Site and extent of cassava starch digestion in ruminants

Therdchai Vearasilp and Choke Mikled

Department of Animal Science, Faculty of Agriculture, Chiang Mai University,
Chiang Mai 50200, Thailand

Abstract

A series of experiments was carried out to study cassava starch digestion in ruminants. A higher starch content in the cassava was found compared with other cereals. A high rate of digestion of cassava starch in the rumen was also found. Substitution of cassava chips for broken rice improved the starch digestibility coefficient in ruminant rations. Increasing the protein content of cassava meal by addition of Glutamic Mother Liquid (a waste product from glutamate production), or Effluent Dry Powder “L” (a waste product of L-Lysine production), and substituting these mixtures for maize at the level of 50:50 gave the highest average daily live weight gain of White Lamphun cattle (866 and 813 g /day, respectively).

Key words: Cassava, starch, digestion, cattle, grrowth

Introduction

Cassava or tapioca (Manihot esculenta, Crantz) is one of the major crops grown in Thailand. The cassava products most commonly used as feed resources for livestock and poultry, such as cassava chips and cassava pellets, for many years were mainly exported to the European Union (EU). Recently, a shortage of energy feeds in Thailand has stimulated demand for cassava as a substitute for cereal grains in ruminant feeds in particular, and in manufactured feeds in general. However research has mainly focused on substituting cereals by cassava in either pig or poultry rations, and relatively little work has been done on ruminant feeds. This paper discusses a series of experiments carried out at Chiang Mai University to study the digestion of cassava starch, and the utilization of cassava as an energy source for ruminants.

Nutritive value of cassava

The starch content of cassava chips is the same as in broken rice and higher than in ground paddy, sorghum and maize, but the protein content is much lower (Table 1).

Table 1. Chemical composition of cassava chips compared to other feeds (% of DM)
	Starch	Protein	Dry matter	Reference
Maize	63.3	10.7	92.3	Therdchai 1987
Ground paddy	69.9	7.15	90.7	Therdchai Vearasilp and Choke Mikled 2001
Broken rice	87.8	9.05	89.3	Kriangsak et al 1990
Cassava chips	87.8	3.11	89.6	Therdchai Vearasilp and Choke Mikled 2001
Sorghum	65.3	-	-	Spicer et al 1986

Digestibility of cassava starch

An experiment was carried out with dairy cattle fitted with permanent rumen fistulae, and duodenal and ileal cannulas, to study the digestibility of cassava starch in comparison with other cereal grains. From Table 2 it can be seen that cassava starch was completely digested in the gastro-intestinal tract of ruminants, of which 94% was digested in the rumen, 5% in the small intestine and only 1% in the large intestine. Mueller et al (1978) also reported that the digestibility of cassava starch was relatively high compared with cereals. Thus it is probable that cassava could provide the energy yielding substrates required by the microbial population in the rumen. Nevertheless, due to a relatively low protein content in cassava chips, an additional supply of nitrogen sources to increase the efficiency of microbial synthesis is required.

Table 2. Digestibility of cassava starch in the total tract, rumen, small intestine and large intestine in comparison with other cereals
	Total tract	Rumen	Small intestine	Large intestine
Broken rice	95	66	29	5	Therdchai Vearasilp and Choke Mikled 2001
Ground paddy	99	93	5	2	Kriangsak et al 1990
Cassava chips	100	91	5	1	Therdchai Vearasilp and Choke Mikled 2001
Maize	92	56	29	15	Therdchai 1987
Sorghum (dry rolled)	90.8	75.2	8.9	6.9	Hibberd et al 1982

Cassava as a substitute for cereals

The first serious scientific approach to substituting cereals with cassava in commercial feed rations for livestock was in the early years post World War II. In Europe, especially in Germany, farmers utilized cassava as a major source of energy to solve the post-war shortage of grains. Studies to determine the maximum level of substitution of cereals with dried cassava root products indicated that they could replace cereals at a level of 20 to 40% in ruminant feeds and 10 to 20% in pig and poultry rations (Mueller et al 1978).

In studies carried out at Chiang Mai University, the digestibility coefficient and the amount of digested starch were improved by substituting broken rice with cassava chips (Tables 3 and 4). The proportion of the starch digested in the rumen increased, and in the intestine decreased, as the ratio of cassava to broken rice in the feed was increased.

Table 3. Amount of starch digested, and digestibility coefficients in different parts of the digestive tract of cattle fed different ratios of cassava chips and broken rice (Therdchai and Wichien 1992, personal communication)
	Cassava: rice
	25 : 75	50 : 50	65 : 35	80 : 20	25 : 75	50 : 50	65 : 35	80 : 20
	Starch digested (g/day)				Digestibility coefficient
Rumen	1,262	1,650	1,803	1,920	0.53^a	0.71^b	0.78^b	0.82^b
Small intestine	779^b	521^ab	311^a	294^a	0.71	0.74	0.59	0.68
Large intestine	158	160	191	122	0.45^a	0.83^b	0.81^b	0.84^b
Total tract	2,197	2,330	2,305	2,327	0.93	0.99	0.98	0.99

Table 4: Proportions of the digested starch that were digested in successive sections of the gastro-intestinal tract of cattle fed different ratios of cassava chips and broken rice
Cassava chips: broken rice
	25: 75	50: 50	65: 35	80: 20
Rumen	57^a	71^ab	79^b	82^b
Small intestine	36^b	22^ab	13^a	13^a
Large intestine	7	7	8	5
Total tract	100	100	100	100
ab Means with different superscripts within rows are different (p<0.05)

Performance of White Lamphun cattle fed with cassava meal as a substitute for maize

The shortage of grains has given an important stimulus to the utilization of cassava root products in ruminant rations. However, the lack of nitrogen supplied from cassava means that it is important to include nitrogen sources to balance the energy-nitrogen supply for the microbial activities in the rumen. In these studies two nitrogen sources were used, as follows:

GML: Glutamic Mother Liquid (Cassavi 3.5), a waste product from glutamate production
EFPL: Effluent Dry Powder “L” (EFP “L”), a waste product of L-Lysine production

These products were mixed with different ratios of cassava root meal and maize to raise the protein content to 11.1 (GML) and 9.5% (EFPL). The mixtures were fed together with rice straw toWhite Lamphun cattle (Table 5).

Table 5. Performance of While Lamphun cattle fed rice straw and maize/cassava chips mixed with either Glutamic Mother Liquid or Effluent Dry Powder “L”
	Maize: cassava meal
	100 : 0	50 : 50	25 : 75	0 : 100
Cassava meal mixed with Glutamic Mother Liquid
Dry matter intake (kg/day)
Concentrate	3.66	3.70	3.42	3.23
Rice straw	1.88	2.13	1.35	2.01
Total	5.54	5.83	5.37	5.23
Live weight gain (g/day)	794^ab	866^a	779^ab	695^b
Cassava meal mixed with Effluent Dry Powder “L”
Dry matter intake (kg/day)
Concentrate	2.51	3.77	3.44	3.50
Rice straw	1.98	2.47	2.41	2.33
Total	4.49	6.24	5.85	5.83
Live weight gain (g/day)	556^b	813^a	773^a	751^a

Conclusions

From these studies it is clear that cassava is a high energy feed. The digestibility of the starch in cassava is higher than in maize and sorghum and similar to that in rice. The partial (50%) or complete substitution of cassava chips for broken rice increased the proportion of starch digested in the rumen and the total tract digestibility.
After adjusting the protein content by mixing cassava meal with protein-rich byproducts (Glutamic Mother Liquid or Dry Powder Effluent “L”), the partial (50%) or complete substitution of maize grain in the diet improved the growth rates of White Lamphum cattle.

References

Hibberd C A, Wagner D G , Schemm R L, Mitchell E D , Weibel D E and Hintz R L 1982 Digestibility characteristics of isolated starch from sorghum and corn grain. Journal Animal Science 55 : 1490 – 1497.

Kriangsak Sathapanasiri, Therdchai Vearasilp and Chanvit Vajrabukka 1990 Digestibility of starch of cassava chips, ground paddy and broken rice in the digestive tract of dairy cows. Jourrnal of Agriculture 6: 265 – 280.

Mueller Z, Chon K C and Nah K C 1978 Cassava, a total substitute for cereals in livestock and poultry rations. Ruminant nutrition : selected articles from World Animal Review, FAO, 1978 pp: 155 – 160.

Spicer L A, Theurer C B, Sowe J and Noon T H 1986 Ruminal and post-ruminal utilization of nitrogen and starch from sorghum, corn and barley based diets by beef steers. Journal Animal Science. 62: 521 – 530.

Therdchai Vearasilp 1987 Starch digestion in ruminants. Journal Veterinary Science 17 : 78 – 92.

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