Citation of this paper

Effects of replacement of fish meal and soybean meal by brewers’ yeast extract on growth and feed conversion of Landrace x Yorkshire pigs

Ha Xuan Bo, Ho Tuan Anh¹, Phan Xuan Hao, Phan Thi Tuoi² and Do Duc Luc

Faculty of Animal Science, Vietnam National University of Agriculture, Vietnam
hxbo@vnua.edu.vn
¹ Faculty of Food Technology, University of Economics - Technology for Industries, Vietnam
² Faculty of Agriculture - Forestry - Fishery, Hong Duc University, Vietnam

Abstract

This study was conducted at Phu Dong farm in Gia Lam district, Hanoi, Vietnam from June to December 2018. Landrace x Yorkshire fattening pigs (92 gilts and 92 barrows) were fed diets in which fish and soybean meals were replaced by 0, 2, 4 and 6% high-protein (73% CP) brewers’ yeast extract (BYE) on equal protein basis. There were 3 replicates per treatment with 15, 15 and 16 pigs in the first, second and third treatment/replicates.

Partial replacement of fish meal and soybean meal by brewers’ yeast extract (BYE) in the diet of growing-fattening pigs increased growth rate and improved feed conversion and did not affect carcass quality. It is likely that BYE is a superior source of protein than spent brewers’ grains as in the former it is derived 100% from the yeast cell contents while in the latter is from a combination of the residual protein from the cereal grain used in the brewing process plus that from the spent yeast. The advantage of BYE is that the extraction process incorporates the hydrolysis of the yeast cell wall thus ensuring the presence of β-glucan – a proven “prebiotic“ - in the final product.

Keywords: β-glucan, brewers’ spent grain, prebiotic, protein replacement, Vietnam

Introduction

Vietnam is one of the top beer consuming countries and the growth rate of alcoholic production is estimated to reach 10 to 15 percent annually. Yeast biomass generated from the brewing industry is of the order of 1.5 kg of yeast extract powder for every 1000 liters of beer (Nguyen Thi Hoang Anh et al 2008). Beer production in Vietnam is estimated to be from 2.5 to 3.0 billion liters annually, which means that about 3500 to 4000 tons of brewers’ yeast extract (BYE) powder are produced per year (Pham Quynh Trang 2012). The poor utilization of this by-product is a serious source of environmental pollution.

Yeast fermentation derivatives - yeast cells and yeast extracts - have long been known as alternative sources of protein in animal feeds (Trinh Vinh Hien 2010). Yeast cell wall is a gluco-manano-lipo-protein complex. The cell wall glucans are polymeric structures in which monomers are glucose bounded by β-1.3 and β-1.6 linkages (Popova 1992). β-glucan has been recognized for its capacity to bind and activate specialized cells that are related to the immune system. By triggering these responses, β-glucan increases the body's immunity against infection and disease (ICFOOD 2014). Yeast byproducts are also rich in other nutrients as well as protein, such as minerals and B-vitamins. In addition, yeast extracts have bioactive components that prevent pathogen growth and modulate the immune system (Shurson 2018).

Many studies have shown that brewers’ yeast extracts have been used as alternative sources of animal feed and provide beneficial effects on animal growth and health (Nguyen Thi Hoang Anh et al 2008; Trinh Vinh Hien 2010; Pham Quynh Trang 2012). However, according to our knowledge, information on effects of BYE in diets for fattening pigs in Vietnam has not previously been reported.

The aim of our study was to evaluate the effects of partially replacing of fish meal and soybean meal by brewers’ yeast extract on growth performance and feed conversion of fattening pigs in Vietnam.

Materials and methods

Experimental design, animals and diets

This experiment was conducted on 184 Landrace x Yorkshire fattening pigs (92 gilts and 92 barrows) of 2 months of age at Phu Dong pig farm in in Gia Lam district, Hanoi, Vietnam from June to December 2018. There were 3 replicates for each of the 4 treatments with 46 pigs (23 gilts and 23 barrows) in each treatment. The experiment was divided into two phases (growing and finishing phase). The pigs were kept in closed pens, with free access to feed and water. The pigs were vaccinated according to the standard procedures of the farm.

Diets

The experimental diets were formulated as detailed in Table 1.

Table 1. Feed ingredients in the diets (% air-dry basis)
Ingredient	% BYE (20 to 45 kg)				% BYE (45 to 100 kg)
Ingredient	0	2	4	6	0	2	4	6

BYE	0.00	2.00	4.00	6.00	0	2.00	4.00	6.00
Soybean meal	20.00	18.00	16.30	14.30	13.00	11.00	9.00	7.00
Fish meal	5.00	3.50	2.00	0.50	4.50	3.00	1.50	-
Maize	47.30	48.70	49.80	51.20	48.50	49.70	50.90	52.10
Wheat bran	24.00	24.00	24.00	24.00	30.00	30.00	30.00	30.00
Vegetable oil	1.00	1.10	1.20	1.30	1.00	1.30	1.60	1.90
Premix	0.25	0.25	0.25	0.25	0.25	0.25	0.25	0.25
Methionine	0.10	0.10	0.10	0.10	0.10	0.10	0.10	0.10
Lysine	0.20	0.20	0.20	0.20	0.10	0.10	0.10	0.10
Dicalcium phosphate	1.80	1.80	1.80	1.80	2.00	2.00	2.00	2.00
Bazyme#	0.00	0.00	0.00	0.00	0.10	0.10	0.10	0.10
Salt	0.25	0.25	0.25	0.25	0.35	0.35	0.35	0.35
Toxisorb@	0.10	0.10	0.10	0.10	0.10	0.10	0.10	0.10
# Enzymes protease, amylase and phytase for protein and starch digestion @ SiO2, Al2O3 and Fe2O3 for mycotoxin absorption

The chemical composition of the diets (Table 2) was determined by the methods of AOAC (1990).

Table 2. Chemical composition of experimental diets (air-dry basis)
Nutrient	% BYE (20 to 45 kg)				% BYE (45 to 100 kg)
Nutrient	0	2	4	6	0	2	4	6

Dry matter (%)	88.92	89.04	89.11	89.22	89.30	89.41	89.44	89.50
Crude protein (%)	18.82	18.02	18.64	18.19	15.75	15.83	15.78	15.61
Crude fat (%)	3.86	4.02	4.20	4.11	4.58	4.58	4.52	4.51
Crude fiber (%)	4.35	4.54	3.94	3.54	4.97	4.87	4.79	4.73
Ash (%)	5.11	5.05	4.87	5.00	4.38	3.96	4.34	3.81
Calcium (%)	0.54	0.57	0.60	0.61	0.50	0.52	0.55	0.56
Phosphorus (%)	0.73	0.61	0.74	0.74	0.71	0.74	0.74	0.76
ME (kcal/kg)	3234	3230	3308	3311	3246	3295	3282	3320

Brewers’ yeast extract (BYE)

The BYE used in this experiment was supplied by the project: “Applied biotechnology in recycling by-products from beer production as animal feed in Hanoi”. It was produced according to the following protocol: the brewers’ yeast waste was pre-treated with NaOH (320 mg/L) for 60 minutes to remove bitter substances. The suspension was then centrifuged at 6000 rpm for 20 minutes. The biomass was hydrolysed by suspension in water (ratio 1:2.5) with added β-glucanase at 55°C during 48h. β-glucanase was added in the hydrolysate to increase the hydrolysis of the yeast cell wall and thus obtain more β-glucan in the extract. The hydrolyzate was then centrifuged at 4500 rpm for 25 minutes to separate the yeast cell wall from the yeast cell contents. The extract obtained after centrifugation was concentrated up to 25-26% dry matter by heating at 100°C and the water vapour was removed by exhaust fan. The mixture obtained after concentration was spray-dried at pressure of 0.6 Mpa with a spinning disk at 1800 rpm, inlet air temperature of 150°C and outlet temperature of 50 – 60°C. The final product (BYE) contained total nitrogen of 11.7% in DM, equivalent to 73.1% protein, of which amino-nitrogen (as N*6.25) accounted for 5.2%. Residual moisture was 4.8% and NaCl 1%.

Data collection

Initial and final live weights for each growth phase were determined with a Mettler Toledo scale. At the end of the finishing phase, backfat thickness (BFT) and depth of longissimus dorsal muscle (DLD), between the third and fourth last rib, were measured by ultrasound (Agroscan ECM, France) at 6 cm from the middle line, following the methods of Youssao et al (2002). Feed conversion ratio (FCR) was calculated from body weight gain and feed intake.

Statistical analyses

The data were analysed according to the linear model in the ANOVA program of the SAS software (SAS 1989). Sources of variation were: diet, sex and interaction between these factors as presented in the model:

Y_ijk = µ + DIET_i + Sex_j + DIET_i *Sex_j + e_ijk

Where, Y_ijk = IBW, FBW, ADG, BFT, DLD, LMP, FI or FCR of pig k, sex j and DIET i; µ = overall mean; DIET_i = fixed effect of diet i (CON, T1, T2 and T3); Sex_j = fixed effect of sex j (gilt and barrow); DIET_i*Sex_j = interaction between diet and sex; e_ijk = residual errors.

Results

In both growth and finishing phases the feed intake was reduced and live weight gain and feed conversion were improved as fish meal and soybean meal were replaced by BYE (Tables 3 and 4). Backfat thickness and depth of muscle over third - fourth last rib were not affected by source of diet protein (Table 4).

Table 3. Effects of brewer yeast extract replacement in the diet on production performance and feed conversion ratio of Landrace x Yorkshire fattening pigs in the growing phase
	n	BYE, %				SEM	p
	n	0	2	4	6	SEM	p

Initial LW (kg)	46	20.1	20.1	19.9	19.9	0.217	0.835
Final LW (kg)	46	45.0	45.0	45.1	45.3	0.388	0.959
Daily gain (g)	46	498^b	526^ab	540^ab	545^a	12.8	0.0461
Feed intake (kg)	3	1156^a	911^b	893^b	842^b	19.2	0.0027
Feed conversion	3	2.53^a	2.38^b	2.30^b	2.16^c	0.030	<0.001
^abc Within a row, means without a common superscript differ at p<0.05

Table 4. Effects of brewer yeast extract replacement in the diet on production performance and feed conversion ratio for Landrace x Yorkshire fattening pigs in the finishing phase
	n	BYE, %				SEM	p
	n	0	2	4	6	SEM	p

Initial LW (kg)	46	45.0	45.0	45.1	45.3	0.388	0.959
Final LW (kg)	46	96.2	97.7	98.7	99.5	1.29	0.264
Daily gain (g)	46	689^b	730^ab	756^ab	760^a	19.0	0.0312
Backfat (mm)	46	15.1	15.1	15.3	15.7	0.299	0.544
Muscle (mm)	46	58.0	58.9	58.3	57.8	0.668	0.678
Feed intake (kg)	3	2297	2081	2035	2080	47.8	0.435
Feed conversion	3	2.92^a	2.58^b	2.48^c	2.50^c	0.0153	<.0001
^abc Within a row, means without a common superscript differ at p<0.05

Discussion

The overall effects of partially replacing fish and soybean protein with brewers’ yeast extract (BYE) were curvilinear trends (R² >0.97) for a decrease in feed intake, and improvements in live weight gain and feed conversion (Figure 1).



Figure 1. Effects on feed intake, live weight gain and feed conversion of brewers’ yeast extract replacing fish meal and soybean meal in diets of fattening pigs over the weight range 20-98 kg live weight

Similar results were reported when forage-based diets were fed to native Moo Lath pigs during the growth phase (Sivilai et al 2017) and during pregnancy-lactation (Sivilai et al 2018). Sivilai et al (2017, 2018) fed the “unprocessed ” brewers’ spent grains – mainly composed of residual unfermented grain and “spent” yeast - hence the much lower content of protein (about 26% in DM) compared with the BYE (73% protein). Positive effects on growth of cattle, goats and pigs from feeding low quantities (4% of diet DM) of spent brewers’ grains or rice distillers’ byproduct (the residue after fermentation-distillation of rice to make “wine”) were attributed to the “prebiotic” effect of the β-glucan released from the yeast cell wall during the fermentation stage. The contrast between BYE and Spent Brewers’ Grains (and rice distillers’ byproduct) is that supposedly the benefits from BYE relate to the superior biological value of the protein in the yeast extract compared with the protein in spent brewers’ grains, which is derived in part from the original barley (or rice) grains as well as residual spent yeast. Both BYE and brewers’ spent grains byproduct are presumed to contain β-glucan, although the exact quantities in each are not known. However, it is likely that BYE is a much superior source of protein than spent brewers’ grains as in the former it is derived 100% from the yeast cell contents while in the latter is from a combination of the residual protein from cereal grain plus that from the yeast. There is an obvious need to have more precise information concerning the concentrations of β-glucan in both BYE as well as in spent brewers’ gains and rice distillers’ byproduct (Hien in the Vietnamese language).

The benefits of mannanoligosaccharides (MOS) for animal health and growth have been ascribed to several factors: as sources of digestive enzymes (Kemp and Kiser 1970); and because they bind and limit the colonization of pathogens in the gastrointestinal tract, improving the integrity of the intestinal mucosa, enhancing immune system activity, and being involved in antioxidant and antimutagenic defenses (Spring et al 2015; Zhao et al 2012). The immunomodulator function of β-glucan may positively eﬀect digestion and absorption rate by strengthening the immune system, maintaining gut health in the face of infectious diseases, and inhibiting the production of cytokines and inflammatory response to save the nutrients for growth (Hiss and Sauerwein 2003). Zhang et al (2019) reported that yeast hydrolysate resulted in increased digestibility of feed in growing-finishing pigs.

There are thus a number of factors that could explain the superiority of brewers’ yeast extract (BYE) compared with combined fish meal and soybean meal as a protein source for growing-fattening pigs.

Conclusions

Partial replacement of fish meal and soybean meal by brewers’ yeast extract (BYE) in the diet of growing-fattening pigs increased growth rate and improved feed conversion and did not affect carcass quality.
It is likely that BYE is a superior source of protein than spent brewers’ grains as in the former it is derived 100% from the yeast cell contents while in the latter is from a combination of the residual protein from the cereal grain used in the brewing process plus that from the spent yeast.
The advantage of BYE is that the extraction process incorporates the hydrolysis of the yeast cell wall thus ensuring the presence of β-glucan – a proven “prebiotic“ - in the final product.

Acknowledgement

The study was conducted as a part of project to apply Biotechnology in recycling by-product from beer production as animal feed in Hanoi (code number: TC.01-2016-03), granted by technological apply and development funds of Hanoi City. The authors thank the owner, technicians and workers who participated and supported to this study.

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Received 1 April 2020; Accepted 23 April 2020; Published 1 June 2020

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