Apparent digestibility and N retention in growing local pigs fed ensiled Taro foliage (Colocasia esculenta) replaced by protein-enriched cassava root (Manihot esculenta Crantz)

Nouphone Manivanh, T R Preston¹, Le Van An² and Tran Thi Thu Hong²

Faculty of Agriculture and Forest Resource, Souphanouvong University, LuangPrabang, Lao PDR
noumanivanh@gmail.com
¹ Centro para la Investigación en Sistemas Sostenibles de Producción Agropecuaria (CIPAV), Carrera 25 No 6-62 Cali, Colombia
² Faculty of Animal Science and Veterinary Medicine, Hue University of Agriculture and Forestry, Hue University, Vietnam

Abstract

Four castrated male pigs (Moo Lath breed), weighing on average 15 kg were allotted at random to 4 diets within a 4*4 Latin square design, to study effects on DM intake, digestibility and N retention of levels of protein-enriched cassava root (PECR) of 0, 25, 50 and 75% in combination with taro silage 80, 55, 30 and 5% with constant levels of ensiled banana stem (20%) (all on DM basis

Enriching the protein content of cassava root (PECR) by fermenting it with urea, diammonium phosphate and yeast and including the PECR at 25% in a diet of ensiled cassava root, ensiled taro foliage and ensiled banana pseudostem, led to increases in feed intake, diet digestibility and N retention in native Moo Laath pigs. These criteria declined linearly when the proportions of PECR were 50% and 75% of the diet DM. It is suggested that: (i) the benefits from the 25% PECR diet may have been partially a response to its content of live yeast estimated to be of the order of 1% of the diet DM; and (ii) the results provide confirmatory evidence that pigs are able to utilize small quantities of NPN recycled to the small intestone for microbial synthesis to amino acids.

Key words: banana pseudo-stem, diammonium phosphate, probiotic, solid-state fermentation, urea, yeast

Introduction

In mountain areas, most smallholder farmers prefer to keep native (Moo Lath) pigs as they adapt well to the foraging system (Phengsavanh et al 2010). Scarcity and poor quality of feeds, especially with respect to protein, appear to be the major cause of the low productivity (Stur et al 2002). The main problem is the supply of protein as soybean and fish meals are not available in rural areas. Phengsavanh and Stur (2006) showed that growth rates were increased from 100 to 200 g/day by providing some protein-rich forage in the form of stylosanthes. However, other forages appear to have more potential in pig diets based on rice bran (Preston 2006).

Taro is a locally available feed resource with good potential for use in diets of pigs, because of its nutritional quality ( www.feedipedia,org). The difficulty in the use of taro foliage is because of its content of oxalic acid which cause itching in the mouth and throat of animals consuming it. Farmers usually boil the taro before feeding it to the pigs as this appears to reduce the oxalate content. A specific advantage of the Taro plant is the high sugar content in the petioles (or stems). By ensiling the combined leaves and stems there was no need to add an additional source of sugar (Rodríguez et al 2009). Ensiling not only preserves the foliage of taro; it also decreases the level of oxalates (Hang et al 2018).

Cassava (Manihot esculenta Crantz) is an annual crop grown widely in the tropical and subtropical regions. Cassava roots are a good energy source (75 to 85% of soluble carbohydrate) but are low in protein (2 to 3% CP); one way to improve the protein content of carbohydrate-rich feeds is by solid-state fermentation with fungi and yeasts (Hong and Ca 2013).

A series of experiments has been carried out recently in Lao PDR (Manivanh and Preston 2015; Manivanh and Preston 2016; Manivanh et al 2016; Manivanh et al 2018; Sengxayalth and Preston 2017a,b; Vanhnasin and Preston 2016; Vanhnasin et al 2016) with the aim of defining the potential of the solid-state fermentation process as a means of raising the protein content of cassava roots and cassava root pulp as the basis of the diet of indigenous pigs (Moo Lath in Lao PDR and and Mong Cai in Vietnam).

The results of these experiments showed that fermenting the fresh cassava roots or cassava root pulp with a combination of urea (1-2%), DAP (1-2%) and yeast (3%) over periods of 5 to10 days resulted in increases of true protein to levels of 7-8% (DM basis) representing about 60% of the total crude protein derived from the added urea, DAP and yeast. It has not yet been possible to exceed this true protein fraction by procedures such as: prior steaming of the carbohydrate source, and/or fermentation under anaerobic or aerobic conditions. The nature of the approximately 30% of residual non-protein nitrogen has not been identified. Data presented by Manivanh et al (2018) showed that ammonia levels were minimal. These authors hypothesized that the residual NPN it could still be in the form of urea, the hydrolysis of which by urease might be reduced due to the rapid fall in pH with the onset of fermentation.

Despite the apparent limitation of having some 30-40% of the nitrogen in non-protein form there have been positive results when the protein-enriched pulp or root was fed to pigs at levels to provide some 25% of the diet protein replacing protein from ensiled taro foliage (Manivanh and Preston 2015; Vanhnasin et al 2016; Sengxayalth and Preston (2017b). At levels exceeding 25% of the diet protein, growth rates were depressed slightly when the PECR replaced a balanced protein source (eg: ensiled taro foliage) but fell to little over maintenance when the diet was composed of 75% PECR and 25% of ensiled cassava root, a diet in which all the protein was from PECR (Sengxayalth and Preston (2017b).

The following experiment was designed to generate more information on the effects of increasing dietary levels of PECR replacing a combination of ensiled taro foliage and ensiled banana pseudo-stem in the diet of growing Moo Lath pigs.

Material and methods

Location and duration

The experiment was conducted in the experimental area of Souphanouvong University (SU), in Luang Prabang province, Lao PDR, from 1^st May to 11^th June, 2018.

Experimental design

Four treatments were compared in a 4*4 Latin Square arrangement with 4 pigs and 4 periods. The treatments (DM basis) were:

PECR0: Taro silage (TS) 80% + ensiled banana stem (BS) 20%

PECR25: TS 55% + BS 20% + Protein-enriched cassava root 25%

PECR50: TS 30% + BS 20% + Protein-enriched cassava root 50%

PECR75: TS 5% + BS 20% + Protein-enriched cassava root 75

The duration of the experiment was 48 days with 4 periods each of 12 days, the first 7 days for adaptation then 5 days for data collection (feed residues, feces and urine).

Animals and housing

Four male castrated local (Moo Lath) pigs, with average live weight of 15 kg were housed in cages made of bamboo, designed to separate feces and urine.

Experimental feeds

Taro foliage (leaves and petioles) was harvested from ponds in the Univesity campus. It was chopped, wilted for 8 hours to reduce the moisture content, then ensiled for 14 days before starting the experiment.

Fresh cassava roots were peeled and chopped by hand into small pieces (1-2 cm) then mixed (DM basis) with yeast (3%), urea (1.4%) and di-ammonium phosphate (DAP) (2%). The mixtures were then allowed to ferment in closed polyethylene bags for 7 days.

Banana stems were collected from the garden around the University. They were chopped by hand into small pieces and ensiled in 200 liter PVC containers for 7 days without additive.

The pigs were fed twice daily (8:00 am and 4:00 pm). The three ingredients were mixed together before each feed. Feed was offered at ad libitum but with careful observation of the intake so as to minimize residues. Drinking water was permanently supplied through drinking nipples.

Measurements and data collection

The pigs were weighed in the morning before the start of each period and one day after the end of the last period. Feed offered and refused was recorded collected daily. Samples of feeds offered and refused were taken daily and sored at until the end of each collection period when they were mixed and sub-samples take for analysis of DM, ash and N. Feces and urine were collected daily. Each day 20 ml of 15 % H₂SO₄ were added to the urine container to maintain the pH of the urine below 4.0. The feces were stored at 4°C until the end of each collection period when they were mixed and a sub-sample taken for analysis of DM, ash and N. A sub-sample of urine was taken daily and stored at 4°C until the end of each collection period when the samples was mixed and a sub-sample taken for analyses on N.

AOAC (1990) methods of analysis were followed for analysis of: DM, ash and N in feeds offered and refused and in feces; N in urine; and true protein after reacting the samples with trichloro-acetic acid.

Statistical analysis

The data were analysed with the general linear model (GLM) procedure for repeated measures in the SAS software (SAS 2010), as a latin square split design . The repeated measures were the data for each of the 5 consecutive days of data collection within each period. The statistical model was: Yijk = μ + Ti + Cj+ R(k) + timel + time(pen) + eijk
Yijk = Dependent variables; μ = Overall mean; Ti = Treatment effect (i=1-4), Cj = period effect (j=1-4); R(k) = pen effect; time effect (l=1-5); pen within time effect (Error a), and eijk =random error (b).

Results and discussion

Crude and true protein

The true protein in the PECR accounted for 53% of the crude protein (Table 1), a value similar to that reported by Manivanh et al (2016), Sengxayalth and Preston (2017a) and Vanhnasin and Preston (2016).

Feed intake

The daily DM intake followed a curvilinear trend (y = -56.4x² + 276x + 366; R² = 0.70) increasing to a maximum as the proportion of PECR was raised from 0 to 25% then declining with higher proportions of PECR (Table 2; Figure 1). As a function of liveweight the intakes were high (33 to 44 g DM/kg live weight).

Figure 1. Mean values for DM intake by pigs fed diets in which taro silage was replaced by PECR

Apparent digestibility

The curvilinear trend for apparent digestibility of DM was similar to that for DM intake (Table 3; Figure 2) with increases in the digestibility coefficient as PECR replaced ensiled taro foliage at the 25% level subsequently declining with increasing degree of replacement by PECR (Figure 2). However, for protein the depression was a linear negative trend over the whole range of replacement of ensiled taro foliage by PECR.

Figure 2. Mean values for apparent digestibility of DM and crude protein in pigs fed diets in which taro silage was replaced by PECR

Nitrogen balance

N intake and N retention increased with curvilinear trends reaching maximum levels with 25% PECR in the diet thereafter decreasing (Table 4; Figure 3). Part of the increase in N retention was apparently due to the increased N intake; however, correction of the data by covariance for differences in N intake did not change the relative pattern of response to PECR level in the diet. The improvement in N retention with increasing levels of PECR replacing mixed silages of taro foliage and banana stem contrasts with the observed linear decrease in apparent N digestibility (Table 3).

Figure 3. Effect on N retention by replacing ensiled taro foliage with PECR (with and without correction by covariance for differences in N intake)

Discussion

The optimum level of crude protein in a diet based on ensiled taro foliage and ensiled banana pseudo-stem was reported by Sivilai and Preston (2016) to be 12% in the DM. In the present experiment, the crude protein level was planned to be 10% on the premise that in an experiment to compare different sources of protein, the protein should be limited to slightly less than the optimum level. However, because the proportion of true to crude protein in PECR was only 0.53, the actual levels of true protein in the diets decreased from 9.63% on the control (PECR0) diet to only 5.44% in the diet containing 75% PECR (Table 5).

It was to be expected that the growth rate of the pigs would have declined linearly as the proportion of true protein in the diet was reduced. On the contrary, the response to increasing PECR level was curvilinear with feed intake and N retention increasing by 33 and 28%, respectively for the diet with 25% PECR, which was associated with a decline in the true protein content of the diet from 9.6 to 7.9%. Only when the PECR level was raised to 50% and 75% of the diet (percent true protein reduced to 6.9 and 5.4%), did the expected decline in performance occur.

The issues that are raised are: (i) the benefits from 25% PECR in the diet were due to the presence of live yeast (estimated to be about 1% of the DM of the PECR25 diet) acting as a probiotic and: (ii) pigs can apparently utilize small quantities of non-protein-nitrogen through absorption of the NPN from the large intestine and subsequent recycling in the blood to the small intestine where microbes use the NPN for synthesis of amino acids (Colombus et al 2014).

The other interesting observation from this experiment is that N retention was only marginally depressed even with as much as 75% of the diet in the form of PECR, which is in marked contrast with the report of Sengxayalth and Preston (2017b) that when 75% of the diet was in the form of PECP the growth rates were reduced almost to zero. The difference between the two experiments was the nature of the remaining 25% of the diet DM. In the research of Sengxayalth and Preston (2017b) this was in the form of ensiled cassava root pulp whereas in the present experiment it was a combination of ensiled taro foliage (5%) and ensiled banana pseudo-stem (30%). These latter feeds would have been much richer in vitamins, minerals and trace elements than the PECR which formed the balance of the diet in the experiment of Sengxayalth and Preston (2017b). This cannot be proved in the absence of relevant biochemical analytical data in both trials, but it is an argument for the benefits of having at least a part of the dietary protein being provided by nutrient-ich foliages such as taro.

Conclusions

• Enriching the protein content of cassava root (PECR) by fermenting it with urea, diammonium phosphate and yeast and including the PECR at 25% in a diet of ensiled cassava root, ensiled taro foliage and ensiled banana pseudostem, led to increases in feed intake, diet digestibility and N retention in native Moo Laath pigs.
  
  
• These criteria declined linearly when the proportions of PECR were increased to 50 and 75% of the diet DM.
  
  
• It is suggested that: (i) the benefits from the 25% PECR diet may have been partially a response to its content of live yeast estimated to be of the order of 1% of the diet DM; and (ii) the results support earlier research showing that pigs are able to utilize small quantities of NPN recycled to the intestine for microbial synthesis of essential amino acids.

Acknowledgements

This research was done by the senior author as part of the requirements for the PhD degree in Animal Production in the Hue University of Agriculture and Forestry. The authors would like to express sincere gratitude to the MEKARN II program, financed by Sida (Swedish International Development Agency) for supporting this research.

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Received 12 August 2018; Accepted 29 August 2018; Published 3 September 2018

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