Citation of this paper

Effect of sweet potato tuber by-product provision on feed intake, nutrient digestibility and nitrogen retention of Boer crossbred goats

Nguyen Binh Truong^1,2* and Tran Trung Tuan^1,2

¹ An Giang University, An Giang, Vietnam
* nbtruong@agu.edu.vn
² Vietnam National University Ho Chi Minh City, Vietnam

Abstract

This study aimed to determine the effect of sweet potato tuber by-products on feed consumption, nutrient digestibility and nitrogen retention in goats. The study was carried out from September to December 2023 at the experimental farm of An Giang University, Vietnam National University Ho Chi Minh City, Vietnam.

Five Boer crossbred goats about 9 months old (23.4±1.91 kg) were used for the Latin Square design with 5 treatments and 5 periods (21 days/period). The difference between the five treatments was sweet potato tuber by-product at 0, 10, 20, 30 and 40% dry matter intake (DMI) corresponding to SPTB0, SPTB10, SPTB20, SPTB30 and SPTB40 treatments. The feed basic was tofu waste, soybean meal, operculina turpethum vines, elephant grass, urea and premix. The result showed that the SPTB40 treatment was higher DMI (p<0.05) than SPTB0, SPTB10 and SPTB20 but it was not different (p>0.05) with SPTB30 treatments (770, 546, 622, 7637 and 688 g/goat/day, respectively). However, the proportion of DMI/body weight (%) was lowest (p<0.05) in SPTB0 (1.97%) and highest in SPTB40 treatments (2.69%) but SPTB10 (2.27%), SPTB20 (2.29%), SPTB30 (2.46%) and SPTB40 were not different (p>0.05) in this study. The nutrient digestibility was different (p<0.05) in the experiment for dry matter, organic matter, neutral detergent fiber and acid detergent fiber. The value was highest in the SPTB40 treatment (79.0, 79.8, 70.4, 56.3%) and lowest in the SPTB0 treatment (61.7, 63.3, 55.0, 37.3%, respectively). However, crude protein digestibility was not different (p>0.05) in this study about 80.8-83.5%. Nitrogen retention was 9.84, 11.1, 11.0, 12.5 and 13.7 g/goat/day corresponding to SPTB0, SPTB10, SPTB20, SPTB30 and SPTB40 treatments.

Therefore, 30% of sweet potato tuber by-products was good for goats in the present study.

Keywords: small ruminants, feeds, digestibility, rumen, agricultural by-products

Introduction

In recent years, goat production has played an important role in rural areas in Viet Nam, contributing income improvement of thousand households. Goat population in Viet Nam increased from 1.29 to 2.65 million heads bet ween 2010 and 2020, equivalent to an average annual increase of 10.5% (Don et al 2023). Developing ruminant production based on local feed resources such as peanut, watermelon and potato vines are an essential factor to reduce feed cost have been done. However, the utilizing starch content from agricultural by-products still are potential sources for dietary ruminant and reducing methane emission (Nhu et al 2016 and Dung, 2014).

According to Tham and Hanh (2023), harvested sweet potato tubers had a yield to be 26.97 tons/ha and the yield of their by-products was 4.76 tons/ha (tubers did not meet commercial standards concerning the tuber size and other agents). Sweet potato tuber by-product (SPTB) were tubers that did not meet market standard such as less than 50g scratches due to harvesting, rat bites and defects due to diseases caused by Cylas formicarius (Thu et al 2021 and Linh et al 2016). Average nutrient contents in sweet potato tuber byproduct were 27.9% DM, 3.12% CP, 20.8% NDF and 7.78% ADF (Tham and Hanh 2020). This tuber considered as potential energy source due to high nitrogen free extract content (Dominquez 1992). In vitro study used sweet potato flour to replace corn starch at level of 0, 33, 66 and 100%. The result showed that there was an increasing linear difference between dietary fermentation parameters and the degree of replacement of sweet potato flour, therefore sweet potato starch can be a viable starch source in ruminant diets (Demarco et al 2020).

This study determined the effect of providing sweet potato tuber by-products in goat diets on feed intake, nutrient digestibility and nitrogen retention.

Materials and methods

Location

The experiment was conducted at the experimental farm in An Giang University, An Giang Province, Vietnam. Five crossbred Boer goats, with an average initial body weight used in this experiment, was 23.4±1.91 kg at about 9 months old. The feeds and refusals were analyzed at laboratory E205 of the Faculty of Animal Sciences, Agriculture University of Can Tho University.

Animals and experimental design

The experiment was designed as Latin Square with 5 treatments and 5 periods. Five treatments were supplied sweet potato tuber by-product at 0% (SPTB0), 10% (SPTB10), 20% (SPTB20), 30% (SPTB30), and 40% (SPTB40) (Table 1).

Table 1. Ingredient composition of the diet
Ingredient composition, % DM	Treatments
Ingredient composition, % DM	SPTB0	SPTB10	SPTB20	SPTB30	SPTB40

Sweet potato tuber by-product	0.00	10.0	20.0	30.0	40.0
Tofu waste	5.00	5.00	5.00	5.00	5.00
Soybean meal	5.00	5.00	5.00	5.00	5.00
Operculina turpethum vines	40.0	40.0	40.0	40.0	40.0
Elephant grass	49.5	39.3	29.2	19.0	8.80
Urea	0.290	0.465	0.645	0.820	1.00
Premix	0.200	0.200	0.200	0.200	0.200
Total	100	100	100	100	100

Feeding procedure

All the feeds were weighed before feeding and supplied separately to the experimental goats. In detail, the sweet potato tuber by-product was fed at dry matter consumption depending on treatments. The tofu waste, soybean meal and urea were mixed with premix supplements before feeding. Forage sources were fed ad libitum and drinking water was always available. Refused feeds were weighed each morning.

Measurements

Feed offered, refusals and feces were analyzed for dry matter (DM), organic matter (OM) and ash contents according to the procedures of AOAC (1990), and the nitrogen (N) content of the feeds, refusals, feces, and urine were analyzed using the Kjeldahl methods (AOAC, 1990). However, neutral detergent fiber (NDF) and acid detergent fiber (ADF) were analyzed by the procedure of Van Soest et al (1991).

The apparent digestibility of DM, OM, CP, NDF, and ADF was done following the method of McDonald et al (2010). Each period lasted for 3 weeks with 2 weeks for adaptation time, followed by 1 week for data collection of feed intake, feces, and urine to determine the nutrient digestibility and nitrogen retention.

The metabolizable energy (ME) was calculated by Bruinenberg et al (2002), in which ME (MJ/animal/day) = 14.2 x DOM + 5.9 x DCP (with DOM/DCP<7.0) of the diets or ME (MJ/animal/day) = 15.1 x DOM (with DOM/DCP>7.0). Where: DOM is digestible organic matter and DCP is digestible crude protein.

Daily N retention was calculated by daily collected N intake, N feces and N urine as following formula: N retention = N intake - (N feces + N urine).

The goats were weighed on two consecutive days at the beginning and end of each experimental period.

Statistical analysis

The data were analyzed using the ANOVA Linear Model (GLM) of Minitab Reference Manual Release 20 (Minitab, 2021). Tukey's pairwise comparisons (p<0.05) were applied to determine differences between treatments. Data were analyzed using the model Y _ijk = µ + T _i + A _j + P _k + e_ijk; where Y_ijk: = the dependent variable, µ: the overall mean, T _i = the effect of treatment (i = 1 to 5), A_j: the effect of animal (j = 1 to 5), P _k = the effect of period (j = 1 to 5), e _ijk = the random error.

Results

Chemical composition of ingredients using in this experiment

Table 2. Chemical composition of ingredients
Ingredients	DM, %	in DM, %
Ingredients	DM, %	OM	CP	PS	NDF	ADF

SPTB	26.9	97.0	2.34	14.30	39.4	7.88
Tofu waste	18.8	96.8	15.7	4.45	34.4	23.4
Soybean meal	85.4	92.9	43.4	2.22	23.8	19.5
Operculina turpethum vines	12.3	87.1	15.8	3.98	41.8	31.3
Elephant grass	13.9	90.3	9.84	2.67	68.2	33.6
Urea	99.6	-	286		-	-
SPTB: sweet potato tuber by-product

Feed and nutrient intake

Table 3. Feed and nutritive intakes of goat
Criteria	SPTB0	SPTB10	SPTB20	SPTB30	SPTB40	SEM	p

Feed intake, g DM/animal/ day
SPTB	0 ^e	65.6 ^d	132 ^c	219 ^b	314 ^a	10.10	0.001
Tofu waste	26.7 ^b	29.5 ^ab	29.3 ^ab	33.1 ^ab	35.1 ^a	1.670	0.028
Soybean meal	27.6 ^b	30.6 ^ab	30.3 ^ab	34.2 ^ab	36.3 ^a	1.760	0.031
Operculina turpethum vines	236	259	263	289	303	17.50	0.128
Elephant grass	255 ^a	233 ^a	177 ^ab	106 ^bc	73.1 ^c	20.00	0.001
Urea	2.23 ^d	3.51 ^cd	4.30 ^bc	5.81 ^ab	7.21 ^a	0.447	0.001
Premix	1.10 ^b	1.21 ^ab	1.20 ^ab	1.36 ^ab	1.44 ^a	0.068	0.028
Nutritive intakes, g DM/ animal/ day
DM	549 ^c	622.3 ^ba	637 ^ab	688 ^ab	770 ^a	27.50	0.001
DM/BW, %	1.97 ^b	2.27 ^ab	2.29 ^ab	2.46 ^ab	2.69 ^a	0.106	0.006
OM	495 ^c	563 ^bc	579 ^bc	629 ^ab	707 ^a	24.80	0.001
CP	92.2 ^b	99.5 ^ab	98.0 ^ab	105 ^ab	118 ^a	4.660	0.022
PS	18.0 ^e	27.9 ^d	36.1 ^c	47.9 ^b	61.3 ^a	1.790	0.001
CP/DM, %	16.8	16.0	15.4	15.2	15.3	0.430	0.094
PS/CP, %	19.5 ^e	28.0 ^d	36.7 ^c	45.9 ^b	52.2 ^a	0.861	0.001
NDF	253	279	271	268	285	15.40	0.654
ADF	137	147	137	127	132	8.680	0.613
ME, MJ/ animal/ day	4.88 ^c	6.01 ^bc	6.40 ^bc	7.33 ^ab	8.60 ^a	0.368	0.001
Output, animal/ day
Feces, gDM	211 ^a	203 ^ab	186 ^ab	174 ^ab	161 ^b	10.20	0.026
Urine, g	1,766	1,891	1,798	1,682	1,750	88.80	0.582
SPTB: sweet potato tuber by-product ^abcd Mean values within rows with different superscript are different at p<0.05

Apparent digestibility

Table 4. Apparent digestibility of nutrients in this study
Criteria	SPTB0	SPTB10	SPTB20	SPTB30	SPTB40	SEM	p

Digestibility, %
DMD	61.7 ^d	66.9 ^cd	70.9 ^bc	75.0 ^ab	79.0 ^a	1.690	0.001
OMD	63.3 ^c	68.8 ^bc	72.2 ^ab	76.4 ^ab	79.8 ^a	1.710	0.001
CPD	81.9	81.0	80.8	83.1	83.5	1.650	0.706
NDFD	55.0 ^b	60.7 ^ab	61.1 ^ab	66.4 ^ab	70.4 ^a	2.850	0.023
ADFD	37.3 ^b	46.2 ^ab	48.2 ^ab	50.7 ^ab	56.3 ^a	3.860	0.050
Digestibility, g DM/animal/ day
DDM	338 ^c	419 ^bc	451 ^bc	515 ^ab	609 ^a	26.30	0.001
DOM	312 ^c	390 ^bc	417 ^bc	480 ^ab	565 ^a	24.00	0.001
DCP	75.8	80.9	79.2	86.8	98.3	5.310	0.077
DNDF	139	173	165	176	201	14.90	0.120
DADF	50.9	70.9	65.7	64.0	74.4	8.330	0.375
SPTB: sweet potato tuber by-product ^abcd Mean values within rows with different superscript are different at p<0.05

Figure 1. Dry matter digestibility is increased with a curvilinear trend as the feeding level of SPTB was increased

Nitrogen balances and weight gain

Table 5. Nitrogen balances and average weight gain of goats in this study.
Criteria	SPTB0	SPTB10	SPTB20	SPTB30	SPTB40	SEM	p

N balances, g/ animal/ day
N intake	14.7 ^b	15.9 ^ab	15.7 ^ab	16.7 ^ab	18.8 ^a	0.745	0.022
N feces	2.63	2.97	3.02	2.83	3.12	0.159	0.282
N urine	2.28	1.81	1.67	1.37	2.03	0.368	0.459
N retention	9.84	11.1	11.0	12.5	13.7	1.010	0.131
N retention/ BW ^0.75	0.81	0.93	0.91	1.03	1.10	0.081	0.166
Body weight, kg
Initial	27.4	27.0	27.0	26.9	27.7	0.453	0.655
Final	28.3 ^b	28.3 ^ab	29.0 ^ab	29.2 ^ab	29.8 ^a	0.345	0.034
Average daily gain, g/ animal/ day	40.9	62.9	94.5	110	102	19.50	0.129
SPTB: sweet potato tuber by-product ^ab Mean values within rows with different superscript are different at p<0.05

Figure 2. Average daily weight is increased with a curvilinear trend
as the feeding level of SPTB was increased

Discussion

The results in Table 3 revealed the SPTB provision affected (p<0.05) the DM intake (g/goat/day) and DM/BW (%). Moreover, the calculated ME intake of goats fed the SPTB40 treatment was higher twofold compared to the SPTB0 treatment. In this study, the SPTB40 treatment displayed the highest DM, OM and CP intake values (770, 707 and 118 g/goat/day, respectively). However, the provision of SPTB did not affect NDF and ADF intakes among treatments (p>0.05). It was hypothesized that providing SPTB in goat diets may increase the DM intake of goats leading to an improvement of productivity. Demarco et al. (2020) claimed that sweet potatoes can be an effective source of starch in ruminant diets. Because, sweet potato root starch is a fiber-free carbohydrate, microbial fermentation occurs faster. In agreement with the results of nutrient intakes from Truong et al. (2024), when goats were fed with a starch combination of corn and cassava chip, corn and wheat, broken rice and cassava chip, broken rice and wheat. Moreover, the result from the SPTB40 diet agreed with the NRC Recommendation (2007), which recommended that ME and CP intake should be 8.72 MJ and 94.5 g, respectively; and Steele (2006) recommended ME intake for goats at 30 kg live weight in tropical areas should be above 7.2 MJ and CP intake for cereal diet was 10-12% in DM intake.

The nutrient digestibility as affected by the provision of SPTB is shown in Table 4. DM digestibility (%) in goats receiving SPTB addition was higher than that of the control goats (p<0.05). The DM digestibility (%) with linear increases (Figure 2) when diets provided up to 40% of diets (y = 0.427x + 62.16, R ² = 0.997). Providing SPTB in the goat diet significantly increased (p<0.05) the OM digestibility (%) compared to without providing group. However, there were no significant differences (p>0.05) in the CP digestibility (%) among diets. Both NDF and ADF digestibility (%) were increased (p<0.05), but the differences in digestive nutrients (g/goat/day) were non-significant (p>0.05) when providing goats with SPTB. The results showed that the provision of 40% SPTB into the goat diet displayed the highest values of DM, OM, CP and NDF (% and g/goat/day). The noticeable improvement in digestibility of DM and OM could be attributed to SPTB provision into goat diets. Previous in vitro research indicated that fermentation parameters of diets containing sweet potato flour replacing corn at levels of 0, 33, 66 and 100% in ruminant diets were increased linearly (Demarco et al 2020). Starchy diets alter microbial ecosystems by favoring more propionic acid production (Bannink et al 2006). Moreover, Kumar et al (2013) claimed that high starch in diet produced less methane. The nature of the rumen fermentation in terms of methane production. Less methane means more propionic acid, therefore more glucose at sites of metabolism and increased animal productivity (Preston and Leng, 1987). The result of the SPTB30 treatment agreed with Truong et al (2024), when goats were fed with a 30% starch combination of corn and cassava chip, corn and wheat, or broken rice and cassava chip, or broken rice and wheat, however higher when provided up to 40%.

The data in Table 5 shows the SPTB provision into diets affected by nitrogen balances and body weight of crossbred Boer goats. Overall, there was a linearly increased in nitrogen intakes when providing SPTB into diets (p<0.05) with the highest value in SPTB40 (18.8 g/animal/ day) compared to without provision (14.7 g/ animal/ day). The SPTB addition did not affect N retention and N retention/ BW0.75 of the goats (p>0.05), although the N retention of the goats provided with SPTB was quantitatively higher than that of the goats consumed basal diet only (13.7 g of SPTB40 compared to 9.84 g of basal diet). Moreover, dietary provision of SPTB had a significant effect on the final body weight of goats (p<0.05) in Figure 2; and the average daily gain (ADG) of goats fed a diet providing 30% SPTB was higher about two times than goats consumed without provision of SPTB. Previous publications indicated that the increase in the percentage of starch in the diet promoted the synthesis of microbial proteins (Zhang et al 2015; Gómez et al 2016). Under an environment of abundant nitrogen supply, the fermentation of carbohydrates affected the efficiency of microbial protein synthesis in the rumen (Feng et al 1993; Hall and Herejk, 2001).

Conclusions

It was concluded that increasing SPTB supplement levels in the diets of Boer crossbred goats improved feed and nutrient intake, feed conversion, and daily weight gain.

A level of 30% SPTB in the diet would be recommended to implement performance studies in the goat for better local by-product source utilization for farmers.

Acknowledgements

This research is funded by An Giang University (AGU) under grant number 23.09.NN. The Author thanks the experimental farm, An Giang University, Vietnam National University Ho Chi Minh City (VNU-HCM).

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