Dairy cattle feed from stover derived from mature and immature maize crops in small holder crop–livestock production systems in Vietnam
 

Nguyen van Hiep and Ngo Van Man
 

University of Agriculture and Forestry, Thu Duc, Ho Chi Minh city
manmy@hcm.vnn.vn

Abstract

Two experiments were carried out to evaluate three systems of producing maize (baby, boiled and mature maize), involving harvesting the crop at 50, 65 and 95 days;  and to test  appropriate methods to preserve and  improve the nutritional value of the residual forage (stover).  Data were obtained on field productivity for the three systems of production and on ways of preserving the stover.

For the high moisture stover (50 and 65 days harvest), the forage was ensiled with 2 levels of molasses;  the stover from the 50 and 65 day harvest was treated with urea after three days of drying. Samples of preserved material were evaluated by the in sacco method.

The income of farmers growing "boiled" maize and "baby" maize was nearly double compared  to traditional mature maize. In addition, the amount of stover was higher and less insecticide was required compared to growing mature maize.

Based on the colour, smell, mould appearance and pH  of the silages, ensiling is a good method to preserve high moisture maize stover with or without additive. Urea treatment was an effective way to preserve and improve low moisture stover. Young maize stover needs to be dried  to ensure the success of the urea treating process.

Key words: ensiling, urea treatment, maize stover, degradability
 

Introduction

As a result of economic development in recent decades the demand for animal products in Vietnam has increased markedly.  Many state programs are focusing on increasing local animal feed supply and maize production is being promoted in several ecological regions of Vietnam, especially in the deltas of the Mekong and Hong rivers.  Besides  production of maize for animal feed, there are also opportunities for using it as  human food ("baby" and "boiled" maize), for which it is harvested at the immature stage of between 50 and 65 days after planting. This system is prevalent in the  peri-urban areas of the big cities, the product being destined for export in cans as well as for local consumption. The forage residue (stover) after harvesting immature maize is potentially valuable as a feed resource for cattle (Göhl 1998). However, the production is seasonal and appropriate conservation techniques are needed to store the material to facilitate feeding it to animals over a long-term period. Ensiling of whole crop maize is a common practice done by farmers in North America for hundreds of years; while urea treatment  of green forage has been tested successfully by a number of researchers (Singh and Taparia 1992; Ambre and Toro 1993; Matsuzaki and Ogawa 1994).

Vietnam dairy cattle production started only a couple of decades ago with a total population today of around 30,000 heads, managed mostly in small-scale crop-livestock systems. Feeds are based mostly on natural grasses and crop residues with supplementation of concentrate. Shortage of roughage and especially of good roughage for dairy cattle development has been reported by many researchers (Cuong 1993; Man 1995). Better use of young maize stover  produced in small-scale crop-livestock systems could help to alleviate the shortages of good roughage for dairy cattle.   

The aims of this study were to measure the stover production from maize grown for "baby", "boiled" and feed grain; and to test appropriate methods for preserving and  improving the  nutritional value of this material as feed for  dairy cattle.

Materials and methods
 

Maize stover production

The experiment was carried out in 2002 at a farm in Damri village, Da Hoai district, Lam Dong province, Vietnam. Three maize production systems and varieties were tested in a completed randomized block design with 4 replicates (blocks). The treatments were:  Field maize (Pacific 963 variety), baby maize (Pacific 161 variety) and boiled maize (MX2 variety).  The area of each plot was 5.6 x 10 m (56 m²) and a 1 m border was left between the plots and the blocks. The soil was classified as a humic ferralic acrisol with the following characteristics (UAF Soil Chemistry Laboratory data): Sand 49.2%, Silt 17.2%,  clay 33.6%, C 1.72%, N 0.21%, pH_KCl 4.05, CEC 6.29 meq/100g, Ca  0.79 meq/100g, Mg =0.45 meq/100g; P₂O₅ 3 meq/100g.

The maize cultivation techniques followed the common practice applied in the region and the directions of the seed production company with a 70  x 25 cm spacing and 1 plant per hill for field and boiled maize  and 2 plants per hill for baby maize. Two tonnes of bio-organic fertilizer (Humix) and a mixture of chemical fertilizers (Urea, Super phosphate and potassium chloride) (130N 60P₂O₅ 45K₂O) were applied per hectare. The Humix and phosphate fertilizer were applied in the plant row 5 days before planting. Urea and potassium fertilizers were divided into 3 lots and applied 10, 20 and 30 days after planting. Basudin 10H was the insecticide used in the experiment to prevent maize stem borer.

At the time of harvesting the baby maize (1to 2 days after silking), boiled maize (soft kernel) and field maize (hard kernel), one sample from 11.2 m² (2.8 x 4m) on each plot was collected. The stover and maize grains were separated and weighed.  A sample of 2 kg of stover was collected for dry matter yield determination and chemical analysis using procedures described by AOAC (1984) and Van Soest and Robertson (1980).

Maize stover preservation

An additional plot of 1200 m² was planted for supplying the stover corresponding to 3 different plant ages: baby maize stage (50 days), milky stage (65 days) and hard kernel stage (95 days). These materials were preserved by ensiling and urea-treatment

Ensiling

Sugarcane molasses (640 g DM/kg and 375 g WSC/kg ) was used as an additive at 40 kg per tonne of fresh stover. The main treatments (with or without molasses and storage periods of 20 and 50 days) were compared  in a 2 by 2 factorial combination in a randomized complete block design. Each treatment was replicated 3 times using a total of 36 plastic bags of 40 cm diameter. Maize stover was collected in the field immediately after harvesting the main products (hard kernel maize, baby maize and milky maize). The stover was chopped into pieces of 2 to 3 cm length and placed in plastic bags of  around 10 kg capacity. Molasses was mixed with the chopped stover at the time of filling and the materials were compacted by hand pressing on the bags. After filling the tops of the bags were bound by plastic string and pressed by placing 1 kg sand bags on top. The bags were stored in the shade under a roof.

Samples were collected for chemical analysis immediately before ensiling and on two later occasions, 20 and 50 days after ensiling. The physical characteristics of the silages, colour, presence of fungus and smell, were evaluated and the following determinations made: pH (pH-ORION model 420 A), DM, WSC, CP, ash, and ether extract (EE),  using procedures described by AOAC (1984). ADF, Ash-free NDF and permanganate lignin were analyzed according to Van Soest and Robertson (1980).

Urea treatment

Urea was applied at the level of 4% of the DM of the stover corresponding to the three ages of 50, 65 and 95 days, which were either dried for 3 days (50 and 65 day harvests) under shade or not dried (50, 65 and 95 day harvests). There were two storage periods  (20 and 50 days) for each treatment according to a 2 by 2 factorial combination in a randomized complete block design.  Each treatment was replicated 3 times using a total of 36 plastic bags of 40 cm diameter. Sampling times and evaluation procedures were the same as in the ensiling study.  

Determination of degradation characteristics

Three cross-bred (Sindhi x Yellow) cattle (282 to 316 kg LW)  each fitted with a 40 mm diameter rumen cannula were used for the in sacco, following the method of Ørskov et al (1980). They were kept in individual pens and offered a ration of elephant grass, maize stover and a mineral supplement. Each forage sample was duplicated in each cow and repeated in each of the three cows,  in a complete randomized block design. A total of 72 bags were used with 24 bags per cow. The bags each contained 5 g of air-dry sample and were anchored to a 40 cm plastic ring and withdrawn from the rumen after 48 h of incubation. After being withdrawn the bags containing the un-degraded residues of the samples were washed in a washing machine for half an hour. Dry matter loss after 48 h incubation was assumed to represent the total degradability of a roughage and to be a measure of its nutritive value.

Statistical analysis

The data were subjected to analysis of variance (ANOVA) using the General Linear Model (GLM) procedure of the Minitab (1998) software. When the F test was significant (P<0.05), Tukey’s test for paired comparisons was used (Minitab 1998) to separate the means.
 

Results and discussion
 

Maize stover production study

The growing periods (Table 1) were 5 to 10 days longer compared to some reports done in this region (Thom 1995; Cuong 1998). Low solar radiation (cloudy weather) in the latter part of the rainy season may be the reason for the slower growth.

At the present price of mature maize grain (kg), boiled maize (10 maizes) and baby maize (kg) was 1500, 300 and 5600 VND, respectively (field price survey, Dec., 2002), the estimate of gross income from growing maize per season is highest in boiled maize followed by baby maize and field maize. Yield of maize stover from the "baby" maize system was 1.2 times higher than for mature maize and 1.9 times higher than for boiled maize. The chemical composition of the stover was not so different  for the three systems, with low values for crude protein and high values for the fibrous components, especially for mature maize stover (Table 2).

Ensiling and urea treatment

Observations at 20 and 50 days after ensiling (Table 3) showed a normal colour appearance of pale green, yellow brown to brown green, and dark brown.  The addition of molasses  increased the brown colour in the silage.

Molds were not seen in any of the treatments  after  20 days. A thin layer of molds was observed in the top layer of the 50-day silage and the non-molasses 65-day silage.  Silage produced from ensiling high moisture materials creates a suitable media for molds to develop and needs more water soluble carbohydrate as suggested by Petersson (1988).

Based on the colour, smell and mold appearance, the silages of maize stover with or without additive were considered to be acceptable except for mold layer after long-term storage in low DM material treatments (50 and 65 days harvesting). In urea-treated maize stover, the product of treating low DM materials (50 and 65 days harvesting) without drying was not acceptable because of the bad smell and viscosity.

Chemical composition and pH value of silage  and urea-treated maize stover

The addition of  molasses lowered the pH value of the silages (Table 4).  In the present study, the DM content of 50-days maize stover was low (14.0%: Table. 5) and molasses clearly improved the ensiling process. No effect  of molasses was seen in the other ensiling treatments. The silage was better with the older maize stover,  especially in 65 days harvesting.

Drying the maize stover affected the  pH value of the urea-treated maize stalk (Table 4). Urea treatment of dried maize stover  (50 and 65 days harvesting) and non-dried (95 days) produced alkaline products with pH value > 8 . In this condition, ammonia (generated from urea) inhibited oxidation and fermentation and kept the stover in a good condition with strong smell of ammonia and absence of  molds. The same observation was reported by Wilkin (1988).  Urea treatment of the high moisture stover  (50 and 65 days harvesting) resulted in a  pH of 7.95 and 7.36 after 20 days storage, and this was reduced to 5.82 and 6.43 after 50 days storage. The acid to neutral pH, combined with the bad smell and viscosity of these urea-treated products, indicates that this method cannot be used to preserve stover from maize harvested at an immature stage.

After 3 days drying under shade, the DM of the  stovers from immature maize was increased from 14.0 to 28.5% in the 50 days material and from 19.1 to 39.9% in the 65 days material. In this condition the ammoniation process developed quickly and inhibited the microbial fermentation.  The alkaline condition was created and kept the treated maize stover in a good condition. The same process also happened in the urea treatment of the mature maize stover (95 days harvesting).   

DM concentration in the maize stover increased as the harvesting time increased (Table 5). CP concentration was not so changed in the early harvests: 9.3 and 9.2% in DM in 50 and 65 days harvesting and reduced quickly at maturity: 5.8% in DM at 95 days harvesting. The lignin concentrations increased with advancing maturity. The same trend was not the case for ADF and NDF concentration, which were reduced in 65 days harvesting compared with 50 days harvesting. The high assimilation of starch during this phase of growth may have brought about a comparative reduction of ADF and NDF concentration.

Urea treatment of the maize stover increased the CP concentration but to a much lesser degree compared with urea treatment of rice straw (Promma et al 1994; Rajeev et al1996 and Chowdhury and Huque 1996). A two-fold  increase in CP content was reported by Man and Wiktorsson (2001) in urea-treated fresh rice straw. The magnitude of the increase varies according to factors such as the nature of the material, the environment and the treatment process. In the present study, the high moisture content of the stover may have favoured the formation of of water soluble ammonia-N and water soluble non-ammonia-N, most of which would have been lost during the drying of the samples.     

Dry matter loss in the in sacco incubation

As expected, the 48 h DM loss of the maize stover was reduced with increasing maturity (Table 6).  Ensiling the maize stover tended to increase the DM loss and this was more pronounced when molasses was included in the silage. The urea treatment only increased the DM loss in the stover harvested at maturity.

 

Conclusions

The results of this study indicate:

• In the farming systems in the South-Eastern region of Vietnam farmer income is nearly doubled by growing immature maize for human consumption as  "boiled" and "baby" maize  compared with mature maize growing. In addition to the increased income, the farmer can collect almost twice as much stover of superior feeding value, with reduced use of insecticide.

• Ensiling appears to be the best method of preserving the stover from immature maize stalk and does not require addition of molasses.

• Urea treatment is a suitable method to preserve and improve the nutritive value of stover from mature maize.
  Drying of immature maize stover is needed to ensure the success of the urea-treatment of this material.

 

Acknowledgements

This research was partially financed by the bilateral SAREC project 2000-2002.

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