Growth performances, organ development and blood parameters of rats fed graded levels of steeped and cooked taro tuber (Colocasia esculenta var esculenta) meal

A Teguia, P B Telefo^* and R G Fotso*

Département des Sciences Animales, Faculté d'Agronomie et des Sciences Agricoles (FASA), Université de Dschang, BP. 70 Dschang, Cameroun. Tel. (237) 781 11 37.
Email: alexisteguia@yahoo.fr ; alexisteguia@justice.com
*Département de Biochimie, Faculté des Sciences, Université de Dschang, BP. 67 Dschang, Cameroun
bphelix@yahoo.co.uk and ghislainefotso@yahoo.fr

Abstract

A 42-day study on subchronic toxicity of the steeped and cooked taro meal was conducted using 16 males and 16 females 28-day old rats. Corn meal was substituted in a complete randomized design either at 0, 25, 50, or 100% levels with steeped and cooked taro meal in the usual rats' diet.

The incorporation of steeped and cooked taro meal in the diet didn't have any significant effect (p>0.05) on feed consumption, weight gain, and feed efficiency ratio of rats and on the macroscopic state of organs from tested animals. No significant difference (p>0.05) was recorded between the groups of animals for relative weights of the organs and studied blood parameters. No significant effect (p>0.05) of taro was recorded on total hepatic proteins, total serum cholesterol and alanine aminotransferase. However, total serum proteins and aspartate aminotransferase significantly (p<0.05) decreased with increasing incorporation of steeped and cooked taro meal in the diet of rats. The steeped and cooked taro meal was not found toxic at short-term and could be recommended for animal feeding.

Key words: blood parameters, growth performances, rats, steeped and cooked taro meal

Introduction

Maize is the main cereal involved in animal nutrition. It represents the main energy source and constitutes 60 to 70 % of monogastrics' diets especially pigs and poultry. Worldwide, about 66 % of all maize is used for feeding livestock, 25 % for human consumption and 9 % for industrial purposes (Raemaekers 2001). In tropical countries including Cameroon, there has always been competition between human and animals for maize and the importation has partially solved the problem. However, with the increase demand of maize for feed production; its price on international market is forecast to increase very rapidly. This insufficient cereal production has led to an increasing interest for substitution of maize with other agricultural products in animal.

The studies on the substitution of maize in the finisher diet of poultry with dried leaves of sweet potatoes (Hypomoea batatas) and ndole (Vernonia spp) showed that these leaves could be used efficiently to replace maize in the finisher diet up to 300 g.kg^-1 without significantly (p>0.05) affecting the body weight gain, feed consumption and feed efficiency ratio (Teguia et al 1993). Lyayi et al (2001) established the possibility of formulating diets for pigs including cocoa husk pods which, when treated with urea, improved the nutritive value of feed thus resulting in better production performance. Whole cassava plant could also be used to replace 25 to 50 % of maize in the starter diet of broiler chicken without any negative effect on their health but, with 13 to 26 % reduction of feed conversion (Akinfala et al 2002). Leterme et al (2005) studied the chemical composition, the nutritive value and voluntary intake of cocoyam (Xanthosoma sagittifolium) leaves and those of two tropical tree (Trichanthera gigantean, Morusalba) foliage in pigs and it was concluded that low energy density is the main limiting factor of tree foliage for pig nutrition but that they are good sources of minerals and well-balanced proteins. However, performances recorded in all these studies where limited by the low energy content of tested products.

Taro (Colocasia esculenta) has an energy content of above 4000 kcal/kg of dry matter and can be a good source of energy in animal feed. The total production in Africa in 1998 reached about 6.5 millions metric tons representing 75 % of the total world production (8.5 millions tons) (Onwueme 1999). The average taro yield in Africa is about 5.1 t/ha as compared with 1.6 t/ha for maize (Raemaekers 2001). However, in general, taro corm has a poor post harvest storage quality. In Cameroon, the high rate of post harvest loss and lack of proper scientific attention to this problem has been associated with more than 70 % drop in annual production (MINAGRI 1981, MINAGRI 1999). In addition, taro contains oxalates which altered its nutritive value by fixing some minerals such as calcium, zinc, iron that become therefore unavailable to the animal body. Different methods have been developed to eliminate or to least reduce the effect of antinutritionnal factors (ANFs) in animal feed among which, cooking in water, steeping and the combination steeping and cooking in water.

Although taro is consumed by human in Cameroon, no toxicological information on rodent or other species of livestock is available. The objective of this study was therefore to evaluate the subchronic toxicity and potential of steeped and cooked taro meal as a replacement of maize in the diets of laboratory rats.

Materials and methods

Animals and diets

Raw taro tubers brought from the local market were washed, peeled with a sterile knife and cut into slices of about 5 mm diameter. The sliced tubers were steeped in water (1 l/kg tubers) at room temperature for four days, and then cooked in water at about 100° C for one hour. Steeped and cooked tubers were oven-dried at 45° C for 5 days, grounded in a feed mill then stored in hermetically closed container. In the usual diet of rats consisting of 66 % maize flour, 20 % roasted soybean flour, 10 % fish meal, 1.4 % of oyster shell, 1 % cooking salt, 0.5 % cotton oil and 0.1% of biomultivitamins used as control diet, maize flour was replaced with steeped and cooked taro meal at either 25 % (diet 1), 50 % (diet 2) or 100 % (diet 3) level. The experimental chemical characteristics of steeped and cooked taro meal and the calculated chemical characteristics (Sauvant et al 2002)of experimental diets are given in table 1.

Table 1. Chemical characteristics of steeped and cooked taro meal and experimental diets containing graded level of steeped and cooked taro meal
Diets	Crude protein, g/100 g	Crude cellulose, g/100 g	Crude lipids, g/100 g	Total ash, g/100 g	Total carbohydrates, g/100 g	Crude energy, kcal/kg
Steeped and cooked taro meal	7,08	5,61	3,93	2,38	86,61	4389,94
Control	18.18	2.96	9.05	5.72	66.98	4234.97
Diet 1	17.95	3.52	9.09	5.91	66.91	4322.41
Diet 2	17.78	4.08	9.13	6.11	66.85	4409.85
Diet 3	17.44	5.21	9.19	6.49	66.72	4584.73

Thirty-two 28 days-old wistar albino rats (16 males and 16 females) were randomly divided into four groups of four males and four females each. The feed and water were provided ad libitum. Group 1 serves as control and was fed the diet without any taro meal (diet 0). Groups 2, 3 and 4 were respectively fed diets 1, 2 and 3 containing respectively 25, 50 and 100 % of steeped and cooked taro meal as a replacement of maize for 42 days.

Daily feed intake and weekly body weight were recorded and weekly feed efficiency ratio calculated. After the 42 experiment days, all the animals were submitted to an eight-hour fasting, anaesthetized with chloroform vapors and bled. Blood samples were collected by cardiac puncture using a sterile syringe. Samples of heart, liver, spleen, lungs, kidney, surrenal glands, ovaries, uteruses, deferent canal, epididymis, seminal vesicle, prostate, testicles, were immediately collected and weighed, their relative weights calculated. The livers samples were frozen at -20° C, and later processed for hepatic protein.

Biochemical and hematological analysis

Serum samples were analyzed for aspartate aminotransaminase (AST), alanine aminotransaminase (ALT) activities using commercial kits as described by Reitman and Frankel 1957) and Bergmeyer (1972), creatinine concentration using commercial kit Creatinine Liquicolor (Germany) as described by Schirmeister (1964). Serum was analyzed for Total protein concentration using Biuret method (Gornal et al 1949) Cholesterol concentration was by using commercial kit established by CHRONOLAB as described by Richmond (1973) and Flegg (1973). The liver supernatant was analyzed for Total proteins using Biuret method (Gornal et al 1949).

White blood cell (WBC) and red blood cell (RBC) count were determined as described by Theml (2000) while packed cell volume (PCV) was evaluated according to Benson et al (1992).

Statistical analysis

All the data collected during the 6-week study period on weight gain, feed intake, feed efficiency ratio, biochemical and hematological parameters were submitted to a one-way analysis of variance. The Student's t-test was used for the separation at 5% probability level. The JMPIN software version 4 of SAS (2001) was used.

Results

Growth performances and relatives weight organs of rats

Average feed intake and feed efficiency ratio increased with increasing level of taro meal in the diet over the 6-week period (table 2).

Table 2. Average weekly feed intake (g) of diets, feed efficiency ratio (g feed/g weight gain) and animals growth rate (% increase in weight gain) of wistar albino rats fed graded level of steeped and cooked taro meal
Treatments	Feed intake	Feed efficiency ratio	Growth rate
Control	167.26^NS	3.82^NS	203.80^NS
Diet 1	179.83^NS	4.85^NS	170.11^NS
Diet 2	183.40^NS	5.04^NS	165.00^NS
Diet 3	191.07^NS	5.12^NS	177.62^NS
SEM	12.06	1.14	11.17
NS: Mean within the column are statistically comparable (p>0.05). SEM: Standard error of the mean

In contrary, the higher growth rate was recorded with the control diet. However, no significant difference (p>0.05) was observed among the treatment groups for average feed intake, growth rate and feed efficiency ratio. No mortality was recorded over experimental period.

At killing, no significant difference was observed on the relative weights of collected organs from the different groups of animals (tables 3 and 4).

Table 3. Average relative weights (weight organ ×100/weight animal) of some organs of wistar albinos rats fed graded level of steeped and cooked taro meal
Treatments	Heart	Lungs	Spleen	Liver	Pancreas	Kidneys	Surrenal glands
Control	0.276 ^NS	0.639^NS	0.216^NS	3.371^NS	0.284^NS	0.551 ^NS	0.024^NS
Diet 1	0.285 ^NS	0.639^NS	0.235^NS	3.181^NS	0.120^NS	0.555 ^NS	0.019^NS
Diet 2	0.293 ^NS	0.578^NS	0.263^NS	3.320^NS	0.157^NS	0.592 ^NS	0.028^NS
Diet 3	0.283^NS	0.663^NS	0.224^NS	3.345^NS	0.187^NS	0.628^NS	0.021 ^NS
SEM	0.011	0.076	0.023	0,172	0,655	0,232	0,039
NS: Means within column are statistically comparable (p>0.05) SEM: standard error of the mean

Table 4. Average relative weights (Weight organ × 100/weight animal) of reproduction organs of wistar albinos rats fed graded level of steeped and cooked taro meal
Groups	Males					Females
Groups	Prostate	Seminal vesicle	Epididymis	Testes	Deferent Canal	Ovaries	Uterus
Control	0,034^NS	0,302^NS	0,200^NS	0,824^NS	0,035^NS	0,058^NS	0,208^NS
Diet 1	0,048^NS	0,166^NS	0,271^NS	0,879^NS	0,047^NS	0,034^NS	0,128^NS
Diet 2	0,046^NS	0,212^NS	0,209^NS	0,932^NS	0,044^NS	0,048^NS	0,219^NS
Diet 3	0,037^NS	0,184^NS	0,208^NS	0,895^NS	0,035^NS	0,057^NS	0,161^NS
SEM	0.009	0.039	0.014	0.040	0.006	0.006	0.046
NS: Means within columns are statistically comparable (p>0.05), SEM: standard error of the mean.

Hematological and biochemical parameters of rats

The PCV percentage and RBC counts tend to decrease with increasing level of steeped and cooked taro meal in the diet while WBC counts tended to increase (table 5).

Table 5. Average packed cell volume, red blood cells and white blood cells changes in rats fed experimental diets containing steeped and cooked taro flour as a replacement of maize meal
Groups	PCV, %	RBC, ´10⁵/mm³	WBC, ´10²/ mm³
Control	45.88^NS	95.08^NS	56.75^NS
Diet 1	45.00^NS	90.43^NS	56.75^NS
Diet 2	44.75^NS	89.43^NS	57.25^NS
Diet 3	43.50^NS	84.21^NS	57.75^NS
SEM	0.95	4.85	3,92
NS: Means within column are statistically comparable (p>0.05) SEM: standard error of the mean.

However, no significant (p>0.05) effect of the taro meal in the diet was recorded on PCV percentage, RBC and WBC counts.

The effects of steeped and cooked taro meal on serum parameters are given in table 6.

Table 6. Concentration of serum and hepatic constituents of rats fed graded levels of steeped and cooked taro meal
Groups	Total hepatic Protein, mg/g	Total serum protein, mg/ml	Total serum Cholesterol, mg/dl	Serum AST, U/L	Serum ALT, U/L	Serum creatinine, mg/dl
Control	177.00^a	116.12^a	86.72^a	107.35^a	57.58^a	2.97^a
Diet 1	188.87^a	90.93^b	97.66^a	80.57^b	38.67^a	3.00^a
Diet 2	210.25^a	81.54^b	68.36^a	68.58^b	39.38^a	2.57^a
Diet 3	170.77^a	78.55^b	70,70^a	72.47^b	45.70^a	3.00^a
SEM	19.12	3.92	10,16	5.17	3.32	0,37
a, b: Means carrying the same superscript within a column are statistically comparable values (p>0.05), SEM: standard error of the mean.

No significant differences (p>0.05) were recorded between the treatment groups for ALT activity, total cholesterol, total hepatic protein and creatinine concentration. AST activity and total serum protein concentration were significantly lower (p<0.05) in rats feed diet containing steeped and cooked taro meal as compared with control group.

Discussion

The increase in feed intake and feed efficiency ratio associated with a decrease in growth rate of animals as levels of steeped and cooked taro meal in the diets increased could be due to a poor utilisation of diet containing tested feedstuff. Steeped and cooked taro meal contained 5.61 % of crude fibre as compared with 2.2 % for maize (Sauvant et al 2002). These results agree with reports that, chickens' growth rate decreases with increase of fiber in diet (Agbede 2003). In the same thought, Djopnang (2004) demonstrated that, the increase incorporation level of "karité" flour in rats' diet led to growth delay associated with increase dietary fiber from 1.6 to 3.8 %.

The absence of significant difference among treatment groups for the relative organ weight and hematological parameters added to the absence of mortality suggested that steeped and cooked taro flour was not toxic. An increase in the weight of spleen (Robins 1974), a decrease in that of testes (Bhargava 1984) liver and kidney (Solomon et al 1993) could indeed be an indication of a toxic environment. However, although no significantly (p>0.05), RBC counts decreased while WBC count increased. According to Robins (1974), in a toxic environment, RBC count significantly decreased while WBC increased. The results of the present study could suggest the presence of residual ANFs in steeped and cooked taro meal.

The concentration of creatinine, cholesterol and hepatic proteins varied but not significantly. No clear effect of taro meal on these parameters was observed as inclusion level increased. The significant reduction of total serum proteins with increasing level of taro meal could be associated with the corresponding increase of dietary fibre known to alter bioavailability of dietary proteins. Cossack and Rojhani (1992) reported that excessive dietary fibers disturb digestive enzymes action by binding to minerals and B group vitamins that usually act as enzyme cofactors in proteins metabolism. According to Solomon et al, (1993) and Adam (1998), AST and ALT activities into the blood stream significantly increase in a toxic environment. In rats, 90 % of AST are present in holoenzyme form. During pyridoxine deficiency, the activity rate of these holoenzymes in relation with the total activity is significantly reduced but after a pyridoxine injection, the rate of holoenzyme raises rapidly while the total activity rises after several days (Okada et Kondo 1982, Koruda et al 1982). Koruda et al (1982) demonstrated the formation of an inactive form of AST in liver of pyridoxine deficient rats. In the present study, the activities of these enzymes decreased and this evolution was significant for AST. This fact could probably result from the lack of pyridoxine in the studied taro meal.

Conclusions

The steeped and cooked taro meal was not found toxic in short-term and could be recommended for animal feeding.
The 25% substitution level of corn flour by the steeped and cooked taro meal in the diet seems to give the most promising results as compared with the 50 and 100% substitution levels.
However, further studies are necessary to apply this study on pigs and poultry which are the most important maize consumers.

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