Effect of cowpea ( Vigna unguiculata ) grain on growth performance of Cobb 500 broiler chickens

A total of 300 day old Cobb and 500 broiler chicks distributed randomly to 20 pens with 15 chicks each were allocated to 5 different dietary treatments with 4 replicates per treatment in order to evaluate the growth performances of Cobb 500 broiler chickens. A complete randomized design (CRD) was used. Cowpea inclusion levels were 0% (T1), 5% (T2), 10% (T3), 15% (T4) and 20% (T5). A partial budget analysis was done for the treatments. The results of the study revealed that crude protein, dry matter (DM) and the metabolisable energy content of cowpea grain were 25.76%, 89.94% and 3307.37 kcal/kg DM, respectively. Feed intake did not differ significantly (P>0.05) between treatments or inclusion levels. Starter phase ranged from 44 to 45.16 g/bird/day; finisher phase ranged from 113.9 to 117.20 g/bird/day; and the complete experimental period ranged from 83.78 to 85.88 g/bird/day. Daily body weight gains for the entire experimental period were 34.82, 34.27, 36.81, 35.74 and 33.08g (SEM=0.46) for T1, T2, T3, T4 and T5 respectively. There was no significant (P>0.05) difference in growth performance for the complete experimental period. Mortality was at 5% for treatment T1 and T4, while for T2, T3, and T5, respectively, no mortality occurred. Partial budget analysis of the different treatments was calculated based on changes in total return. Change in total return was greater in T3 followed by T5, T4, T2 and marginal rate of return was greater in T3 (32.96) than in T2 (5.62), T5 (3.42) and T4 (2.4). This study indicate that inclusion of cowpea from 5 to 20% in the diet of broiler chickens have no adverse effect on growth performance and from the point of partial budget analysis, T3 (10% inclusion level) was the most profitable.

bridging the protein gap in developing countries where the average daily consumption is far below recommended standards (Onyimonyi et al., 2009).Studies have shown that the Cobb 500 broiler chickens are more economically efficient due to their high growth potential, slaughter trait and roasting weight (Hristakieva et al., 2014).However, the productivity of poultry in the tropics has been limited by scarcity and consequent high prices of the conventional protein and energy sources.Protein sources are limiting factors in poultry feed production especially in the tropics (Atawodi et al., 2008).A potential source of proteins for poultry is legume seeds.A protein that contains a high level of lysine and a low level of methionine (Akanji et al., 2012) characterizes them.Many locally available sources of protein and energy, like grain legumes, contribute to the dietary supply of poultry industry in Africa (Akanji et al., 2012).Soybean meal and other oil crop byproducts, like noug cake, are also major sources of protein in poultry diets.However, inadequate production and specific location make them expensive and not easily accessible.An important mitigation strategy to alleviate such problems is the use of alternative sources of protein like cowpea (Vigna unguiculata).Cowpea varieties are temperature and drought tolerant crops require low input costs and are well adapted to the arid and semi-arid agro-ecologies.Cowpea, as well as other legumes (such as peas, lentil seeds), can be an excellent source of dietary protein in animal nutrition (Igbasan and Guenter, 1997;Ciurescu et al., 2017;Ciurescu and Pana, 2017).The nutrient and energy concentration of cowpea varieties compared with those of soybean varieties, with similar amino acid content (Ravindran and Blair, 1992) are often less expensive.
The cultivation of this legume is practiced in Tigray National Regional State since long time and it was used as feed source for animals.Intercropping this legume with maize and sorghum improves soil fertility as well as increases productivity and striga control (Dwivedi et al., 2015;Matusso et al., 2014;Fasil and Verkleij, 2007).Many legume varieties, which are used as sources for human food and animal feed, were not studied and properly documented.As an indicator of its suitability in the region, recently, a new variety of cowpea has been released from Humera Agricultural Research Center.The average grain yield of this genotype was 30.6 quintals per ha in three consecutive years (Solomon and Kibrom, 2014).This variety also adapt in the central zone of Tigray and its performances was very promising.It may be used as a potential alternative source of feed that can be incorporated into the poultry diets in order to reduce the high cost of conventional protein sources (Nworgu and Fasogbon, 2007;Iheukwumere et al., 2008).This cultivar of cowpea (Temesgen) is better in its performance when compared with the local legumes such as pigeon pea, which are produced in the region.Moreover, a good source of protein, which is soybean, is not produced in the Tigray National Regional State.On the other side, the small scale poultry production has increased from time to time.In this case, feed sources are a major challenge in the small-scale poultry production in the region, especial in central zone of Tigray.Hence, this study is designed to assess the recently introduced cowpea (Vigna unguiculata) variety in the region as a source of protein for poultry diets, to evaluate its effect on growth performance of Cobb 500 broiler chickens and to analyze the partial cost benefit of feeding cowpea grain as a source of protein.

Description of the study area
The study was carried out in Axum town, central zone of Tigray National Regional State, Northern Ethiopia.Standard protocol approved by the research center for animal care and welfare was followed during sample collection.

Experimental feed ingredients and treatments
The feed ingredients used in the formulation of the different experimental rations for the study were corn grain, wheat middling, noug seed cakes (NSC), soybean meal (SBM), cowpea grain (CG), vitamin premix, salt, limestone, di-calcium phosphate, L-lysine and D-methionine.All the ingredients, except for SBM, wheat middling, vitamin premix, salt, limestone, dicalcium phosphate, L-lysine and d-methionine, were also milled in a 5 mm sieve size.
Treatments were: T1, 0% CG; T2, 5% CG; T3, 10% CG; T4, 15% CG and T5, 20% CG.The diets were formulated to be isocaloric and isonitrogenous with metabolizable energy (ME) content: 3000 kcal ME per kg DM and 22% CP for the starter phase (0 to 21 days of age) and 3200 kcal per kg DM and 20% CP for the finisher phase (22 to 49 days of age) by using a feed win software.

Management of birds and experimental design
Three hundred unsexed Cobb 500 broiler chickens were randomly assigned to five dietary treatments with four replications per treatment in a complete randomized design with 15 chicks per replicate or pen.The pens were prepared by using Eucalyptus (a local material) and wire mesh (industrial material), size 3/1.5 m, with the assumption of required space for the finisher phase.Birds were vaccinated against Newcastle (HB1 at day 7 at an eye drop, LaSota at day 21 in drinking water) and Infectious Bursal Disease (Gumboro) at the age of 14 and 28 days, with the drinking water.Before the commencement of the actual experiment, the experimental pens were cleaned and disinfected 14 days before the arrival of the chicks, using disinfectants and fumigated by using formaldehyde solution and calcium phosphate powder.Watering and feeding troughs were thoroughly prepared and cleaned 24 h before the arrival of the chicks.The temperature of the shelter was adjusted to the desired temperature and humidity, using thermohydrometer and digital room temperature 12 h before the arrival of the chicks.Immediately after arrival, the chicks were brooded using 250 watt infrared electric bulbs with gradual height adjustment as sources of heat and light.The floor with deep litter was covered with Teff straw mixed with the sawdust.Clean water and feed were offered ad libitum throughout the experiment.

Measurements and data collection
The amount of feed offered and refused was recorded daily in order to calculate the feed consumption.The given feed and refusals were sampled daily for each pen and pooled per treatment for the entire experimental period for chemical analysis.Birds were weighed weekly in a group per pen and pen average was calculated.Body weight (BW) change was calculated as the difference between the final and initial BW.Average daily gain (ADG) was calculated as BW change divided by the number of experimental days.Feed conversion ratio (FCR) was computed as the ratio of average daily feed intake to ADG.Mortality was recorded as it occurred and calculated as %age.

Laboratory analysis
Feed ingredients of the formulated diets and samples of feed offered and refused from the respective treatments were analyzed for dry matter (DM), crude protein (CP), crude fiber (CF), ether extract (EE) and ash (AOAC, 1995).Calcium and total phosphorus content were also determined by atomic absorption and vanadomolybdate method, respectively (AOAC, 1998).Metabolizable energy (ME) content of the experimental diets was determined according to Wiseman (1987) as ME (kcal/kg DM) = 3951+54.4EE-88.7CF-40.80Ash.Chemical analyses were conducted at Jije laboclass and Ethiopian public health institute Addis Ababa.

Data analysis
Data were analyzed using the general linear model (GLM) procedures of Statistical Analysis Systems software (SAS, 2002) with the model containing treatments.One-way Analysis of variance (ANOVA) was used to compare the treatment means of the groups and for the existence of significant differences among treatments; the differences between treatment means was separated using Tukey Kramer test at P <0.05 significance level.The following model was used for the experiment (Gomez and Gomez, 1984): Where, Yij = Overall Responses , µ = overall mean, Ti = i th treatment effect of feeding level and eij = random error effect.

Partial budget analysis
To estimate the economic benefit of cowpea grain level inclusion mixed with maize, noug seed cake, wheat middling and soybean, the partial budget was analyses by considering the feed expense and chicken price according to the principle developed by Upton (1979).The chicks cost, feed cost, labor cost, electric cost, water expense, vaccine expense and bedding material's expense were measured.Profit obtained from the sale of finished broiler chickens after completion of the experiment was estimated based on the differences between gain and losses for the proposed change.The net income (NI) was calculated by subtracting total variable cost (TVC) from total return.

NI= TR-TVC
The change in net income (∆NI) was calculated as the difference between the changes in total return and total variable cost (∆TVC),

∆NI= ∆TR-∆TVC
The marginal rate of return (MRR) was analyzed by considering the changes in return and total variable cost and it was measured the increased in net income (∆NI) associated with each additional unit of expenditure (∆TVC) MRR= ∆NI/∆TVC Chicks sale cost to feed cost ratio was also calculated as additional parameter to evaluate the efficiency of the change in the feed ingredients.Feed cost per live weight gain was calculated as follows as an indicator of cost and biological efficiency:

Chemical composition of feed ingredients
The results of laboratory analysis for the different feed ingredients and formulated experimental diets are shown in Table 1.Cowpea grain contained 25.76% CP and 89.94% DM, 6.22% CF, 1.65% EE, 4.6% ash, 3307.37 kcal/kg DM ME, 0.75 g/kg DM tannin and 1.5 g/kg DM phytate.This makes the cowpea grain a good source of protein and energy for poultry production, which can contribute towards overcoming the predicted protein content.Chemical composition of cowpea seed might differ mainly due to variety, treatments and environmental factor.Cowpea, like other legume, contributes to the level of dietary protein in starchy tuber-based diets through their relatively high protein contents, and their quality by forming complementary mixtures with cereals.
The result of chemical analysis of cowpea grain in the current experiment was in line with the finding of Henshaw (2008), Tshovhote et al. (2003) who found that the protein content ranged from 25.35 to 26.43% and the DM content was of 90.7, 90.2 and 90.15% respectively for three cowpea cultivars (Glenda, Agrinawa and Indigenous cowpea).The same researchers reported that the CF content of the same three cultivars ranged from 5.15 to 5.81%.Muamer et al. (2012) also reported that the raw cowpea contain 24.78, 93.66, 0.91, 3.46 and 3.33%, and 3153 kcal/kg DM for CP, DM, EE, CF, Ash and ME, respectively.Except for the DM content, all the other chemical parameters were below the current results.In addition to this, the current proximate composition results were within the range of other authors' result who worked on different varieties of cowpea seeds (Otitoju, 2015;Balaiel, 2014;Agbogidi and Egho, 2012;Tresina and Ramasamy, 2011) and greater than those reported by Abdelatief and El-Jasser (2011).Generally, cowpea genotypes are highly flexible for seed protein and its soluble fraction contents (Noubissié et al., 2011).The same researcher found a variation of CP from 20.79 to 31.78% among different varieties of cowpea seeds.The similarities and the difference of chemical composition between cowpea in this experiment and other reports might be due to variety differences.Feed consumption, Feed intake and feed conversion ratio of Cobb 500 broiler chickens fed diets with different inclusion levels of cowpea grain during experimental period are presented in Table 4.The whole feed consumption and average daily feed intake on the bases of DM during the starter phase, finisher phase and the whole experimental period was not influenced (P>0.05) by the different treatments when compared with control (T 1 ).Inclusion of cowpea grain up to 20% in the diet of broiler did not have a significant impact on feed intake of Cobb 500 broiler chickens.The current results were in line with findings of Eljack et al. (2010) who found that an inclusion of 0, 10, 20 and 30% cowpea grain had no significant effect on feed consumption at starter phase, finisher phase and whole experimental period.Chakam et al. (2010) also found that the inclusion of cooked cowpea (0, 15, 20, 25 and 30%) into the diets of finisher male Hubbard broiler chickens had no significant effect in terms of feed consumption.On the other hand, increasing the level of inclusion of untreated cowpea seed into the diet of broiler chickens showed a significant reduction in feed intake (Balaiel, 2014) due to an increased residual effect of anti-nutritional factors found in cowpea grain.

Growth performance
The growth performance of Cobb 500 broiler chickens fed different levels of cowpea grain inclusion is shown in Table 5.In this experiment there was a significant difference (P<0.05) on final body weight gain and average daily weight gain in starter phase.T 3 and T 4 were greater than T 1 , while values for T 2 and T 5 were similar with T 1 , T 3 and T 4 .At finisher phase, initial weight of T 3 and T 4 was significantly (P<0.05)higher compared to T 1 , whereas average daily weight gain was significantly (P<0.05) in T 3 which was greater than T 5 , while values for T 1 , T 2 and T 4 were similar with T 3 and T 5 .Final body weight gains in finisher phase were not significant (P>0.05)among treatments.There was no significant (P>0.05)difference in final body weight gain and average daily weight gain in the complete experimental period in all treatments.The difference in the starter might be due to slight differences in crude fiber of the ingredient formulated the diet; while, reduction in daily weight gain on T 5 of finisher phase might be related to increased levels of cowpea inclusion in the diet.This might relate to the nature of legume seeds contain anti-nutritional factors which reduces the utilization of proteins and palatability of diets.
The current result was in line with Adebiyi et al. (2008) who found that supplementing broiler chickens diets with fungi degraded cowpea seed hulls had no significant effect in weight gain of broiler.At 49 days of age, body weight gain of Cobb 500 broiler chickens among treatments ranged from 1621.13 g to 1803.85 g in the present study which was less than the weight gain of2599 g and 2435 g reported for Cobb 500 and Ross 308 broiler chickens, respectively (Hristakieva et al., 2014).The current results showed that for the complete experimental period, there was no statistical difference between treatments; whereas, Eljack et al. (2010) found that as the inclusion level of cowpea increased the growth performance increased also.On the other hand inclusion of 15% untreated cowpea seed and 20% raw and dehulled, dehulled roasted cowpea, grain of broiler chickens recorded a significant (P<0.05)reduction on growth performance as compared with control and dehulled cooked cowpea (Akanji et al., 2015;Balaiel, 2014).Differences might be due to diet formulation ingredients, environmental factors, difference of cowpea seed variety and treatment used to reduce anti-nutritional factors.Any variation in the environment surrounding the birds resulted in stunted growth and major production losses (Czarick and Fairchild, 2012;Blackely et al., 2007).

Mortality
The inclusion of different levels of cowpea grain did not show significant difference in mortality rate on T 2 , T 3 and T 5, respectively.There was a sudden death syndrome of chickens on T 1 and T 4 .In both treatments 5% mortality rate occurred at finisher phase.The phenomenon of lameness occurred in all treatments, T 1 , T 2 , T 3 , T 4 and T 5, which was 15, 11.67, 10, 13.33 and 15 %, respectively.Lameness in broiler chickens occurred in relation to lack of the micro mineral (Na + , K + and Cl -) in the diet, due to unbalanced growth of muscle and bone.In this case due to genetic selection meat chickens are fast growing, as a result, they deposit large amount of muscle which is above the capacity of the bone.Finally lameness has occurred as a major problem in broiler production.In the most recent large-scale broiler production studied in the United Kingdom 27.7 % of the birds assessed closed to slaughter age (40 days) showed poor locomotion, and 3.3% were also unable to walk (Knowles et al., 2008).Other authors also reported that, selection for faster and short fattening period leads to an increase of skeletal disorders, which are related to transient difficulty during the phase of fast growth of long bones, especially tibia, since the proximal tibia is the site of the most fast growing growth plate (Angel, 2007).

Partial budget analysis
Partial budget analysis for Cobb 500 broiler chickens fed different levels of inclusion of cowpea grain is presented in Table 6.The net income was determined depending on the cost of the feed consumed by each bird, chicks cost, labor cost and vaccine expenses, cost of bedding materials, cost of water and electricity.The greater net income per treatment was shown in T 3 followed by T 5 , T 4 and T 2 respectively.Change in net income per treatment (∆NI) showed that T 3 was highest, followed by T 5 , T 2 andT 4 .The differences in change of net income were due to the difference in feed consumption, selling price of individual chickens and the number of chickens in each treatment that reached to market.The marginal rate of return (MRR) showed that for each additional unit of 1 ETB per treatment cost increment, resulted in additional income of 32.90, 5.62, 3.42 and 2.40 for T 3 , T 2 , T 5 and T 4 respectively.Between treatments, T 3 was the more profitable based on the consideration of change in net income (∆NI) and marginal rate of return (MRR).
The feed costs per weight gain of Cobb 500 broiler chickens were also calculated as additional parameter to indicate the cost of feed and biological efficiency in which feed cost expensed for production of 1 kg body weight.In this experiment, the result showed that T 4 was lower in feed cost per weight gain of chicken followed by T 3 , T 5 , T 2 and T 1, respectively.This indicated that T 4 was better in terms of feed utilization to produce 1 kg body weight gain followed by T 3 , T 5 , T 2 and T 1, respectively.

Conclusion
Based on the current study, it is possible to conclude that inclusion of cowpea grain up to 20% in the diet of broiler chickens do not have any adverse effect on growth performance of broiler chickens.Therefore, levels of inclusion from 5-20% can be used as an alternative protein sources in broiler diets.However, based on the partial budget analysis T 3 (10% inclusion level of cowpea grain) on the diet of broiler chickens was more profitable than the other treatments.

Table 1 .
Chemical composition of feed ingredients used to formulate the experimental ration.

Table 2 .
Proportion of ingredients used in formulation of broiler starter and finisher diets.

Table 3 .
Chemical composition of the starter and finisher diets of Cobb 500 broiler chickens

Table 4 .
Feed intake and feed conversion ratio of Cobb500 broiler chickens.

Table 5 .
Body weight change of Cobb500 broilers chickens.