Soybean foliage Glycine max (L.) for growing goats in the Mekong Delta of Vietnam

Nguyen Thi Thu Hong^1,2, Nguyen Van Khanh³ and Nguyen Thi Ngoc Trang⁴

¹ An Giang University, An Giang, Vietnam
ntthong@agu.edu.vn
² Vietnam National University Ho Chi Minh City, Vietnam
³ Animal husbandry and Veterinary department of An Giang province, Vietnam
⁴ Kiengiang University, Vietnam

Abstract

The 70-day DM yield of soybean managed as a forage cop was 13.0 tonnes/ha with 15.9 % crude protein content in DM. Feed intake and growth rates of goats fed a basal diet of Pennisteum grass were increased linearly when their diet was supplemented with increasing amounts of fresh soybean foliage. There were no effects of soybean foliage supplementation on feed conversion.

Key words: biomass, legume, protein, small ruminant

Introduction

Soybean (Glycine max L. Merr.) cultivation supports more diversified agroecosystems and flexibility in crop rotations (Mustafa and Seguin 2003). A recent development in Vietnam is growing the crop to produce soybeans as a vegetable for direct human consumption. Varieties developed for grain production in tropical environments could potentially be harvested as forage to supplement diets of ruminant livestock (David 2018).

Soybean can be produced even in the wet tropics for forage at much lower cost than for grain because it does not require a dry season coincident with the time of seed ripening nor any expensive harvesting machinery (Tobía and Villalobos 2004). Another advantage of using forage soybean is the flexibility of harvest dates since its quality is good over a long period andit can be harvested at any stage of growth (Blount et al 2006). At the 70 day stage of development, soybean seeds have reached their highest dry matter content and represent the part of the plant with the best nutritional value (Hintz and Albretcht 1994). Soybean forage harvested at the 90-day growth stage (full seed) (Fehr and Caviness 1980) can produce between 1200 and 2000 kg/ha of protein. When using management practices for forage production, quality of soybean as forage was equivalent to that of alfalfa (Hintz et al 1992). Moreover, forage soybean also contains higher levels of protein than many other types of forage and possesses nitrogen fixation capability (Redfearn et al 1999).

Material and methods

Location

This experiment was carried out on farm in Chauphu districts, An giang province.

In this paper, we report the results of (i) an agronomic study to determine yield and composition at the time of green bean harvest; and (ii) a trial to evaluate the nutritive value of the foliage when fed as the supplement in a grass-based diet for growing goats.

Experiment 1: An agronomic survey to determine by-product yield and composition

Biomass productivity of soybean foliage (Photo 1) was measured 70 days following planting (Photo 2). During harvesting, the biomass of soybean foliage was weighed and then separated into full seed and leaves with stems. Five farms were involved in the survey and, in each farm, five 1 m² blocks, chosen at random, were considred as replicates. Foliage (stem and leaf) samples were analysed for DM and CP according to AOAC (1990).

Photo 1. The soybean plants growing in the field	Photo 2. The soybean foliage harvesting in the field

Experiment 2: Soybean foliage in diets of growing goats

Treatments and design

Sixteen growing male goats (16 ± 0.2kg), hired from small-holder goat keepers in the area, were housed in individual cages according to a Completely Randomized Design with 4 replications of 4 treatments: 0, 10, 20 and 30% fresh soybean foliage (% in DM). The basal diet was Varisme 06 (Pennisetum americanum x P. purpureum).

Feeds and management

The goats were vaccinated against foot and mouth disease and de-wormed with Ivermectin before the start of the experiment. They had free access to water and mineral blocks. After a 15 days adaptation to the experimental diets, the live weights were taken at the beginning of the experiment and then every 15 days until the end of the 100-day trial.

New feed was offered 2 times daily at 08:00 and 16:00. Varisme 06 grass was collected every day and offered ad libitum (about 120% of recorded intake). Fresh soybean forage was tied in bunches in the racks for goats to choose freely. The feed offered and refused was weighed every morning to determine daily feed intake.

Samples of feed offered and refused were analyzed for proximate components by AOAC (1990) methods and for neutral detergent fibre (NDF) and acid detergent fibre (ADF) using the methods of Van Soest and Robertson (1985).

Statistical analysis

The data were analyzed using the general linear model of the ANOVA program in the Minitab software (Minitab 2010). Sources of variation in the model were treatments and error.

Results and discussion

Spybean as a forage crop

The mean DM yield of the soybean foliage at full seed stage (70 days) (Table 1) was 13.0 tonne/ha with 15.9 % crude protein content (Table 2).

Lee et al (2014) evaluated the quality of several soybean cultivars for forage by developmental stage and found that the samples harvested at the full seed stage (70 days) had an optimal quality with a range of crude protein of 16.6-25% after 89 days of sowing. Rogers et al (2017) reported that forage genotypes had a greater amount of stem biomass 484 g/m ² and leaf biomass 244 g/m² at 70 days. Altinok et al (2004) found an average 7343 kg/ha DM yield with six grain-type soybean cultivars at 70 days stage in Ankara, Turkey. Forage soybeans yielded 4500–13,900 kg/ha in the central USA (Nayigihugu et al 2000).

Soybean foliage as protein supplement for goats

The soybean foliage had twice the content of DM and of crude protein compared with the grass (Table 3). NDF was lower in the soybean but ADF was similar to the grass reflecting the presence of the stems in the soybean foliage.

There were linear increases in DM intake and in growth rate when the grass diet was supplemented with fresh soybean foliage (Table 4; Figures 1 and 2). However, by contrast, the feed conversion showed no differences. The implications are that the improved growth reflected an intake response due to the additional crude protein from the soybean foliage but that the balance of nutrients, and specifically the supply of glucogenic precursors, was only marginally improved by the supplementation with soybean foliage.

Figure 1. Effect on feed intake of supplementing Pennisetum spp grass with fresh soybean foliage	Figure 2. Effect on live weight gain of supplementing Pennisetum spp grass with fresh soybean foliage

Conclusions

• The 70-day DM yield of soybean managed as a forage cop was 13.0 tonnes/ha with 15.9 % crude protein content in DM.
  
  
• Feed intake and growth rates f goats fed a basal diet of Pennisteum grass were increased linearly when their diet was supplemented with increasing amounts of fresh soybean foliage.
  
  
• There were no effects of soybean foliage supplementation on feed conversion.

Acknowledgments

We wish to thank the Department of Science and Technology, An Giang Province for funding this study.

References

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Received 3 May 2020; Accepted 10 May 2020; Published 1 July 2020

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