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Livestock-Based Farming Systems, Renewable Resources and the Environment |
Citation of this paper |
An experiment was conducted to determine effects on growth performance and digestibility of supplementation of paddy rice and/or rice grain and/or rice husk to sweet potato (Ipomoea batatas) vines fed as basal diets to New Zealand White rabbits. A total of 28 male New Zealand White growing rabbits at 6 weeks of age were allocated to 4 treatments with 7 rabbits in single cages on each treatment . The treatments were: Sweet potato vines (SPV), SPV plus paddy rice grain at 20 g/day (PRG20); SPV plus broken rice grain at 20 g/day (BRG20); SPV plus 16 g broken rice grain and 4 g rice husk in separate feed bowls (BRGH). The experiment lasted 8 weeks following 1 week of adaptation.
Digestibility coefficients of DM, OM and crude protein were not affected by supplementation of sweet potato vines with paddy rice, broken rice or broken rice with added rice husk.There were indications that digestibility of the cell wall constituents was less when paddy rice, or the combination of broken rice and rice husk, were fed. Supplementation of sweet potato vines with paddy rice, broken rice, or broken rice with added rice husk, all led to improvements in live weight gain of the order of 17%; DM feed conversion was improved by 9% by supplementation.
Rabbits efficiently utilize fibrous feeds 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. 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 high protein forage, supplementation with highly digestible carbohydrate would seem to be a logical strategy. However, an attempt to do this by using broken rice was not successful in the experiment reported by Hongthong Phimmmasan et al (2004). By contrast, in other experiments (Hue and Preston 2006; Gang et al 2006), supplements rich in fibre gave positive results with rabbits fed diets based on water spinach. In the experiment reported by Tam et al (2009), rabbits fed on water spinach had greater feed intake and better live weight gain when they were supplemented with paddy rice. Recently, in our laboratory (Huyen et al 2010), we showed that supplementation of either sweet potato vines or water spinach with paddy rice improved live weight gain but at the same time reduced feed digestibility. So far, there has not been any answer to the opposing effects of paddy rice and broken rice grain on growth and digestibility in 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.
Twenty-eight male New Zealand White growing rabbits at 6 weeks of age were allocated to 4 treatment groups with 7 rabbits each in single cages. The rabbits were fed sweet potato vines (SPV) as the basal diet. Supplementation was as follows:
SPV: Sweet potato vines only
PRG20: SPV plus paddy rice grain at 20g/day
BRG20: SPV plus broken rice grain at 20g/day
BRGH: SPV plus 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 adaptation to the feeds and housing. Before the experiment began the rabbits were vaccinated against hemorrhagic diarrhea and drenched against intestinal parasites. They were fed three times a day at 8:00, 14:00, and 20:00h. Drinking water was 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 time.
Total feed and feces collections were made 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 feces (10%) were collected daily from the total feces collection and stored at -25°C. At the end of the 7 days the samples were bulked for individual animals. Feed and feces were subjected to chemical analysis.
Chemical analyses of diets and feeces 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 analysis of variance (ANOVA)using the General Linear Model (GLM) of Minitab (2000) software. Pair-wise comparisons of means were done using the Tukey test in the same Minitab software.
As expected there were major differences in the fiber components of the supplements (Table 1).
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Table 1. Chemical composition of feeds used in the experiment |
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CP |
NDF |
ADF |
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DM (%) |
As % in DM |
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Broken rice |
88.1 |
7.6 |
5.3 |
3.3 |
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Rice husk |
90.2 |
2.2 |
80.0 |
56.3 |
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Paddy rice |
90.5 |
6.6 |
32.2 |
15.0 |
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Sweet potato |
11.4 |
25.1 |
36.1 |
22.4 |
Feed intake was not affected by supplementation (Table 2).
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Table 2. Mean values for feed intake as affected by supplementation (± SE) |
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Diet |
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SPV |
PRG20 |
BR20 |
BRGH |
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Supplement DM, g/d |
0.0 ± 0.0 |
18.1 ± 0.0 |
17.6 ± 0.0 |
17.7 ± 0.0 |
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Forage DM, g/d |
106a ± 3.8 |
90.8b ± 3.8 |
95.8ab ± 4.1 |
97.8ab± 4.1 |
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Total DM, g/head/d |
106 ± 3.8 |
109 ± 3.8 |
114 ± 4.1 |
115.5 ± 4.1 |
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Total DMI, % LW |
6.0 ± 0.2 |
5.7 ± 0.2 |
5.9 ± 0.2 |
5.9 ± 0.2 |
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CP intake, g/d |
26.5 ± 0.9 |
24.7 ± 0.9 |
25.9 ± 0.9 |
26.2 ± 0.9 |
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NDF intake, g/d |
39.5a ± 1.22 |
39.4a ± 1.22 |
35.5b ± 1.32 |
40.5a ± 1.3 |
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a, b within a row, means without a common superscript differ at P <0.05 |
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Digestibility
Digestibility coefficients of DM OM and crude protein were not affected by supplementation (Table 3). There were indications that digestibility of the cell wall constituents was less when paddy rice, or the combination of broken rice and rice husk, were fed.
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Table 3. Mean values for coefficients of apparent digestibility (%) as affected by supplementation (± SE) |
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Nutrients |
Diets |
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SPV |
PRG20 |
BR20 |
BRGH |
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DM |
73.8 ± 1.42 |
70.6 ± 1.42 |
75.2 ± 1.53 |
73.2 ± 1.53 |
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OM |
74.6 ± 1.33 |
72.2 ± 1.33 |
76.1 ± 1.44 |
74.0± 1.44 |
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CP |
80.4 ± 1.09 |
77.7 ± 1.09 |
79.6 ± 1.18 |
79.1 ± 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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ab within a row, means without a common superscript differ at P < 0.05 |
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Live weight gain and feed conversion
All the supplements promoted an increase in live weight gain of the order of 17% (Table 4), and improvements in DM feed conversion of the order of 9%, but there were no apparent advantages from providing additional fibre in the form of the husk of the rice (either as paddy rice or as rice grain with additional rice husks offered in a separate feeder). For the positive effects of paddy rice, the results are similar to those we reported earlier (Huyen et al 2010) and were recently recorded by Luyen and Preston (2012). In both cases, paddy rice supplementation increased live weight gain on a basal diet of sweet potato vines. Tam et al (2010) found that paddy rice increased growth rate of rabbits when the basal diet was water spinach; they also observed that more fibrous feeds such as cabbage leaves also stimulated live weight gain.
The positive effect on growth rate in this experiment of supplementation with broken rice grain is different from the earlier findings of Hongthong Phimmmasan et al (2004) where there were no advantages from supplementation with broken rice when the basal diet was water spinach. However, the basal diet was also different: sweet potato vines in the present experiment versus water spinach in the work of Hongthong Phimmmasan et al (2004).
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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 |
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Initial LW, g |
1101 ± 73.8 |
1095 ± 73.88 |
1051 ± 79.80 |
1073 ± 79.80 |
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Final LW, g |
2069b ± 59.4 |
2221a ± 59.4 |
2185a ± 64.2 |
2237a± 64.2 |
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LW gain, g/d |
17.2b ± 1.24 |
19.9a ± 1.24 |
20.6a ± 1.34 |
21.3a ± 1.34 |
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DM conversion |
6.4a ± 0.45 |
5.6b ± 0.45 |
5.6b ± 0.49 |
5.6b ± 0.49 |
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a, b within a row, means without a common superscript differ at P < 0.05 |
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The consensus now seems to be that sweet potato vines generally are slightly superior to water spinach when given as the sole feed to growing rabbits, and that growth rates and feed conversion are at economically acceptable levels with both these basal diets. Paddy rice is seen to consistently improve the growth rates and feed conversion on both water spinach and sweet potato vines but the degree of improvement, of the order of 20%, may not always compensate for the additional cost of the paddy rice. By contrast, effects of supplementation with broken rice are not consistent. The reason for the consistent positive effects of paddy rice appear to be associated with the fibrous coating (the husk) as a source of fiber, but the bran which is also present in paddy rice (but not in broken rice) may also contribute critical nutrients (eg: B-vitamins, oil). The positive effect of paddy rice is not explained by effects on digestibility which mostly appear to be negative.
It is now clear that satisfactory growth and feed conversion can be achieved
with rabbits by feeding them as herbivores, and especially with diets
exclusively composed of either sweet potato vines or water spinach. Some
supplements, but especially paddy rice, can further increase performance but
improvements may not be compensated by the additional costs of the supplement.
The issue of food for people or for animals is another reason for directing
future developments to all-forage diets.
Digestibility coefficients of DM, OM and crude protein were not affected by supplementation of sweet potato vines with paddy rice, broken rice or broken rice with added rice husk.
There were indications that digestibility of the cell wall constituents was less when paddy rice, or the combination of broken rice and rice husk, were fed.
Supplementation of sweet potato vines with paddy rice, broken rice, or broken rice with added rice husk, all led to improvements in live weight gain of the order of 17%; DM feed conversion was improved by 9% by supplementation.
We are very grateful to the
Swedish International DevelopmentAgency (Sida), through the regional MEKARN
Project, for the financial support of this study.
References
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