Effect of different levels of cabbage waste (Brassica olerea) replacement in para grass (Brachiaria mutica) basal diet on growth performance and nutrient digestibility of crossbred rabbits in Mekong delta of Viet Nam

Nguyen Thi Kim Dong and Nguyen Thanh Van

Department of Animal Husbandry, College of Agriculture & Applied Biology
Cantho University, Viet Nam
ntkdong@ctu.edu.vn

Abstract

The objective of the study  was to evaluate the effects of cabbage waste replacement in the basal diets of paragrass on nutrient digestibility, growth performance and economic returns of crossbred rabbits. The sixty rabbits were arranged in a complete randomized design with 5 treatments and 3 replications. The treatments were cabbage waste (CW) replacement to paragrass (DM basis) at levels of 0 (CW0), 20 (CW20), 40 (CW40), 60 (CW60) and 80% (CW80). In the Exp 1, the dry matter (DM) intake was not significant difference among diets. The CP intake was significantly higher (P<0.01) in CW60 and CW80 diet (12.2 and 12.5 g/rabbit/day, respectively) as compared to the others. No  significant differences were found on the feed conversion ratio (FCR), however the daily weight gain was significantly different (P<0.01) among the treatments. The daily weight gain was 16.8, 19.9, 19.6, 21.8 and 21.4 g/rabbit/day for CW0, CW20, CW40, CW60 and CW80 diet, respectively. In Exp 2 the apparent digestibility of  DM, OM, CP and NDF tended to increase proportionally to the increasing levels of cabbage replacement in diets. The differences were  statistically significant (P<0.01) except EE digestibility. The nitrogen intake ranged from 1.31 to 1.42g/kg W^0.75 , however it was not significant difference among diets (P>0.05). The nitrogen retention tended to increase with inclusion of cabbage waste in diets. The results of this study indicated that cabbage waste could be used as a basal feed source to raise rabbits. The levels of cabbage waste from 60 to 80% (DM basis) replaced para grass gave high growth performance and better benefits.

Key words: cabbage waste, digestibility, growing rabbits, para grass, weight gain  

Introduction

In recent year, rabbit production has a considerable potential in the developing countries due to low rabbit raising investment, short generation  interval, high reproductive yield,  rapid  growth  rate and  the  ability  to  utilize  forages  and by-products  as major  diet  components. Besides rabbit meat  is of high quality, being high  in protein  and  low in fat content (Holmes  et  al.,  1984). Rabbit  production  can  be  integrated  into  small  farming  systems,  with  the  rabbits  being  fed  crop residues,  weeds, waste  fruits  and vegetables, etc.. In Mekong delta, there are a numbers of  by-products from agriculture such as  water spinach, sweet potato, cabbage waste, ect. Particularly, cabbage waste is by-product left at markets with a large amount. The proplem is how to treat them in order  not to make polluted environment and convert vegetable protein to animal protein with better income. Therefore this study aims to determine effect of  cabbage waste replacement of para grass in the diets on the feed utilization and growth performance and economic returns of growing rabbits.

Materials and methods

Location and duration

The experiments were carried out in the experimental farm of Department of Animal Husbandry, College of Agriculture and Applied biology, Can Tho University from January to May in 2008.

Experimental design

Exp.1:  Feeding experiment

The crossbred rabbits of two months of age were arranged in a complete randomized design with 5 treatments and 3 replications. Two males and two females were in an experimental unit. The treatments were cabbage waste replacement of para grass in the diets at levels of 0, 20, 40, 60 and 80% (DM basis), while para grass was fed ad libitum. The concentrate and fresh soya waste were supplied with the same amount for all dietary treatments of 10-20 and 100-200 g/rabbit/day, respectively. The experimental period lasted 8 weeks.

Chemical analyses

The feeds and refusals were taken for analyses of DM, OM, CP, EE, NDF 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 individual and weekly. Daily feed intakes, growth rate, and feed conversion ratios were measured and calculated. The economic analysis was also done among the treatments.

Exp. 2: Digestibility experiment

The second experimental design was similar to that of the feeding trial, however, the 12-week old rabbits were used. The animals had one week for adaptation and another week for getting experimental samples according to by fecal collection for 6 days. Feeds and refusals were daily measured. Urine was also collected for nitrogen analysis to calculate the nitrogen retention. DM, OM, CP, EE and NDF digestibility were employed according Mc Donald et al (2002).

 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). 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

Exp. 1: Feeding experiment

The chemical composition of feed ingredients

Table 1 showed that DM content of  cabbage waste (8.24%) was lower than that of para grass (20.3%). The DM content of para grass  in this experiment was higher than the result reported by Mo (2003), probably due to different harvest time. The DM  of cabbage waste of 8.24% was higher than that indicated by  Nam (2008) (6.8%). The CP content of cabbage waste (16.2%) was considerably higher than that of para grass (10,0%). Thus cabbage waste replaced para grass in the diets to supply protein for rabbits. However, the NDF content of para grass (67.0%) was higher as compared to  that of cabbage waste. The NDF content of para grass in this study was similar to the result stated by Chau (2008) (68.8%).

Soya waste and concentrate were protein and other nutrient supplements for rabbits. The values of DM, CP and NDF of concentrate were similar to those reported by Dong et al (2005). 

Feed and nutrient intakes

The para grass intake was significantly different (P<0.001) among the diets showed in table 2. The para grass intake decreased significantly with increasing levels of cabbage waste. The highest value was in the CW0 diet (52.6g/rabbit/day), the lowest being in the CW80 diet (16.6g/rabbit/day). Total DM intake ranged  from 72.7 to 75.5 g/rabbit/day. The results were lower than the range reported by Lieu (2008) ( 76.9 – 92.5g/rabbit/day). The CP intake significantly arised  (P<0.01) in the diets included cabbage waste and the lower CP intake for animals fed para grass only (CW0). The CP intake in the present study was consistent with those stated by Hung (2006) from 10.0 - 14.9g/rabbit/day. The NDF intake significantly reduced (P<0.01) when increasing levels of cabbage waste in the diets,  due to low NDF concentration in the cabbage waste. The values in this study were within the range found by Dong et al (2005).

Growth rate, feed conversion ratio and economic returns

The final live weight tended to increase with increasing the levels of cabbage waste replacement, the highest being in the CW60 diet. However, there were no significant differences among the diets (P>0.05). The daily weight gain was significantly higher (P<0.01) for the rabbits fed 60% and 80% cabbage waste in the diets (21.8 and 21.4g/day, respectively) as compared to those fed only para grass (16.8g/day). This was explained that the animals had higher CP intakes in the CW60 diet than those in the rest diets, because of a large of cabbage waste  consumed. The results in the present study were lower than the fingdings by Xuyen (2008) when rabbits fed the different levels of Operculina turpethum (from 20.1-23.9g/rabbit/day). The FCR was not significantly different among the diets in this study (P>0.05). These values were acceptable and better than the results of 4.9-6.0 reported by Akinfala et al (2003).

The economic analysis was done for 8 weeks, showed that the cost for feeds was hihger with increasing the level of cabbage waste included in the diets, however, due to the better rabbit growth rate of the increasing cabbage waste in the diets which gave more benefits. The results indicate that the promising diets for the rabbits could be up 60 to 80% cabbage waste.

Exp 2: Digestibility experiment

The results of the digestibility trial are showed in Table 4, 5 and 6 

Chemical compositions of feeds used in the Exp 2 were similar to those of the Exp 1. Feed intake values of the growing rabbits ranged from 65.6 to 72.2 gDM/day. The results were lower than those stated by Thu and Dong (2005) (from 100 to 139g/day). There were no significant differences (P>0.05) among of diets for DM and OM intakes  in the present study. The significantly higher (P=0.05) CP intake was found in the CW80 diet. The NDF intake was significantly higher in the CW0 diet as compared to those in the other diets ( P<0.01) and tended to reduce with increasing the levels of cabbage waste replacement in the diets. The explanation was the NDF content of cabbage waste was lower than para grass.

Apparent nutrient digestibility and nitrogen retention

The apparent digestibility of DM, OM, CP and NDF were improved with the increase of cabbage waste in the diets. The DM and OM digestibility coefficients were significantly lower (P<0.01) in the diets involved para grass only (55.6 and 59.7% respectively), the highest values were found for rabbits fed 80% cabbage waste in the diet (75.2 and 75.5% respectively). There were no significant differences on the CP digestibility.  The EE digestibility was significantly higher (P<0.05) in the diets included cabbage waste than that in the diet with para grass only. These results were similar to the range stated by Lieu (2008) from 64,8-81,9%. The NDF digestibility was significantly different among the diets (P<0.01), the lowest and highest results  were found in the CW0 and CW60 diets (46.2 and 59.1% respectively). The results of NDF digestibility in this study were similar to those reported by Linh (2005) from 33.4 to 56.9%. The explanation was that high fiber content in PG leading high intake of fiber for rabbits consumed large amount of para grass. Gidenne et al (1998) and Perez et al (1996) stated that an increase of fiber leads to decrease of retention time and an increase of caecotrophe production because of increasing bacterial fibrolytic activity which in turn results in a reduction of digestibility of diets (Gidenne et al 1998; De Blas et al. 1999). The nitrogen retention had tendency to increase slightly with increasing levels of cabbage  in the diet, however no significant differences were found among the diets (P>0.05). The values in the present study are similar to those stated by Thu and Dong (2005) and  Samkol et al.(2006).

Conclusion

The results of this study indicate increasing proportion of cabbage waste to replace para grass in the growing rabbit diets improved feed utilization, nutrient digestibility, daily weight gain and profits. The levels of cabbage waste from 60 to 80% (DM basis) replaced para grass gave high growth performance and better benefits.

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