Use of groundnut foliage (Arachis hypogaea L.) in the cattle diet in Dak Lak province, Central Highlands of Vietnam

Tran Thi Thuy Van¹, Bui Quang Tuan, Vu Anh Tai¹ and Nguyen Xuan Trach

Vietnam National University of Agriculture, Hanoi, Vietnam
nxtrach@vnua.edu.vn
¹ Institute of Geography, Vietnam Academy of Science and Technology, Hanoi, Vietnam

Abstract

A laboratory experiment and an on-farm feeding trial were conducted to test possibility to make silage of groundnut foliage (GF) as feed for cattle. At the laboratory level, GF was ensiled with whole crop maize (WCM) according to 4 formulae: (1) GFS25 (25% GF + 75% WCM), (2) GFS50 (50% GF + 50% WCM), (3) GFS75 (75% GF + 25% WCM), and (4) GFS100 (100% GF). Cassava meal was added to all mixtures at 5% based on as fed weight. The mixture of each formula was ensiled in 6 jars of 10 liters each. Silage samples were taken after 1 and 2 months of ensiling and evaluated based on sensible indicators (color, smell, texture, mold) and chemical parameters (pH, lactic acid, acetic acid, butyric acid, NH₃-N). Results showed that GFS25, GFS50, and GFS75 had good fermentation quality with satisfactory sensible indicators, high lactic acid and low butyric acid contents. In contrast, GFS100 had poor fermentation quality with low lactic acid and high butyric acid contents, and a high proportion of rotten biomass. Next, an on-farm feeding trial was conducted to evaluate responses of cattle to GFS75 and groundnut foliage hay (GFH) as replacement of whole crop maize silage (WCMS) in the control diet. A total of 18 Lai Sind bulls 17-18 months of age were assigned into 3 groups of 6 each according to a completely randomized design. The control group (WCMS ration) were fed ad libitum WCMS as normally practiced in the locality. The two other groups were either fed ad libitum GFS75 (GFS ration) or ad libitum GFH (GFH ration) to replace WCMS in the control diet. The other ingredients in the diets (fresh elephant grass, maize meal, soybean cake, mineral-vitamin premix, urea) were the same in all groups. Results showed that dry matter intake (DMI), average daily gain (ADG) and feed conversion ratio (FCR) were similar among the three groups. It was therefore concluded that GF can be made into good silage when combined with WCM and a source of readily fermentable carbohydrates and that GF based silage (75% GF + 25% WCM) or groundnut foliage hay (GFH) can be used to replace WCMS in the cattle diet without loss of feeding efficiency.

Keywords: byproducts, groundnut foliage hay, roughage, silage

Introduction

Dak Lak is a province of the Central Highlands of Vietnam, which is heavily affected by the harsh weather conditions with two distinct seasons, the rainy season and the dry season. The dry season, from November to the next April, often witnesses prolonged drought spells, which seriously affect the growth of vegetables, making it difficult for cattle feeding during this period of time. Whereas, the province has huge amounts of crop byproducts such as rice straw, groundnut foliage, maize stalks, maize cobs, cassava leaves and and sugar cane tops, which all could be utilized as feeds for cattle. Nevertheless, so far these byproducts have not been properly utilized for ruminant feeding, except for rice straw (Truong La 2012). It is of special interest that Dak Lak has 6,178 hectares of groundnuts per year (Dak Lak Department of Statistics 2019), giving around 53,000 tonnes of groundnut foliage (GF) as a byproduct from 2 crops, one harvested in August-September and the other in October. The GF should have a high nutritional value as a cattle feed. However, the fact is that both groundnut crops are harvested during the second half of the rainy season, making the foliage easy to develop molds and be spoiled when dried under the sun. In addition, green GF contains saponins, which can cause bloat and diarrhea in cattle. Therefore, to improve utilization of GF as feed for cattle, it is necessary to preserve it right after harvest and at the same time inhibit the negative effects of saponins on cattle. The hypothesis of the present study was that it would be possible to make silage to preserve GF for a long time to feed cattle at least without any negative effects on animal responses. This paper presents the results of a laboratory experiment and an on-farm feeding trial on use of groundnut foliage silage (GFS) and groundnut foliage hy (GFH) in the diet of cattle in Dak Lak province, in the Central Highlands of Vietnam.

Materials and methods

Laboratory ensiling of groundnut foliage

The study was carried out at the Central Laboratory of the Faculty of Animal Science, Vietnam University of Agriculture, from August to December 2018.

Groundnut foliage was ensiled with whole crop maize (WCM) according to 4 formulae based on as fed weight: (1) GFS25 (25% GF + 75% WCM), (2) GFS50 (50% GF + 50% WCM), (3) GFS75 (75% GF + 25% WCM), and (4) GFS100 (100% GF).

After nut harvest, GF was collected as the upper part of the plants, leaving 20-30cm lower vines. WCM was cut at 95-100 days after sowing. Both GF and WCM were chopped into 2-3cm in length, then mixed together according to predetermined proportions. Each mixture of GF and WCM was ensiled in 6 jars of 10 liters each. Cassava meal was added to all the ensiling mixtures at a rate of 5% based on as fed weight.

Measurements

Silage samples were taken after 1 and 2 months of ensiling and evaluated based on sensible indicators (color, smell, texture, and mold) and chemical parameters (pH, lactic acid, acetic acid, butyric acid, and NH₃-N).

On-farm feeding trial

Study site and time

The feeding trial was conducted on a farm in Buon Don district, Dak Lak province, the Central Highlands of Vietnam, from August 2019 to January 2020 to evaluate responses of cattle to replacement of WCMS in the diet with GFS or GFH.

Preparation of experimental feeds

Groundnut foliage silage was made according to the best formula among the 4 silage formulae tested at the laboratory level, viz. GFS75 consisting of 75% GF and 25% whole crop maiz (WCM). After nut harvest, GF was collected as the upper part of the plants, leaving 20-30cm lower vines. WCM was cut at 95-100 days after sowing. Both GF and WCM were chopped into 2-3cm in length, then mixed together according to the above ratio. The mixture was ensiled airtight in thick plastic bags of 1.5m in diameter and 2.5m in length, with around 0.8 tons per bag. Cassava meal was added to the ensiling mixture at a rate of 5% of the fresh weight. The silage was used for cattle feeding, beginning 1 month after ensiling.

Groundnut foliage hay was made from the green GF left after nut harvest being spread thinly on the cement yard and dried directly under the sun for 2-3 days. The GFH was preserved in a shelter for the whole period of experiment.

Most of diet ingredients used in the feeding trial (Table 1) were available on the farm, except for GF, that was collected from a neighboring farm. Elephant grass was grown on the farm and fed fresh after chopping into 2-3cm in length. Soybean cake, maize meal and mineral-vitamin premix were purchased from a local feed agency and mixed together before feeding.

Experimental design

Eighteen intact Lai Sind bulls 17-18 months of age were assigned into 3 groups of 6 each to be fed three different diets according to a completely randomized design as presented in Table 2. The control group (WCMS ration) were fed ad libitum WCMS as normally practiced in the locality. The two other groups were either fed ad libitum GFS (GFS ration) or ad libitum GFH (GFH ration) to replace WCMS in the control diet. The other ingredients in the diets (fresh elephant grass, maize meal, soybean cake, mineral-vitamin premix, urea) were the same for all groups.

Animal management and feeding

The experimental period was 3 months after 15 days of adaptation. Prior to the trial, all the animals were vaccinated against intestinal parasites, liver fluke, foot-and-mouth disease and pasteurellosis. During the trial, the animals were kept in individual stalls and fed twice a day at 8:00am and 4:00pm. After feeding the concentrate mix (soybean cake, maize meal, and mineral-vitamin premix) and chopped elephant grass, the experimental ingredients (WCMS, GFS or GFH) were provided ad libitum to each bull. The supplied amounts of WCMS, GFS and GFH were adjusted to maintain the individual leftovers at around 10% of the total amounts fed. Water was supplied freely at all times.

Measurements

Feed intake

Total supplied feeds and leftovers were weighed every day for each bull during the whole feeding trail to determine feed intake. Samples of feed offered and leftovers were taken before the last morning feeding of each week. After homogenization, an amount of around 0.5kg of feed offered was taken for each bull and put into a plastic bag. The leftovers were mixed well together, then an amount of around 10% was sampled for each bull and placed into a plastic bag. All the feed and leftover samples were stored at -18°C in freezers immediately after collection until the end of the experiment. After thawing, the composite samples were dried in a forced-ventilation oven at 60°C for 72 hours. Next, they were processed in a knife mill with 1mm sieve and stored in glass bottles at room temperature for later chemical analyses. Dry matter intake (DMI) and CP intake (CPI) were calculated by the difference between the amount offered and the amount in the leftovers.

Weight gain

The bulls were weighed in the morning before the first feeding on the first two days and last two days of the trial, using an electromagnetic scale (RudWeight, Australia). Bulls were also weighed at one-month intervals throughout the experimental period to monitor the animal performance and identify any possible anomalies.

Chemical analysis

Analyses of dry matter (DM), crude protein (CP), crude fiber (CF), ether extract (EE) and total ash were made according to methods of AOAC (1990). The silage samples were tested for pH according the method of Hartley and Jones (1978). The organic acids were analyzed with high pressure liquid gas chromatography (HPLC). Ammonia nitrogen (NH₃-N) was analyzed according to the Kjeldahl method. using MgO to push NH₃ out of the solution.

Statistical analysis

Data were statistically analyzed using Proc GLM in MINITAB software. The sources of variation were ration and error term. Tukey’s pairwise comparisons were applied to find significant differences between means at p<0.05.

Results and discussion

Quality of groundnut foliage silage

Sensible quality indicators

As can bee seen in Table 3, after 30 days of ensiling, GFS25, GFS50, and GFS75 became slight yellow, greenish, soft but not crumble with a mild sour smell and no mold was detected on the surface. Whereas, GFS100 was molded on around two thirds of the surface which became black and white, slightly crumble with a slight sour smell. After 60 days of ensiling, GFS25, GFS50, and GFS75 had a yellow color, soft texture and sour smell with a thin layer of mold on around one third of the surface, which looked as normal as for any other silage surface. The silage contents under the mold layer had normal indicators of good quality. In contrast, GFS100 became brown yellow, heavily molded on the entire smashed surface with black and white spots, and unpleasant musty smell. The observations indicated that GFS25, GFS50, and GFS75 had good quality after 60 days of ensiling, while GFS100 was unsatisfactory right after 30 days of ensiling.

It has been known that WCM is easy to make silage owing to its high content of readily fermentable sugar, while it is difficult to make silgae of GF due to its low sugar content and strong buffering capacity as a result of its high protein content (Bui Quang Tuan et al 2012). Therefore, the combinations of GF with WCM made GFS25, GFS50, and GFS75 have favourable conditions for microbial fermentation resulting in good quality silages. Although 5% cassava meal was added, it was not possible to preserve GFS100 without WCM for a long time.

Changes in pH and chemical composition of silages

Figure 1 shows that the pH values of GFS25, GFS50, and GFS75 dropped below 4.30 after 30 days and below 4.20 after 60 days of ensiling. This would be a sign of good fermentation, indicating sufficient production of organic acids in the silages. With such low pH values, the three silages could be well preserved for a long time. Whereas, the pH values of GFS100 were relatively high (>4.5) after 30 and 60 days of ensiling; therefore it could not be preserved for a long time.

Figure 1. Changes in pH of silages after different ensiling times

All the silages had DM contents within the range suitable for fermentation (25-35%) (Table 4). . NH₃-N contents of GFS25, GFS50, and GFS75 were within the normal range of good quality silage. The value of GFS100 was much higher, which should have lead to its higher pH compared to the other three silages. GFS25, GFS50, and GFS75 showed good fermentation quality in terms of high lactic acid and low butyric acid contents. In contrast, GFS100 showed poor fermentation quality as indicated by its low lactic acid and high butyric acid contents; that may explain why the silage was much rotten.

Groundnut foliage has been made into silage in several prevous studies with good results. Mai Thi Thom et al (2010) ensiled GF with salt and maize meal with 3 treatments, viz GF with 0.5% salt, GF with 0.5% salt plus 3% maize meal, and GF with 0.5% salt plus 6% maize meal. Results showed that GF ensiled with 0.5% salt had a green color and those ensiled with 0.5% salt plus 3% or 6% maize meal had a light yellow color with a pleasant smell. The pH values of 3 silages were all around 4.0. The lactic acid contents were relatively high (2.45, 2.61, and 2.76%, respectively). Do Thi Thanh Van (2009) ensiled a mixture of GF and natural grass in different ratios of GF to natural grass, viz. 100:0, 75:25, 50:50, plus 5% cassava meal and 0.5% salt. After 90 days of ensiling, all the 3 silages had a pH of 4.1-4.2, high lactic acid content (2.15-2.75%), without any rot nor mold. In our present study, GFS100 actually composed of GF plus 5% cassava meal as a source of fermentable starch within the range of application as in the two previous studies; however, it did not give the desired results with a much higher pH and a much lower lactic acid content. The comparisons indicate a possibility that salt, which was not used in the present study, plays an important role in silage making of GF without any additional source of green forage such as natural grass or WCM; whereas, cassava meal may actually have little value in stimulating fermentation of GF. If in the present study there had been another ensiling formula using GF combined with only WCM, the role of cassava meal might have been clarified. So, to have insights into further research is needed.

Johnson et al (1979) ensiled GF with or without a mixture of propionic acid-formaldehyde (67:10 w/w) at a rate of 0.93% DM. The pH values of the silages in the formula with and without propionic acid-formaldehyde mixture were 4.5 and 5.24, respectively. The lactic acid contents of the silages with and without propionic acid-formaldehyde mixture were 4.02 and 0.85% DM, respectively. The higher pH value should reflect the lower lactic acid content and both indicated poorer fermentation quality. The results should have an implication that ensiling of GF needs to add fermentation stimulants and/or inhibitors to improve fermentation quality. From this study it may be reckoned that salt used in the previously mentioned studies could act as such an inhibitor of undesired microganisms in the ensiling biomass under tropical weather conditions. This would warrant further research to investigate.

The results of the present laboratory study and our concurrent field surveys (not reported herewith) on availability of GF in the study area showed that GFS75 would be most suitable for making GFS in the Central Highlands of Vietnam. Therefore, this formula was chosen for the subsequent on-farm feeding trial.

Responses of cattle to groundnut foliage silage and hay

After 3 months of the feeding trial, the body weights (BW) and the average daily gains (ADG) of bulls in the three groups were similar (Table 5). This GFS and GFH can replace WCMS in the cattle diet without loss of growth performance. The similar ADGs can be explained by the similar total DMIs of the three groups (Table 6). As a result, FCRs were not much different among the three groups.

Since GFS and GFH accounted for 42% of the total DMIs with their higher crude protein (CP) content than that in WCMS, the crude protein intakes (CPI) of bulls in the two experimental groups were higher than in the control group. However, ADG was not different among the three groups. That may be because the levels of CPI in GFS and GFH fed groups were more than the requirement. For beef cattle at that range of BW and ADG, the NRC (2016) recommended are 12.6% CP in dietary DM. Whereas, in the present study, the actual DMI of the control WCMS fed group already contained 13% CP. That may help explain no further effect on ADG of higher CP levels in GFS or GFH compared to WCMS.

The responses of cattle to GFS or GFH were, to some extent, different from those reported in previous studies. Do Thi Thanh Van et al (2009) fed beef cattle with different levels of GFS to replace cassava meal as a supplement to a diet based on 4kg of natural grass, 50g urea, and ad libitum urea treated rice straw. It was shown that ADG was lower in the group that did not receive GFS compared to the groups that received 3kg or 6kg GFS/head/day. The higher ADGs of cattle fed GFS can be explained by the fact that GFS had a higher protein content than cassava meal. Similarly, Johnson et al (1979) conducted a feeding trial using WCMS in combination with GFS as contrast to WCMS alone as roughage in the diet of dairy heifers. The ratio of roughage to concentrate in the diet was 80:20 and the ratio of WCMS to GFS in the experimental group was 50:50 (DM/DM). Results showed that DMI of the control WCMS based diet and the experimental WCMS-GFS based diet was 6.18 and 6.66 kg/day, respectively. It was also explained that the combination of WCMS with protein-richer GFS helped improve the nutritional balance of the diet. Recently, Pok Samkol (2018) used GFH as a protein supplement in a basal diet consisting of rice straw and para grass for growing cattle. It was found that increased levels of GFH improved total DMI, CP digestibility, and nitrogen retention in cattle. The ADG was higher for the GFH supplemented diets than the control, but did not differ among levels of GFH supplementation. Supplementation of GFH at 2 or 3g CP/kg BW increased microbial protein production and the efficiency of microbial CP production in the rumen. The results indicated that nitrogen balance was improved when adding GFH to the low protein content diet.

However, in our present study, GFS or GFH did not improve cattle responses in terms of DMI, ADG and FCR compared to WCMS, but simplely played as an equivalent replacement of WCMS. As already discussed above, the responses were possibly dependent on the level of CP in the diet. Due to a high level (around 45% of DMI) of concentrate mix, which already contained soybeen cake as a protein supplement, the CP content in DMI of the WCMS fed group was 13%, which was higher than needed according to NRC (2016); therefore, GFS or GFH did not give any further effect owing to their higher CP contents compared to WCMS. Anyway, the possibility to replace WCMS with GFS or GFH without detrimental effects would have a very important implication for sustainable cattle production in the Central Highlands of Vietnam where there are huge amounts of GF available for utilization as cattle feed.

Conclusions

• Groundnut foliage can be made into good silage when combined with WCM. It is recommended to use 3 ensiling formulae depending on the availability of GF and WCM as follows: (1) 25% GF + 75% WCM, (2) 50% GF + 50% WCM, and (3) 75% GF + 25% WCM.
  
  
• Groundnut foliage silage (75% GF + 25% WCM) and groundnut foliage hay can be used to replace of WCMS up to 42% DMI in the cattle diet at least without impairing the feeding efficiency.
  
  
• It is warranted to investigate if cassava meal as a source of starch has any actual stimulating role to favourable microorganisms and if common salf has any inhibiting role to undesired microorganisams in making silage of GF.

Acknowledgements

The present research was sponsored by Project coded TN17/T05 under financial support of the National Program “Science and Technology Support for Economic and Social Development in the Central Highlands of Vietnam in the period 2016-2020” coded KHCN-TN/16-20. We would also like to thank the support of the staff of the Central Highlands Program Office for their assistance during the study.

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