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Hydration as a means of improving utilization of maize stover fed to steers

L. R. Ndlovu and Z. Manyame
Department of Animal Science
University of Zimbabwe
P.O. Box MP 167
Mt Pleasant
Harare, Zimbabwe


Abstract
Introduction
Materials and methods
Results
Discussion
Conclusion
Acknowledgements
References

Abstract

Maize stover chopped to particles 4-6 cm in length was fed to steers either soaked in water (1 kg stover/1.5 l) for 24 hours or unsoaked. For each main roughage, four protein supplements were provided viz. control, urea, soyabean meal or blood treated soyabean meal plus urea.

Soaking increased (P<0.05) intake of dry matter (DM) (4.8 vs 3.7 kg/d) but apparent DM digestibility and rumen digestion kinetics were not affected by soaking (P>0.05). Protein supplementation increased (P<0.05) DM intake (4.9 vs 4.4 kg and 3.8 vs 3.4 kg) for hydrated and unhydrated stover, respectively. Apparent DM digestibility and nylon bag degradability were, however, not affected by protein supplementation (P>0.05).

It was concluded that soaking per se has a potential to overcome constraints to intake of maize stover, particularly in situations where protein sources are scarce or expensive.

Introduction

Most of the ruminant livestock in Zimbabwe depend on maize stover as the main energy source during the dry season. Voluntary feed intake of this roughage is usually low mainly because the stover is harvested at a very mature stage and allowed to dry extensively before being fed to the animals Maturity increases cell wall constituent fractions (for instance) and decreases protein content; both factors are inimical to digestion of a forage. Dryness increases time spent chewing per bolus (Welch, 1982) and thus reduces total intake.

Hydration has a potential to overcome these constraints. Soaking causes swelling of cell wall structures and thus should make them more accessible to cellulolytic microbes. In addition it reduces the dustiness and dryness of the feed. However, results from experiments where rice straw was soaked or wetted have been unequivocal as to the effects of this treatment (Doyle et al, 1986).

The main objective of this experiment was to investigate the effect of hydration on the utilization of maize stover by steers. The second objective was to investigate if there were any interactions between protein (source) and soaking.

Materials and methods

Animals and diets

Eight Hereford-Cross steers, two years old and fitted with permanent rumen cannulae were randomly assigned to two 4 x 4 Latin squares. Each square represented hydration or lack of it of the maize stover, the basal diet. Hydration was effected by soaking stover in water at the rate of 1 kg stover/1.5 litres of water for 24 hours.

Unsoaked stover was wetted with an equal amount of water at feeding. The chemical composition of the stover used was: dry-matter (g/kg) 890; neutral-detergent fibre (g/kg DM) 930; organic matter (g/kg DM) 978.9; crude protein (g/kg DM) 22.9.

Three protein supplements plus a control (no protein) were the treatments imposed in each square. The protein supplements were:

(i) urea (30 g/kg of stover)

(ii) soyabean meal (300 g/d), and

(iii) urea (30 g/kg of stover) plus blood-treated soyabean meal (250 g/d).

Blood-treatment was effected by coating soyabean meal with blood at a rate of 1 litre blood/2 kg soyabean meal and baking the mixture at 88°C for 36 h in an oven. Urea was dissolved in water before adding to stover and sprinkled at the time of feeding.

The animals were held in individual stanchions and fed twice daily (0800 and 1600 h); orts were weighed and sampled in the morning. Water and a commercial salt lick containing trace minerals were available all the time. Rubber mats were used for bedding to facilitate cleaning and collection of faecal samples.

Measurements

The periods were 33 days long and the schedule of activities is shown in Table 1. During measurement of ad libitum intake, the animals were offered 20% more stover than their previous day's intake. The total collection method was used to measure digestibility while rumen digestion parameters were measured using the nylon bag technique (Orskov and McDonald, 1979) with up to 96 h incubation in the rumen.

Table 1. Schedule of activities in each period.

Day

Activity

1-10

Adjust animals to diet

11-20

Measure ad libitum intake

21

Dose with chromium-mordanted fibre

21-27

Total faecal collection with subsamples for rates of passage measurements

28-32

Nylon bag incubation and removal

33

Empty rumens, weigh digesta sample and return to animal

Laboratory and statistical analysis

Dry matter (DM) of stover, orts and faeces was determined by drying at 100 °C overnight.

Data from the nylon bag technique were analysed using the equation p = a + b (1 - e-ct) where p is total amount that has disappeared from the bag at time ti, a is the amount lost through washing, b the amount that in time will degrade and c the rate at which the b fraction degrades.

Statistical analysis appropriate for a double Latin square that accounts for the effects of square, animals, periods and protein supplements (Snedecor and Cochran, 1967) was used. Treatment means were compared using t-tests.

Results

Intake

Hydration increased intake (P<0.05) by 23% while protein supplementation increased (P<0.05) intake by 11% (Table 2). There was no interaction (P>0.05) between hydration and protein supplements. Protein type had no effect on intake (Table 2).

Apparent digestibility

Both hydration and protein supplementation had no effect
(P>0.05) on apparent dry-matter digestibility though unhydrated stover tended to have higher digestibility (Table 3).

Table 2. Dry-matter intake of hydrated and unhydrated stover supplemented with nitrogen.

Protein Source

Stover intake (kg/d)

Hydrated

Unhydrated

Control

4.4a,f

3.4b,f

Urea

4.9a,g

3.7b,g

Soyabean meal

4.8a,g

4.3b,h

Urea + blood-treated soyabean meal

5.0a,g

3.5b,g

Standard error of mean

0.086

a,b, means in a row with different superscripts differ significantly (P<0.05).

f,g,h means in a column with different superscripts differ significantly (P<0.05).

Table 3. Apparent digestibility of dry matter of hydrated and unhydrated stover supplemented with nitrogen.

Protein source

Apparent digestibility (%)

Hydrated

Unhydrated

Control

49.87

59.03

Urea

51.10

52.10

Soyabean meal

47.51

50.45

Urea + blood-treated



soyabean meal

48.60

45.41

Standard error of mean

8.826

Rumen digestion parameters

Soyabean meal decreased the 'a' fraction for hydrated stover but had no effect on the 'a' fraction of the unhydrated stover (Table 4). Urea decreased (P<0.05) the 'b' fraction in the hydrated stover and all the protein supplements tended to increase the rate of degradation though only significantly for the hydrated stover (Table 4). The patterns of DM degradation for the hydrated and unhydrated stovers are shown in Figures 1 and 2 respectively. In both cases only the control treatments show a distinct deviation from the other treatments.

Discussion

Hydration increased intake but had no effect on digestibility, a result that agrees with those obtained by Chatuverdi et al (1973) who used soaked wheat straw. However, Devendra (1983) reported negative effects on intake and digestion of wetted rice straw by sheep. This discrepancy in research results may be due to differences in species of animals and straw used. On the other hand, it may be caused by differences in soaking and as such it merits further research. Data on soaking maize stover were not found in the literature.

Supplementation of poor quality roughages with nitrogenous material is a common practice among farmers, often leading to increased intakes. Our results showed a similar effect though the low level of response (about 10%) was disappointing. The supplements were chosen to represent a rumen-degradable non-protein nitrogen source, a rumen-degradable protein nitrogen source and a combination of a rumen-degradable nitrogen source and a rumen-undegradable nitrogen source. No differences in intake, digestibility or rumen digestion kinetic parameters were noted between all the nitrogen sources.

All the rates of digestion for the 'd' fractions were similar but this may have been caused by high variabilities within each treatment, thus masking any possible real differences. Further experiments on this issue are in progress.

Table 4. Rumen digestion parameters of hydrated and Unhydrated stover supplemented with nitrogen.

Protein source

'a' (%)

'b' (%)

'c' (%)

Hydrated

Unhydrated

Hydrated

Unhydrated

Hydrated

Unhydrated

Control

12.3a,f

12.6a,f

44.3

35.77

2.55f

2.98f

Urea

12.7a,f

10.8a,f

36.53

35.46

4.09g

4.66g

Soyabean meal

7.7b,g

11.2a,f

40.80

34.32

4.38g

504g

Urea + blood-treated







soyabean meal

6.6b,g

11.0a,f

39.14

39.62

4.68g

4.84g

Standard error of mean

2.36

2.32

0.166

a,b means in the same row within the same fraction with different superscripts differ significantly (P<0.05).

f,g means in the same column with different superscripts differ significantly (P<0.05).

Figure 1. Dry-matter disappearance from hydrated maize stover incubated in nylon bags in the rumen Or steers.

Figure 2. Dry matter disappearance from unhydrated maize stover incubated in nylon bags in the rumen of steers.

Conclusion

Hydration increased DM intake but had no effect on apparent DM digestion and on nylon bag degradation parameters. Protein supplementation increased DM intake over and above that due to hydration but the response was low. In situations where nitrogen sources are scarce or expensive, hydration offers a cheap and unhazardous method of increasing intake of maize stover.

Acknowledgements

We thank the University of Zimbabwe Research Board for financial assistance, Dr. D. Neeley, Department of Animal Science, for help with statistical analysis and Messrs C. Mare, J. Sena and J. Walter for technical assistance.

References

Chaturvedi, M.L.; Singh, U.B. and Ranjham, S.K. 1973. Effect of feeding water-soaked and dry wheat straw on feed intake, digestibility of nutrients and VFA production in growing zebu and buffalo calves. Journal of Agricultural Science, Cambridge 80: 393-397.

Devendra, C. 1983. Physical treatment of rice straw for goats and sheep and the response to substitution with variable levels of cassava, leucaena and gliricidia forages. MARDI Research Bulletin 11(3): 272-290.

Doyle, P.T.; Devendra, C. and Pearce, G.R. 1986. Rice straw as a feed for ruminants. IDP, Canberra, Australia.

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

Snedecor, G.W. and Cochran, W.G. 1967. Statistical methods. 7th edition. Iowa State University Press, Ames, Iowa.

Welch, J.G. 1982. Rumination, particle size and passage from the rumen. Journal of Animal Science 54: 885-894.


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