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THE EFFECT OF THE INCLUSION OF AN IONOPHORE AS A SILAGE ADDITIVE ON MAIZE SILAGE CHARACTERISTICS

 

J.H. Hoon1# & R. Meeske2

1Grootfontein Agricultural Development Institute, Private Bag X529, Middelburg (EC), 5900

2Department of Agriculture, Western Cape, Outeniqua Experimental Farm, P.O. Box 249, George, 6503

#E-mail: Jan Hoon

 


INTRODUCTION

Silage is the acid-fermented product of anaerobic fodder fermentation of greater than 50% moisture content (McDonald et al., 1991), with the aim of preserving summer crops for winter-feeding.  A basic principle of ensiling is to provide adequate compaction of the crop to minimise air filtration (Coetzee, 2000). Once the fresh material has been stacked and covered to exclude air, the ensiling process progresses over four stages: 1) the aerobic phase, where respiration and proteolysis activities occur, 2) the fermentation phase for 7-21 days, 3) the stable phase, during which air is totally excluded and, 4) the aerobic spillage phase, where the silage is exposed to air during feeding (Nkosi, 2003).

 

Silage additives have been developed over years to improve the nutritive value of silages and to reduce some of the risks during the ensiling process. A silage additive should be safe to handle, reduce dry matter (DM) losses, improve the hygienic quality of the silage, limit secondary fermentation, improve aerobic stability, increase the nutritive value of the silage and give the farmer a return greater than the cost of the additive (Henderson, 1993). In several studies, Meeske (2000) determined the effect of adding a lactic acid bacterial inoculant during the silage-making process on silage characteristics of maize, forage sorghum, lucerne, Eragrostis curvula, Digitaria eriantha, oats, etc.  There is, however, still a need to evaluate other silage additives under South African conditions.

 

The ionophores monensin sodium (Rumensin®) and lasalocid sodium (Taurotec®) are commonly used as additives in ruminant diets. Ionophores are polyether antibiotics, known for their ability to transport ions across membranes (Hesse, 1996). The most consistent response to the feeding of ionophores is the increased molar proportion of propionic acid with a concomitant decline in the molar proportion of acetic and butyric acids during volatile fatty acid (VFA) production in the rumen. A decrease in methane production is often associated with this change in VFA production. Ionophores are also known to influence nitrogen metabolism both in the rumen and the animal (Mackie & Kistner, 1985). The main effects of ionophore activity in ruminants are on microbial growth, microbial metabolism, nutrient digestibility and nutrient utilisation (Van Niekerk, 1985). 

 

The aim of this study was to determine the effect of the inclusion of an ionophore as a silage additive during the silage-making process on specific maize silage characteristics for possible future inclusion in silage diets to improve animal performance.

 

MATERIAL AND METHODS

Whole crop maize was harvested at a dry matter content of 32% and the chopped plant material was ensiled in 1.5 litre Weck glass jars. The plant material of the control group (21 jars) was ensiled without additives, while an ionophore (Taurotec®) was added to the plant material of the treatment group (21 jars) at an inclusion level of 0.15 g/kg of fresh plant material. Three jars each of the control and treatment groups were opened on day 1, 2, 4, 8, 16, 32 and 90 after ensiling. The bottles were weighed before and after opening to determine the dry matter and gas loss. Two representative samples of each jar for each ensiling period were taken for analysis. One sample from each jar was placed in an oven at 60 °C for 72 h to determine the dry matter content, while the other sample was frozen at –20 °C. Both samples were kept for further analyses. The dried samples were analysed for acid detergent fibre (ADF), crude protein (CP), ash (to determine organic matter) and in vitro organic matter digestibility (IVOMD). ADF, CP and ash were determined on all the samples, while IVOMD was only done on the Day 90 samples. The wet samples were used to determine lactic acid (LA), water-soluble carbohydrates (WSC), pH, volatile fatty acid (VFA) content (acetic acid, propionic acid, butyric acid, valeric acid) and ammonia nitrogen (NH3-N). Organic matter (OM), ADF, CP, LA, WSC and pH were determined on samples taken at each sampling interval, while VFA, IVOMD and NH3-N were only determined on the samples collected at the end of the ensiling period.

 

An aerobic stability test was done over a 5-day period by measuring the CO2 production of the exposed Day 90 silage and representative samples were also taken at Day 95 for analysis. The Day 95 samples of both the control and treatment groups were analysed for LA, WSC, pH and VFA. All the experimental procedures were done in 2008 and repeated in 2009 and the data of the two years were combined. Statistical analysis was done using the Proc GLM-procedure of SAS (SAS, 2006).

 

RESULTS AND DISCUSSION

The dry matter (DM) content of the plant material tended to decrease with an increase in the period of ensiling. No differences (P>0.10) in DM content between the control and treatment groups were, however, observed. Dry matter and gas loss of the plant material increased with an increase in the period of ensiling. The silage of the treatment group tended to have higher DM and gas losses than the control group, indicating more fermentation losses. The crude protein (CP), acid detergent fibre (ADF) and organic matter (OM) contents of the samples after different periods of ensiling are presented in Table 1. With the exception of CP at Days 4 and 8 and ADF at Day 32, no differences (P<0.10) were observed between the control and treatment groups for CP, ADF and OM at any of the days after ensiling. The lactic acid (LA), water-soluble carbohydrates (WSC) and pH of the samples after different periods of ensiling are presented in Table 2 and Figures 1 to 3.

 

Table 1. Crude protein (CP), acid detergent fibre (ADF) and organic matter (OM) content (± s.e.) of the samples after different periods of ensiling

Days after ensiling

Crude protein (%)

Acid detergent fibre (%)

Organic matter (%)

Control

Treatment

Control

Treatment

Control

Treatment

Day 0

6.44 ± 0.12

6.19 ± 0.12

27.48 ± 0.97

27.39 ± 0.97

95.27 ± 0.21

95.00 ± 0.21

Day 1

5.92 ± 0.14

5.82 ± 0.13

27.27 ± 1.14

27.30 ± 1.04

94.74 ± 0.25

95.25 ± 0.23

Day 2

6.42 ± 0.13

6.19 ± 0.13

26.84 ± 1.04

27.34 ± 1.04

94.41 ± 0.23

94.66 ± 0.23

Day 4

6.40a ± 0.13

5.86b ± 0.18

26.79 ± 1.04

28.87 ± 1.50

94.76 ± 0.23

94.37 ± 0.33

Day 8

6.50a ± 0.13

6.09b ± 0.13

25.73 ± 1.04

25.38 ± 1.04

94.87 ± 0.23

94.72 ± 0.23

Day 16

6.40 ± 0.13

6.28 ± 0.13

25.96 ± 1.04

25.17 ± 1.04

95.17 ± 0.23

95.17 ± 0.23

Day 32

6.32 ± 0.13

6.15 ± 0.13

24.16a ± 1.04

26.87b ± 1.04

94.91 ± 0.23

94.73 ± 0.23

Day 90

6.05 ± 0.13

6.11 ± 0.13

26.11 ± 1.04

26.89 ± 1.04

95.40 ± 0.23

95.22 ± 0.23

ab Values with different superscripts in rows, differ significantly (P<0.10)

 

Table 2. Lactic acid (LA), water-soluble carbohydrates (WSC) and pH (± s.e.) of the samples after different periods of ensiling

Days after ensiling

Lactic acid (%)

Water-soluble carbohydrates (%)

pH

Control

Treatment

Control

Treatment

Control

Treatment

Day 0

0.05 ± 0.07

0.05 ± 0.07

2.28 ± 0.06

2.45 ± 0.06

5.28 ± 0.27

5.32 ± 0.27

Day 1

0.47 ± 0.07

0.45 ± 0.07

1.73 ± 0.06

1.84 ± 0.06

4.49 ± 0.27

4.57 ± 0.27

Day 2

0.80 ± 0.07

0.81 ± 0.07

1.26 ± 0.06

1.24 ± 0.06

4.08 ± 0.27

4.17 ± 0.27

Day 4

1.22 ± 0.07

1.14 ± 0.07

0.86a ± 0.06

0.63b ± 0.06

3.85 ± 0.27

3.94 ± 0.27

Day 8

1.35 ± 0.07

1.45 ± 0.07

0.34 ± 0.06

0.31 ± 0.06

3.77 ± 0.27

3.80 ± 0.27

Day 32

1.54 ± 0.07

1.42 ± 0.07

0.28 ± 0.06

0.27 ± 0.06

3.70 ± 0.27

3.83 ± 0.27

Day 90

2.03a ± 0.07

1.73b ± 0.07

0.53 ± 0.06

0.49 ± 0.06

3.78 ± 0.27

3.77 ± 0.27

Day 95

2.08a ± 0.07

1.89b ± 0.07

0.55 ± 0.06

0.54 ± 0.06

5.52a ± 0.27

6.94b ± 0.27

ab Values with different superscripts in rows, differ significantly (P<0.10)

 

The LA and WSC values over the ensiling period were very low compared to other studies (Meeske, 2000), with higher (P<0.10) LA values at Day 90 and 95 for the control treatment. Differences (P<0.10) in WSC between the control and treatment groups were only observed at Day 4. Both groups of silage were well preserved, as indicated by pH values lower than 4.0 from Day 4 to Day 90. According to Weissbach (1996), the pH required for stability of silage at 150, 250, 350 and 450 g DM/kg is 4.10, 4.35, 4.60 and 4.85 respectively. The growth of most acid tolerant clostridia will also be inhibited by a pH below 5.0 (Jonsson, 1991). The silage of both groups was, however, very unstable after exposure to air (Day 95), with higher (P<0.10) pH values for the treatment group.

 

Figure 1.  The change in lactic acid (LA) of the control and treatment groups



Figure 2. The change in water-soluble carbohydrates (WSC) of the control and treatment groups

 


Figure 3.  The change in pH of the control and treatment groups

 

The volatile fatty acid (VFA) contents of the samples at Day 90, as well as at Day 95 after the aerobic stability test was completed, are presented in Table 3.

 

Table 3. Volatile fatty acid (VFA) content (± s.e.) of the samples at Day 90, as well as Day 95 after the aerobic stability test was completed (% on DM basis)

Volatile fatty

acid

Day 90

Day 95

Control (%)

Treatment (%)

Control (%)

Treatment (%)

Acetic acid

1.383 ± 0.265

1.100 ± 0.265

0.770 ± 0.458

0.260 ± 0.265

Propionic acid

0.033 ± 0.010

0.023 ± 0.010

0.080a ± 0.018

0.020b ± 0.010

Iso-butyric acid

Not found

Not found

0.030a ± 0.007

0.007b ± 0.004

N-butyric acid

Not found

Not found

0.050a ± 0.003

0.003b ± 0.002

Valeric acid

Not found

Not found

0.050a ± 0.007

0.007b ± 0.004

ab Values with different superscripts in rows, differ significantly (P<0.10)

 

Differences (P<0.10) in VFA were observed for propionic, butyric and valeric acid at Day 95, with higher values for the control group compared to the treatment group. No differences in VFA were, however, observed between the control and treatment group at Day 90. The acetic acid values tend to be lower for the treatment group, indicating poorer stability of the silage. No butyric acid was detected in either the control and treatments groups at Day 90, which indicate that both silages were well preserved (Meeske, 2000).

 

The in vitro organic matter digestibility (IVOMD), ammonia nitrogen (NH3-N) content and CO2 production of the Day 90 samples are presented in Table 4.

 

Table 4. In vitro organic matter digestibility (IVOMD), ammonia nitrogen (NH3-N) content and CO2 production (± s.e.) of the Day 90 samples

Trait

Control

Treatment

IVOMD (%)

72.26a ± 0.45

66.92b ± 0.45

NH3-N (% of total N)

9.69 ± 0.42

8.62  ± 0.42

COproduction (g/kg DM)

21.56 ± 7.93

39.89 ± 7.93

ab Values with different superscripts in rows, differ significantly (P<0.10)

 

The IVOMD of the control group was higher (P<0.10) than the treatment group, which indicates better utilisation of the silage.  The NH3-N contents of both groups, express as % of total N, were high, indicating a high level of protein breakdown. Both silages were unstable when exposed to air, as indicated by the pH and CO2 production values, with higher (P<0.10) values for the treatment compared to the control group. The higher CO2 production of the silage of the treatment group indicates that more intensive spoilage processes took place (Meeske, 2000).

 

CONCLUSION

Maize silage normally preserves well, but the stability of the silage is often a problem. The main aim of the inclusion of a silage additive for maize is therefore to improve the stability of the silage. The results of this study indicate that the inclusion of an ionophore as a silage additive did not enhance the fermentation characteristics and might have impaired the aerobic stability of the maize silage. It is therefore not recommended to include an ionophore during the silage-making process, but rather to include it into feed mixtures according to the general recommendation.

 

ACKNOWLEDGEMENTS

The following people are thanked for their contribution to the project:

 

REFERENCES

Coetzee, T.G., 2000. Bunker silo management and its effect on crop quality. Clover SA Forum, March 2000.

Henderson, N., 1993. Silage additives. Anim. Feed Sci. Tech. 45: 35-56.

Hesse, C.H., 1996. Ionophores: Benefits and dangers. Elanco Animal Health, Isando, Johannesburg.

Jonsson, A., 1991. Growth of Clostridium tyrobutyricum during fermentation and aerobic deterioration of grass silage. J. Sci. Food Agric. 54: 557-568.

Mackie, R.I. & Kistner, A., 1985. Some frontiers of research in basic ruminant nutrition. Symposium on “Advances in Animal Science”, 24th Congr. S.  Afr. Soc. Anim. Sci., 2-4 April 1985, Stellenbosch. 

McDonald, P., Henderson, A.R. & Heron, S.J.E., 1991. The biochemistry of silage. Chalcombe Publications, Marlow, Bucks, UK, pp. 9-42.

Meeske, R., 2000. The effect of inoculants on silage fermentation properties and on animal production. PhD thesis, University of Stellenbosch.

Nkosi, B.D., 2003. Silage making from mango and citrus leaves for the resource poor emerging farmer in South Africa. Masters in Sustainable Agriculture, University of the Free State.

SAS, 2006. SAS Procedures Guide, Version 9.1.3. SAS Institute Inc., Cary, North Carolina, USA.

Van Niekerk, B.D.H., 1985. Advances in intensive ruminant nutrition. Symposium on “Advances in Animal Science”, 24th Congr. S.  Afr. Soc. Anim. Sci., 2-4 April 1985, Stellenbosch. 

Weissbach, F., 1996. New developments in crop preservation. Proceedings of the 11th International Silage Conference, University of Wales, Aberystwyth, pp 11-25.

 

Published

Grootfontein Agric 11 (2): 75