Effect of protein-enriched cassava pulp on growth and feed conversion in Moo Laat pigs

Phoutnapha Sengxayalth and T R Preston¹

Champasak University, Lao PDR
Alounptc@gmail.com
¹ Centro para la Investigación en Sistemas Sostenibles de Producción Agropecuaria (CIPAV), Carrera 25 No 6-62 Cali, Colombia

Abstract

Sixteen female Moo Lath pigs (16-18 kg initial weight), housed in individual pens, were used in a growth experiment to evaluate the effect of increasing levels of protein-enriched cassava pulp (PECP) replacing soybean meal in a diet in which cassava pulp was the source of carbohydrate. The treatments replicated 4 times in a completely randomized block design were: PECP levels equivalent to 0, 28, 60 and 94% of the dietary protein, replacing soybean meal. The PECP was derived from a 9-day fermentation of ensiled cassava pulp with yeast (2%), urea (3%) and DAP (1%) (DM basis) under semi-anaerobic conditions.

DM feed intake was not affected when PECP provided 28% of the dietary protein but at higher rates of substitution, feed intake decreased dramatically such that at 94% substitution of diet protein, DM intake was only 1% of live weight. The trends for live weight gain were similar except there was an indication of increased growth rate (from 125 to 153 g/day; SEM ± 12) at the 28% level of soybean protein substitution by PECP, followed by the same dramatic decrease in growth rate with higher levels of substitution of PECP. It is proposed that the improvement in growth with 30% substitution of soybean protein by PECP arose from microbial synthesis of amino acids in the intestine from dietary NPN (ammonia?) present in the PECP.; and that the precipitous decline in feed intake and in growth rate, when the PECP exceeded 30% of the dietary protein, was the result of the presence of excess ammonia, and/or its metabolites, due to their incomplete conversion to yeast protein in the fermentation.

Key words: cassava pulp, DAP, fermentation, indigenous pigs, yeast

Introduction

A recent development in Lao PDR has been the industrial extraction of starch from cassava roots for export to neighboring countries. There are five cassava starch factories with total planted area of 60,475 ha, giving an average yield of fresh roots of 27 tonnes/ha. Annual production is of the order of 1.6 million tonnes (Department of Agriculture 2014). However, not all the starch is extracted. Some 40% of the root DM remains as a residue (http://www.cassavabiz.org/postharvest/starch03.htm). known as “cassava pulp”. The pulp is composed almost entirely of starch and is highly digestible (Phanthavong et al 2014). However, it contains very little protein (less than 3% in the dry matter; http://www.feedipedia.org/). Thus it is necessary to supplement it with protein-rich feeds such as fish and soybean meals in order to make a balanced diet for pigs. These protein meals are expensive in Lao PDR as they are mostly imported.

One way to improve the protein content of carbohydrate-rich feeds is by solid-state fermentation with fungi (Hong and Ca 2013) and yeast (Oboh and Kindahunsi 2005). According to the latter authors, fermentation of cassava meal with yeast enhanced the protein level from 4.4 to 11% in DM and decreased the cyanide content. However, the extent to which the increased “protein” was in the form of “true” protein was not reported.

In a previous paper (Sengxayalth and Preston 2017), we showed that fermentation of the pulp with yeast, urea and diammonium phosphate (DAP) increased the crude protein to 17% in DM; however, only two thirds of the crude protein (11% in DM) was in the form of true protein.

The present experiment was carried out to determine the extent to which the protein-enriched cassava pulp (PECP) could replace soybean meal as the protein source for indigenous (Moo Laat) pigs fed cassava pulp as the source of energy.

Materials and methods

Location and climate of the study area

The experiment was carried out from from October 2015 to February 2016 in the integrated farming system center of Champasak University. The site is located 13 km from Pakse City, Lao PDR. The mean daily temperature in this area at the time of the experiment was 27 ^oC (range 25-32)

Experimental design

The treatments applied to 16 growing pigs in a randomized block design were 4 diets planned so that protein-enriched cassava pulp (PECP) supplied 0, 28, 60 or 94% of the “true” protein in the diet, replacing soybean meal (Table 1). There were 4 replicates per treatment.

Animals and housing

The pigs (Photo 1) were females of the local breed (Moo Laat) of 16-18 kg initial weight housed in individual pens (1.2 m wide, 1.6 m in length and 1m of height) fitted with feed troughs and water nipples. The pens were in an open shed made from wood and bamboo (Photo 2). The pigs were adapted to the diets and the pens for 15 days before starting the experiment.

Feeds and feedingof the bags

Fresh cassava pulp was collected from the starch factory in Pakse province (Photo1) and stored .in closed polyethylene bags where it ensiled naturally (pH 3.5). Each day, sufficient pulp for one day needs of PECP was taken out of the bags and fermented with (DM basis) 2% of yeast (Saccharomyces cerevisiae), 4% urea and 1% diammonium phosphate (DAP) following the procedure described by Sengxayalth and Preston (2017).

Thus each day fresh batches of 9-day fermented PECP were mixed with the ensiled pulp and soybean meal according to the proportions indicated in Table 1. Feeding was twice daily at 8:00m and 16:00pm. The amounts offered (about 4% of LW on DM basis) were adjusted daily to minimize refusals. Residues were collected and weighed prior to offering fresh feed.

Photo 1. Housing of the pigs	Photo 2. Moo Laat pigs in individual pens

Data collection

The animals were weighed in the morning before feeding, at the beginning of the trial, and every 14 days thereafter. Samples of feeds offered and refusals were collected and kept frozen in plastic bags at 4⁰C until analysis.

At the end of each 14 days, samples of feed refused and offered were mixed thoroughly by hand and homogenized in a coffee grinder prior to analysis.

Chemical analysis

Samples were analyzed for DM and nitrogen according to procedures in AOAC (1990). For the true protein measurement, the sample was mixed with trichloracetic acid and allowed to stand for 24h prior to being filtered through Whatman No 4 paper and determining the N in the filtrate by standard Kjeldahl procedures (AOAC 1990).

Statistical analysis

Daily live weight gains of the pigs were determined from the linear regression of live weight on days in the experiment. Responses in DM intake, live weight gain and DM feed conversion, according to proportion of PECP in the diet, were assessed by fitting polynomial regression equations where X was the diet proportion of PECP protein and Y the measured variable.

Results and discussion

Diet composition

The concentrations of crude and true protein in the feed ingredients are shown in Table 2.

Feed intake, growth rate and feed conversion

DM feed intake was maintained when PECP replaced soybean meal at the level of 28% of the dietary protein but at higher rates of substitution of the protein, feed intake decreased dramatically such that at 94% substitution of diet protein, DM intake was only 1% of live weight (Table 3; Figure 1). The trends for live weight gain (Figure 2) were similar except there was an indication of increased growth rate (from 125 to 153 g/day; SEM ± 12) at the 28% PECP level, followed by the same dramatic decrease in growth rate with higher levels of substitution of PECP in the diet, to only slightly above maintenance at the 94% level of protein from PECP.

The trend for DM feed conversion (Figure 3) indicated little change (FCR 4.09, 3.51, 3.69) for levels of PECP protein from 0 to 60% of the diet protein, but with the conversion rate deteriorating to 6.97 at 94% protein substitution by PECP.

Figure 1. Effect of protein enriched cassava pulp replacing soybean meal on DM intake of Moo Laat pigs	Figure 2. Effect of protein enriched cassava pulp replacing soybean meal on live weight gain of Moo Laat pigs

Figure 3. Effect of protein enriched cassava pulp replacing soybean meal on feed conversion in Moo Laat pigs

It has been shown conclusively (Vanhnasin et al 2016; Manivanh et al 2016; Sengxayalth and Preston 2017) that when cassava pulp (or cassava root) is fermented with urea, DAP and yeast, not all the NPN is converted to true protein, and that some 30% of the original urea and DAP remains as some form of NPN possibly ranging from ammonium salts to peptides and amino acids (AA). There is evidence in humans that NPN in the form of ammonium chloride was partly converted to amino acids by the action of microbes in the small intestine (Patterson et al 1995) and Stein et al 1996). Colombus et al (2014) infused urea into the cecum of pigs fed a diet deficient in the amino acid valine, and showed that it was recycled to the small intestine where it was converted by bacteria into amino acids with the result that N retention was increased. These findings were corroborated by Mansilla et al (2015).

Amino acid synthesis from dietary NPN could be the explanation for the positive effects on growth rate at the lower level of substitution of soybean protein by PECP (Figure 1), since protein was set at the limiting level of 10% of diet DM. At this level of dietary protein, additional amino acids resulting from microbial synthesis of amino acids from NPN could have played a critical role in increasing growth rate. However, at higher rates of substitution of 60 and 90% of the soybean protein by PECP, the levels of residual NPN (ammonia?) may have exceeded the capacity of the gut microbes to synthesize it into amino acids with resultant toxic effects of the ammonia leading to reduced feed intake and therefore reduced growth rate.

The other factors to be taken into consideration are the possible “prebiotic and probiotic” effects arising from the live yeast and lactobacilli present in the fermented cassava pulp. Thiep (2017 unpublished data) reported concentrations of yeast of 9 million CFU/g and lactobacilli 17 million CFU/g in cassava pulp fermented with yeast, urea and DAP. Positive effects on N retention in Moo Laat pigs were reported by Sivilai et al (2017) when rice distillers’ by-product and brewers’ grains were fed at 4% of the diet DM. Both these dietary supplements are equally rich in live yeast and lactobacilli (Thiep 2017, unpublished data).

We propose: (i) that the improved growth rate from low level supplementation with protein enriched cassava pulp may have been the result of an increase in amino acid supply arising from microbial protein synthesis from residual ammonia in the feed coupled with the beneficial effects on the immune system arising from prebiotic and probiotic properties of the yeast and lactobacilli in the yeast fermented cassava pulp; and (ii) that the reduction in growth rate when the PECP provided 60 and finally 90% of the dietary protein was due to the residual NPN negatively affecting feed intake and therefore growth rate, because the quantity of NPN increasingly exceeded the capacity of the gut microbes to utilize it.

Conclusions

• DM feed intake was not affected when PECP provided 28% of the dietary protein but at higher rates of substitution, feed intake decreased dramatically such that at 94% substitution of diet protein, DM intake was only 1% of live weight.
  
  
• The trends for live weight gain were similar except there was an indication of increased growth rate (from 125 to 153 g/day; SEM ± 12) at the 28% level of soybean protein substitution by PECP, followed by the same dramatic decrease in growth rate with higher levels of substitution of PECP.
  
  
• It is proposed that the improvement in growth with 30% substitution of soybean protein by PECP arose from microbial synthesis of amino acids in the intestine from dietary NPN (ammonia?) present in the PECP.; and that the precipitous decline in feed intake and in growth rate, when the PECP exceeded 30% of the dietary protein, was the result of the presence of excess ammonia, and/or its metabolites, due to their incomplete conversion to yeast protein in the fermentation.

Acknowledgements

This research was done by the senior author with support from NUFU as part of the requirements for the MSc degree in Animal Production "Specialized in Response to Climate Change and Depletion of Non-renewable Resources" of Cantho University, Vietnam. The authors acknowledge support for this research from the MEKARN project financed by Sida. Special thanks to Mrs Le Thi Thuy Hang and Mr Ho Xuan Nghip who provided valuable help in the laboratory

References

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Received 10 August 2017; Accepted 19 August 2017; Published 1 September 2017

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