Evaluation of carcass characteristics and meat composition of broiler chicken fed graded levels of tannia (Xanthosoma sagittifolium) corm meal as a replacement for maize

ABSTRACT

A study was conducted to investigate the effect of replacing maize grain with tannia corm meal (TCM) on carcass characteristics and meat proximate composition. A total of 180-day-old Ross 308 broiler chicks were randomly divided into 15 pens, each with 12 chicks, and assigned to five dietary treatments with 3 replications. The five treatments were a replacement of maize grain with TCM at 0 (T₁), 15 (T₂), 30 (T₃), 45 (T₄) and 60% (T₅) levels. Slaughter, carcass, breast, thighs, drumsticks, wings, gizzard and skin weights among the treatments were significant (p < 0.05). The proximate composition of ether extract (EE) both in breast and thigh muscles was lower in birds fed 45 and 60% levels of TCM. The crude protein (CP) level of breast muscle and the ash content of thigh muscle were significantly (p < 0.05) different. On the other hand, moisture content in breast and thigh muscles, CP from thigh muscle and ash from breast muscle were comparable for all the treatment diets. In conclusion, based on the chemical composition of the meat noted in this study, TCM in broiler diets could substitute maize grain up to 60%. However, using TCM beyond 45% would affect most broiler carcass characteristics.

KEYWORDS:

• Broiler chicken
• carcass characteristic
• meat composition
• tannia corm meal

1. Introduction

Though the national chicken population of Ethiopia is estimated to be 57 million, the contribution of the sector to producers and the national economy at large is usually lower than its size (FAO, 2019). The productivity of the poultry sector in Ethiopia is mainly affected by feed scarcity and a consequently high price of conventional energy and protein source feed ingredients (Melesse et al., 2011). As Shapiro et al. (2017) also stated, the amount and quality of available feed will be one of the key determinants of the future livestock development potential of Ethiopia.

The cost of energy feedstuffs constitutes the largest component, which reaches about 50–55% of formulated poultry diets (Aman et al., 2021). Since intake of other nutrients is controlled by energy intake, it becomes imperative that poultry rations contain ingredients that will supply an adequate amount of energy to meet the birds’ requirements for production (Uchegbu et al., 2011), and cereal grains like maize are the primary sources of energy in this regard. Unfortunately, the rapid growth of the human population has intensified the competition between human beings and livestock for these energy-source cereal grains, mainly in developing countries (Abdulrashid and Agwunobi, 2009). The utilization and incorporation of Xanthosoma sagittifolium (one of the root crops) into broiler feed will go a long way towards increasing broiler production by reducing the pressure on major energy source cereals in broiler production (Ahaotu, 2018).

Tannia (Xanthosoma sagittifolium) and Taro (Colocasia esculenta) are the most important species under edible aroids (family Acraea), and together they are also called cocoyam in many parts of the world, especially in Africa (Opara, 2003). Xanthosoma sagittifolium is often higher-yielding than taro, and its average yield on a global basis is about 12–20 tons per hectare (Ubalua, 2016). According to CSA (2012), the production area coverage of taro and tannia in Ethiopia for the production year 2011/12 reached 39,696 ha with a total production volume of 315,242 tons. Because Xanthosoma sagittifolium is high-yielding, disease resistant and less in competition with human beings (Onunkwo et al., 2016), it is a cheap source of available energy for poultry. Though tannia has a moderate energy content as compared with maize (Anyaegbu et al., 2017), like other root and tuber crops, its drawback to use in animal feed is the presence of some antinutritional factors. However, different processing methods like fermentation, sun drying, boiling and soaking can be applied to minimize the problem (Apata and Babalola, 2012).

As several previous studies revealed, tannia can be a cheap source of feed ingredient in the poultry industry as a replacement for the scarce maize grain. According to Abdulrashid and Agwunobi (2019), boiled tannia could replace maize completely without any adverse effect on carcass characteristics, while 100% sun-dried tannia replacement poses an adverse effect on organ weight. Tannia corm meal can be a good feed ingredient in broiler chicken production up to 15% level without adversely affecting the quality and acceptability of the meat (Cagas, 2017). In terms of growth performance, feeding efficiency, rate of mortality and cost of production, partial energy replacement of maize by tannia corm meal revealed acceptable results (de la Cruz, 2016). However, in Ethiopia, tannia remains an underexploited crop, and there is no reference work on its utilization as an alternative energy source in the production of animals. Therefore, it was impressive to see the feeding value of tannia corm meal substitution in broiler chicken diets to evaluate its effect on carcass yield characteristics and proximate chemical composition of breast and thigh meat.

2. Materials and methods

2.1. 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 west of 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 1710mm to 1892 mm. The mean minimum and maximum daily temperatures range from 18.1° C to 19.4°C (Assefa et al., 2015).

2.2. Preparation of experimental feed ingredients

Tannia 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 anti-nutritional factors as well as to minimize its moisture content for convenient storage. Then, the dried chopped tannia corm was milled in a sieve size of 5 mm and stored for formulation. Feed ingredients used to formulate rations in this study were maize grain, soybean meal, bone and meat meal, Noug seed cake, wheat middling, TCM, limestone, salt, vitamin premix and synthetic amino acids (methionine and lysine) (Table 2). 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).

2.3. Feed analysis, experimental rations and treatment

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 by proximate analysis such as dry matter (DM), crude fibre (CF), total ash, ether extract (EE), crude protein (CP), calcium and phosphorus. Calcium and phosphorus were determined by Titrimetric and Calorimetric methods, respectively, while 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. Anti-nutritional factors (phytate, oxalate, tannin and saponin) for fresh and sun-dried tannia corm were also determined.

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 contained tannia corm meal as a source of energy at 15%, 30%, 45% and 60% to replace maize, respectively. To meet the nutrient requirements of the broiler chicken, the treatment rations used in this study were formulated to be nearly isocaloric and isonitrogenous at 3000 kcal ME/kg DM and 22% CP for starters and 3200 kcal ME/kg DM and 20% CP for finishers.

2.4. Experimental design and management of chickens

One hundred eighty unsexed day-old Ross 308 chicks were randomly distributed in a completely randomized design of five treatment diets with three replicates of 12 birds in each replication. For the first 28 days of feeding trials, experimental birds were fed starter treatment diets 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 sugar solution through drinking water. To provide sufficient ventilation and 12 h of natural lighting, the experimental house used in this study was partially open on both sides, and wire mesh was installed. Each replicate was kept in a deep litter partitioned pen, with 1.75 × 1 m floor space. Wood shaving was used as litter to cover the floor to a thickness of nearly 5 cm. Before the commencement of the actual experiment, the feeding and watering troughs were made ready and thoroughly cleaned and disinfected against disease causing pathogens with formalin. Two-hundred-watt electric light bulb was used as a source of light and heat, and charcoal¹ 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 56 days feeding period. Experimental chickens were vaccinated against Newcastle (HB1 and Lasota) and infectious bursal (Gumboro) diseases as recommended by the manufacturers. Throughout the experimental period, health precautions and disease control measurements as well as other routine managements such as lighting and brooding, feeding and watering space, which cause unwanted variation, other than treatment feed, were treated in a similar manner.

Table 1. Chemical composition of major feed ingredients used in this study.

Nutrients	Feed ingredients
	Maize	Soybean Meal	Noug-seed Cake	Wheat Middling	Meat and bone meal	TCM
Dry Matter (%)	92.00	90.80	92.30	89.00	93.40	90.60
Crude Protein (% DM)	8.80	43.00	31.50	15.60	45.14	3.70
Crude Fibre (% DM)	2.10	4.89	20.98	11.89	0.03	2.20
Ether Extract (% DM)	4.60	4.50	6.60	2.80	14.00	1.20
Ash (% DM)	2.30	6.50	11.90	2.50	31.45	2.20
NFE (% DM)	74.20	31.91	21.32	56.21	2.78	81.30
ME (kcal/kg DM)	3335.98	3091.91	2801.70	2462.24	2914.07	3121.21
Ca (% DM)	0.05	0.32	0.35	0.09	10.20	0.14
P (% DM)	0.31	0.69	0.91	0.45	4.04	0.16

Note: DM: Dry matter; NFE: Nitrogen Free Extracted; ME: Metabolizable Energy; TCM: Tannia Corm Meal.

Table 2. Proportions of ingredients used in formulating the experimental diets.

Feed ingredients (%)	Starter ration: 0–28 days (CP:22%, ME: 3000 kcal/kg DM)					Finisher ration: 29–56 days (CP:20%, ME: 3200 kcal/kg DM)
	Treatments					Treatments
	T1	T2	T3	T4	T5	T1	T2	T3	T4	T5
Maize	47.00	39.96	32.90	25.85	18.80	60.00	51.00	42.00	33.00	24.00
Soybean meal	23.00	24.30	24.45	27.00	26.00	22.50	23.50	23.30	23.00	24.50
Noug-seed cake	10.00	10.00	11.10	6.40	10.00	5.00	3.00	3.00	3.50	2.60
Wheat middling	11.80	10.10	8.00	9.70	6.60	5.20	5.50	4.70	3.80	2.00
Bone & meat meal	6.80	6.70	7.00	7.00	7.00	6.00	6.00	6.40	6.50	7.00
Tannia corm meal	0.00	7.54	15.10	22.63	30.17	0.00	9.63	19.26	28.89	38.52
Salt	0.32	0.32	0.32	0.32	0.32	0.32	0.32	0.32	0.32	0.32
Limestone	0.30	0.30	0.30	0.30	0.30	0.30	0.30	0.30	0.30	0.30
Premix*	0.50	0.50	0.50	0.50	0.50	0.50	0.50	0.50	0.50	0.50
Lysine	0.14	0.12	0.18	0.14	0.14	0.06	0.10	0.10	0.06	0.10
Methionine	0.14	0.16	0.15	0.16	0.17	0.12	0.15	0.12	0.13	0.16
Total	100	100	100	100	100	100	100	100	100	100
Calculated values
Crude protein (%)	22.17	22.10	22.0	21.64	21.39	20.12	19.55	19.06	18.62	18.46
Crude fibre (%)	5.61	5.50	5.50	4.86	5.21	4.03	3.72	3.64	3.64	3.33
Ether extract (%)	5.14	4.90	4.73	4.35	4.22	5.09	4.71	4.44	4.15	3.88
ME kcal/kg DM	3065.34	3055.64	3039.45	3049	3020.41	3148.41	3141.61	3123.67	3103.66	3095.13
Calcium (%)	1	1	1.02	1.04	1.05	0.9	0.91	0.95	0.97	1.03
Phosphorus (%)	0.75	0.74	0.74	0.71	0.71	0.68	0.66	0.65	0.64	0.65

Note: DM: Dry matter; ME: Metabolizable energy; T1: Treatment without TCM substitution; T2: Treatment replacing maize at 15% TCM; T3: Treatment replacing maize at 30% TCM; T4: Treatment replacing maize at 45% TCM; T5: Treatment replacing maize at 60% TCM; *Vitamin Premix = 25 kg contains: Vit A 2,000,000 IU/kg, Vit D3: 400,000 IU/kg, vit E: 10,000 mg/kg, Vit k3: 400 mg/kg, Vit B1: 300 mg/kg, Vit B2: 1000 mg/kg, Calcium-D-Pantothenate: 1800 mg/kg, Vit B6: 600 mg/kg, Vit B12: 4000 mg/kg, Niacin: 6000 mg/kg, Folic Acid: 200 mg/kg, Choline chloride: 40,000 mg/kg, Iron sulphate monohydrate: 9000 mg/kg, copper sulphate pentahydrate: 1000 mg/kg, Manganese Oxide:12,000 mg/kg, Zinc: 14,000 mg/kg, Iodine: 200 mg/kg, Selenium: 80,010 mcg/kg, Citric Acid, 25 mg/kg, Butylated Hydroxytoluene: 166 mg/kg, Propyl Gallate: 14 mg/kg, Calcium: 28.47%.

2.5. Data collection

2.5.1. Carcass characteristics

At the end of the experiment (at 56 days of feeding trail), one male and one female from each replicate (weighing near the mean of the group), six birds per treatment were selected and weighted after 12 h of feed withdrawal. Then the birds were slaughtered by severing the throat and hung upside down to ensure nearly complete bleeding. Following proper bleeding; scalding, de-feathering, removal of head and shank, dissection and evisceration (removing non-edible organs like crop, intestine, caeca and proventriculus) were conducted manually. Carcass weight was determined after removing blood, feathers, shanks, head and all non-edible internal organs (offals) and the dressing percentage was determined as the proportion of carcass weight to slaughter weight multiplied by 100, mathematically expressed as. $\mathrm{Carcass}\mathrm{dressing}\mathrm{percentage}={\displaystyle \frac{\mathrm{Crcass}\mathrm{weight}(g)}{\mathrm{Starved}\mathrm{live}\mathrm{weight}\mathrm{at}\mathrm{slaughter}(g)}\times 100}$As described by Kleczek et al. (2007), thighs, breast, wings, drumsticks and back (the major carcass parts) including neck and skin were gently separated and measured. The giblets (heart [without pericardial sac], kidney, liver [without gallbladder] and gizzard [without chyme and keratin epithelium]) were also separated and weighed.

2.5.2. Meat proximate analysis

After the required data on carcass characteristics had been recorded, samples of thigh and breast meat were taken from the same birds used for carcass cut evaluation. The breast and thigh meat samples were prepared² and stored in air-tight plastic bags in a deep freezer at - 4°C for 5 days. The moisture content of breast and thigh muscles was determined through oven drying of samples at 65°C for about 72 h. For the sake of convenience and homogeneity, the dried samples were ground and minced, and analysis for crude protein (CP), ether extract (EE) and ash was done following AOAC methodology (AOAC, 2003). A 2 g sample of ground meat was used to determine N content through the Kjeldahl method, and %CP content was determined as N × 6.25 while the lipid content was determined from a 1.5 g sample by diethyl ether extraction using the Soxhlet apparatus at 55°C for an hour. The total ash content was analysed by igniting a 2 g sample in a muffle furnace at 550°C for about 4 h until light grey ash resulted.

2.6. Statistical analysis

All data were subjected to the analysis of variance (ANOVA) procedure in determining a significant difference. Whenever the analysis of variance declared significance difference among treatment means, Tukey Kuramer Test was employed to separate the difference between means. A p- value of ≤0.05 was considered to declare significant difference. For the analysis, the following linear model was used. Yij = μ + Ti + eij, where: Yij = represents the jth observation in the ith treatment level, μ = over all mean, Ti = treatment effect and eij = random error.

3. Results and discussion

3.1. Levels of anti-nutritional factors

The anti-nutritional composition of fresh and sun-dried tannia corm is presented in Table 3. Relatively, the levels of phytate and tannin were the first and second components, respectively, which were effectively reduced in the course of drying. The amount of phytate in sun-dried tannia corm was 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 oxalate, it was not considerable. In the present study, the percentages of reduction in anti-nutritional factors were 31.67, 65.86, 1.08 and 14.78% for tannin, phytate, oxalate and saponin, respectively. According to Onunkwo et al. (2016) the percentages of reduction for phytate, tannin, oxalate and saponin in Xanthosoma sagittifolium after sun-drying were 4.95, 21.95, 13.99 and 9.08%, respectively.

Table 3. Levels of antinational factors in fresh and sun dried tannia corm (mg/100 g).

Parameters	Fresh tannia corm	Sun dried tannia corm
Tannin	784.00	535.70
Phytate	106.50	36.36
Oxalate	756.20	748.00
Saponin	1200.00	1022.65

3.2. Carcass characteristics

The results of carcass yield and edible internal organs in the present study are presented in Table 4. Slaughter weight, dressed carcass weight and weights of the breast, thighs, drumsticks, wings, skin and gizzard were significantly (p < 0.05) affected by TCM substitution. On the other hand, dressed percentage, the weights of the back, neck, liver, heart and kidney were not affected (p > 0.05) by TCM substitution for maize. Slaughter weights for the groups fed on treatments containing 15, 30 and 45% TCM were comparable with the control group, whereas in 60% TCM substitution, it was significantly (p < 0.05) lower than T1 but comparable with others. More or less, carcass weight in this study revealed a consistent result with the mean final BW of experimental birds, where T1 was statistically similar with T2 and T4 but significantly (p < 0.05) higher than T3 and T5. This value for T2 was higher (p < 0.05) than T5 and comparable with T3 and T4. Treatment means for breast and thigh weight followed exactly similar trend in that groups in the control were comparable to T2 and T4 but significantly (p < 0.05) higher than T3 and T5, while in all the rest treatments (T2 - T5) they were statistically similar. The highest weight of drumsticks was recorded in T4, the value of which was comparable with T1 and T3 and significantly (p < 0.05) different from T2 and T5. However, drumstick weights for T2 and T5 were comparable to the control group. Wings weight from T1 to T4 were similar, while the lowest value was noted in groups fed on 60% TCM substitution (T5) which was significantly (p < 0.05) different from T2 and comparable to the others. In the present study, skin weight in T4 was significantly (p < 0.05) higher than in T5, and this value among T1, T2, T3 and T4 as well as among T1, T2, T3 and T5 was comparable. Since the highest and lowest skin weights were observed at higher levels of substitution (45% and 60%), the relationship of skin with the level of TCM substitution was unclear.

Table 4. Carcass characteristics and giblets of experimental chickens feed on graded levels of tannia corm meal.

	Treatments					Mean	SEM
Parameters	T1	T2	T3	T4	T5
Slaughter weight (kg)	2.56^a	2.55^ab	2.45^ab	2.49^ab	2.41^b	2.49	0.01
Carcass weight (kg)	2.00^a	1.95^ab	1.72^bc	1.96^ab	1.68^c	1.86	0.09
Dressed percentage	78.26	76.78	69.96	78.60	70.01	74.72	4.21
Breast weight (g)	723.28^a	672.55^ab	589.33^b	672.08^ab	567.12^b	640.87	40.86
Thigh weight (g)	319.08^a	312.67^ab	271.67^b	314.75^ab	271.49^b	297.93	16.77
Drumstick weight (g)	228.32^ab	213.95^b	243.25^a	246.43^a	214.38^b	229.27	10.19
Back weight (g)	202.17	204.82	193..27	192.22	184.42	195.38	14.45
Wings weight (g)	155.35^ab	163.50^a	141.43^ab	154.40^ab	128.92^b	148.72	11.74
Neck weight (g)	74.28	75.10	67.47	75.05	71.27	72.63	5.19
Gizzard weight (g)	46.30^a	44.28^ab	37.00^c	41.65^abc	38.82^bc	41.61	2.56
Liver weight (g)	44.04	44.67	42.57	41.65	40.83	42.75	3.25
Heart weight (g)	10.10	9.92	8.97	8.73	8.78	9.30	0.85
Kidney weight (g)	11.93	10.17	10.42	11.85	9.63	10.80	0.96
Skin weight (g)	144.03^ab	151.10^ab	124.13^ab	155.30^a	117.17^b	138.35	13.25

^a-c Means within a row with different superscripts differ significantly (p < 0.05); SEM: Standard error of the mean; T1: Treatment without tannia corm meal; T2: Treatment containing 15% tannia corm meal to replace maize; T3: Treatment containing 30% tannia corm meal to replace maize; T4: Treatment containing 45% tannia corm meal to replace maize; T5: Treatment containing 60% tannia corm meal to replace maize.

At a 60% rate of TCM substitution, more or less all carcass components in weight were reduced despite the increase in feed intake. This poor performance mainly might be as a result of deficiencies in some nutrients and the presence of antinutrients in the treatment diet that limit nutrient utilization. Incorporating varying levels of boiled tannia corm meal into the broiler’s diet (Anyaegbu et al., 2019) negatively affected the dressed carcass weight in that the present study noted a concurrent result. This significant difference in the decreasing dressed carcass weight of broilers when maize grain was replaced by soaked tannia corm meal was also observed by Onunkwo et al. (2016). However, the result of dressed carcass weight in the current study was in disagreement with de la Cruz (2016) and Abdulrashid and Agwunobi (2009), who reported a non-significance difference in dressed weight as broilers fed on 0, 25 and 50% of tannia corm meal and 0, 25, 50 and 100% of taro corm meal, respectively, replacing maze as a source of energy. The weight of major meat cuts such as breast, thighs, drumsticks, and wings in this study was found to be in line with Etalem et al. (2013), who reported a significant difference among groups of birds treated by diets containing 0, 25, 50, 75 and 100% of cassava root chips as a source of energy in substitution for maize grain. Though the effect of sun-dried taro corm meal lacks consistency as it increases in treatment diets, at higher levels of substitution, Aman et al. (2021) also reported a lower value of carcass components in Pochefstroom Koekoek chicken. In contrast to the present study, none of the carcass components indicated a significant difference in groups of chickens treated by diets containing 0, 5, 10 and 15% of sundried tannia corm meals (Cagas, 2017). Anyaegbu et al. (2019) also reported that, except for breast muscle, all the other major chicken meat cuts showed similar carcass weight despite the use of different rates of tannia corm meal in their diets. Moreover, the weight of broiler meat cuts, live weight, dressing percentage and eviscerated weight of chicken fed on raw sun-dried and boiled tannia indicated comparable results (Abdulrashid and Agwunobi, 2019). The result of the present study was also in disagreement with Adetunji et al. (2020), who reported a non-significant difference in major meat cuts of broilers which treated with fortified composite cassava stump meal as a source of energy.

Among the internal edible organs, only gizzard weight across treatment diets declared the presence of a significant (p < 0.05) difference. Significantly (p < 0.05) heavier gizzards were recorded in the control groups than in T3 and T5, but comparable to the others. In line with this finding, Onunkwo et al. (2017) observed a significant effect of tannia corm meal on the gizzard weight of broilers, but the levels of substitution with the weight of the gizzard lack any association. However, according to Aman et al. (2021), the weight of the gizzard significantly decreased as the levels of taro corm meal substitution as a replacement for maize grain increased. On the other hand, Etalem et al. (2013) observed significantly higher gizzard weight in the control and 25% of substitution diets than treatment diets containing 75% and 100% cassava root chips in substitution for maize. Moreover, according to Anyaegbu et al. (2019), the replacement of cooked tannia corm meal for maize did not affect the weight of the gizzard. Other studies done by Abdulrashid and Agwunobi (2009) and Adejoro (2013) also noted, a lack of significance difference in the gizzard weight of broilers when taro corm meal substituted maize at varying levels. As it was reported by Iyayi and Yahaya (1999), any factor that enhances feed intake and growth rate will also influence live weight, dressed carcass weight, carcass parts and organ weights positively. However, feed intake and these parameters in the present study were negatively associated in most cases, indicating that intake by itself is not an ultimate predicator of better performance; rather, the extent of feed digestibility and utilization of nutrients may be determinant factors. On the other side, it is well documented (Han et al., 2017; Olajide, 2017; Widjastuti and Abun, 2019) that the level of fibre in the poultry diet positively affects the development of the gizzard. For instance, Olajide (2017) indicated an increase in weight of the gizzard as fermented wild cocoyam in the diets of broiler finishers increased and suggested that it was the result of the physical activity of handling relatively higher fibre in cocoyam-based diets. However, the weight of the gizzard and fibre content of diets in the present study seemed in absence of such a relation, rather, the weight of the gizzard more or less directly related to the slaughter weights of birds.

3.3. Proximate composition of meat

The proximate composition of the breast and thigh meats in the different treatment diets of the current study is presented in Table 5. The EE of breast and thigh meats, breast CP and ash in thigh meat were significantly (p < 0.05) affected by TCM substitution in diets. On the other hand, the content of ash and CP in breast and thigh muscles, respectively, as well as the moisture content of both breast and thigh muscles were statistically non significance among all treatment groups. The %CP content in breast meat revealed an increasing trend from T1 to T5 where T1 was significantly different from T5 and all other treatments were statistically similar to both T1 and T5. On the other hand, ash content in thigh meat for T1 was significantly higher than T4. At higher levels of TCM replacement for maize grain in T4 (45% TCM substitution) and T5 (60% TCM substitution), the EE both in breast and thigh muscles revealed a significantly (p < 0.05) lower value than T1 and T2. On the other hand, breast muscle EE for groups T1, T2 and T3 was comparable. However, EE for thigh muscle was statistically similar among T1 – T3 and T3 was similar with T4 and T5. As Bogosavljević-Bošković et al. (2010) reported, the type of raw materials and their chemical composition, as well as the protein and energy values of the formulated ration were among the major factors that affect the chemical composition and quality of poultry meat. The levels of protein and energy across treatment diets in the present study were iso nitrogenous and iso caloric and less likely to be the determinant factors for the observed variations in nutrient composition of meats, especially for crude fat, which showed a strong association with the level of TCM substitution.

Table 5. Chemical composition of breast and thigh muscles of broiler chicken fed chicken on graded levels of TCM.

Meat cuts	Parameter (%)	Treatments					Mean	SEM
		T1	T2	T3	T4	T5
Breast muscle	Moisture	72.28	73.21	70.46	69.78	71.30	71.40	1.79
	Crude Protein	24.95^b	26.11^ab	25.85^ab	27.20^ab	28.13^a	26.45	0.96
	Ether Extract	6.38^a	6.40^a	5.19^ab	3.81^b	3.70^b	5.09	0.82
	Ash	8.36	7.58	7.06	7.24	7.75	7.60	0.59
Thigh muscle	Moisture	75.39	74.55	74.44	76.09	75.57	75.21	1.61
	Crude protein	23.43	22.29	23.54	23.84	23.78	23.38	0.97
	Ether Extract	7.72^a	7.78^a	6.46^ab	4.84^b	4.66^b	6.29	1.02
	Ash	7.10^a	6.22^ab	6.50^ab	5.43^b	5.81^ab	6.21	0.51

Note: a–b Means within a row with different superscripts differ significantly (p < 0.05); SEM: Standard error of the mean; T1: Treatment without tannia corm meal replacing maize; T2: Treatment containing 15% tannia corm meal replacing maize; T3: Treatment containing 30% tannia corm meal replacing maize; T4: Treatment containing 45% tannia corm meal replacing maize; T5: Treatment containing 60% tannia corm meal replacing maize.

The compound flavonoids, tannins and phenols (Aiura and Carvalho, 2007) and tannins (Selvi and Basker, 2012) had been reported to have anti-lipid properties, and the possible justification in the current study might be attributed to the presence of tannins in TCM that played a role in lowering fat contents proportional to the rate of TCM substitutions. Petersen (1969) also reported that, chickens fed sorghum diet had the highest fat deposition, while the fat content of chickens fed sorghum plus tannin diet was 20% less. In addition, broiler chicken fed 0.9% saponins (Jenkins and Atwal, 1994) had reduced lipid digestibility and a marked increase in cholesterol excretion. In this regard, the use of TCM in place of maize grain in broiler diets has the potential to improve meat quality and have better effects on human health since a reduction in total fat, saturated fat and cholesterol consumption prevents the incidence of most common chronic disorders in consumers. As Sultana et al. (2016) reported, the reduction of fat in meat is definitely worth more in terms of fetching higher market prices since high animal fat causes elevated blood cholesterol, leading to heart failure. Proteins, lipids and minerals are the major components of raw poultry meat (Culioli et al., 2003), while the amount of water in muscles is a functional component that maintains the tenderness, juiciness, firmness and appearance of muscle tissue (Mir et al., 2017). Different studies have focused on the use of dietary strategies to improve the quality of poultry meat, but as reported by Barroeta (2007), of all constituents, the lipid fraction was found to be the most susceptible to modification. Nevertheless, literature reviews that reveal the effect of TCM on broiler chicken meat composition are not yet available. However, according to Mir et al. (2017), the response of a bird to its feed is closely related to the changes in growth of the skeleton, muscle and fat deposits.

4. Conclusion

In general, the use of TCM in broiler chicken production seems attractive under the current Ethiopian conditions by reducing the burden of competition for maize grain. As the result of this study indicated, incorporating TCM up to 60% did not show any negative effect on the chemical composition of the meat. However, replacement of TCM at 60% reduced most broiler carcass characteristics and should not be more than 45%.

Acknowledgement

The authors would like to acknowledge South Agricultural Research Institute for financial funding and Bonga Agricultural Research Center for the provision of all required resources and research physical facilities.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Notes

1 A fuel obtained by heating wood in the absence of oxygen.

2 All exterior fat and connective tissue were removed