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| Figure 1: Changes of live weight of rabbits during the experiment |
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An experiment was conducted to determine effects of supplementation of paddy rice and/or rice grain and/or rice husk to sweet potato (Ipomoea batatas) vines as basal diets for growing New Zealand White rabbits on feed intake, digestibility, average daily gain (ADG), feed conversion ratio (FCR) and economic returns. A total of 28 male New Zealand White growing rabbits at 6 weeks of age were allocated into 4 treatment groups with 7 rabbits each in single cages. Supplementations were designed as following: 1. Sweet potato vines (SPV): Basal diet without supplement, 2. PRG20: SPV plus paddy rice grain at 20 g/day, 3. BRG20: SPV plus broken rice grain at 20 g/day, 4. BRGH: SPV plus 16 g broken rice grain and 4 g rice husk in separate feed bowls. The experiment lasted 8 weeks following 1 week of adaptation.
It was found that total DMI among the experimental and control groups were not significantly different (P>0.05), either in an absolute term (g/head/day) or as percentage of LW. However, supplementation of paddy rice, broken rice and rice husk all reduced forage intake and had a positive effect on ADG and FCR (P<0.05). No significant differences were found for the effects of the different supplements.
Rabbits efficiently utilize fibrous feed by courtesy of their feeding and digestive strategies (Leng 2006). Rabbits can get energy from forages; they always have done in the wild state and their digestive system is developed for this purpose. Among other forages, sweet potato (Ipomoea batatas) vines is a common vegetable used for rabbit feeding in Vietnam as a basal and even the only diet. To improve the nutritional balance in diets based on forage, supplementation with highly digestible carbohydrate in the form of broken rice was not successful in the experiment reported by Hongthong Phimmmasan et al (2004). By contrast, in other experiments (Khuc Thi Hue and Preston 2006; Doan Thi Giang et al 2006), supplements rich in fibre gave positive results with rabbits fed diets based on water spinach. In the experiment reported by Nguyen Huu Tam et al (2009) in which rabbits fed on water spinach had higher feed intake and live weight gain when they were supplemented with paddy rice. Recently, in the work by Nguyen Thi Duong Huyen et al (2010), supplementation of paddy rice improved live weight gain but at the same time reduced feed digestibility of New Zealand rabbits fed on either sweet potato vines or water spinach. So far, there have been not yet any answer to the opposing effects of paddy rice on growth and digestibility of rabbits. The present study was aimed to test the hypothesis that there are some characteristics in the rice husk that have beneficial effects on growth of rabbits.
A total of 28 male NZW growing rabbits at 6 weeks of age were allocated into 4 treatment groups with 7 rabbits each in single cages. The rabbits were fed sweet potato vines (SPV) as basal diet. Supplementations were designed in the four diets as below:
- SPV: Sweet potato vines only
- PRG20: SPVplus paddy rice grain at 20g/day
- BRG20: SPVplus broken rice grain at 20g/day
- BRGH: SPVplus 16g broken rice grain and 4g rice husk in separate feed bowls
The experiment was carried out at the experimental farm of Hanoi University of Agriculture. It lasted for 8 weeks following 7 days of feeding adaptation. Before the experiment began the rabbits were vaccinated against hemorrhagic diarrhea and drenched against intestinal parasites. The animals were fed three times a day at 8:00, 14:00, and 20:00h in individual cages. Drinking water was made available at all times.
All animals were individually weighed at the beginning and thereafter once a week until the end of the experiment to calculate the average daily gain (ADG) as the slope of the linear regression of live weight on raising time.
Total feed and faeces collections were taken over 7 consecutive days in the middle of the experiment. The feeds offered and refusals were collected and weighed with samples taken daily in the morning. Representative samples of faeces (10%) were collected daily from the total feaces collection and stored at -25°C. At the end of the 7 days the samples were bulked for individual animals. Feed and faecece samples were subjected to chemical analyses. Digestibility (%) was calculated as = (A-B/A)*100, where A and B are total nutrient intake and total nutrient in the faeces. Feed conversion ratio (FCR) was calculated as a ratio of DM intake/live weight gain.
Chemical analyses of diets and faeces were undertaken following the methods of AOAC (1990) for DM, OM, CP, EE and ash. Contents of NDF and ADF were determined following the procedures of Van Soest et al (1991).
The experimental data were subjected to analyses of variance (ANOVA) made for a CRD model using the General Linear Model (GLM) of Minitab 16. Pair-wise comparisons of means were done using the Tukey’ test.
Chemical compositions of feeds used and the experimental diets were presented in Table 1
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Table 1. Chemical composition of feeds used in the experiement |
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Feed |
DM (%) |
CP (%DM) |
NDF (%DM) |
ADF (%DM) |
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Broken rice |
88.1 |
7.6 |
5.3 |
3.3 |
|
Rice husk |
90.2 |
2.2 |
80.0 |
56.3 |
|
Paddy rice |
90.5 |
6.6 |
32.2 |
15.0 |
|
Sweet potato |
11.4 |
25.1 |
36.1 |
22.4 |
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Table 2. Feed intake as affected by supplementation (Mean ± SE) |
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Intake |
Diet |
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SPV |
PRG20 |
BR20 |
BRGH |
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Grain DMI (g/head/d) |
0.0d ± 0.0 |
18.1a ± 0.0 |
17.6c ± 0.0 |
17.7b ± 0.0 |
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Forage DMI (g/head/d) |
106a ± 3.8 |
90.8b ± 3.8 |
95.8ab ± 4.1 |
97.8ab± 4.1 |
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Total DMI (g/head/d) |
106a ± 3.8 |
108.9a ± 3.8 |
113.5a ± 4.1 |
115.5a ± 4.1 |
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Total DMI (% LW) |
6a ± 0.2 |
5.7a ± 0.2 |
5.9a ± 0.2 |
5.9a ± 0.2 |
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CP intake (g/head/d) |
26.5a ± 0.9 |
24.7a ± 0.9 |
25.9a ± 0.9 |
26.2a ± 0.9 |
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NDF intake (g/head/d) |
39.5a ± 1.22 |
39.4a ± 1.22 |
35.5b ± 1.32 |
40.5a ± 1.3 |
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N.B.: a, b within a row, means without a common superscript differ (P <0.05) |
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Feed intake as affected by supplementation is shown in Table 2. Although grain and forage dry matter intake (DMI) among diets were significantly different, total DMI did not differ (P<0.05). The DMI (g/head/d) was highest for the BRGH diet. The present results were significantly higher compared with a study by Nguyen Thi Duong Huyen et al (2010) on sweet potato DMI (62.99 g/head/d) and water spinach DMI (51.42 g/head/d). Supharoek Nakkitset (2007) reported that DMI of rabbits fed water spinach was 66 g/head/d, which was also lower than the present result. This can be explained by the impact of adverse weather conditions during March. The average temperature was below 200C and humidity was above 80 %. This resulted in heat loss in rabbits, feed intake was therefore increased to meet their maintenance and growth requirements as well as to protest against cold stress. Because of high forage intake, total DMI was higher than in previous studies, but lower when compared with a study by Doan Thi Giang et al. (2006) on New Zealand White rabbits, in which DMI was 119 and 121 g/head/d in the basal diets of water spinach and sweet potato, respectively.
Digestibility as affected by supplementation is presented in Table 3. There were no significant differences among the control and experimental diets (P>0.05). Nguyen Thi Duong Huyen et al (2010) reported that digestibility was 76.40% and 76.20% for sweet potato and water spinach, respectively, higher than those determined in the present study. However, Nguyen Kim Dong et al (2006) showed that digestibility of Para grass (Brachiaria mutica) was 62.7%, lower compared with the present study. It was probably due to the fact that sweet potato is high in protein and low in fiber content compared with Para grass. According to Nguyen Kim Dong et al (2006) supplemention of water spinach to Para grass as basal diet at 0, 25, 50 75% resulted in DM digestibility of 62.7, 70.5, 71.7, and 73%, respectively.
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Table 3. Apparent digestibility as affected by supplementation (Mean ± SE, %) |
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Nutrients |
Diet |
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SPV |
PRG20 |
BR20 |
BRGH |
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DM |
73.8a ± 1.42 |
70.6a ± 1.42 |
75.2a ± 1.53 |
73.2a ± 1.53 |
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OM |
74.6a ± 1.33 |
72.2a ± 1.33 |
76.1a ± 1.44 |
74a± 1.44 |
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CP |
80.4a ± 1.09 |
77.7a ± 1.09 |
79.6a ± 1.18 |
79.1a ± 1.18 |
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NDF |
62.6a ± 2.09 |
54.5b ± 2.09 |
58.4ab ± 2.26 |
56.1a ± 2.26 |
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ADF |
59.4a ± 2.24 |
49.7b ± 2.24 |
54.9ab ± 2.42 |
53.2ab ± 2.42 |
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EE |
68.1a ± 1.77 |
63.9b ± 1.77 |
68.6a ± 1.91 |
65.9ab± 1.91 |
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N.B.: a, b within a row, means without a common superscript differ (P < 0.05). |
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Changes of live weight of rabbits during the experiment are presented Figure 1. Live weight gain and feed conversion ratio (FCR) as affected by supplementation is shown in Table 5. Supplementation resulted in an increase in live weight gain (P<0.05); however, live weight gain among the three supplemented diets were not significantly different (P>0.05).
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| Figure 1: Changes of live weight of rabbits during the experiment |
According to Doan Thi Khang et al (2007) supplementatiing Calliandra to basal diets of water spinach and Ghine grass (Panicum maximum) to feed New Zealand rabbits, the average daily gain (ADG) was 17.2, 16.6 and 18.8 g/head/d for diets of of water spinach, water spinach and Ghine grass, and water spinach and Calliandra, respectively. Khuc Thi Hue et al (2006) reported that ADG of rabbits fed 100% water spinach, water spinach and Stylo grass, water spinach and Ghine grass, and water spinach and broken rice were 18.1, 22.4, 23.1 and 22 g/head/d, respectively. Nguyen Thi Duong Huyen et al (2010) supplemented 0, 2, 3 and 4% paddy rice in rations of water spinach and sweet potato, the weight gains of rabbits were 19.83, 23.67, 23.58 and 24.03 g/head/d, respectively. In the present study ADG was lower than those found in the studies by Nguyen Thi Duong Huyen et al (2010) and Khu Thi Hue et al (2006).
The feed converted ratio (FCR) was lower for the control compared to the supplemented diets (P<0.05), among which no significant differences were found (P>0.05). The average of FCRs in the present study was 5.8 kg DM/kg LW gain, which was higher than that reported by Supharoek Nakkitset et al (2007) being 3.6 kg DM/ kg gain or by Nguyen Thi Duong Huyen et al (2010) being 3.86 kg DM/kg LW gain New Zealand rabbits given water spinach or 4.71 kg DM/kg LW gain for those given sweet potato vines.
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Table 4. Live weight gain and feed conversion as affected by supplementation (Mean ± SE) |
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Diet |
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SPV |
PRG20 |
BR20 |
BRGH |
|
|
Initial live-weight (g/head) |
1101a ± 73.9 |
1096a ± 73.9 |
1052a ± 79.8 |
1073a ± 79.8 |
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Final live-weight (g/head) |
2068b ± 59.4 |
2221a ± 59.4 |
2185a ± 64.1 |
2236a± 64.2 |
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Total weight gain (g/head) |
967b ± 61.0 |
1125a ± 61.0 |
1133a ± 65.9 |
1163a ± 65.9 |
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ADG (g/head/d) |
17.2b ± 1.24 |
19.9a ± 1.24 |
20.6a ± 1.34 |
21.3a ± 1.34 |
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FCR |
6.4a ± 0.45 |
5.6b ± 0.45 |
5.6b ± 0.49 |
5.6b ± 0.49 |
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N.B.: a, b within a row, means without a common superscript differ (P < 0.05). |
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We are very grateful to the Swedish International Development Cooperation Agency, Department for Research Cooperation (Sida-SAREC) through the regional MEKARN Project, for the financial support of this study.
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