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

Nguyen Thi Kim Dong and Nguyen Van Thu 
 

Cantho University, Vietnam

ntkdong@ctu.edu.vn

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 years rabbit production and rabbit 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 throughout the 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) and Cuc (Wedelia trilobata).  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 for rabbit production forages of sweet potato vine and water spinach supplemented with fiber sources from Hymenache acutigluma or Wedelia trilobata.
 

Materials and methods

Experiment 1.  Feeding trial

Animals and experimental design

The experiment was conducted in the experimental farm and laboratories of Cantho University. Seventy two male-crossbred rabbits (local x improved breeds) at 60 days of age were allocated in a 2*3 factorial design, with 3 replications and four male rabbits in one experimental unit. The first factor was kind of vegetable: water spinach (WS) and sweet potato vines (SPV) as main feeds. The second factor was fiber source supplement; Hymenache acutigluma (HA), Wedelia trilobata (WT) or 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. 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 was 8 weeks.

Feeds, feeding and management

Wedelia trilobata (WT) and Hymenache acutigluma (HA) were collected daily  in the areas belonging 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 rabbit hemorrhagic and parasite diseases.

Measurements

The feeds and refusals were taken for analyses of DM,  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 every week. Daily feed intakes, growth rate, and feed conversion ratios were measured and calculated. After finishing the experiment the rabbits were slaughtered for evaluating carcass and meat quality. The economic analysis was also done. 

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. Diets were divided into 3 parts and fed at 7.00, 13.00 and 17.00. The adaptation period for the diets was 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.  At the end of the third week the rabbits in each experimental unit were slaughtered at 9.00 am (3 hours post feeding) to get the caecum content which was treated immediately for measuring VFA 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). The 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 the feed ingredients fed to rabbits in the trial is shown 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.

The DM intake was not significantly different between main feeds (WS and SPV) and among different supplements (Table 2).

These results are consistent with reports of Nguyen Van Thu and Nguyen Thi Kim Dong (2005) being from 51.4 to 61.5 g DM/rabbit/day in a study with SP replacing para grass in growing rabbit diets.

Daily weight gain, feed conversion ratio and economic analysis

Daily weight gain, feed conversion ratio and economic analysis are shown 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 the 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). Significantly lower values were found in the diets without HA or WT supplementation (P<0.01).  The economic analysis showed that benefits got from the SPV diet and diet supplemented with WT were higher than the rest of the diets due to lower cost of feeds, despite growth rate and feed conversion ratio of the WS diet and the vegetable diet without supplement being better. Thus the local green feed sources available can 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