumen-reticulo-microbial activity, which if it (N) is below 1.33 % causes a reduction in the rate of rumen microbial proliferation that leads to rumenstasis (Minson 1983). When the rumen function is impaired due to N-limitation, both degradative feed fermentation and intake are reduced such that the animal loses weight.

Roughage degradation

Maize stover based treatments were better degraded in comparison to the dry veld based treatments (Tables 2 and 4). Dry veld grass based treatments diets had higher NDF and ADF (Table 1) values hence the extent of degradability was reduced. Higher values of ADF found in dry veld grass based treatments suggest the presence of high ligno-cellulose content. Microbial enzymes (from rumen resident microbes) cannot break the ligno-cellulose bonds and this reduces the rate and extent of degradability of the roughages (Clark 1975). However, within the dry veld grass based treatments, treatment with AN significantly reduced the NDF and ADF content of the grass in comparison to treating with urea (Table 1) such that % ADMD (Table 2) was higher in the AN treated grass compared to the urea treated grass during the first 24 hours of incubation. The lower NDF and ADF content in AN treated dry veld grass suggest that AN better managed to break the ligno-cellulose bonds and other fibres into easily degradable constituencies than urea. Ammonium nitrate is less volatile compared to urea that quickly decomposes to ammonia thus losing the molecules that would otherwise be used in the bleaching of the ligno-cellulose bonds and the ammonification of the roughage. The bleaching effect by either urea or AN results in the breakage of the ligno-cellulose bonds effecting an unlocking of the once unavailable N to the rumen microbes resulting in their proliferation and increased dry matter digestibility (DMD) (Wilson 1994). The high degree of volatility of urea reduces the amount of N added to the roughage by the urea thus limiting on the amount of physiological N threshold critical for effective and efficient rumen function. Clark (1975) points out that the degree of rumen microbial proliferation and rate and extend of degradation is dependent on the proportion of N in the feed. The higher the N content the more the microbes proliferate and the higher and faster the rumen fermentation rate hence increased dry matter digestibility (DMD). Alkali treatment (as with NaOH, NH₄NO₃ and or NH₂CONH₂) increases the surface area of readily digestible material for rumen microbes to work on causing an increase in degradation rate; voluntary feed intake and digesta out flow rate (Tables 2, 3, 4 and 5). The concomitant reduction in gut fill effect (as a result of increased ruminal digesta outflow rate) results in reduced effective degradability (ED) of the feed (Tables 4 and 5).

Degradability constants

Alkali treatment of low quality roughages increased the quantity of soluble fraction 'a' and reduced the potentially degradable fraction 'b' (Tables 4 and 5). The relationship of 'a' and 'b' is clearly shown when comparing the degradability constants of untreated roughages and ammonium nitrate treated roughages (Table 4). Roughage treatment with AN generally increased the ED of DM indicating the efficacy of AN (due to its lower volatility) in comparison to urea. This seems to point out AN as a better alkali option in increasing the 'a' fraction. An increase in this 'a' fraction causes increased feed digestibility and an eventual improvement in feed utilization as the fraction of readily soluble material in the feed increases.

Treatment of the roughages (dry veld grass and maize stover) increased the concentration of ammonia in the rumen to a level high enough to support the microbial activity. Norton (1994) pointed out that 70 milligrams/litre of ammonia is the minimum level required by the microbial population in the rumen to support optimum microbial proliferation. This suggests that ammonia level in the rumen less than 70 milligrams/litre is associated by hindrance in microbial activity (degradation) and it is an indicative in N deficiency. Norton (1994) also concluded that feeds containing 1.35 % N are considered to be N deficiency since they cannot provide the minimum ammonia levels required. In this study all treated roughages had a N content higher than 1.35 % (Tables 1) that was high enough to support rumen-reticulo microbial activity. Rumen degradation characteristics of DM (Table 5) show that maize stover based treatments were highly degradable as compared to the dry veld grass based treatments. UMS was degraded more and DVG was the least degraded (Table 5). The lower degradation of DVG is due to its high content of ADF (Table 1) that refracts the hydrolytic effect of the exogenous digestive enzymes produced by the rumen resident microorganisms. The low CP content (3.6 %) of the dry veld grass used indicates that it was cropped very late in the season as standing hay that had lost most of its CP (Table 1). Minson (1983) indicated that at very late growth stages the grass contains high fibre content, low CP and reduced N that translates into reduced digestibility. McDonald et al (1995) indicated that the stage of growth at cutting and conservation method affects the nutritive value of forages. High fibre forages such as the dry veld grass used quickly enhance gut fill and depress appetite. The high N degradation rate found in untreated maize stover (MS) could be attributed to highly soluble hence readily available N fraction. Although MS had lower N and CP (9.4 % and 58.7 g/kg respectively) in comparison to UMS and ANMS its nitrogen content was above the required threshhold (above 1.35 %) necessary for the support of rumination and rumen fermentation of feeds hence the similarity in DM loss among the three treatments. However MS had a low value of effective degradability (ED) of N may be due to a lower fraction of 'b' in the feed. Ammonium nitrate (AN) treatment of roughages increased the effective degradability (ED) values of ANDVG (Tables 4 and 5) across all fractional outflow rates (k). It would appear that AN increased both the readily degradable fraction (a) and the potentially degradable material (b) all of which are parameters that contribute to ED value. Therefore it can be said that ammonium nitrate increased the quantity of 'a'. In comparison, urea treated diets had lower ED values than ammonium nitrate treated values. This could be due to the high volatilisation nature of urea (Sundstol et al 1978) hence the contribution of urea to N pool in the diet is lower than that of ammonium nitrate.

Conclusion

• Ammonium nitrate effectively improved the nutritive value of roughages and reduced the ligno-cellulose bonds and effected an increase in ED of DM and N across different ruminal outflow rates and incubation time periods. It is therefore possible to use ammonium nitrate for the nutritional enhancement of poor quality roughages in place of urea.
   

Acknowledgements

The authors wish to express their gratitude to the Department of Livestock and Wildlife Management of the Midlands State University for funding the project. Matopos Research Station is heartily thanked for providing the kapaters, pens, roughages and the laboratory space used in the experiment.

References

AOAC 1990 Official Methods of Analysis (15^th Edition) Association of Official Analytical Chemists (Washington D.C, USA.

Bhargava P R and Ørskov E R 1987 Manual for the use of nylon bag technique in the evaluation of feedstuffs, pp. 1 - 20. The Rowett Research Institute, Bucksburn, Aberdeen, Scotland.

Chivandi E 2001 Fodder and forages development and utilisation in smallholder dairy projects. Farm Applied Research Methods for Southern Africa (FARMESA) Project Final Report ZIM 01-02D. Animal Production Branch, Department of Agricultural, Technical and Extension Services (Agritex), Harare, Zimbabwe

Clark J H 1975 Nitrogen metabolism in ruminants; Protein solubility and rumen by-pass of protein and amino acids. Marcel Dether Inc., New York, USA.

GenstatRelease 6.1. 2002 Lawes Agricultural Trust. Rothamsted Experimental Station, UK.

Magadzire Z 2002 Foraging strategies of cattle and goats in mixed-species grazing systems. PhD Thesis, University of Edinburgh, U.K, pp 165.

Males J R, Munsinger R A and Johnson R R 1979 Invitro and in vivo ammonia release from 'slow' release urea supplements. Journal of Animal Science, Volume 484, Number 4.

McDonald P, Edwards R A and Greenhalgh J F D 1995 Animal Nutrition. (5^th Edition) Longman Group Limited. U.K., Essex, CM20 2JE, England.

MinsonD 1983 Effects of chemical and physical composition of herbage eaten upon intake. In: Hatcher J B (Edition) Nutritional limits to animal production from pasture. CAB Farmham Royal pp 167-182.

Norton B W 1994 The nutritive value of tree legumes In: Gutteridge R C and Shelton P (Editors). Forage Tree Legumes in Tropical Agriculture CAB International pp 178-191. http://www.fao.org/ag/agP/agpc/doc/Publicat/Gutt-shel/x5556e0j.htm

OsujiP O,  Sibanda S and Nsahlai V 1993 Supplementation of maize stover for ethiopian menz sheep: effects of cottonseed, noug (Guizotia abyssinica) or sunflower cake with or without maize on the intake, growth, apparent digestibility, nitrogen balance and excretion of purine derivatives. Animal Production, 57 (3): 429 - 436.

Ørskov E R, Hovell F D deB and Mould F 1980 The use of the nylon bag technique for the evaluation of feedstuffs. Tropical Animal Production, 5: 195 - 213. http://www.fao.org/livestock/agap/frg/tap53/53_1.pdf

Ørskov E R and McDonald I 1979 The estimation of protein degradability in rumen from incubation measurements weighted according to the rate of passage. Journal of Agricultural. Science, Cambridge,92: 499-503.

Preston T R 1986 Better utilisation of crop residues and by-products in animal feeding - research guideline 2: A Practical Manual for Research Workers. FAO Animal Production and Health Paper 54/2. FAO, Rome, Italy http://www.fao.org/DOCREP/003/X6554E/X6554E00.HTM

Reynolds L 1984 Alkali treatment of forages. Proceedings of the Zimbabwe Society for Animal Production, pp 143-153.

Smith T, Manyuchi B and Mikayin S 1990 Legume supplementation of maize stover. In: Utilization of research results on forage and agricultural by-products materials as animal feed resources in Africa, ILCA, Addis Ababa. Ethiopia, pp 2-320. http://www.ilri.cgiar.org/InfoServ/Webpub/Fulldocs/X5536e/x5536e0l.htm

Sundstol F, Coxworth E and Mowart D N 1978 Improving the nutritive value of straw and other low quality roughages by treatment with ammonia. World Animal Review 26, 13-21.

Van Soest P J 1988 Effect of environment and quality of fibre on the nutritive value of crop residues. in: Plant breeding and the nutritive value of crop residues. Proceedings of a workshop held at ILCA, Addis Ababa, Ethiopia, December 1987.

Van Soest P J, Robertson J B and Lewis B A 1991 Methods for dietary fibre, neutral detergent fibre and non-starch polysaccharides in relation to animal nutrition. Journal of Dairy Science 74: 3583 - 3597. http://jds.fass.org/cgi/reprint/74/10/3583.pdf

Ward H K, Richardson F D, Denny R P and Dye P J 1979 Matopos Research Station: A Perspective. Rhodesian Agricultural Journal 76: 5-18.

Wilson J R 1994 Cell wall characteristics in relation to forage digestion. Journal of Agricultural Science, Cambridge 122: 173-182.

Received 19 February 2006; Accepted 30 November 2006; Published 8 February 2007

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