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)
 

Nguyen Thi Duong Huyen, Nguyen Xuan Trach and  T R Preston*

Hanoi University of Agriculture, Hanoi, Vietnam
nghuyen.hua@gmail.com
*Center for Research and Technology Transfer
Nong Lam University, Thu Duc District, Ho Chi Minh City, Vietnam

Abstract

A total of 40 male growing rabbits were equally divided into 2 main groups of 20 each to be fed on either of the two basal diets: water spinach (Ipomoea aquatica) or sweet potato vines (Ipomoea batatas). Each of the two main groups were divided into 5 sub-groups (treatments) of 4 rabbits each to receive one of 5 graded levels of paddy rice, which were 0, 1, 2, 3, 4% of live weight (LW). I

Level of paddy rice had no effect of total DM intake, reduced digestibility but improved feed conversion and  LW gain. Compared to sweet potato vines, water spinach was consumed less but better converted to weight gain with similar digestibility. Due to the opposing effects of paddy rice supplementation on feed digestibility and growth of rabbits, further investigations are warranted to find the underlying mechanisms.

Key words: Carbohydrate, digestibility,

Introduction

Rabbits can efficiently utilize fibrous feed by courtesy of their feeding and digestive strategies (Leng 200?).  Among other forages, water spinach (Ipomoea aquatica) and sweet potato (Ipomoea batatas) vines are protein-rich vegetables which have been commonly used as a basal diets for rabbits (Nguyen Thi Kim Dong et al 2006a,b; Pok Samkol et al 2006a,b,c; Doan Thi Giang et al 2006). To improve the nutritional balance in diets based on such protein-rich vegetables, different supplements rich in digestible starch or in fiber have been carried out (Hongthong Phimmmasan et al 2004; Nguyen Huu Tam et al 2008).  However, results obtained from those studies have been in marked contrast, with no growth response to broken rice (Hongthong Phimmmasan et al 2004); but with positive effects from paddy rice (Nguyen Huu Tam et al 2008).  The present study was aimed to test  production responses of growing rabbits to graded levels of paddy rice, and to relate these to effects on digestibility in basal diets of water spinach or sweet potato vines.

Materials and methods

The experimental design was a  5 x 2 factorial arrangement with 5  levels of paddy rice (0, 1, 2, 3, and 4% of live weight) supplemented to water spinach (Ipomoea aquatica) or sweet potato (Ipomoea batatas) vines fed as basal diets for growing New Zealand White rabbits.  A total of 40 male growing rabbits at 8 weeks of age were equally divided into 2 main groups of 20 each to be fed on either of the two basal diets. Each of the two main groups was divided into 5 sub-groups (treatments) of 4 rabbits each to receive one of the 5 graded levels of paddy rice.

The experiment lasted for 10 weeks following 7 days of adaptation at the experimental farm of the Faculty of Animal Science and Aquaculture, Hanoi University of Agriculture, Hanoi, Vietnam, during the period from late March to end of May 2010. Before the experiment began the rabbits were vaccinated against hemorrhagic diarrhea and drenched against intestinal parasites. During the experiment, rabbits were housed and fed in individual cages. The animals were fed either water spinach or sweet potato vines ad libitum three times a day at 8:00, 14:00, and 20:00h. Paddy rice was fed once per day at 11:00am. 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 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 daily in the morning. Representative samples of feces (10%) were collected daily from the total feces collected and stored at -25°C. At the end of the 7 days, the samples were bulked according to individual animals. Feed samples were taken over the same period.

Feed and feces samples were analyzed for DM according to AOAC (1990).  Feed conversion ratio (FCR) was calculated as a ratio of DM intake/live weight gain. Apparent total tract DM digestibility was computed as DM digestibility (%) = (A-B/A)*100, where A and B are total DM intake and total DM in feces, respectively.

Data were subjected to analyses of variance (ANOVA) for a 5x2 factorial model with interactions, using the General Linear Model (GLM) of Minitab 16 (2010). Pair-wise comparisons of means were done using the Tukey method. Regression analyses were made using Microsoft Excel (2007).

Results and discussion

Intake of the basal diet decreased as the offer level of paddy rice was increased (Table 1) but there were no differences in total DM intake. DM intake on sweet potato vines was 15% higher than on water spinach.

The higher the level of paddy rice that was offered, the more it was consumed (Table 1; Figures 1 and 2); however, at the same time, intake of the basal diet was reduced accordingly, so that total DM intake was not affected (Figures 3 and 4).

Growth rates on both sources of forage were increased by supplementation with paddy rice (Table 2; Figure 5) but the effects were relatively small (on average about 20 g paddy rice were needed to increase growth rate by 1 g/day). There were no differences in growth rate between the two forages, although there was an indication that the response to paddy rice was less with water spinach than with sweet potato vines (Figure 5).

Figure 5. Effect of paddy rice intake on growth rates of rabbits fed basal diets of sweet potato vines or water spinach

To find the mechanism behind the positive effect of paddy rice supplementation on live weight gain of rabbits fed a basal diet of protein-rich vegetables, improvement in digestibility might have been expected. However, relationships between proportion of paddy rice in the diet and DM digestibility in rabbits fed a basal diet of sweet potato or water spinach vines in the present study, as reflected in Table 4 as well as in Figures 7 and 8, show the opposing effect. The more paddy rice was consumed, and the higher proportion of it in the diet as a result, the lower the digestibility was; whereas feed utilization (FCR) tended to be better. This should be questions for further investigation. Where was the effect inserted? Was it because of low digestibility of the husk, which lowered digestibility of the total diet? Is there something in the husk or somewhere in paddy rice, not in broken rice, that can improve post-digestive metabolism in favor of live weight gain? Or was it due to other reasons?

It should be also noted that type of forage (water spinach vs. sweet potato vines) had no significant effect on digestibility of the total diet DM (P>0.05). However, water spinach had a better (lower) FCR compared to sweet potato vines (P<0.05). No interactions between level of paddy rice supplementation and type of forage (basal diet) on  digestibility and FCR were found significant (P>0.05).

Assuming the  sale value of a live rabbit is VND 40 000/kg live weight and that paddy rice has a cost of VND4000kg then even at the point of maximum response to paddy rice supplementation (between 0 and 1% of LW), the value of the increased growth rate (1.2 g/day = 48 VND is considerably less that the cost of the supplement (20.4 g/day = VND 81). Thus under most circumstances the mostg economical feeding system is likely to be either water spinach or sweet potato vines fed as the sole diet.

4.  CONCLUSIONS

The more paddy rice was supplemented, the less was the intake of the protein-rich vegetables in the basal diet (P<0.001) without affecting total feed intake (P>0.05) by the rabbit.  Paddy rice supplementation reduced digestibility of feed (P<0.01) but increased liveweight gain of rabbits (P<0.001). Due to the opposing effects of paddy rice supplementation to protein-rich vegetables as basal diets on digestibility of feed and growth of rabbits, further investigations are warranted to find the underlying mechanisms.

ACKNOWLEDGEMENTS

The authors 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.

REFERENCES

AOAC (1990) Official Methods of Analysis of the AOAC International.

Doan Thi Giang, Khuc Thi Hue, Dinh Van Binh and Nguyen Thi Mui (2006). Effect of Guinea grass on feed intake, digestibility and growth performance of rabbits fed a molasses block and either water spinach (Ipomoea aquatica) or sweet potato (Ipomoea batatas L) vines. Workshop-seminar "Forages for Pigs and Rabbits" MEKARN-CelAgrid, Phnom Penh, Cambodia, 22-24 August,  2006. Article #23 Retrieved June 8, 108, from http://www.mekarn.org/proprf/gang.htm

Hong T. T. T. (2003). Evaluation of Sweet potato leaves as a protein source for growing pigs in Central Vietnam. MSc Thesis in the programme "Tropical Livestock Systems". SLU, Dept. of Animal Nutrition and Management, P.O.Box 7024, Uppsala, Sweden.

 Hongthong Phimmmasan, Siton Kongvongxay, Chhay Ty and T. R. Preston (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

Khuc Thi Hue and T. R. Preston (2006). Effect of different sources of supplementary fibre on growth of rabbits fed a basal diet of fresh water spinach (Ipomoea aquatica). Livestock Research for Rural Development. Volume 18, Article #58. Retrieved June 8, 2008, from http://www.lrrd.org/lrrd18/4/hue18058.htm

Ly Thi Luyen (2003) Effect of the urea level on biomass production of water spinach (Ipomoea aquatica) grown in soil and in water; Retrieved, from MEKARN Mini-projects. http://www.mekarn.org/msc2003-05/miniprojects/webpage/luyen.htm

Microsoft Excel (2007). Microsoft Corporation. USA.

Minitab 16 (2010). Statistical Software. Minitab, Inc., USA.

Nguyen Huu Tam, Vo Thanh Tuan, Vo Lam, Bui Phan Thu Hang and T. R. Preston (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

Nguyen Thi Kim Dong, Nguyen Van Thu and T. R. Preston (2006a). Effect of dietary protein supply on the reproductive performance of crossbred rabbits. Proceedings of the MEKARN workshop on forages for pigs and rabbits, Phnom Penh, Cambodia, 22-24 August 2006.

Nguyen Thi Kim Dong, Nguyen Van Thu, R B Ogle and T. R. Preston (2006b). Effect of supplementation level of water spinach (Ipomoea aquatica) leaves in diets based on Para grass (Brachiaria mutica) on intake, nutrient utilization, growth rate and economic returns of crossbred rabbits in the Mekong Delta of Vietnam. Proceedings of the MEKARN workshop on forages for pigs and rabbits, Phnom Penh, Cambodia, 22-24 August 2006.

Pok Samkol, T. R. Preston and J. Ly (2006a) 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 # 22. Retrieved June 8, 108, from http://www.lrrd.org/lrrd18/02/samk18022.htm

Pok Samkol, T. R. Preston and J. Ly (2006b). Effect of increasing offer level of water spinach (Ipomoea aquatica) on intake, growth and digestibility coefficients of rabbits. Livestock Research for Rural Development. Volume 18, Article #25. Retrieved March 7, 2006, from http://www.lrrd.org/lrrd18/2/samk18025.htm

Pok Samkol, T. R. Preston and R. A. Leng (2006c). Effect of offering leaves or stems of water spinach on patterns of eating, consumption of caecotropes and excretion of feces by growing rabbits. Proceedings of the MEKARN workshop on forages for pigs and rabbits, Phnom Penh, Cambodia, 22-24 August 2006.