Effect on performance of replacing broken rice by molasses with supplementation of soya wastes in diets for growing ducks

Nguyen Thi Kim Dong, Pham Tan Nha, B Ogle and T R Preston

College of Agriculture, Cantho University, Cantho
ntkdong@ctu.edu.vn

*Department of Animal Nutrition and Management, Swedish University of Agricultural Sciences,
PO Box 7024, 750 07 Uppsala, Sweden
brian.ogle@huv.slu.se,
UTA TOSOLY, AA 48, Socorro, Santander, Colombia

regpreston@utafoundation.org

Abstract

A study on using molasses to replace broken rice in growing duck diets was carried out at the research farm of Cantho University. One hundred and fifty Crossbred Super-Meat ducks at 21 days of age were used in a complete randomized design with 5 diets as treatments and 3 replicates. The control diet (DM basis) was 76.5% broken rice, 20% soya waste and 2.5% duckweed. The experimental diets were: Control diet, and levels of 75 (BR75), 50 (BR50), 25 (BR25) and 0% (BR0) of the broken rice in the control. On BR75, BR50, BR25 and BR0, the molasses (type "B") was offered to the ducks ad libitum. The soya waste and duckweed were supplied at the same levels in all diets as protein sources.

Total dry matter (DM) intake increased when the broken rice was restricted to the 75% level, but declined thereafter with increasing restriction of the broken rice. Daily weight gain and carcass gain decreased linearly with increasing degree of restriction of the broken rice and feed conversion became poorer.

It was concluded that molasses can replace broken rice in growing duck diets at levels of 25to 50% without markedly reducing growth performance, although at current prices complete replacement of broken rice by molasses gave the lowest feed cost per kg gain.

Key word: Ducks, growth, carcass, molasses, soya waste, duckweed

Introduction

Molasses and soybean wastes are produced in large amounts by sugar cane factories and food processing factories in Cantho province. Sugar cane is one of the main crops in South Vietnam and in numerous other tropical countries. By-products of the sugar cane industry in the form of molasses have been widely used as a cereal substitute in livestock feeds (Preston 1995). These products have been shown to be promising for fattening pigs (Bui Hong Van and Le Thi Men 1994) and meat ducks (Becerra 1994; Toung Naren 1994). Molasses varies in its nutritive value for monogastric animals depending on the system of processing, and specifically the number of times the concentrated sugar cane juice is heated and subsequently the sugar extracted by centrifugation (Figueroa and Ly 1990). In the artisan production of sugar as practiced in the Cantho region, the concentrated juice is centrifuged twice, producing "A" and "B" sugars and "B" molassses. Figueroa and Ly (1990) showed that the "B" molasses contained about 20% of non-identified organic matter which had a negligible nutritive value to monogastric animals.

The studies on molasses as a feed for growing ducks are limited and there are none in which "B" molasses has been combined with soya waste. As both "B" molasses and soya waste are widely available in the Cantho area, it was decided to evaluate these feeds for growing ducks. Duckweed was included in the diets as this a common practice by local farmers as a means of supplying minerals and vitamins.

The hypotheses to be tested was that "B" molasses can be used as an energy source that can substitute for broken rice for fattening ducks.

Materials and Methods

Experimental design

A complete randomized design with 5 treatments (diets) and 3 replicates was used to test the performance of 150 growing Crossbred Super-Meat ducks. The control diet (DM basis) was 76.5% broken rice, 20% soya waste and 2.5% duckweed. The experimental diets were: Control diet, and levels of 75 (BR75), 50 (BR50), 25 (BR25) and 0% (BR0) of the broken rice in the control. On BR75, BR50, BR25 and BR0, the "B" molasses was offered to the ducks ad libitum.

Feeding and measurements

All the ingredients were fed separately and fresh quantities were given twice daily. The molasses was mixed with water in the ratio of 1 kg molasses to 5 kg water. All treatments included 400 g fresh soya bean waste and 65 g fresh duckweed per duck per day. The broken rice on the control treatment was fed ad libitum and the amounts on the other treatments calculated on the basis of the observed intake on the control diet. Bone meal was added to the broken rice at a level of 2% bone meal. The experimental period was 7 weeks.

The feeds offered and the refusals were recorded and samples taken for analysis of chemical composition. The ducks were weighed weekly. At the end of the experiment two representative ducks in terms of live weight (one male and one female) in each replicate were slaughtered to evaluate carcass parameters. Economic efficiency was also calculated. All data were analyzed by the General Linear Model option of the Minitab (Version 12.21) software.

Results and discussion

Chemical composition of feedstuffs

The chemical composition of the feeds used in the experiment is shown in Table 1.

Table 1. Chemical composition of experimental feeds (on DM basis, except for DM, which is on air-dry basis)
	DM	CP	EE	NFE	NDF	ADF	Ash
Broken rice	87.9	8.70	1.50	82.0	1.50	4.78	3.30
"B" Molasses	76.9	5.14	4.50	80.0	2.00	-	9.89
Soya waste	8.38	23.8	4.50	43.0	32.0	25.0	3.70
Duckweed	5.16	32.8	5.60	36.0	27.3	17.0	9.30

Feed intakes

Total DM intake increased when the broken rice was restricted to 75% of the control intake and "B"molasses given ad libitum; however, further restrictions of the broken rice led to decreases in DM intake (Table 2), with a marked decrease in intake when no broken rice was fed (Figure 1).

Table 2. Daily feed and nutrient intakes (g/bird) of ducks on diets with molasses replacing broken rice
Criteria	BR100	BR75		BR50	BR25	BR0	SEM / Prob.
Feed intake, g/bird/day
Total DM	136^b	146^a		133^b	124^c	90^d	3.05/0.001
Broken rice	104^a	79.9^b		57.7^c	35.9^d	-	0.89/0.001
Molasses	-	35.4^a		43.9^b	56.2^c	58.4^c	2.88/0.001
Soya waste	28.5^a	27.1^b		28.0^ab	28.2^ab	28.4^ab	0.48/0.05
Duckweed	3.36	3.36		3.36	3.36	3.36
Crude protein	16.9^a	16.3^b		15.1^c	13.8^d	10.9^e	0.11/0.001
Performance data
Daily weight gain, g	36.7^a	33.5^b		32.5^b	26.9^c	23.7^d	0.472 / 0.001
Feed DM conversion	3.72^a	4.35^bc	4.08^b		4.59^c	3.80^ab	0.125/0.001
abcde Means in the same row without letter in common are different at P<0.05

Figure 1: Relative intakes of broken rice and "B" molasses by fattening ducks

The rate of live weight gain was significantly depressed as intakes of broken rice decreased (Table 2), which in turn led to decreased intakes of crude protein, as the protein supplements (soya waste and duckweed) were given in fixed quantities, and the crude protein in the molasses was only 5.14% in DM compared with 8.7% for broken rice. There appears to be no information about the amino acid composition of "B" but it is almost certainly inferior to that in broken rice due to the heating of the protein in the molasses in the presence of the sugars leading to denaturation of part of the protein. The decrease in performance of the ducks on the high molasses diets was therefore almost certainly a reflexion of the reduced supply of protein. There was no difference in feed conversion between the control diet with 100% broken rice and the molasses diet without broken rice. There is no obvious explanation for this result as usually when the growth rate decreases the feed conversion becomes worse. The poorer feed conversion ratios on the intermediate broken rice / molasses diets (BR75, 50 and 25), compared with the control, can be explained by the lower energy density and reduced weight gains on these diets compared with the control.

The growth rate on the diet with molasses and no broken rice (23.7 g/day) was lower than the growth rates reported by Becerra (1994) (from 24.1 to 32.6 g/day) and Toung Naren (1994) (19.5 to 31.8 g/day) for sugar cane juice supplemented with duckweed and water spinach, respectively.

Carcass evaluation

The effects of the diets on the carcass parameters reflect the differences in final weights, since when the data were corrected for differences in carcass weight there were no differences between treatments (Table 3)

Table 3. Carcass parameters of ducks fed diets where broken rice (BR) was successively replaced by molasses
	BR100	BR75	BR50	BR25	BR0	SEM/Prob.
Final live weight, kg	2.66^a	2.46^ab	2.36^b	2.09^c	2.02^c	54.4/0.001
Carcass weight, kg	1.75^a	1.70^a	1.60^ab	1.43^bc	1.37^c	75.8/0.001
Carcass percentage	68.4	69.4	68.2	68.2	67.7	2.48/0.95
Breast muscle, g
Uncorrected	263^a	257^ab	251^ab	221^bc	202^c	15.0/0.01
Corrected#	244	243	247	235	222	13.1/0.64
Breast muscle, % of carcass	15.1	15.1	15.7	15.5	14.8	0.90/0.12
Thigh muscle, g
Uncorrected	215^a	192^ab	181^ab	172^b	160^b	13.73/0.01
Corrected#	204	184	179	180	171	12.9/0.43
Thigh muscle, % of carcass	12.2	11.3	11.3	12.0	11.7	0.51/0.50
Gizzard, g	79.2	65.9	67.6	64.5	63.9	0.12/0.19
abc Means in the same row without letter in common are different at P<0.05 # Corrected by covariance according to carcass weight.

Conclusions and recommendations

Under the conditions of this experiment replacing broken rice by "B" molasses led to decreased performance probably because of the lower protein content of the molasses compared with the broken rice
Although performance was poorer with the molasses diets, the feed costs were much lower because of the lower market price of "B" molasses (VND 1,200/kg) compared with broken rice (VND 2,200/kg).
In view of the confounding of protein supply with molasses substitution, it is necessary to repeat this study with diets of similar protein status.

Acknowledgements

This research was partially financed by the bilateral SAREC project 2000-2002.

References

Becerra M 1994 Evaluation of feeding systems for growing ducks based on aquatic plants and sugar cane juice. MSc thesis, Swedish University of Agricultural Sciences, Uppsala.

Bui Hong Van and Le Thi Men 1994 Evaluation of a protein diet based on raw sugar and water spinach (Ipomea aquatica) for growing pigs. Proceedings of National Seminar- Workshop “ Sustainable Livestock Production on Local Feed Resources”, HCM City, November 22-27, 1993: 47-49.

Figueroa V and Ly J 1990 Alimentación porcina no convencional. Colección GEPLACEA, Serie DIVERSIFICACION: México pp215.

Nguyen Thi Kim Dong and Ogle B 2002 Effect of using soya waste to replace soybean meal in diets of growing ducks. Unpublished data.

MINITAB 1999 MINITAB Reference Manual Release 12.21

Preston T R 1995 Tropical animal feeding: A manual for research workers. No 126, pp 305 (English)
http://www.fao.org/docrep/003/v9327e/v9327e00.htm

Toung Naren 1994 Optimum protein supply and level of inclusion of water spinach (Ipomea aquatica) in sugar cane juice based diets for growing ducks. MSc thesis, Swedish University of Agricultural Sciences, Uppsala.

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