Effect of dietary fiber sources on feed intake, nutrient digestibility, growth rate of growing rabbits fed water spinach or sweet potato with or without supplement of Wedelia trilobata and Hymenache acutigluma

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

Cantho University, Vietnam

ntkdong@ctu.edu.vn

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

Abstract

Two experiments were carried out in the experimental farm of Cantho University to evaluate the effect of dietary fiber sources from vegetables and fiber supplements. Both experments were 2*3 factorial designs, with 3 replications and. The first factor was vegetable kind [water spinach (WS), and sweet potato vines (SPV)]; the second one was fiber supplement with Wedelia trilobata (WT), Hymenache acutigluma (HA), or none. The feeding trial (Expt. 1) was done on 4 male growing crossbred rabbits at 8 weeks of age in one experimental unit to evaluate on feed intake, growth performance and economic returns. In the digestibility trial (Expt. 2) nutrient digestibility, nitrogen retention and caecum fermentation were determined in 2 twelve-week old rabbits in one experimental unit.

In Expt. 1, the dry matter (DM) and organic intakes were similar (P>0.05) between vegetables and among fiber source supplements. The final weight and weight gain were significantly higher (P<0.05) in the diets fed WS only compared to SPV, and for the none fiber supplement. The lower feed cost resulting in higher benefits was found in the diets fed only SPV and the diet supplemented WT. In Expt. 2 the apparent digestibility (%) of DM, OM were significantly higher in the diet fed only WS (P<0.05), and the diets without fiber supplemented or supplemented WT (P<0.001). NDF and ADF digestibility values were significatly lower (P<0.01) in the diet with HA supplement. The total volatile fatty acids (VFAs) were similar between WS and SPV diets, but significantly higher (P<0.05) in the diets with WT supplement and none compared to the supplemented HA.

It is concluded that water spinach is superior to sweet potato vine as the basal diet for rabbits and that there are no nutritional benefits from offering higher fiber supplements such as Wedelia trilobata or Hymenache acutigluma.

Key words: Digestibility, growing rabbit, Hymenache acutigluma, sweet potato vine, water spinach, Wedelia trilobatas

Introduction

In recent year rabbit production and meat have been popular in the Mekong delta of Vietnam due to the human demands during the bird flu outbreak. Crossbred rabbits (Local and improved pure breeds) are popularly raised in the Mekong delta, because of good natural conditions such as suitable ambient temperature, rich soil and available fresh water through out a year. The local green feed resources are abundant in this region for both planted and natural plants such as sweet potato (Ipomea batatas), water spinach (Ipomoea aquatica), Mom grass (Hymenache acutigluma), Cuc (Wedelia trilobata), etc. However, there has been a limitation of studies of these feeds in the rabbit diets for further research and farmers’ production.  Therefore, the objectives of the study were to evaluate effects of vegetable of sweet potato vine and water spinach supplemented with fiber sources from Hymenache acutigluma or Wedelia trilobata in the diets on feed and nutrient utilization, growth performance, meat production and economic returns of growing crossbred rabbits. The positive results of the study would be recommended disseminated for farmers’ production.

Materials and methods

Experiment 1.  Feeding trial

Animals and experimental design

The experiment was conducted in experimental farm and laboratories of Cantho University. Seventy two male-crossbred rabbits (local x improved breeds) at 60 days of age were allocated in 2*3 factorial design, with 3 replications and four male rabbits in one experimental unit. The first factor was vegetable kind (water spinach (WS), and sweet potato vines (SPV) as main feeds and the second one was fiber source supplement (Hymenache acutigluma (HA) and Wedelia trilobata (WT), none).  The rabbits had free access to water spinach or sweet potato vine, each with or without access to Wedelia trilobata or Hymenache acutigluma or nothing. The rate of the two feeds in the diets was 1:1 based on DM basis. Paddy rice was supplemented to all the dietary treatments at the same level of 15g per day per rabbit to provide energy.  The experimental period lasted 8 weeks.

Feeds, feeding and management

Wedelia trilobata (WT) and Hymenache acutigluma (HA) were daily collected in the areas belong to Cantho University. Water spinach and Sweet potato vine were bought from one farm in the city. The animals were fed three times a day at 8:00h, 15:00h and 19:00h.. 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 precise feed intake. The animals were vaccinated to prevent some diseases such as rabbit hemorrhagic and parasite 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). During the experiment the rabbits were weighed individually in every week. Daily feed intakes, growth rate, and feed conversion ratios were measured and calculated. After finishing the experimental the rabbits were slaughtered for evaluating carcass and meat quality. 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, thirty six growing male crossbred rabbits at 12-week of age were used. Dietary feeds were divided in to 3 parts and fed at 7.00, 13.00 and 17.00. The adaptation period for the diets were 2 weeks and feed offered, refusals, faeces and urine were collected for 7 days of the third week to measure feed and nutrient digestibility and nitrogen retention.  The end of the third week the rabbits per experimental unit were slaughtered at 9.00AM (3 hours postfeeding) to get the caecum content and it was treated immediately for measuring VFAs concentration following the methods described by Barnett and Reid (1957).

Statistical analysis

The data from both experiments were analyzed by analysis of variance using the ANOVA of General Linear Model of Minitab Reference Manual Release 13.21 (Minitab, 2000). While Tukey test was used to compare the means of the criteria (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

Feed Characteristics

The chemical composition of feed ingredients fed rabbits in the trial was showed in Table 1.

Mom grass (Hymenache acutigluma) had the highest DM content (15.7%) compared to those of Cuc (Wedelia trilobata), water spinach and sweet potato vine (12.1, 9.63 and 8.56%, respectively). These figures were similar to reports of Nguyen Hai Phu (2004), Danh Mo (2003) and Dao Hung (2006). Crude protein content was higher for sweet potato vine and water spinach. These values were slightly lower than those of Nguyen Thi Xuan Linh (2005) and Danh Mo (2004) due to the affects of rainy season for the experiment. The NDF content was high in Mom grass (66.3%). The ADF content of Mom grass and Cuc was higher than those of sweet potato vine and water spinach. Paddy rice supplemented had DM and CP content of 87.4 and 6.68%, respectively.

Feed and nutrient intakes of growing rabbits was presented in Table 2.

The DM intake (g/rabbit/day) was not significantly different between main feed (WS and SPV) and among different supplementations. These results were consistent with report of Nguyen Van Thu and Nguyen Thi Kim Dong (2005) being from 51.4-61.5 gDM/rabbit/day in a study with SPV replacing para grass in growing rabbit diets. In general DM intake of rabbits in the present experiment was good with the values ranged from 61.1 to 64.4g/day/rabbit. The CP intake was similar between main feed, however, the significantly higher CP intake was in the dietary treatment without supplementation of HA or WT, and the lowest value in the diet supplemented WT. The NDF and ADF intakes of the diet supplemented HA were significantly higher than others because of higher NDF and ADF contents of the HA.

Daily weight gain, feed conversion ratio and economic analysis

Daily weight gain, feed conversion ratio and economic analysis were showed in Table 3.

Final weight and daily weight gain were significantly higher in the WS diet and  in the diet including WS or SPV without supplement of HA or WT (P<0.05).  The results of daily weight gain of crossbred rabbits fed local green foliages in present experiment ranged from 14.8 to 16.0g. They are consistent with those (from 11.0 to 19.0g) of other reports in Vietnam by Nguyen Thi Xuan Linh (2005) Dao Hung (2006), Nguyen Van Thu and Nguyen Thi Kim Dong (2005) and Nguyen Thi Kim Dong et al. (2006). The values were also within the range reported by (Samkol et al., 2006). They were slightly lower than those found by Phimmasan et al. (2004) and Khuc Thi Hue and Preston (2006). Feed conversion ratio of the rabbits was from 3.63 to 4.42, and the WS diet had better FCR than the SPV diet (P<0.05), and the significantly lower value was found in the diet without HA or WT supplementation than the rest of diets (P<0.01). The obtained values for feed conversion ratio were better than the results being from 4.9 to 6.0 reported by Akinfala et al. (2003). The economic analysis showed that benefits got from the SPV diet and diet supplemented WT were higher than the rest of diets due to lower cost of feeds, despite growth rate and feed conversion ratio of the WS diet and the vegetable diet without supplement were better. Thus local green feed sources available could be used as staple feeds in the rabbit diets to get better benefits by farmers.  

Mean values for slaughter weights, carcass traits and meat quality of growing rabbits

The criteria of carcass, thigh meat, lean meat and meat quality were no significant effect by two kind of vegetables (WS, SPV diet) and three kind of fiber supplement (none, HA, WT diet) (Table 4). Nguyen Van Thu and Nguyen Thi Kim Dong (2005) in a study of sweet potato vine replacing para grass in the diets reported that the carcass and lean meat percentage of growing crossbred rabbits were from 41.6 to 47.1% and from 67.8 to 79.2%, respectively. Crude protein content of rabbit meat in the present experiment was from 18.9 to 19.2%, while this was 22.5% reported by Nguyen Chu Chuong (2003). The difference could be caused by feed sources and supplements. In the current experiment paddy rice was supplemented with a average level of 15g/day/rabbit, while other experiments on pure improved breeds concentrates were mostly used for supplementing.

Experiment 2: Digestibility trial

Chemical composition of feedstuffs used (Table 5) was similar to those in experiment 1, except for a slightly lower CP content of the SPV. Feed intakes ranged from 57.8 to 61.0g DM/day, and the values were closed between main feed and among fiber supplements.

In Table 6, the apparent DM digestibility coefficients were significantly different between vegetables (P<0.05) and among fiber supplements (P<0.01) and the values from 62.9-73.2%. It was significant lower values for the SPV diet and the diet supplemented HA, possibly due to high fibre concentration in HA. The CP digestibility was closed between main feed and among the fiber supplement (P>0.05). The NDF and ADF digestibilities were also significantly lower (P<0.01 and P<0.001, respectively) in the diet supplemented HA than the rest. The probable explanation was the high fibre content in HA. Gidennce et al. (1998) and Perez et al. (1996) stated that a high level of fibre in the diet leads to decrease of rentention time and an increase of caecotrope production because of increasing bacterial fibrolytic activity, which in turn results in a reduction of diet digestibility (DeBlas et al. 1998). In a recent study of water spinach leaves feeding growing rabbits, Nguyen Thi Kim Dong et al. (2006) reported that the DM digestibility and CP digestibility were from 62.7 to 73.0 and 82.0 to 84.5, respectively.Samkol et al. (2006) reported that DM, CP and NDF digestibilities are similar to those in a study with rabbits fed water spinach based diets had DM, CP and NDF digestibility values were 73.5-78.3%, 59.9- 70.9% and 48.2-56.3%, respectively.

Figure 1 and 2 illustrate that the increase NDF intake resulted in decrease digestibility of DM and NDF (R²= 0.88, R²= 0.83, respectively)

Nitrogen intake and retention of the rabbits were not significantly different in both main feed and fiber supplement with the values from 0.95 to 1.08 and from 0.57 to 0.67 g/kg W^0,75, respectively. These values obtained were lower than report of Nguyen Thi Xuan Linh (2005) and Nguyen Thi Kim Dong et al. (2006) with the nitrogen retention from 0.71 to 0.92 and 0.76 to 1.07 g/kgW^0.75, respectively. They were also corresponding to the daily weight gain of the rabbits in the experiment. The content of volatile fatty acids was similar between two vegetables (WS and SPV), however, the significantly higher value was found in the diet with WT supplement than the rest (P<0.05). There was also a relationship between DM digestibility and VFAs concentration in caecum content (Figure 3) (R² = 0.52).

Conclusions

The conclusion of the study was that:

·         Water spinach was better to sweet potato vine as the basal diet for rabbits.

·          There are no nutritonal benefits from offereing higher fibre supplements such as Wedelia trilobata or Hymenache acutigluma.

·         Water spinach and sweet potato associated Hymenache acutigluma or Wedelia trilobata gave better economic benefits.

Acknowledgements

Financial support of this work from SIDA-SAREC through the MEKARN project is gratefully acknowledged. The authors would like to thank the Department of Animal Science, Faculty of Agriculture and Applied Biology of Cantho University for infrastructure support, and also thank to the valuable helps of Prof. Dr. Brian Ogle.

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