Effects of different graded levels of tannia (Xanthosoma sagittifolium) on growth performance of broiler chicken

Abstract An investigation was undertaken to study the effect of replacing maize grain with tannia corm meal (TCM) on growth performance parameters and economic feasibility of Ross 308 broiler chickens. A total of 180 unsexed day-old chicks were randomly divided into 15 pens, each with 12 chicks, and assigned to five dietary treatments in a completely randomized design with 3 replications. The treatments were replacement of maize grain with TCM at 0 (T 1), 15 (T 2), 30 (T 3), 45 (T 4) and 60% (T 5) levels. Feed intake, growth performance and mortality when it occurred were recorded, while weight gain and feed conversion ratio (FCR) were calculated. DM, CP, CF, EE and ash composition of TCM were 90.6, 3.7, 2.2, 1.2 and 2.2%, respectively, while its ME was 3121.21 kcal/kg DM. Daily feed intake of birds during starter phase was significantly different (P < 0.05) and increased as TCM inclusion level increased. However, during the finisher and entire production period, this value was comparable. Average daily gain (ADG) and FCR during starter and entire production period and final body weight of chickens were significantly (P < 0.05) different among treatment diets, while ADG and FCR during finisher phase and mortality rate were comparable across dietary treatments. Based on feed intake and rate of mortality recorded in this study, TCM in broilers diet could substitute maize grain up to 60%. However, taking the growth performance and economic benefits into consideration, its substitution should not be more than 45%.


PUBLIC INTEREST STATEMENT
Though Ethiopia has a large poultry population, the country has less benefit from this subsector, and one of the main reasons is the poultry feed problem.An ever-increasing cost of poultry feed is a serious challenge for producers, where more than 70% of production costs in an intensive poultry production system goes to feed expenses.The primary reason for this cost increment is the escalating price of conventional energy and protein feed ingredients.Cereal grains generally and maize in particular are used as sources of energy while compounding poultry feed.Unfortunately, due to stiff competition with human beings, relying on cereal grains to use as poultry feed sources in the future, especially in developing countries, is unaffordable.Hence, searching for locally available poultry feed sources is becoming a priority issue, and the current study was aimed to test the potentiality of tannia corm meal as a replacement for maize grain in broiler feed.and rate of mortality recorded in this study, TCM in broilers diet could substitute maize grain up to 60%.However, taking the growth performance and economic benefits into consideration, its substitution should not be more than 45%.

Introduction
Meeting consumer demand for more meat, milk, eggs and other livestock products is dependent to a major extent on the availability of regular supplies of cost-effective and safe animal feeds (Etalem et al., 2013).For many decades, global poultry production, like other livestock production enterprises, has been negatively affected by the high and raising cost of feed (Omede et al., 2017).Feed represents the greatest single expenditure associated with poultry production (Pym, 2013), accounting for about 60-80% (de la Cruz, 2016;Esonu et al., 2006;Oyedeji et al., 2003) of the total production cost in intensive production systems.Thus, as feed cost increases, poultry product prices also increase, which become unattainable for low level standard individuals, especially in developing countries.This persistent increase in the cost of poultry feed is caused primarily by the escalating cost of conventional energy and protein feed ingredients used to compound poultry diets (Omede et al., 2017).In this scenario, developing diet formulations with alternative ingredients is the best way to overcome the problem, especially when the alternative ingredients are locally available (Saleh et al., 2021).
Globally, maize is the major feed ingredient in broiler and layer rations, with an inclusion level of up to 60% (Tadele et al., 2018).This is mainly because its energy source is starch, which is highly digestible for poultry as well as highly palatable and free of antinutritional factors; thus, metabolizable energy value of maize is generally considered the standard with which other energy sources are compared (Pym, 2013).Unfortunately, the use of this cereal grain in ration formulation, especially in developing countries, is unaffordable, and its futurity is under question due to stiff competition with human consumption and industrial inputs (Abang et al., 2015;Tadele et al., 2018).Thus, high cost of cereals and uncertainty about their sustainable supply as an energy source for livestock led to the search for alternatives.The practical application of alternative feedstuffs for chicken nutrition in developing countries has received a great deal of attention (Saleh et al., 2021).But these alternative and locally accessible feedstuffs must be continuously assessed (Saleh et al., 2022).
Tannia (Xanthosoma sagittifolium) is one of the promising alternative feedstuffs that provides readily available energy with easily digestible carbohydrates (Abdulrashid & Agwunobi, 2012).However, the inclusion of tannia in poultry feed is generally limited over the world (de la Cruz, 2016), and in Ethiopia, it is totally untouched.Besides this, these limited works indicated a controversial result.According to the results reported by Abdulrashid and Agwunobi (2012), properly processed tannia will effectively replace maize up to 50% level of inclusion.Soaked tannia tuber meal (Xanthosoma sagittifolium) in the diets of starter broilers could be used up to 30% without affecting weight gain, feed intake and feed conversion ratio (Anyaegbu et al., 2017).However, a 10% tannia inclusion level in the diets of finisher broilers seems to be the best in terms of daily weight gain, feed conversion ratio and cost-effectiveness (Uchegbu et al., 2010).On the contrary, replacement of fermented tannia tuber meal up to 100% did not affect weight gain, feed intake and feed conversion ratio in broilers diets (Anyaegbu et al., 2018).On the other hand, all the previous studies have been conducted either on starter or finisher phases, and none of them have shown the effects of incorporating this material into chickens' diets for their entire production period.Therefore, this work investigates the feeding value of tannia corm meal as a substitute for maize grain in the starter and finisher diets of broiler production.

Description of the study area
The experiment was conducted at Bonga Agricultural Research Center, located in Kafa zone, South West Ethiopia (SWE), which is 450 km to the west from the capital city, Addis Ababa.The area lies within 07°00"−7°25'N latitude and 35°55"-36°37'E longitude, at an altitude of 1753 m above sea level.It experiences one long rainy season, lasting from March/April to October and its mean annual rainfall ranges from 1710 mm to 1892 mm.The mean minimum and maximum daily temperatures range from 18.1°C to 19.4°C (Assefa et al., 2015).

Preparation of experimental feed ingredients
Tannia (Xanthosoma sagittifolium) was obtained from farmers who cultivated the crop in Gimbo district, Kafa zone.The corm was harvested, cleaned of soil, washed, peeled and sliced into bits of about 0.2 cm and subjected to sun drying for 4-6 days by spreading on plastic sheet with the objectives of reducing antinutritional factors as well as minimizing its moisture content for convenient storage.Thereafter, the dried chopped tannia corm was milled in a sieve size of 5 mm and stored for feed formulation.Feed ingredients used to formulate rations in this study were maize grain, soybean meal, bone and meat meal, Noug seed cake, wheat middling, tannia corm meal, limestone, salt, vitamin premix and amino acids (methionine and lysine) (Table 1).Maize grain, Noug seed cake, limestone and salt were also run through a hammer mill sieve size of 5 mm to produce the meal, as indicated by Abdo et al. (2015).

Feed analysis, experimental rations and treatments
Prior to the experimental starter and finisher ration formulation, the chemical composition of the major feed ingredients (maize, soybean meal, tannia corm meal, bone and meat meal, Noug seed cake and wheat middling) was determined for proximate values such as dry matter (DM), crude fiber (CF), total ash, ether extract (EE), crude protein (CP), calcium and phosphorus.Chemical composition of minerals (calcium and phosphorus) and those of DM, CF, EE, CP and total ash were analyzed at JIJE Analytical Testing Service Laboratory in Addis Ababa and Jimma University College of Agricultural and Veterinary Medicine (JUCAVM) Animal Science Department Feed Laboratories, respectively.Calcium and phosphorus were determined by titrimetric and calorimetric methods, respectively, while the proximate values of the feed were determined according to AOAC (2003).The nitrogen-free extract (NFE) was calculated indirectly by subtracting all other chemical compositions from 100 and the metabolizable energy (ME) values were calculated according to Pauzenga (1985) as ME = (37 × crude protein) + (81.8 × crude fat) + (35.5 × NFE) × 10.
Antinutritional factors (phytate, oxalate, tannin and saponin) for fresh and sun-dried experimental material tannia corm were determined at JUCAVM, Post-harvest Management Department Laboratory.
All prepared feed ingredients were mixed following proper procedures.Accordingly, five experimental starter and finisher broiler diets were formulated based on the laboratory chemical analysis results.The control diet (diet 1) without tannia corm meal contained maize as the major source of energy.Diets 2, 3, 4 and 5 comprised tannia corm meal as a source of energy at 15, 30, 45 and 60% rates to replace maize, respectively.To meet the nutrient requirements of the broilers, the treatment rations used in this study were formulated to be nearly isocaloric and isonitrogenous, with 3000 kcal ME/kg DM and 22% CP for starters and 3200 kcal ME/kg DM and 20% CP for finishers.

Experimental design and management of chickens
Here, 180-day-old unsexed Ross 308 chicks with an initial body weight of 43.54 ± 1.04 (mean ± SE) were used.A completely randomized experimental design of five treatment diets with three replicates of 12 birds each was used.For the first 28 days of feeding trials, experimental birds were fed on a starter treatment diet and then shifted to finisher diets for the next 28 days of feeding trials.
To minimize transportation and handling stresses, at the time of arrival, chicks were provided with a sugar solution through drinking water.Each replicate was kept in a deep litter partitioned pen with 1.75 × 1 m of floor space.Wood shaving was used as litter to cover the floor, nearly to a thickness of 5 cm.Before the commencement of the actual experiment, the feeding and watering troughs were made ready, thoroughly cleaned and disinfected against disease causing pathogens with formalin.A two-hundred-watt electric light bulb was supplied as a source of light and heat, and charcoal (a fuel obtained by heating wood in the absence of oxygen) was also used as an additional heat source, specifically during the brooding period and in the absence of electric power.Feed was offered to the experimental chickens twice a day, nearly at 08:00 am and 04:00 pm ad libitum, and clean water was also available throughout the day.Initially, chicks were weighed in groups and allowed to continue with the assigned diets for a 56-day feeding period.Experimental chickens were vaccinated against Newcastle (HB1 and Lasota) and infectious bursal diseases as recommended by the manufacturers.Throughout the experimental period, health precautions and disease control measures, as well as other routine managements such as lighting and brooding, feeding and watering spaces that cause unwanted variation, other than treatment feed, were treated in a similar manner.

Feed intake and growth performance
The experimental period lasted for 56 days, during which data on the growth performance of birds was recorded.The birds were weighed at the beginning of the experiment and then on a weekly basis in groups per replicate so that the average body weight was calculated.Weighing was done in the morning before providing feed and water.Body weight change was calculated for each week as the difference between the final and initial body weight, whereas average daily gain was obtained by dividing the change in body weight to the time interval.To obtain the feed consumed daily, records of the feed provided to the birds were taken, and the left-over feed in the trough was subtracted.Feed conversion ratio was determined from the feed consumed and weight gain in the period computed as

Partial budget analysis/economic evaluation
To estimate the economic benefits of each treatment ration, partial budget analysis, as indicated by Upton (1973) was employed.Variable costs and returns from the sale of live birds were considered for calculation.Costs for all feed ingredients during the time of purchase and also the costs of transporting and processing tannia corm meal were recorded, and the total variable cost (TVC) for each replicate was computed by summing up those expenses.The total return (TR) was obtained by multiplying the mean live body weight of birds in a treatment with the current price.Therefore, deducting the total variable cost from the total return (TR) resulted in the net income (NI), i.e., NI= TR-TVC.The cost per body weight gain (BWG) of birds in a treatment was calculated by using the TVC of production and its mean BWG as:

Statistical analysis
To determine the significant difference, all data were subjected to an analysis of variance (ANOVA) procedure using the Statistical Analysis System (SAS, 2012, ver. 9.4).Whenever the analysis of variance declared a significant difference among treatment means, Tukey-Kramer test was employed to separate the difference between means.A p-value of less than 0.05 was considered to declare a significant difference.For the analysis, the following linear model was used: Y ij = μ + T i + e ij , where: Y ij = represents the j th observation in the i th treatment level, μ = over all mean, T i = treatment effect and e ij = random error.

Chemical composition of experimental feed
The chemical composition of major feed ingredients used to formulate experimental diets is indicated in Table 2.The ME value of TCM (3121.21kcal/kg DM) was higher than that of other major feed ingredients used in this experiment, but next to maize (3335.98 kcal/kg DM).Due to its high energy content, maize has become the standard against which other cereals, cereal byproducts and other energy-yielding ingredients are compared (Leeson & Summers, 2005).Dietary energy level is often used as the starting point in the formulation of practical diets for poultry, as birds eat primarily to satisfy their energy needs, and hence feed intake is primarily determined by ME (Pym, 2013).On the other hand, the CP content of TCM (3.70) was lower than other feed ingredients.
The CF content of TCM (2.20) was nearly similar to the CF value of maize (2.10).Being a monogastric species, poultry have little capacity to digest crude fiber, and feeds containing high crude fiber have low digestibility for poultry (Sobolev et al., 2019); hence, it is generally used as an index of nutritive value in poultry feeding.The EE of TCM (1.20) noted in this study was found to be lower than the other major feed ingredient EE (fat) values.Besides supplying energy, addition of fat to the poultry diet improves the absorption of fat-soluble vitamins, decreases the dustiness of a feed, increases the palatability of the rations, increases the efficiency of consumed energy and reduces the passage rate of the digesta in the gastrointestinal tract, which allows a better absorption of all nutrients present in the diet (Baião & Lara, 2005;Ravindran et al., 2016).

Levels of antinutritional factors
Antinutritional composition of fresh and sun-dried tannia corm is presented in Table 3. Relatively, the levels of phytate (36.36 mg/100 g) and tannin (535.70 mg/100 g) were the first and second components, respectively, which were effectively reduced in the course of drying.Hence, the amount of phytate in the sun-dried tannia corm decreased by about three times as compared to the fresh one.However, the degrees of reduction in saponin after sun-drying were lower, and for

Feed intake
The mean daily feed intake of experimental chickens is presented in Table 4.No significant (P > 0.05) difference in mean daily feed intake of experimental chickens among all treatment groups in the first week of the feeding trial was found.However, the mean daily feed intake of the experimental birds from 2 to 4 weeks of the feeding trial was significantly (p < 0.05) different among treatment diets.Lower feed intake in these weeks was seen in the control groups.In general, the mean feed intake of birds among treatment diets during the starter phase (0-4 weeks) in the present study was significantly (P < 0.05) different and increased progressively with the substitution level of TCM in the diets of chickens.Accordingly, during this phase of production, experimental birds that received T 1 had a significantly (P < 0.05) lower mean daily feed intake than T 5.However, there was no significant difference in mean daily feed intake for birds receiving T 2, T 3, and T 4 from that of birds receiving T 1 and T 5.In line with the current result, it has been reported that the feed intake of laying hens fed on dried tannia corm meal was significantly different and increased with increasing its level of substitution (Okonkwo, 2020).Similarly, according to Abang et al. (2013), feed intake of quails steadily increased, and groups fed 75 and 100% levels of taro corm meal consumed significantly more than groups receiving a control diet and lower levels of substitution.However, in disagreement with this result, Onu and Madubuike (2012) reported a decrease in feed intake of chickens during the starter phase, despite the levels of taro corm meal in their diet had increased.On the other hand, according to Jiwuba et al. (2016), birds fed on control and 15% taro corm meal inclusion diets had comparable intake with each other and were significantly lower than birds fed on 5 and 10% taro corm meal inclusion, which failed to show a linear association between intake and level of inclusion.
During the finisher phase of production, except for week 6 of the feeding trial, there was no difference (P > 0.05) in mean weekly feed intake among treatment groups fed on varying levels of TCM (Table 4).Though it showed a tendency of increasing intake as the level of TCM in their diets increased, the mean daily feed intake of chickens during this phase of production did not vary among the treatment diets.This result in feed intake of birds during the finisher phase in the present result was found to be concurrent with the work of Olajide (2017), who noted a similar feed intake among groups of birds receiving 0, 10, 20 and 30% rates of wild cocoyam corm meal.Adejoro et al. (2013) also indicated that broilers fed different levels of processed taro (Colocasia esculenta) corm meal had similar feed intake to those fed the control.However, the result in the present study was in disagreement with other authors' findings (de la Cruz, 2016; Uchegbu et al., 2010), who reported partial replacement of maize with cocoyam tannia corm meal fed to finisher broiler revealed a significant difference in total feed intake such that feed intake was increased in line as the level of replacement increased.The mean daily feed intake of birds for the entire experimental period (0-8 weeks) fed on different graded levels of TCM in the present study was not also affected (P > 0.05) by the substitution.However, as the level of TCM substitution in the diet increased, numerically, the mean daily feed intake of experimental birds also increased, except in T 3, which was less than T 2. Hence, the mean feed intake of birds fed on the control diet was 112.17 g/head, while birds fed T 5 on average consumed 117.88 g/head for the entire period of production.In agreement with this result, mean daily feed intake among groups of weanling rabbits treated with 0, 25, 75 and 100% rates of TCM replacement for maize grain had similar results (Agwunobi, 1999).However, replacement of cassava root chip for maize as a source of energy for the entire broiler production period revealed a significant difference where feed intake at 100% level of replacement was greater than 50 and 75% levels (Etalem et al., 2013).In general, the result of the current study showed that the replacement of TCM with maize positively affected the feed intake of chickens during the starter phase of production, but there seemed to be an absence of such impact during the finisher phase as well as for the entire period of production.
According to Abdulrashid and Agwunobi (2012), the low daily feed intake of birds in control as compared to other treatment levels of tannia corm meal substitution could be due to the higher energy in maize (control) diet.But the ME of the experimental diets in Abdulrashid and Agwunobi (2012) was highly different; it ranged from 3072.6 to 2793 kcal/kg DM, while ME in the present study ensured quite isocaloric and unlikely to be a reason.Rather, the observed difference in feed intake in the current study might be due to the difference in crude fat value of treatment diets, which was found to be reduced as the level of experimental feed replacement increased.Supplemental fat in the diets of poultry increases the transit time of ingesta and improves digestibility of other dietary constitutes, thereby increasing the utilization of energy in the feed (Mateos et al., 1982).Therefore, the current result agreed with this finding that diets low in fat levels as TCM replacement increased might be passed quickly during digestion as a result of a low chance of being exposed to enzymatic action and peristatic movement of digestion as well as absorption; hence, birds tend to eat more to fulfill their biological requirements.On the other hand, Ndimantang et al. (2006) reported that tannia corm meal was rich in nutrients and palatable, thereby increasing its acceptability in poultry diets.To the contrary, some reports (Ahaotu, 2018; Means within a row with different superscripts differ significantly (P < 0.05); SEM: Standard error of the mean; T1: Treatment without tannia corm meal substitution; T2: Treatment containing 15% tannia corm meal; T3: Treatment containing 30% tannia corm meal; T4: Treatment containing 45% tannia corm meal; T5: Treatment containing 60% tannia corm meal.Anyaegbu et al., 2018;Okon et al., 2007) showed that feed intake and cocoyam meal substitution in the diet of birds were inversely related.Nevertheless, the results of the present study revealed that the toxicity level of antinutritional factors in TCM as a replacement maize grain, up to 60%, was not high enough to depress feed intake in broiler chickens.According to Ferket and Gernat (2006), meat-type birds tend to consume to maximum gut fill if not limited by dietary toxicity or other factors like disease.As a result, it can be noted that incorporating tannia corm meal to such an extent in broiler diets indicates a promising result.

Growth performance of experimental chickens
The growth performance of chickens fed different graded levels of TCM is presented in Table 5.The mean initial BW of chicks among treatment diets was similar.Except for week 3, the growth performance of chickens in the other feeding trial weeks of the starter phase was significantly (P < 0.05) different among treatments.Thus, the growth performance of chickens during the starter phase was affected by the level of TCM substitution in diet; hence, the mean live body weight of chickens receiving T 5 was significantly lower (P < 0.05) than that of the control group.Consequently, the average daily weight gain of experimental chickens fed on T 5 was significantly (P < 0.05) lower than that of chickens treated with the control diet.This marked reduction in mean daily weight gain at 60% TCM substitution level despite the higher fed intake of birds indicated that the feed was not adequately converted to increased body weight gain, which might be attributed in part to low digestibility and utilization of nutrients.This was in agreement with Abang et al. (2013), who reported that the weight gain of growing quails fed on graded levels of taro corm meal (0-100%) was significantly different and decreased linearly despite increasing feed intake.According to Liu and Selle (2015), the extent and rate of starch and protein digestion in poultry feeding determined the growth and feed conversion efficiency.
On the other hand, average daily weight gain among groups of chickens that received diets containing 15 (T 2), 30 (T 3) and 45% (T 4) of TCM was compared favorably to the control group (T 1).However, this average daily weight gain revealed a tendency toward a steadily decreasing trend as the level of substitution in TCM increased, which was again a manifestation of low utilization of nutrients and hence a decrease in performance.In agreement with the current result, Anyaegbu et al. (2019) and Ahaotu (2018) reported the presence of a significant difference in daily body weight gain among treatments, which decreased linearly as the amount of boiled tannia corm meal in starter broiler chickens increased, and antinutritional factors were suggested for the observed difference.Likewise, Okon et al. (2007) reported that substitution of varying levels of boiled taro for maize also brought a significant difference in mean weekly body weight and weight gain of quails (Coturnix japonica), with a decreasing custom as the substitution elevated.On the other hand, the use of fermented tannia corm meal in place of maize grain up to 100% in starter broilers indicated a comparable result in daily body weight gain (Anyaegbu et al., 2018), which might be due to the method of experimental feed processing (fermentation) employed in that study, which reduced the antinutritional factors in it and enhanced nutrient utilization.
During the finisher phase, mean live body weight at the end of weeks 5 and 7 did not show a difference among all treatment groups.But, in weeks 6 and 8, mean live body weight was significantly (P < 0.05) different (Table 5).The mean final live body weight measured at the end of week 8 of the current study was significantly (P < 0.05) different and higher for T 1 than T 3 and T 5.However, this value among T 1, T 2 and T 4, as well as among T 3, T 4 and T 5 did not show a difference.
As indicated in Table 5, the average daily weight gain of experimental birds during the finisher phase of the current study was not different among treatments.This comparable result in average daily weight gain among the treatment diets during this phase as compared to the starter phase in the present work suggests that the adaptation of the experimental birds to the experimental material (TCM) thereby results in a relative improvement in digestion and better utilization of nutrients.In addition, this could also be due to the ability of the bird to utilize the available nutrients in tannia corm meal as their digestive system became well developed, resulting in an improvement in performance.According to Dorcas (2016), the digestibility of nutrients at the finisher phase was higher than at the starter phase due to the trend in age differences and the fact that the digestive tract systems of broilers are not well developed at the starter phase.Similarly, Farrell (2005) states that, as poultry mature, their ability to digest feedstuffs increases.The result of the current study agreed with de la Cruz ( 2016), who reported that broiler finishers treated with diets containing 0, 25 and 50% levels of TCM were statistically similar in terms of final body weight and average daily gain.On the other hand, Uchegbu et al. (2010) noted a nondirectional relationship where the average daily body weight of broiler finishers receiving 10% sundried TCM was significantly higher, and those treated with 5 and 15% were comparable to the control group.However, according to Abdulrashid and Agwunobi (2009), the final live weight and average daily gain of broilers during the finisher phase were linearly decreased as the level of taro corm meal substitution in the diet increased.Similarly, Abang et al. (2013) indicated that the mean final body weight of Japanese quails decreased significantly as fermented taro corm meal replaced maize grain at 0, 25, 50, 75 and 100%.
As indicated in Table 5, the average daily body weight gain of birds during the entire production period (0-8 weeks) was affected by the substitution of TCM in their diets.However, numerically, in Means within a row with different superscripts differ significantly (p < 0.05); SEM: Standard error of the mean; ADG: Average daily body weight gain; T1: Treatment without tannia corm meal substitution; T2: Treatment containing 15% tannia corm meal; T3: Treatment containing 30% tannia corm meal; T4: Treatment containing 45% tannia corm meal; T5: Treatment containing 60% tannia corm meal.chickens receiving T 3, the average daily gain was lower than in chickens receiving T 4, the general trend of weight gain followed a decreasing fashion, and birds in T 1 scored significantly (P < 0.05) higher values than birds in T 3 and T 5.However, average body weight gain among T 1, T 2 and T 4 as well as among T 3, T 4 and T 5 was not different (P > 0.05).In general, the result of the current study disclosed that the use of TCM in broilers as a replacement for maize grain up to 45% was promising in terms of final body weight and average daily weight gain, though groups under T 3 significantly lower than T 1 for these values.This comparable result for chickens fed up to 45% levels of TCM substitution with those fed on the control indicates its potential to replace maize without much detrimental effects on the bird's performance.However, to improve the performance of animals, rations containing roots, tubers, or their by-products must be formulated to contain a good protein source and sufficient sulfur-containing amino acids (Apata & Babalola, 2012).According to Ndabikunze et al. (2011), the low level of protein in cocoyam limits its utilization in the preparation of protein-rich food, and it can be improved by combining with other high protein source materials.
The decreasing tendency in the performance of experimental animals parallel to the increment of treatment diets might also be the result of antinutritional factors present in tannia corm, causing the nutrients to be less available.According to Apata and Babalola (2012), antinutrients are potentially harmful and give rise to a genuine concern for human and animal health in that they prevent digestion and absorption of nutrients.It is well documented that increasing the level of TCM in broiler diets reduces nutrient availability and thus reduces weight gain, mainly due to its bulkiness, raphides and semi-powdery nature (Ahaotu, 2018).Deficiencies of phosphors and nutritionally important minerals in monogastric animals as they fed on alternative feed resources such as cassava and tannia can be a result of cations bound in the phytic acid salt and the low bioavailability of phosphorus (Apata & Babalola, 2012), which reflects a progress decreasing in the performance of animals.

Feed conversion ratio and mortality rate
The feed conversion ratio (FCR) of experimental birds fed at different substitution rates of TCM is presented in Table 6.With the exception of the first week of the feeding trial, the observed daily mean FCR of chickens during the starter phase of this study was significantly (P < 0.05) affected by the treatment diet as it was described on a weekly basis.Treatments mean FCR in each week of the starter phase lacks consistency; however, for the whole production period of the phase (0-4 weeks), this parameter followed an increasing trend with the rate of TCM substitution.Accordingly, birds fed on the control diet had a better (P < 0.05) FCR than groups fed on T 4 and T 5 but statistically similar to T 2 and T 3. On the other hand, the mean FCR in T 5 was comparable with T 4 but significantly (P < 0.05) higher than T 2 and T 3. The mean FCR among T 2, T 3 and T 4 was also statistically similar.The observed increasing result in FCR was consistent with Ahaotu (2018), who noted a significantly higher FCR of starter broilers fed on 7.5 and 10% rates of tannia corm meal diets than groups receiving 0, 2.5 and 5% substitution.However, other previous studies reported a contradictory result, that starter broilers fed on 100% fermented TCM had a better FCR of 1.34, significantly lower than the values of 1.54, 1.41, 1.45 and 1.46 for groups fed on 0, 25, 50, and 75% TCM substitution diets, respectively (Anyaegbu et al., 2018).This difference in the FCR of broilers in the present study and that of Anyaegbu et al. (2018) might be a result of the different processing methods of TCM.According to Olajide et al. (2011), fermentation is the best method of processing to reduce antinutrients in wild cocoyam.
On the other hand, FCR among treatment means did not show a difference during all individual weeks in the finisher phase.Likewise, the daily mean FCR for the whole week (5-8) in the finisher phase that ranged from 2.71 (T 1 and T 2) to 2.95 (T 5) was similar.The absence of variations in FCR during this phase of production suggests that the adaptation trend of birds as they fed a long time and the ability of the birds to withstand antinutritional factors as they grew up were greater than during the starter phase.Thus, because feed conversion is economically important in the raising of poultry, the substitution of TCM in broiler diets at the finishers phase in the current study was found to be more impressive.In line with this, the use of tannia corm meal as a partial energy replacement in broiler finishers at 0, 25 and 50% rates of replacement resulted in a similar FCR (de la Cruz, 2016).Okon et al. (2007) also noted a similar FCR among different groups of quails as they fed varying levels (0-100%) of boiled taro corm meals as a replacement for maize.However, this result was in disagreement with Anyaegbu et al. (2018), who indicated a general FCR improvement in finisher broilers for these treated with varying levels of fermented tannia corm meal compared to the control groups.
However, daily mean FCR of birds for the entire production period (0-8 weeks) in the current study was affected by the level of TCM substitution and positively correlated with the rate of experimental material (TCM), as was seen in the starter phase.As a result, the group in T 5 had a higher FCR value, which was significantly (P < 0.05) greater than those of T 1 and T 2, but similar to T 3 and T 4.Although feed conversion ratios from T 1 to T 4 during the entire production period numerically increased, the observed difference was not significant (P > 0.05), and this comparable result suggested that incorporating TCM up to this level can replace maize grain in broilers without adversely affecting feed utilization.From the result, the rate of mortality across all treatment diets did not show any significant (P > 0.05) difference, which indicated substitution of TCM up to 60% in the broiler diet had no impact on the survival rate of broilers.

Partial budget analysis
The cost implication of broiler birds' production fed on graded levels of TCM for 56 days of the experimental period is presented in Table 7.The price of feed ingredients as well as the transport and processing costs of TCM were considered as variable production costs, while sales from live birds were the only returns.All the other costs of production were assumed to be common for all treatments and not used here.The cost of feed in kg both for the starter and finisher phases was significantly (P < 0.05) different among all treatment groups, and it was linearly reduced as the level of TCM replacement increased as a result of its cheap cost as compared to maize grain.In line   with this finding, a linear reduction in the cost of broiler feed when TCM substitution in diets increased was indicated by several authors (Anyaegbu et al., 2019;Olajide, 2017;Uchegbu et al., 2010).The cost of feed charged per bird during the starter phase of production did not show a significant (P > 0.05) difference.This was the reflection of an increment in feed intake as the substitution of TCM in the ration increased.On the other hand, this result in the finisher phase was significantly (P < 0.05) affected by the substitution of treatment diets.On the other hand, feed cost per bird in T 1 was significantly (P < 0.05) higher than in T 3 and comparable with T 2. The result of total feed cost (birr/bird) for the entire production period was also significantly different among all treatments, and it followed the trend in the finisher phase.
The result in the total variable cost of production, which stands for feed cost as well as transport and processing cost of TCM, showed a significant (P < 0.05) difference among treatment means.In T 5 (60% TCM substitution), total variable cost (birr/bird) was significantly (p < 0.05) reduced than T 1 (control) and T 2 (15% TCM substitution) and statistically similar to T 3 and T 4 (30 and 45% TCM substitution, respectively).Total variable cost in T 3 and T 4 was comparable to each other, and both were significantly lower than T 1 but statistically similar to T 2. The linear reduction in total variable production cost when maize grain is replaced by TCM in broiler diets in this result agreed with the findings of Abdulrashid and Agwunobi (2012).The replacement of Taro corm meal for maize (Getiso et al., 2021) also indicated a reduction in production costs for Potchefstroom Koekoek dual-purpose chicken.
In the present study, gross income was calculated by multiplying the sale price of a bird by its live body weight.The market price of live birds at the end of the feeding trial was determined through negotiation between the seller and buyer, where live weight was the single criterion taken into consideration.Thus, the price of a bird weighing 3 kg of live body weight was sold at 375 birr (125 birr/kg) at the local market level.Here, the lower average sale (312.37birr/head) was recorded in birds fed on 60% TCM (T 5), which was significantly (P < 0.05) different from groups fed on control (T 1) and 15% TCM (T 2), but it was found to be comparable with groups receiving T 3 and T 4 (30 and 45% TCM substitution, respectively).On the other hand, gross income for groups fed on T 1-T 4 did not reveal a significant difference among them.
In the present study, net income among treatment means did not show a significant difference, where 147.16, 150.60, 142.82, 154.07 and 145.00 birr/head were the respective earnings from groups treated by control (0), 15, 30, 45 and 60% TCM diets.The highest profit (154.07birr) that came from the group placed on T 4 (45% TCM diets) was associated with its relative low total variable cost of production as well as its comparable live body weight.The cost per body weight gain in birds from the current study also revealed a non-significant difference for all treatment diets.However, the least cost required to produce a unit kg of live body weight was obtained from T 4 (66.99 birr), while the highest cost was in the control diet produced at 71.18 birr.This result indicated that for every kilogram gain in weight of a bird in T 4 (45% TCM substitution), 4.19 birr was saved as compared with the control diet.According to Onu and Madubuike (2006), the maximum cost savings in birds fed on graded levels of wild cocoyam was at 20% substitution.However, the level of substitution in the Onu and Madubuike (2006) study was limited to 20%, and there would have been a chance of getting more cost reduction if the degree of replacement was beyond it.From the present study, based on the result of net income and cost per body weight gain, replacing the energy value of maize grain with TCM at 45% is better from an economic perspective.

Conclusion
In this study, feed intake was in a tendency of increasing with the level of TCM substitution, while the growth performance of birds at higher level of substitution (60% TCM diet) was negatively affected.However, values up to 45% TCM substitutions for most of the parameters were comparable.The result indicated that the replacement of TCM for maize grain in the broiler's diet was more effective at the finisher phase.In general, depending on the production performance and the economic feasibility, the use of TCM in broiler production as a substitution for maize grain up to 45% seemed to be attractive under the current Ethiopian and similar countries conditions.In order to reduce the cost of broiler production and the pressure of demand for maize, demonstration of this root crop for partial replacement of cereal grains at large-scale production should be encouraged.However, the use of TCM regarding its variety, stage of growth and agro-ecology whether it affects the production performance and mortality of birds need further study.