Sweet potato tuber and paddy rice as energy supplements for growing rabbits in the Mekong Delta of Vietnam

Nguyen Thi Kim Dong, Nguyen Van Thu and T. R. Preston*

Cantho University, Cantho City, Vietnam

ntkdong@ctu.edu.vn

*UTA, TOSOLY, AA#48, Socorro, Santander, Columbia

Abstract

A study was conducted at the experimental farm in Cantho City to evaluate the effects of energy supplement sources from paddy rice (PR) and sweet potato tuber (SPT) in the sweet potato (SP) basal diets for growing rabbits. Two experiments were 2*4 factorial designs of two factors and three replications and four rabbits per experimental unit. The first factor was supplement feed with 0.43MJ/day/animal (45 g paddy rice or 115g fresh sweet potato tuber) and the second one was the level of SP (DM basis) offered (5, 6, 7 and 8% of LW). The first trial was done on growing rabbits at 8 weeks of age to evaluate feed intake, growth performance and economic returns, while the second experiment of feed digestibility and nitrogen retention of rabbits was determined at twelve weeks of age.

In EX. 1, the dry matter (DM) and organic matter (OM) intakes were similar between supplements and among the four levels of feed offered (5, 6, 7 and 8% of LW) (P>0.05). Crude protein (CP) intake was significantly higher for the paddy rice (P<0.001) and numerically it increased with higher levels of feed offered (P=0.07). ME intakes were significantly higher (P<0.01) for the PR diet supplement and for the 8% feed offered. The daily gain and values of carcass were significantly higher for the diets supplemented PR (P<0.01) and 8% feed offered (P<0.01). The higher profits were found for the diet supplemented SPT and for the level of DM feed offered at 8% of live weight. In EX. 2 the apparent digestibility (%) of DM, OM were significantly higher in the supplemented PR diet (P<0.01) and in the diet of 8% feed (P<0.001). It was concluded that the diets including PR and offering 8% feed had higher growth performance, however, the SPT supplement gave better economic returns.

Key words: crossbred rabbits, nutrient digestibility, paddy rice, sweet potato tuber, weight gain

Introduction

Organic rabbit farming based on green forages is an opportunity for the poor farmers for producing to erase starvation and to evaluate poverty in villages of Vietnam. Within these feeding strategies, green forages are used as the main protein sources and fiber, while for the improved performance of growing and reproductive rabbits, sources of soluble carbohydrate supplementation are very important. This is a cause of low performance of the forages-fed rabbits in the villages as compared to the concentrate/pellet-fed rabbit in the industries (Nguyen Thi Kim Dong and Nguyen Van Thu, 2009). Sweet potato (Ipomoea batatas L.) is planted widely and availably by farmers in the Mekong, with both purposes for foliage and tuber production. This plant give high yield of foliage biomass that use for human and animals, with CP content ranged from 19-22% and CF content is 13.0 -19.3% (Le Van An et al., 2003). Sweet potato tuber is considered as a good soluble carbohydrate source for the mono-gastric animals, particularly the wastes of small fresh sweet potato tuber is refused by human consumption, which are cheap and could be utilized for feeding rabbits with the advantage of one-week storage. Also paddy rice is a local available energy feed source for animals in almost farmer households. Samkol, et al. (2006) reported that increasing the offer levels of water spinach from 8-18% of live weight increased the proportion of leaves consumed, the intake of crude protein and the digestibility of the DM and CP. However, the understanding of this scientific area for rabbit performance has still limited. Therefore a study of growing rabbit performance offered green forages with supplementation of fresh sweet potato tuber or paddy rice should be investigated for improving village rabbit production and farmers’ income. 

 Materials and methods

Experiment1. Feeding trial

Animals and experimental design

The experiment was conducted at Experimental farm in Cantho City. Ninety-six young crossbred rabbits (local x improved breeds) at 8 weeks of age with similar live weight around 900g were arranged in a factorial design with 2 factors and four rabbits in an experimental unit. The first factor was energy feed supplementation with 0.43MJ/day/animal (45 g paddy rice or 115g fresh sweet potato tuber) and the second one was the levels of sweet potato (SP) offered at 5, 6, 7 and 8% of live weight (DM basis). The first trial was done on growing rabbits at 8 weeks of age and three replications were applied for all experiments in the study. The experimental period lasted 10 weeks.

Feeds, feeding and management

 Sweet potato was bought daily from farmers in the city. The animals were fed three times a day at 8:00h, 15:00h and 19:00h. Sweet potato and paddy rice and sweet potato tuber were offered and recorded daily. The diets were adjusted weekly following their live weights.  Fresh water was available for all rabbits almost all day and night time. The refusals and spillage were collected and weighed daily in the morning to calculate the feed intake. The animals were vaccinated to prevent some diseases, especially rabbit hemorrhagic, parasite and other common diseases.

Measurements

The feeds and refusals were taken for analyses of DM, OM, CP, EE, NDF, ADF, and Ash following procedure of AOAC (1990) and Van Soest et al. (1991). At the beginning of the experiment four rabbits per experimental unit were weighed individually weekly. Daily feed intakes, growth rate, and feed conversion ratios were measured and calculated. The economic analysis was also done among the treatments.

Experiment 2: Digestibility trial

Animals and experimental design

The second experimental design was similar to that of the feeding trial, however, the 12-week old rabbits were used. The animals had two weeks for adaptation and another week for getting samples according to by fecal collection for 7 days. Feeds and refusals were daily measured. Urine was also collected for nitrogen analysis to calculate the nitrogen retention.  DM, CP, EE, NDF and ADF digestibility were employed according Mc Donald et al. (2002).

Statistical analysis

The data from both trials were analyzed by analysis of variance using the ANOVA of General Linear Model of Minitab Reference Manual Release 13.21 (Minitab, 2000). Economic analyses were done using current prices in Vietnamese Dong (VND) to compare differences of income and the feed cost in different treatments.

Results and discussion

Experiment 1: Feeding trial

Feed characteristics

Chemical composition of feed ingredients of rabbits is presented in Table 1.

Sweet potato had higher CP, NDF, ADF contents and lower ME component compared with the paddy rice (PG) and sweet potato tuber (SPT) (Table 1). In the study using SP was a basal feed to provide CP and fiber with energy supplementation of PR or SPT to make balanced nutrient diets for growing rabbits. The DM content of SP used in our experiment is slightly lower, but CP content is higher than the values reported by Lam Thanh Binh (2008), however, these values are lower than those reported by Le Thi Lan Phuong (2008), might be due to different variety and harvest season of sweet potato.

Feed and nutrient intakes in the Ex.1

Daily intakes of feed and nutrients are shown in Table 2.

Daily intakes of DM and most nutrients such as CP, EE and ADF, except for NDF, were significantly higher in the PR supplement diet (P<0.05), possibly due to the higher concentrations in PR and the lower contents in SPT. These values slightly increased when increasing feed levels offered from 5 to 8% SP, but being not significantly (P>0.05).  The daily ME intake had tendency higher in the SPT supplement and in the higher SP diet (P>0.05). This indicated that increasing feed level offered (8% of live weight) rabbits consumed not much different feed and other nutrients. The obtained results are not consistent to those indicated by Samkol et al. (2006) that the offered level of water spinach from 8 to 18% of live weight (DM basis). The DM intakes in present study are similar to those (74-89g/day) of rabbits fed water spinach and vegetable wastes supplemented paddy rice (Nguen Huu Tam et al., 2008), but being considerably lower than the results of 97.6-125g/day in the trial that rabbits fed sweet potato vine replaced with cassava foliage meal (Nguyen Kien Cuong et al., 2008) . The findings of CP intakes in current study are similar with those stated by Duong Thi Bich Loan (2010) (9 -13.1g/day).

Growth rate, feed conversion ratio and economic analysis in Ex.1

The results were presented in Table 3.

The significantly higher final live weight and daily gain were found for rabbits supplemented PR (P<0.05) and at level of 8% SP offered (P<0.01) (Table 3). The results of the present study were promising for production in the crossbred rabbits as compared with the weight gain of the pure New Zealand rabbits fed para grass and sweet potato vines supplemented extracted soybean with broken rice was 20.2g per day (Phan Thuan Hoang, 2009). The daily gains of rabbits in this study were also within the ranges (17 to 19g/day) reported by Duong Thi Bich Loan (2010). However, the values are higher than the results of 15.9 to 19.4g/day and 11.2- 20.9g/day) found by Nakkitset (2007) and Nguyen Van Hiep and Ngo Van Man (2008), respectively. Feed conversion ratio was quite similar between two factors (P>0.05). The obtained values for feed conversion ratio were better than those of 4.5 to 5.5 indicated by Phiny and Kaensombath (2006).

The effects of intakes of CP (g/day) and ME (MJ/day) on daily gain of growing rabbits were presented in regression equation Y1 = 0.0039 x² + 0.66x + 10.6, with regression coefficient R² = 0.818 and Y2 = - 7.78 x² + 20.9x + 6.8, with regression coefficient R² = 0.829, respectively.
 

Fig. 1. Relationship between CP and ME intakes and DG of growing rabbits

 The economic analysis was done and showed that the cost for feeds was lower in the SPT and due to being not much different feed cost among graded feed levels of live weight, and higher income in the 8% SP diet, resulting in more benefits in these diets. The results indicated that the promising diets giving better economic returns for rabbit production could be at level of 8% sweet potato with supplement of sweet potato tuber.

Mean values for slaughter weights and carcass traits of growing rabbits.

The results of carcass, lean meat and thigh meat were significantly higher in the diet supplemented PR and in the 8 %SP diet (P<0.05) (Table 4). The results in our study are better than those in a previous study of sweet potato vine basal diets supplemented molasses and soya waste of growing rabbits stated by Nguyen Truong Giang (2010).

Experiment 2: Digestibility trial

Feed characteristics

*: Calculated by Maertens et al. (2002)

Chemical composition of feeds used (Table 5) was similar to those in Experiment 1.

Daily intakes of feed and nutrients of growing rabbits in digestibility Ex.

Daily intakes of DM and most of nutrients such as CP, EE, NDF, ADF and ME of the rabbits between two factors were slightly lower than those obtained in the feeding trial, may be due to data recorded in one week of the digestibility experiment.

Apparent digestibility of dietary nutrients, nitrogen retention of growing rabbits

The apparent digestibility coefficients of DM and OM were significantly higher (P<0.05) in the PR supplement diet, possibly due to higher ADF intake in the SPT supplement diet. Also, these values considerably increased when increasing feed levels offered in the diets (P>0.001) (Table 7). Our results are also in agreement with the findings that the digestibility indices of DM and CP were improved with increasing water spinach levels offered in the diets (Samkol et al., 2006).  The obtained DM digestibility values were similar to those (65.4 to 75% and 66.6- 78.5%) of   studies reported by Akinfala et al. (2003) and Nguyen Truong Giang (2010), respectively.

The results indicated that there was no significant difference in both the nitrogen intake and nitrogen retention between two factors (P>0.05), this probable explanation is not much different CP intakes in all dietary treatments.

Conclusions  

·         The level of 8% sweet potatoes based on live weight  offered and supplementation of paddy rice gave higher rabbit  growth rate and cacass traits.

·         Supplementation of sweet potato tuber had better economic returns.

·         Nutrient digestibility was improved with increasing levels of sweet potatoes in diets.

Acknowledgements

Fund support of this work from MEKARN Project financed by Sida/Sarec gratefully acknowledged. The authors would like to thank the Department of Animal Science, Faculty of Agriculture & Applied Biology of Cantho University for infrastructure supports.

References

Akinfala E O, Matanmi O & Aderibigbe AO 2003: Preliminary studies on the response of weaned rabbits to whole cassava plant meal basal diets in the humid tropics. Livestock            Research for Rural Development. Vol. 15 (4): http://www.cipav.org.co/Irrd/Ịrrd/4/akĩn.htm. 

AOAC 1990: Official methods of analysis (15th edition), Washington, DC, Volume 1: 69-90.

Duong Thi Bich Loan 2010: Effect of energy feed supplement on growth performance and nutrient digestibility  and reproductive performance of crossbred rabbits, MSc thesis. College of Agriculture and Applied Biology, Cantho University

Lam Thanh Binh 2008: Effect of supplementation of soya waste and energy feed diets on growth performance and nutrient digestibility  and economic returns of crossbred rabbits, MSc thesis. College of Agriculture and Applied Biology, Cantho University

Le Thi Lan Phuong 2008: Evaluation of local forages for rabbits in Central Vietnam. International Workshop “Organic Rabbit Production from Forages”, 25-27 November, 2008, Cantho University, Cantho City, Vietnam.

Le Van An, Lindberg B EF and Lindberg J E 2003: Effect of harvesting interval and defoliation on yield and chemical composition of leaves, stems and tubers of sweet potato (Ipomoea batatas L) plant parts. Field Crops Res. 82, 49-58.

Maertens L, Peter J M, Villamide M, Cervera C, Gidenne T and Xiccato G 2002: Nutritive value of raw materials for rabbit. World rabbit Science 10 (4), pp. 157-166.

McDonald P, Edwards R A, Greehalgh J F D and Morgan C A 2002. Digestibility evaluation of foods. In Animal Nutrition. 6^th Edition. Longman Scientific and Technical. New York. Pp: 245-255.

Minitab  2000. Minitab reference manual release 13.20. Minitab Inc.

Nakkitset S 2007: Evaluation of head lettuce (Lactuca sativa) residues and Mimosa pigra as feed resources for growing rabbits. MSc Thesis. Swedish University of Agricultural Science, Uppsala 2007.

Nguyen Huu Tam, Vo Thanh Tuan, Vo Lam, Bui Phan Thu Hang and Thomas R. Preston 2008: Effects of supplementing a basal diet of water spinach (Ipomoea aquatica) with vegetable wastes on rabbit performance. International Workshop “Organic Rabbit Production from Forages”, 25-27 November, 2008, Cantho University, Cantho City, Vietnam. http://www.mekarn.org/prorab/thuhang.htm

Nguyen Kien Cuong, Duong Nguyen Khang & Preston T.R 2008: Digestibility and growth in rabbits fed a basal diet of sweet potato vines replaced with cassava foliage meal. International Workshop “Organic Rabbit Production from Forages”, 25-27 November, 2008, Cantho University, Cantho City, Vietnam. http://www.mekarn.org/prorab/cuong.htm.

Nguyen Thi Kim Dong and Nguyen Van Thu 2009: The use of agro-industrial by products for raising crossbred rabbits in the Mekong delta of Vietnam. Conference on Asian Rabbit Production Development. Sep 10-11 2009. Changchun, China.pp: 156.

Nguyen Truong Giang 2010: Effect of different supplement of sweet potato tuber and molasses in diets on growth performance, nutrient digestibility and economic returns of crossbred rabbits in the Mekong delta, MSc thesis. College of Agriculture and Applied Biology, Cantho University.

Nguyen Van Hiep and Ngo Van Man 2008: Utilization of tropical kudzu leaves (Pueraria phaseoloides) as protein source for growing rabbits. International Workshop “Organic Rabbit Production from Forages”, 25-27 November, 2008, Cantho University, Cantho City, Vietnam. http://www.mekarn.org/prorab/hiep.htm

Phan Thuan Hoang 2009: A study ability of nutrient utilization, growth rate and economic returns of crossbred rabbits and New Zealand, California in the Mekong delta of Vietnam. MSc thesis. College of Agriculture and Applied Biology, Cantho University.

Phiny C and Kaensombath L 2006: Effect on feed intake and growth of depriving rabbits access to caecotropes. MEKARN Proceedings of Workshop on Forages for Pigs and Rabbits.(Editors: T R Preston and R B Ogle). Phnom Penh, Cambodia, 22-24 August 2006. Agricultural Publishing house – Hanoi. P 183-190.

Samkol P, Preston T R and Ly J 2006:  Effect of increasing offer level of water spinach (Ipomoea aquatica) on intake, growth and digestibility coefficients of rabbits. Livestock Research for Rural Development. Vol. 18 (2).

Samkol P, Preston T R and Ly J 2006: Digestibility indices and N balance in growing rabbits fed basal diet of water spinach (Ipomoea aquatica) supplemented with broken rice. Livestock Research for Rural Development. Vol. 18 (2).  

Van Soest P J, J B Robertson & B A Lewis 1991: Symposium: Carbohydrate methodology, metabolism and nutritional implications in dairy cattle: methods for dietary fiber, and nonstarch polysaccharides in relation to animal nutrition. J. Dairy Sci. 74: 3585-3597.