Effect of protein deficiency on utilization cassava peel by growing pigs

Materials and methods
Results
Discussion
References

E. A. Iyayi and O. O. Tewe

Cassava peel has been used to replace maize as an energy source in the diets of growing pigs. 154 weanling crossbred pigs (Landrace x Large White) were provided with either cassava-based or maize-based diets. A 40 percent level of cassava peel in place of maize was adequate for growing pigs. Performance in terms of feed intake and growth rate was enhanced when the diets were supplemented with plant and animal protein sources. A dietary protein level of at least 15 % was necessary for satisfactory animal performance.

The widespread occurrence of cyanide in the Manihot species has been largely documented. The role of cyanide in the etiology of diseases such as goitre, cretinism, tropical amblyopia, ataxic neuropathy, and pancreatic diabetes has been demonstrated from clinical and epidemiological studies. In the manifestation of some of these diseases, cyanide may act directly or through its product thiocyanate. Most often, the ingestion of cyanide-either from a dietary source of cassava or other roots or vegetables containing cyanogenic glycosides-requires its detoxification in the body, to thiocyanate. The use of sulfur amino acids for the detoxification process often results in a shortage of these amino acids. Therefore, the introduction of cyanide in situations of low or marginal protein levels in the diets of animals can further aggravate an already critical protein situation. Since cassava is now extensively used in animal production programs, as well as for human consumption, it is important to elucidate the effect of low protein intake on metabolic processes. The studies reported in this paper were conducted to answer the following questions.

· Is a 40% level of cassava peel in diets of pigs suitable for their rearing under tropical conditions?

· What minimum level of protein is permissible in the diets of growing pigs when cassava peel is substituted for maize?

Materials and methods

The cassava peels used were obtained from the Texaco gari factory at Opeji near Abeokuta, Ogun State, Nigeria. They were sun-dried and milled for incorporation into the diets. In the first study, 64 pigs (Landrace x Large White) were weaned for 3 weeks before they were put on eight experimental diets, as shown in table 1. All the diets were isocaloric but diets 1, 3, 5, and 7 were maize-based and had respectively 20, 15, 10 and 5 % dietary protein levels. Diets 2, 4, 6 and 8 were cassava peel-based (at 40% replacement) and also had, respectively 20, 15, 10, and 5 % dietary protein levels. The animals were randomly allocated to treatments on the basis of body weight and sex, with two replicates per treatment.

In the second study, 96 pigs (Landrace x Large White) were weaned and randomly allocated to six experimental diets (table 2), according to body weight and sex. Diets 2, 4, 5, and 6 had respectively 20, 10, 20 and 10 % dietary protein levels. The four diets also contained cassava peel (40%) in place of maize. Diets 1 and 3, based on maize and without cassava peel, were formulated to contain respectively 20 and 10 % dietary protein. Diets 5 and 6 contained added cyanide as potassium cyanide.

Table 1. Composition of diets for animals (Experiment 1)

Ingredient (%)		Diet
		1	2	3	4	5	6	7	8
Yellow maize		51.5	29.0	54.5	42.5	41.0	55.5	23.0	25.5
Cassava peel		nd	40.0	nd	40.0	nd	40.0	nd	40.0
Cassava flour		nd	nd	nd	nd	26.0	nd	64.5	27.0
Groundnut cake		9.0	15.0	9.0	nd	nd	nd	nd	nd
Fish meal		3.0	4.5	3.0	9.0	nd	nd	nd	nd
Blood meal		3.0	4.5	3.0	3.0	nd	nd	nd	nd
Palm oil		nd	4.5	nd	3.0	nd	12.0	10.0	4.0
Wheat bran		31.0	nd	31.0	nd	30.5	nd	nd	nd
Bone meal		1.5	1.5	1.5	1.5	1.5	1.5	1.5	1.5
Salt		0.5	0.5	nd	0.5	0.5	0.5	0.5	0.5
Min. /Vit. mix a		0.5	0.5	0.5	0.5	0.5	0.5	0.5	0.5
	Total	100.0	100.0	100.0	100.0	100.0	100.0	100.0	100.0
	Protein (%)	20.00	20.00	15.03	15.20	10.01	10.10	5.20	5.15
	Metabolizable energy (kcal/kg)b	3321.00	3217.00	3220.20	3204.00	3211.30	3222.00	3230.00	3204.60

Notes: ^a Min. /Vit. Mix: Zoodry YM501 Vitamin and trace mineral Premix [Content /kg-Vit. A 1200000IU, Vit. D 32000000IU, Vit. E 7000IU, Vit. B₂ 4000mg, Nicotinic acid 15000mg, d-pentothenate 8000mg, Vit. H (Biotin) 40mg, Vit. B₁₂ 10mg, and Mn 20000mg, Fe 50000mg, Zn 100000rng, Cu 10000mg, iodine 750mg, Co 300mgl nd = not included

Results

Effect of 40% cassava peel level and dietary protein on performance

The mean values of performance parameters are presented in table 3. The levels of cassava peel and dietary protein significantly affected daily feed and dry matter intake (P<0.01) and growth rate (P<0.05). Pigs on higher levels of cassava peel-based diets had significantly lower (P<0.01) feed efficiency. Dietary protein level also had a significant (P<0.01) effect on feed efficiency.

Table 2. Gross composition of diets for animals (Experiment 11)

Ingredient (%)		Diet
		1	2	3	4	5	6
Yellow maize		51.5	29.0	41.2	55.5	29.0	55.5
Cassava peel		nd	40.0	nd	40.0	40.0	40.0
Cassava flour		nd	nd	26.0	nd	nd	nd
Groundnut cake		9.0	15.0	nd	nd	15.0	nd
Fish meal		3.0	4.5	nd	nd	4.5	nd
Blood meal		3.0	4.5	nd	nd	4.5	nd
Palm oil		nd	4.5	nd	2.0	4.5	2.0
Wheat bran		31.0	nd	30.2	nd	nd	nd
Bone meal		1.5	1.5	1.5	1.5	1.5	1.5
Salt		0.5	0.5	0.5	0.5	0.5	0.5
Min./vit. mix a		0.5	0.5	0.5	0.5	0.5	0.5
	Total	100.0	100.0	100.0	100.0	100.0	100.0

Notes: ^a Min/vit. mix: Zoodry YM501 Vitamin and trace mineral Premix [Content/kg-Vit. A 1200000IU, Vit. D 32 000 000IU, Vit. E 7000IU, Vit. B₂ 4000mg, Nicotinic acid 15000mg, d-pentothenate 8000 mg,.Vit. H (Biotin) 40mg, Vit. B₁₂ 10mg, and Mn 20000mg, Fe 50000mg, Zn 100000mg, Cu 10000mg, iodine 750mg, Co 300mg] nd = not included

The protein efficiency ratio of animals on the cassava peel-based diets was poorer (P<0.05) than that of animals on the coin-based diets. Table 3 shows that for almost all the performance parameters, a significant (P<0.05) difference was recorded between animals on the 15% and 10% dietary protein levels. Animals on the 5% dietary protein level were runty and malnourished.

Table 3. Performance of pigs on experimental diets

Parameter	Cassava peel (%)		Crude protein (%)
	0	40	20	15	10	5
Initial weight (kg)	11.50	11.80	12.60	11.40	11.50	11.20
Final weight (kg)	30.10	33.52	55.50	30.20	19.30	13.25
Daily weight gain (kg)	0.22b	0.26a	0.51a	0.33b	0.09c	0.03d
Daily feed intake (kg)	0.72b	0.84a	1.33a	0.99b	0.49c	0.32c
Efficiency of feed utilization	5.09b	6.72a	2.64c	3.03c	5.52b	12.44a
Protein efficiency ratio	2.21a	1.90b	2.13a	2.43a	1.99ab	1.68b

Note: Values without common letter on the same horizontal row are significantly different

Discussion

The significantly higher feed consumption of the cassava peel-based diets can be attributed to the supplementation of the diets with rich protein sources and palm oil. Earlier work by Oke (1978) and Tewe (1987) showed that because of its low energy, dustiness, and low protein content, cassava root meal or cassava peel-based diets must be supplemented with rich protein sources and oil in order to improve their palatability and digestibility. Furthermore, such supplementation usually resulted in better profiles of amino acids and essential fatty acids. With respect to the effect of dietary protein, palatability could have played a major role. Since the higher protein diets were supplemented with protein ingredients such as fish meal, blood meal, and groundnut cake, the palatability of such diets could have been enhanced. Shield and Mohan (1980) reported higher feed intake and efficiency for animals on high protein diets.

The growth rate pattern closely follows that of feed consumption. It was clear that higher feed intake enhanced growth. Thus, in this study, apart from the levels of protein in the high protein diets (20 and 15 %) as compared with the low protein diets (10 and 5 %), the better quality of such diets resulted in better growth rates of the animals. More so, the feed efficiency and protein efficiency ratios suggested that the growth rates of animals on the 10 and 5 % protein diets were adversely affected.

The ratios of feed efficiency and protein efficiency for animals on the 20 and 15 % dietary protein levels were not significantly different, but were significantly different at the 10% level for almost all the performance parameters. This showed the 10% protein diet to be largely inferior to the 15% protein diets. Results of the study therefore show that the 10% level of dietary protein is largely unsuitable for rearing pigs, whereas, the 15 and 20 % levels are favorable in terms of performance of the animals. Our present study supports the earlier reports of Job ( 1975) and Tewe ( 1975) that dietary protein and not cyanide of the cassava peel was the major factor of concern in feed intake and growth. When pigs were fed sweet and bitter cassava roots, the toxic factor of bitter cassava did not have any inhibitory effect on growth (Job 1975, Tewe 1975). However, because of the interplay between cyanide and protein or more specifically the sulfur amino acids, high levels of cyanide present in some bitter strains of cassava could be a significant factor in the growth of the animals. Thus, the massive introduction of cassava in the presence of marginal levels of protein may result in the manifestation of poor pig growth.

Diets containing 40% cassava peel in place of maize are adequate for growing pigs, especially if such diets are supplemented with protein sources. A dietary protein level of 15% and above results in favorable performance.

References

Job, T.A. 1975. Utilization and protein supplementation of cassava for animal feeding and the effects of sulphur sources on cyanide detoxification. PhD thesis, University of Ibadan, Ibadan, Nigeria. 540 pp.

Oke, O.L. 1978. Problems in the use of cassava as animal feed. Animal Feed Science and Technology 3: 345-380.

Shield, AM., and D.E. Mohan. 1980. Effect of protein sequences on performance and carcass characteristics of growing finishing swine. Journal of Animal Science 55(5): 1340.

Tewe, O.O. 1975. Implications of the cyanogenic glucoside fractions of cassava in the growth and reproductive performance of rats and pigs. PhD thesis, University of Ibadan, Ibadan, Nigeria.

Tewe, O.O. 1987. Cassava peel utilization in poultry diets. Pages 150- 153 in Root crops and the African food crisis. IDRC-258e: Canada.