Growth performance of New Zealand White rabbits fed sweet potato (Ipomoea batatas) vines supplemented with paddy rice or Guinea grass supplemented with commercial concentrate

Ly Thi Luyen and T R Preston*

GRRC, NIAS, Bavi, Vietnam
manhluyen@yahoo.com
* TOSOLY, AA#48 Socorro, Colombia

Abstract

An experiment was conducted at the Goat and Rabbit Research Centre to determine effects on feed intake, average daily gain (ADG), feed conversion ratio (FCR) and economic returns of New Zealand White rabbits raised on two feeding systems: sweet potato (Ipomoea batatas) vines with supplementation of paddy rice and Guinea grass plus commercial concentrate.  There were 5 levels of supplement (paddy rice or concentrate): 0, 10, 20, 30 and 40 g/head/day.  A total of 30 male growing rabbits at 6 weeks of age were equally divided into 2 main groups of 15 each to be fed on either of the two basal diets. Each of the two main groups was further divided into 5 sub-groups (treatments) of 3 rabbits each. The rabbits were housed and fed in individual cages. The experiment lasted 10 weeks following 7 days of adaptation.

The system of sweet potato vines and paddy rice supported higher growth rates and better feed conversion than Guinea grass plus concentrate. In the Guinea grass-concentrates system the feed conversion became worse as the level of supplement increased; in contrast on the sweet potato vine-paddy rice system, feed conversion was the same irrespective of the level of supplementation.

Key words: Feed conversion, feed cost, feeding system, forages

Introduction

Rabbits are raised almost in all developing countries, and contribute to improving the nutrition and the economy of smallholder families, both as a source of animal protein, as well as a source of extra income through the sale of animals. They can be fed different kind of grasses, tree leaves, fruits (bananas), roots and tubers (eg: cassava and sweet-potatoes), and by-products. In particular they find vegetables such as sweet potato vines and water spinach very palatable. Sweet potato (Impomoea batatas L) can be planted for tuber or forage production, dependent on purpose and season; it can be planted once and cut throughout the year with subsequent harvests every day (Le Van An et al 2003).

Rabbits efficiently utilize fibrous feed by courtesy of their feeding and digestive strategies (Leng 2008). 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, water spinach (Ipomoea aquatica) and sweet potato (Ipomoea batatas) vines are common vegetables used for rabbit feeding in Vietnam as the basal and even the only diet. Both are high in crude protein (>20% in DM), the levels exceeding what are normally recommended for optimum growth rates in rabbits (eg:  16% crude protein in DM; NRC 1977). However, attempt to provider a better balance of nutrients by supplementing the forages with a high energy feed such as broken rice have not led to increases in growth rate or N retention (eg: Hongthong Phimmmasan et al 2004; Pok Samkol et al 2006)).  Paddy rice seems to be a more appropriate energy source according to the findings of Nguyen Huu Tam et al (2008) and Inthapanya and Preston (2009). Nevertheless, so far, it has not been clear what is the reason for the response in terms of growth rate to level of paddy rice supplementation. This is a question not only of nutrition but also economics. It is important to know what are the nutritional and economic advantages of a feeding system in which paddy rice is used to supplement protein-rich vegetables.

In the present study the standard feeding system in the Goat and Rabbit Research Centre, of Guinea grass and commercial concentrates, was used as the control system, to be compared with sweet potato vines supplemented with increasing levels of paddy rice.

Materials and Methods

Location

This study was carried out at the Goat and Rabbit Research Centre (GRRC) in Northern Vietnam from 20^th September to 10^th December 2011. The average temperature in the area is 26.1^oC and the average rainfall 1721 mm / year”.

Treatments and design

Thirty male growing New Zealand White rabbits at 6 weeks of age were equally divided into 2 main groups of 15 each to be fed on either of the two basal diets (Guinea grass or Sweet potato vines). Each of the two main groups was divided into 5 sub-groups (treatments) of 3 rabbits each to receive one of 5 graded levels of paddy rice and/or concentrate, which were 0, 10, 20, 30, 40 g/head/day. The forages were fed ad libitum. The rabbits were housed and fed in individual cages. The experiment lasted 10 weeks following 7 days of adaptation.

Feeds and feeding

Sweet potato vines and Guinea grass were bought daily from farmers around the Centre. Paddy rice was bought every 10 days and stored in sealed plastic bags to avoid uptake of humidity.  The commercial concentrate was purchased from a local Feed Company.

The animals were fed 4 times a day at 8:00h, 10:00h, 14:00h and 17:00h. Feeds offered and refusals were recorded daily.  Fresh water was freely available. The animals were vaccinated to prevent hemorrhagic disease, and treated for internal and external parasites.

Measurements

Live weight was recorded every 10 days, and feed intake daily.  Samples of offer and refusal of sweet potato vine and guinea grass were taken daily, pooled weekly and analyzed for DM and crude protein (AOAC 1990) and NDF and ADF (Van Soest et al 1991).

Statistical analysis

The trends in DM intake, growth rate and feed conversion,due to level of supplementation, were determined separately for each forage using Log_n or linear regression analyses.

Results and Discussion

Chemical composition

The sweet potato vines had more than twice as much protein and less cell wall components compared with the Guinea grass (Table 1). The concentrate had more than twice as much protein as paddy rice.

There were curvilinear (Guinea grass - concentrate) or linear (sweet potato vines - paddy rice) increases in DM intake in both feeding systems as the level of supplementation was increased, the slope of the response curve being steeper on the guinea grass-concentrate system (Table 2; Figure 1). This latter effect probably reflected the increase in the protein content of the diet  as the concentrate supplement (17.5% crude protein) replaced Guinea grass (9.8% crude protein). On the sweet potato vine diet the contrary relationship was observed as the diet protein content decreased as paddy rice (7.5% crude protein) replaced sweet potato vines (22.1% protein).

Figure 1. Trends in DM intake of rabbits fed Guinea grass - concentrate or sweet potato vines - paddy rice

 In both feeding systems the growth rate and feed conversion followed the same trend as the DM intake; however, there were consistent differences between the systems with the sweet potato vine - paddy rice diet being superior to the Guinea grass - concentrate diet at all levels of supplementation (Table 3; Figures 2 and 3). The increasingly poorer feed conversion as the concentrate level was increased on the Guinea grass basal diet implies that nutrients were better utilized when forage was the basis of the diet. This issue merits further investigation. On the sweet potato vine diet the feed conversion rate was not affected by the level of supplement, in this case paddy rice.

In both feeding systems the concentrations of NDF and ADF decreased as the supplements were increased (Table 2). Concentrations of NDF were higher and of ADF lower on the grass system than on the sweet potato vine system; however, it is difficult to draw any conclusions as to the significance of these values in relation to observed growth and feed conversion rates. Similarly the variations in diet crude protein content (increasing with supplementation on the grass system and decreasing on the sweet potato system) appear to be unrelated to rabbit performance.

Figure 2. Growth rates of rabbits on two feeding systems: sweet potato vines with paddy rice versus Guinea grass with concentrates	Figure 3. DM feed conversion of rabbits on two feeding systems: sweet potato vines with paddy rice versus Guinea grass with concentrates

Figure 4. Feed costs per kg LW gain for rabbits on two feeding systems: sweet potato vines with paddy rice versus Guinea grass with concentrate

The assessment of feed costs per unit live weight gain indicate that these increased with similar trends as for DM feed conversion (Figure 4). Lowest cost (and lowest growth rate ) was on Guinea grass alone with costs rising steeply with a curvilinear trend as the concentrate allowance was increased (Figure 4). By contrast, on the sweet potato-paddy rice system, feed costs increased only marginally as the paddy rice level was increased.  The optimum feeding system, on the basis of the results reported here, would thus be with sweet potato vines and the level of supplementation with paddy rice of 40 g/day since this gave the highest growth rate with minimal increase in costs compared with lower levels. Faster growth rate reduces the fixed costs component of the production system , thus if variable costs (of the feed) are not increased, then the system with higher growth rates will be more profitable. However, these relationships will be a function of the actual costs ascribed to the various feed ingredients which will vary according to whether they are purchased or produced with family labour.

Conclusions

• The system of sweet potato vines and paddy rice supported higher growth rates and better feed conversion than Guinea grass plus concentrates. 
  
  
•  In the Guinea grass-concentrates system the feed conversion became worse (and the feed costs per unit LW gain increased), as the level of supplement increased; in contrast on the sweet potato vine-paddy rice system, feed conversion and feed costs were almost the same irrespective of the level of supplementation.

References

AOAC 1990 Official methods of analysis. Association of Official Analytical Chemists, Arlington, Virginia, 15^th edition, 1298 p

Hongthong Phimmmasan, Sitone 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. Volume 16, Article # 34. Retrieved from. http://www.lrrd.org/lrrd16/5/hong16034.htm

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 http://www.mekarn.org/prorab/leng.htm

Le Van An, Lindberg B E F and Lindberg J E 2003 Effect of harvesting interval and defoliation on yield and chemical composition of leaves, stems and tubers of sweet potato (Ipomoea batatas L (Lam.)) plant parts. Field Crops Res. 82, 49-58.

NRC 1977 Nutrient Requirements of Rabbits, Second Revised Edition,  http://www.nap.edu/openbook.php?record_id=35&page=1

Nguyen Huu Tam, Vo Thanh Tuan, Vo Lam, Bui Phan Thu Hang and Preston T R 2008 Effects on growth of rabbits of supplementing a basal diet of water spinach (Ipomoea aquatica) with vegetable wastes and paddy rice. Livestock Research for Rural Development. Volume 21, Article # 174. Retrieved , from http://www.lrrd.org/lrrd21/10/hang21174.htm

Inthapanya S and Preston T R 2009 Effect of supplementation with sweet potato root and paddy rice on growth performance of local rabbits fed water spinach (Ipomoea aquatic) and paper mulberry (Broussonetia papyrifera) as basal diets. Livestock Research for Rural Development. Volume 21, Article #176. http://www.lrrd.org/lrrd21/10/sang21176.htm

Pok Samkol, Preston T R and Ly J 2006  Digestibility indices and N balance in growing rabbits fed a basal diet of water spinach (Ipomoea aquatica) supplemented with broken rice. Livestock Research for Rural Development. Volume 18, Article No. 22. http://www.lrrd.org/lrrd18/2/samk18022.htm

Van Soest P J, Robertson J B and Lewis B A 1991 Carbohydrate methodology, metabolism and nutritional implications in dairy cattle: methods for diatary fibre, and nonstarch polysaccharides in relation to animal nutrition. Journal of Dairy Science 74: 3585 - 3597. http://download.journals.elsevierhealth.com/pdfs/journals/0022-0302/PIIS0022030291785512.pdf

Received 4 June 2012; Accepted 20 June 2012; Published 1 July 2012

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