Effect of different levels of neutral detergent fiber in the diets on feed utilization, growth rate and nutrient digestibility of growing crossbred rabbits
 

Nguyen Thi Kim Dong and Nguyen Truong Giang

 Cantho University, Cantho City, Vietnam

nguyengiang823@gmail.com

Abstract

 An experiment was conducted to determine the effect of different levels of neutral detergent fiber (NDF) on growth performance and nutrient digestibility of crossbred rabbits. It was a complete randomized design with six treatments and three replicates. One female and one male rabbit at 54 days of age were allocated in one experimental unit. The six treatments were fed each diet with NDF at 37, 41, 45, 49, 53 and 57% respectively. They were corresponding to the treatments named 37NDF, 41NDF, 45NDF, 49NDF, 53NDF and 57NDF, respectively. The The results are as follows: The results of exp 1 showed that the dry matter (DM) and organic matter (OM) intakes were significantly increased (P<0.001) when increasing levels of NDF in the diets. The crude protein (CP) intake was the lowest in the 57NDF diet (P<0.001). The NDF and ADF intakes were significantly increased (P<0.001) when increasing levels of NDF in the diets. The daily weight gain was significantly decreased (P<0.001), the daily weight gain in the 41NDF group (20.3g/rabbit/day) was higher than this in the 45, 49, 53 and 57NDF groups, however, the lower feed conversion ratio was found (P<0.05) in the 37NDF group (3.45). In exp 2 The coefficient of total tract apparent digestibility (CTTAD) of DM, OM, NDF and acid detergent fiber (ADF) decreased when levels of NDF increased in the diets (P<0.05, P<0.01). The nitrogen intake of 37NDF group was higher than that of 57NDF group (P<0.05). The retained nitrogen was not significantly different (P>0.05) among diets.

Keywords: neutral detergent fiber, daily weight gain, digestibility, growing rabbit.    

 Introduction

In recent years, the diseases in animals occur serious as avian influenza, foot and mouth disease, ... So to find a model animal raising to prevent these disease is interested, in which rabbit is a promised animal. The Mekong Delta has a lot of the river and branches, hot and humid climate with two seasons (rainy season and sunny season), so feed sources for feeding rabbits are very plentiful, not only in rural areas but also peri urban areas. There are many kinds of forages such as para grass (brachiaria mutica), Mom grass (Hymenachne acutigluma), Sa grass (Panicum maximum),... Vegetables such as sweet potato vine (ipomoea batatas), water spinach leaf, ...

NDF is made up of four main chemical components. Quantitatively the largest, cellulose and hemicellulose are potentially digestible, but due to their complex chemical structures. The other main components of NDF are lignin and cutin, which are virtually indigestible in both the rumen and lower intestines. In addition, both inhibit digestion of the underlying and/or associated cellulose or hemicellulose either by physical or chemical shielding. Therefore, the objectives of study are to evaluate effect of levels of neutral detergent fiber on growth rate and digestibility of growing crossbred rabbits. The results of the study will be disseminated to producers for practice.

Materials And Methods

Exp. 1: Feeding trial

The experiment aimed to measure the effect of different levels of NDF in the diets on feed utilization, growth rate and digestive nutrient of crossbred rabbits. Forty eight growing male and female rabbits (New Zealand x local breed) at 54 days of age (mean live weight of 701g) were allocated in a complete randomized design with 6 treatments and 3 replications (two rabbits in an experimental unit). The treatments were percentage of NDF at levels of 37, 41, 45, 49, 53 and 57% (DM basis), while the concentrate supplementation was the same for all treatments of 20g /rabbit/day.

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

Exp. 2: Digestibility trial

The second experimental design was similar to that of the feeding trial, however, the 14-week old rabbits were used. The animals had one week for adaptation and another week for getting 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, CP, NDF and ADF digestibility were employed according Mc Donald et al (2002).

The data from the experiment were analyzed by analysis of variance using the ANOVA of General Linear Model, while Tukey test was used to compare the means of treatments 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 trial

Chemical composition of feeds was stated in Table 1

In Table 2, the DM of para grass was 18.9% and higher than sweet potato vine of 9.74%, while the CP of sweet potato vine was 17.2% and higher than para grass of 9.11%. The DM of para grass reported  by Trung (2006) of 18.7% by the same, the CP of sweet potato vine in the present study was consisted with the CP of sweet potato vine reported by Dominguez (1990) of 18.5% and Duc (2008) of 19.7%. The NDF content of sweet potato vine was lower than para grass (40.8% vs. 71.8%), so using para grass increased NDF in the diets. The NDF content of para grass is in agreement with the values of Tuyet (2008) and Huyen (2008) (72.9% and 75.1%, respectively). The NDF of sweet potato vine was higher than that presented by Dong and Thu (2005) of 23.4%, while being in accordance with Olorunnisomo (2007) of 44.5%.

Table 3 showed that sweet potato vine and para grass intakes were significantly different (P<0.001) among treatments. Sweet potato vine intake decreased when increasing levels of NDF in the diets, being highest in the 37NDF diet (100gDM/day) and lowest in the 57NDF diet. The para grass intake increased with increasing levels of NDF in the diets, reaching the highest in the 57NDF diet (132gDM/day) and the lowest in the 37NDF diet. Sweet potato vine and para grass intakes of this experiment were higher than those reported by Tam (2007) of 84.8g and 45.3g respectively.  

Fig 1: The sweet potato (■) and the para grass (■) intakes

The DM and OM intakes were significantly different (P<0.001) among treatments, the DM and OM intakes in the 37NDF group was lower than those in the 45, 49, 53 and 57NDF groups, possibly due to the higher DM content in para grass and the lower DM in sweet potato vine, so the total DM intake in rabbits fed para grass only (57NDF) was significantly higher. The DM intake of the experiment was higher than data indicated by Trang (2007) of 79.4g/rabbit/day. The CP intake significantly (P<0.001) decreased when increasing levels of NDF in the diets, the highest was 11.7g/rabbit/day (37NDF) and higher than in the 57NDF group (P<0001), while the NDF and ADF intakes were at least in the 37NDF group (24.0g/rabbit/day and 14.7g/rabbit/day respectively).

Daily weight gain, feed conversion ratio and economic return of the rabbits were presented in Table 4.

Table 4 showed that final live weights and daily weight gains had tendency to decrease when increasing NDF level in the diets. The daily weight gain (WG) was significantly higher (P<0.01) for rabbits fed 37 and 41% NDF diets than those fed higher levels of NDF in the diet. The difference was probably due to higher CP intakes from sweet potato vine. This result was higher than the reports of Dong and Thu (2005) from 11.3-18.1 g/day and Akinmutimi and Anakebe (2008) from 9.04-11.9 g/day.

The feed conversion ratio increased when increase levels of NDF in the diets, the feed conversion ratio was poorest for animals fed the diets included 49, 53 and 57NDF, and improved (P<0.05) with inclusion level of sweet potato vine, as a result of better daily weight gain. The values were lower than the results of study found by Hung (2006) from 4.65-4.87 and Dien (2007) from 4.83-6.20. The economic analysis showed that the 41NDF treatment gave the best benefits from the experiment.

 Exp. 2: Digestibility trial

The chemical composition of the feedstuffs used (table 5) was similar to those in experiment 1.

The feed intake was significantly different (P<0.05, P<0.001) among diets. The DM and OM intakes in the 49NDF group (79.4 gDM/day and 72.1 gDM/day, respectively) were higher than those in the 37NDF group (P<0.05), the DM intake was lower than the values of 87.5-99.3 gDM/day and 77.6-87.7 gDM/day reported by Tam (2008) and Trang (2008) respectively. The CP intake decreased when increasing levels of NDF in the diets (P<0.001), while the NDF and ADF intakes were increased when increasing levels of NDF in the diets (P<0.001), according with experimental design.

Nutrient digestibility and nitrogen retention of rabbits were stated in Table 7.

The digestibility of DM and OM were significantly (P<0.01) decreased when increasing levels of NDF in the diets, being higher value in the 37NDF and 41NDF groups (69.1% and 68.3%) and lower results in the 53NDF and 57NDF groups. The explanation was that high fiber content in PG leading high intake of fiber for rabbits consumed large amount of PG. The findings are consisted with the explanation of Gidenne (1996). 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 results in out study were lower than the reports of Dong and Thu (2005) from 57.5-74% and Linh (2005) from 41.7-73.0%, but being higher than those found by Dien (2007) from 41.2-57.2%. The CP digestibility was not significantly different among diets (P>0.05) from 75.2-79.5%. The digestibility of NDF reduced when increasing levels of NDF in the diets (P<0.05), the significantly lower value was found in the 57NDF group. This result was lower than value of a study reported by Samkol et al. (2006) in which rabbits fed water spinach basal diets by 48.2- 56.3%.

There was an decrease in both the nitrogen intake and nitrogen retention corresponding with increasing levels of NDF in the diets, but being significantly different only for the nitrogen intake (p<0.05). The values in the present study are in the similar range as those and considerably reported by Tam (2007) from 1.20-1.67g/kgW^0,75 and were lower than Thu and Dong (2005) from 2.83-3.23 g/kgW^0,75. The nitrogen retention was from 0.7-0.88 g/kgW^0,75.

Conclusion

The  study showed that increasing levels of NDF in the diets of growing crossbred rabbits was decrease daily weight gain and nutrient digestibility. Levels of 41NDF group in the diet gave higher growth rate and better benefits for producers.

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