Effect of mixed or separate feedings and ration of Centrocema pubescens and Para grass on feed utilization, nutrient digestibility and growth performance of crossbred rabbits

Nguyen Thi Kim Dong and Nguyen Van Thu

 Cantho University, Vietnam
ntkdong@ctu.edu.vn

Abstract

A study was conducted at the experimental farm and laboratory of Can tho University to evaluate feed utilization, nutrient digestibility and growth performance of Crossbred  rabbits. The experiment was a factorial design in which the first factor was feeding method (Separate and mix) and second factor was the levels of Centrocema pubescens : Para grass (20:80, 40:60, 60:40 and 80:20), with three replications and 4 rabbits per experimental unit. The results indicate that values of DM, CP, EE, NDF, ADF, ME intakes were significantly higher (P<0.05) in the separate feeding. The CP and EE intakes gradually increased (P<0.05) when increasing the levels of Centrocema pubescens in the diets. The apparent digestibility coefficients of NDF and CP, nitrogen intake and retention were significantly higher (P<0.05) for the rabbits offered separated feeds and the level of 80:20 Centrocema pubescens and Para grass. The parameters of N-NH3 and volatile fatty acid of caecal fluid were significantly higher (P<0.05) in separate feeding and with increasing levels of Centrocema pubescens in the diets. The daily weight gain, weight of carcass, and thigh meat of rabbits fed separated feeds and the level of 80:20  Centrocema pubescens and Para grass had the highest results (P<0.05).

It was concluded the separate feeding and the level of 80: 20 Centrocema pubescens and Para grass had better growth performance and gave higher economic efficiency.

Key words: Carcass straits, daily weight gain, nutrient intake, nitrogen retention

Introduction

Organic rabbit farming based on forages is a sustainable feeding system for the poor farmers to improve their economical lives in villages of Vietnam. Within these feeding strategies, forages and agricultural by-products are used as the main protein and fibre sources, while for the improved performance of growing rabbits, sources of soluble carbohydrate supplementation are very important (Leng, 2008 and Preston, 2008).

Besides, rabbits have characteristic of high feed selection based on types of feeding or size of feed particles as well as the type of feeds in order to meet nutrient requirement in their diets. Therefore feeding choice will increase feed intake of the forages-fed rabbits resulting in high performance. In the Mekong Delta has abundance of locally available forages almost all year round in which Para grass has high fibre content, while Centrocema pubescens with high crude protein. Thus the appropriated associations between these feeds will give balanced nutrient diets for rabbits. However, the understanding of this scientific area for rabbit performance has still limited in literatures. Therefore a study of nutrient utilization, digestion process and performance of growing rabbits based on forages mixed or separated and supplemented small amount of protein and energy from soya waste and dried sweet potato should be investigated for improving rabbit production and increasing farmers’ income.  

 Materials and methods

Experiment 1.  Feeding trial

Animals and experimental design

The experiment was conducted in the experimental farm in Cantho City. Ninety six Crossbred rabbits (local x improved breeds) at 6 to 8 weeks of age were devised to 3 blocks corresponding with 3 ranges of live weight from 440, 520 and 650 g/rabbit. They were allotted in a factorial design with 2 factors and four rabbits (balanced sex) in an experimental unit. The first factor was feeding method (Separate and mix) and second factor was level of Centrocema pubescens (CPU) and Para grass (PG) (20:80, 40:60, 60:40 and 80:20). Three replicates were applied for all treatments in the study. The Centrocema pubescens (CPU) and Para grass (PG) were hung and fed separately for first factor, while CPU and PG were chopped, then mixed and fed in a trough in the treatments for the second factor. Soya waste, extracted soybean and dried sweet potato waste were supplied at the same level of each feed for all treatments to provide protein and energy. The experimental period was lasted 10 weeks.

Feeds,  feeding and management

The animals were fed three times a day at 8:00 h, 14:00 h and 18:00 h. Centrocema pubescens (CPU) and Para grass (PG) were separately offered in the first factor, while they were chopped and mixed before feeding in the second factor.  Fresh water was available for all rabbits almost all day and night time. The refusals and spillage were daily collected and weighed in the morning to calculate the feed intake. The animals were vaccinated to prevent hemorrhagic and parasite diseases.

Measurements

The feeds and refusals were taken for analysis of DM, OM, CP, EE, NDF, ADF and ash following procedures of AOAC (1990) and Van Soest et al (1991). During the experiment four rabbits per experimental unit were individually weighed every week. Daily feed intakes, growth rate, and feed conversion ratios were measured and calculated. At the end of  experiment the rabbits were slaughtered for evaluating carcass  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, the two rabbits at 12 weeks of age were used. The animals had two weeks for adaptation and another week for getting samples. Feeds and refusals were daily measured. Urine was also collected for nitrogen analysis to calculate nitrogen retention.  DM, CP, EE, NDF and ADF digestibility were employed according to Mc Donald et al (2002). At the end of the third week of this experiment the two rabbits of each experimental unit were slaughtered at 9.00 h (after feeding 3 hours) to get the caecal content that was treated immediately for measuring volatile fatty acid concentration by distillation (Barnett and Reid, 1957).

Statistical analysis

The data from both experiments were analyzed by analysis of variance using the ANOVA option of the 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

The chemical compositions of the feed ingredients of rabbits are presented in Table 1.

Centrocema pubescens (CPU) had twice as much protein and much less than the NDF component compared to the Para grass (PG). The CP content of CPU used in our experiment is consistent with the value (21.2% CP) stated by Nguyen Le Thu Hang (2012), but being higher than the value (17.4 %CP) reported by Van Phu Vinh (2010). The NDF contents of CPU and PG in the current experiment were lower than those reported by Nguyen Thanh Tung (2012). This might have been caused by different collection seasons and soil characteristics.

Feed and nutrient intakes

Daily intakes of Centrocema pubescens, Para grass and nutrients of crossbred rabbits are shown in Table 2.

Table 2 indicated that daily intake of CPU was significantly higher in separate feeding than in the mixed feeding (P<0.05), and the results increased with increasing levels of CPU in the diets, reaching the highest value (47.3 g) in the CPU80-PG20 diet (P<0.05). The significantly higher daily intake of PG was found in separate feeding, however the results decreased when increasing levels of CPU in the diets, the lowest value in the CPU80-PG20 diet (P<0.05). The total daily intakes of DM, OM, CP, EE, NDF, ADF and ME were higher for the separate feeding (P<0.05). The explanation was that the rabbits have high feed selection characteristics thus feeds offered separately stimulated them consume more feeds. However, the DM, OM, NDF, ADF and ME intakes were unaffected by the inclusion of graded CPU levels in the ratios of CPU and PG. The CP and EE intakes were significantly increased corresponding with increasing levels of CPU in the ratios between CPU and PG of the diets, probably due to higher intake of CPU with high CP and EE contents in CPU as compared with those in PG. The daily CP and NDF intakes in this trial are in agreement with the results (10.8- 11.2 gCP/rabbit and 20.7-26.6 g NDF/ rabbit)  reported by Nguyen Truong Giang (2010) of previous study in which rabbits fed Para grass and water spinach leaves with supplemented sweet potato tuber.

Growth rate, final live weight and economic analysis of crossbred rabbits

Daily weight gain (DWG) and final live weight (FLW) were significantly higher for that rabbits offered separate CPU and PG (P<0.05). This was explained that the rabbits consumed higher amounts of DM and nutrients such as CP, EE and ME. These values also gradually increased with increasing levels of CPU in the diets, approaching the highest value in the CPU80-PG20 diet (P<0.05), possibly due to higher CP and EE intakes for animals in this diet. The results of DWG are similar to those found by Tran Thanh Nhan (2011) (18.1-20.4 g) in which Crossbred rabbits fed Psophocarpus scandens and Para grass, but being superior to the reported growth rates within the ranges (15.9 to 19.4 g/day) by Nakkitset (2007) and (15.1-18.2 g/day) obtained in a study on rabbits fed Psophocarpus scandens stated by Nguyen Van Dien (2007). Feed conversion ratio was similar between two feeding methods and among 4 levels of CPU (P>0.05). These values were lower than those of 3.23 -3.89 by Nguyen Truong Giang (2010). There was a close linear relationship between CP intake and daily weight gain of rabbits Figure 2.          

Figure 2: Effect of CP intake on daily gain of rabbits in feeding experiment

The economic analysis showed that the slightly higher total expense, but higher income were found in the seperate feeding and the CPU80-PG20 diet, resulting in giving more benefits in these diets. The results showed that the better separate feeding and the promising diets for the rabbits could be the CPU80-PG20 diet.

Mean values for slaughter weights and carcass traits of growing rabbits

The live weight, carcass weight, thigh meat and percentage of lean meat and carcass weight were significantly affected (P<0.05) by feeding method and graded levels of Centrocema pubescens offered, the highest values were obtained for the animals fed separated feeds and the CPU80-PG20 diet (Table 4). The results in the present study were consistent with those in an earlier study of sweet potato vine replacing para grass in the diets reported by Nguyen Van Thu and Nguyen Thi Kim Dong (2005) that the percentage of carcass (without head) and lean meat of growing crossbred rabbits were from 41.6 to 47.1% and from 67.8 to 79.2%, respectively.

There were no significantly different interactions between two factors of feeding method and diet in feeding trial (P>0.05) for all of the criteria in Table 4.

Photo 3: Carcass weight of rabbits	Photo 4: Thigh weight of rabbits

Experiment 2: Digestibility trial

Feed characteristics

 Chemical compositions of feeds used in digestibility trial are shown in Table 5

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

Feed and nutrient intakes

Feed and nutrient intakes of rabbits in digestibility trial are indicated in Table 6.

There were significantly higher intakes of DM, NDF and ADF for the animals fed separated feeds and for the diets contained high PG levels (CPU20-PG80 and CPU40-PG60 diets) (P<0.05), while higher CP intake was in the diets included high CPU levels (CPU60-PG40 and CPU80-PG20) (P<0.05). There were no significant interactions between two factors of most the results obtained from the digestibility trial in Table 6.

Apparent digestibility of dietary nutrients, nitrogen retention and ceacal fluid parameters   

Apparent digestibility of dietary nutrients, nitrogen retention and caecal fluid parameters are presented in Table 7    

The apparent digestibility coefficients of DM, OM and CP and ADF were close between separate and mixed feeding (P>0.05), exception of higher CP digestibility for rabbits fed separated feeds (P<0.05). However, the values of DM, OM and CP were improved following graded CPU levels in the diets (P<0.05), as a results of decrease PG from 80 % to 20 % in the diets resulting in reducing NDF and ADF intakes (Table 7).  Our results are in agreement with the findings that the lower digestibility indices of DM, CP and CF were found in diets including high fiber supplements (Khuc Thi Hue and Preston, 2006). The results of DM digestibility were similar to those (65.4 to 75.0 % and 69.0 %) in studies reported by Akinfala et al (2003) and Ramchurn et al (2000), respectively.  The CP digestibility values in this trial are consistent with those of 80.6-83.1 % stated by Dang Hung Cuong (2008), but being slightly lower than the results of 79.5-87.0 % in a study of Tran Thanh Nhan (2011).

 N intake was significantly higher for the rabbits fed separated feeds (P<0.05). There was a significant increase in both the nitrogen intake and nitrogen retention in the CPU80-PG20 diet (P<0.05). This probable explanation was a high CP content in CPU. The N retention in the present study is lower than the results obtained (1.22-1.77 g/kgW^0,75 ) by Nguyen Le Thu Hang (2012).  The concentration of N-NH3 and volatile fatty acids were significantly higher (P<0.05) for animals fed separated feeds and considerably increased with increasing levels of CPU from 20 to 80% in the diets (P<0.05).  There was a close relationship between NDF digestibility and VFA concentration in the caecal fluid (Figure 3).

Figure 3: Relationship between NDF digestibility and VFA concentration in the caecal fluid

There were no significantly different interactions between two factors of feeding method and diet in digestibility trial (P>0.05) for all criteria in Table 7.
 

Conclusions 

Based on the results obtained it was concluded that:

·         The separate feeding had higher intakes of feeds, nutrients, better growth performance and higher profit.

·         A ratio of 80 % Centrocema pubescens and 20% Para grass in the diet gave the highest daily gain, better meat performance and profit.

·          There were significant improvement of CP digestibility, N retention, the concentration of N-NH3 and volatile fatty acids in caecal fluid of rabbits  

Acknowledgements

Financial support of this work from MEKARN, SIDA-SAREC is gratefully acknowledged. The authors would like to thank Dr. TR Preston for his valuable advices and the Department of Animal Science, Faculty of Agriculture and Applied Biology of Cantho University for infrastructure support.

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