a lagoon in Hue city, Vietnam
| Livestock Research for Rural Development 34 (5) 2022 | LRRD Search | LRRD Misssion | Guide for preparation of papers | LRRD Newsletter | Citation of this paper |
The foliage from sweet potato offers a range of benefits which justifies it being considered as the logical basal diet for rabbits in the humid tropics. When managed as a perennial forage, the biomass yield is high with the added advantage that the plant can be harvested continuously as the sole diet of rabbits. It also offers flexibility because if the availability of foliage from sweet potato exceeds the demand, the plant can then be left to complete the growth cycle with the tubers serving as a source of carbohydrate for human consumption or as a source of energy-rich feed for livestock.
Key words: broken rice, paddy rice, sweet potato, water spinach
Rabbits are herbivores and the system they possess to recycle the contents of the caecum provide the animal with advantages similar to those in ruminants except that, in the rabbit, fermentation follows the enzymatic digestion. Rabbits efficiently utilize fibrous feed by courtesy of their feeding and digestive strategy. Rabbits can get all their nutritional needs from forages; they always have done in the wild state and their digestive system is developed for this purpose (Leng 2008).
Despite these advantages, systems of rabbit production in developed and developing countries have become dependent on feed ingredients such as soybean and maize, which are largely imported. This practice is contrary to the strategy for reducing the carbon footprint of livestock which requires that their diets should be based to a major extent on feeds grown locally (Preston et al 2021).
In this discussion of research, done in tropical South East Asian countries, we indicate the way that we think research should be developed so that the carbon footprint of the feeding system is in line with the strategy required to reach Net-Zero 2050 so that global temperatures revert to pre-industrial levels.
As is the case for other livestock, the overall strategy must be to use crops that extract maximum levels of carbon from the atmosphere, at the same time providing the nutrients needed for efficient livestock production.
The fact that rabbits are herbivores is a strong justification for why they are more appropriate than broiler chickens as meat producers.
Water spinach grows equally well in water (Photo 1) as in soil (Photo 2) and is cultivated as human food where it is known as “Morning glory”.
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Photo 1.
Water spinach being harvested from a lagoon in Hue city, Vietnam |
Photo 2. Water spinach grown on soil in Cambodia |
Both leaves and stems are rich in protein (Table 1) with levels exceeding the requirements for growth when fed as the sole diet.
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Table 1. Feed characteristics of water spinach (% in DM basis, except for DM which is on fresh basis) |
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DM |
Ash |
Organic matter |
Crude protein |
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Water spinach |
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Leaves |
12.9 |
11.2 |
88.8 |
31.9 |
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Stems |
8.43 |
14.4 |
85.6 |
18.2 |
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However, the attempt to balance the nutritional requirements of growing rabbits has not been very successful. Broken rice appeared to be an appropriate energy supplement but attempts to balance the energy requirements had only limited success (Figures 1-3).
There were curvilineal responses in growth performance with positive results up to 10 g/day of broken rice, followed by a decline in performance with higher levels. The problem with higher levels of broken rice appeared to due to a decreasing capacity to digest the starch in the broken rice, as there was a linear increase in the excretion of short chain fatty acids in the feces as the level of broken rice in the diet was increased (Figure 4). On the highest level of 15 g/day of broken rice one rabbit had severe diarrhea and died because of this problem.
It is concluded that there are no economic benefits from supplementing water spinach with broken rice.
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Figure 1.
Effect on live weight gain of rabbits of supplementing water spinach with broken rice (Hongthong et al 2004) |
Figure 2.
Effect on feed intake of rabbits of supplementing water spinach with broken rice (Hongthong et al 2004) |
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Figure 3.
DM feed conversion of rabbits fed water spinach and increasing levels of broken rice (Hongthong et al 2004) | Figure 4.
Short chain fatty acids (SCFA) in feces of rabbits fed broken rice as a supplement to water spinach (Hongthong et al 2004) |
Sweet potato (Ipomoea batatas L) can be cultivated for tubers or forage; it can be planted once, and the foliage harvested daily throughout the year (Photo 3). For the purpose of this review, it will be discussed only as a source of foliage.
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| Photo 3. Sweet potato in Vietnam; a complete diet for rabbits |
Sweet potato managed as a perennial forage supports high yields of edible biomass and may be more appropriate than water spinach as the basis of a feeding system for intensification of rabbit production in tropical ecosystems.
As was the case for water spinach, the major issue is the relevance of supplementation with energy-rich feeds. Paddy rice was chosen as it seemed to be a more appropriate energy source than broken rice in view of the experience with broken rice as a supplement for water spinach (Figures 1-4). The physical structure of paddy rice with the rice husk acting to "slow down" access to the "starch-rich" interior appeared to be desirable characteristics in favour of paddy rice.
An experiment done at the Goat and Rabbit Research Centre in North Vietnam (Luyen and Preston 2012) helped to put in perspective an appropriate strategy for rabbit production in the tropics.
The feeding system for rabbits at the Center was based on Guinea grass (Panicum maximum) supplemented with traditional (maize-soybean) concentrates. This system was compared with sweet potato vines fed ad libitum and supplemented with increasing levels of paddy rice.
There were major differences in response to the two diets. In the absence of supplementations, DM intake was 70% higher when Sweet Potato foliage was the sole diet compared with Guinea grass (Figure 5). However, as the level of supplementation was increased, the differences between the two diets was much less, such that at high levels of supplementations there were no differences between the control diet of Guinea grass and concentrates and the experimental diet of Sweet Potato foliage and Paddy rice.
These contrasting differences were maintained for live weight gain (Figure
6) which was greater when the basal diet was Sweet Potato foliage
compared with Guinea grass. Growth rates of rabbits fed the Sweet Potato foliage were always superior to those on the basal diet of Guinea grass and concentrates.
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| Figure 5.
DM intake of rabbits fed concentrates and Guinea grass or sweet potato foliage with Paddy rice (Luyen and Preson 2012) |
Figure 6. Live weight gain of rabbits fed concentrates and Guinea
grass or sweet potato foliage with Paddy rice (Luyen and Preston 2012) |
The data in Figure 7 indicate only marginal differences in nutritive value between the two fodder sources. Other issues, such as agronomic factors and ease of harvesting, are likely to be the deciding factor as to which forage is preferred.
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| Figure 7.
Effect on growth rate of rabbits of supplementing basal
diets of water spinach and sweet potato vines with paddy rice (Huyen et al 2013) |
When the feeding system was based on the harvesting of a typical pasture grass, such as guinea grass (Panicum maximum), there was a major response to a supplement rich in digestible protein and metabolizable energy (Figure 5 and 6). However, when the forage source was Sweet Potato, or Water Spinach, the response to Paddy rice supplementation was marginal (Figure 7). DM digestibility of a diet based on Sweet Potato foliage decreased with Paddy rice supplementation (Figure 8). However, feed conversion of DM improved with Paddy rice supplementation, and this was the likely reason for the slight improvement in growth rate (Figure 9). The increased growth rate and improved feed conversion must be weighed against the additional cost of paddy rice.
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| Figure 8. Effect of Paddy rice on DM digestibility in rabbits fed Sweet Potato foliage (Doung Huyen et al et al 2013) |
Figure 9. Feed conversion is improved when Sweet Potato foliage is supplemented with Paddy rice (Doung Huyen et al 2013) |
The foliage from Sweet Potato offers a range of benefits which justifies it being considered as the basal diet for rabbits production in the tropics. When managed as a perennial forage, the biomass yield is high with the added advantage that the plant can be harvested continuously throughout the year as the sole diet of rabbits. It also offers flexibility because if the availability of foliage from Sweet Potato exceeds the demand, the plant can then be left to complete the growth cycle with the tubers serving as a source of carbohydrate for people or livestock.
Duong Huyen N T, Trach N X and Preston T R 2013 Effects of paddy rice on feed utilization and growth of New Zealand White rabbits fed basal diets of water spinach (Ipomoea aquatica) or sweet potato vines (Ipomoea batatas). Livestock Research for Rural Development. Volume 25, Article #100. http://www.lrrd.org/lrrd25/6/huye25100.htm
Hongthong Phimmmasan, Siton Kongvongxay, Chhay Ty and Preston T R 2004 Water spinach (Ipomoea aquatica) and Stylo 184 ( Stylosanthes guianensis CIAT 184) as basal diets for growing rabbits. Livestock Research for Rural Development. Vol. 16, Art. No. 34. http://www.lrrd.org/lrrd16/5/hong16034.htm
Lam V 2016 Agricultural potential of sweet potato (Ipomoea batatas, L. (Lam)) for forage production. Livestock Research for Rural Development. Volume 28, Article #101. http://www.lrrd.org/lrrd28/6/lam28101.html
Leng R A 2008 Digestion in the rabbit – a new look at the effects of their feeding and digestive strategies. Proceedings MEKARN Rabbit Conference: Organic rabbit production from forages (Editors: Reg Preston and Nnguyen Van Thu), Cantho University, Vietnam, 25-27 November 2008
Luyen L T and Preston T R 2012 Growth performance of New Zealand White rabbits fed sweet potato (Ipomoea batatas) vines supplemented with paddy rice or Guinea grass supplemented with commercial concentrate. Livestock Research for Rural Development. Volume 24, Article #127. http://www.lrrd.org/lrrd24/7/luye24127.htm
Preston T R, Leng R A and Gomez M E 2021 Adapting systems of livestock production to be compatible with global commitments to restore the health of planet Earth; ecosystems that remove atmospheric carbon and provide, food, feed and renewable energy. Livestock Research for Rural Development. Volume 33, Article #31. http://www.lrrd.org/lrrd33/3/Editorial3331.html