Cottonseed cake replacement by soybean pulp in the diet of West African Dwarf lambs in Benin: zootechnical and economic performances

Population growth has increased the demand in meat products in Benin and has led to imports of meat and live animals (Babatoundé et al., 2009). This causes a major currency hemorrhage, which is likely to increase in the coming decades as the population increases (Houndonougbo et al., 2012). With 1,836,000 head (FAOstat, 2018), small ruminants play a major role in the coverage of national meat requirements in Benin. Sheep play a very important socioeconomic role particularly in religious festivals (Nantoumè et al., 2006). Sheep fattening has thus increased in rural, and in urban and periurban areas (Gbangboché, 2005).


■ INTRODUCTION
Population growth has increased the demand in meat products in Benin and has led to imports of meat and live animals (Babatoundé et al., 2009). This causes a major currency hemorrhage, which is likely to increase in the coming decades as the population increases (Houndonougbo et al., 2012). With 1,836,000 head (FAOstat, 2018), small ruminants play a major role in the coverage of national meat requirements in Benin. Sheep play a very important socioeconomic role particularly in religious festivals (Nantoumè et al., 2006). Sheep fattening has thus increased in rural, and in urban and periurban areas (Gbangboché, 2005).
Fattening uses several techniques ranging from traditional ones with agricultural by-products to more intensive ones that include agro-industrial by-products (Somda, 2001). Among these agro-industrial by-products, cottonseed and soybean cakes have been the most used (Bougouma-Yaméogo et al., 2002). However, feed rationing based on these by-products (Idrissou et al., 2017) is technically difficult because of their little availability and accessibility especially to small-scale livestock farmers. Soy cheese has now become part of the feed habits of rural and urban populations in Benin. The transformation of soybean into cheese produces a by-product, the soybean pulp also known as okara. This by-product is available locally and less expensive than cakes (cotton and soy). It can therefore be an interesting nutritional and economic alternative in sheep fattening. Studies in Benin report the use of soybean pulp in poultry (Dossou, 2012) and rabbit (Alabi et
studies evaluated the soybean pulp in the diet of ruminants in Benin. The purpose of this study was to evaluate the zootechnical and economic performances of fattening West African Dwarf (Djallonke) sheep fed diets containing different proportions of soybean pulp in place of cottonseed cake.

Study area
The experiment was conducted at the Pélébina livestock farm in Djougou Commune, Donga Department. The farm is located at 32 kilometers from Djougou and covers 25 hectares. It has a tropical climate with two seasons, a rainy season from mid-April to mid-October and a dry season from mid-October to mid-April. The annual rainfall ranges from 1000 to 1500 millimeters for 75 to 140 days of rain. The average annual temperature is approximately 27.5 degrees Celsius (ASECNA, 2017).

Animals
Thirty non-castrated West African Dwarf male lambs (120 ± 10 days old, averaging 12.6 ± 0.16 kg initial body weight), born and raised at Pélébina farm, were used. The experiment took place from November 2016 to February 2017 and lasted 75 days, i.e. a 15-day adaptation period followed by a 60-day fattening period. At the beginning of the adaptation period, the sheep were divided into three groups of 10, based on their body weight and each group received its experimental ration. During the same period, all animals were vaccinated against sheep and goat plague and injected with long-acting oxytetracycline and multivitamins. Internal deworming using albendazole and external deworming using Amitix in tick baths were also carried out. The sheep were indoors in individual stalls, and litter was made of rice husks.

Feed and mode of distribution
Three diets were tested ( Table I). The control diet (R1) consisted of 20% dry matter (DM) cottonseed cakes (CSC), 10% DM corn bran and 70% DM Panicum maximum C1. The experimental diets incorporated soybean pulp at 10% or 20% of the total diet replacing 50% or 100% of CSC, respectively. CSC were purchased in feed stores in Djougou and soybean pulp was purchased in a dry form from women processing soybean into soy cheese. It was stored in the farm.
Panicum maximum C1 was distributed at the feed rack in two meals, at 8:00 am and 12:00 pm. Dietary supplements (corn bran, CSC, soybean pulp) were offered in one meal at 16:00 pm. These supplements were presented in flour form to the animals. The quantities of P. maximum distributed to each animal were determined based on 1.5 kg DM / 100 kg of live weight (LW) and the dietary supplement intake based on 2.5 kg DM / 100 kg of LW. Thus, the amount of feed served varied as the body weight increased. The lambs had free access to water and a Lamdam'Bloc limestone (785 mg Nacl, 647 mg Ca, 3500 mg Mg, 500 mg Mn, 700 mg Zn, 3000 ppm Fe).

Data collection
The feeds were weighed before distribution and served individually to the lambs. Refusals were weighed the next day before a new distribution. The determination of the quantity of feed ingested was made by the difference between the quantities distributed and refused daily. Samples of each type of feed offered and refused were taken in all animal stalls once a week to determine DM, the organic matter (OM), crude fiber (CF), crude protein (CP), fat content, and mineral matter (MM), following official methods approved by AOAC (2005). The neutral detergent fiber (NDF) and acid detergent fiber (ADF) were analyzed by the method of Van Soest and Wine (1967). The fodder unit for meat feed (UFV), the protein digested in the small intestine allowed by the nitrogen (PDIN), and the protein digested in the small intestine allowed by the energy (PDIE) were estimated using equations from the French National Institute for Agricultural Research (Baumont et al., 2007). Analytical results are presented in Table II.  The live weight change in lambs was determined by weighing each animal at the beginning of the experiment, then every two weeks. The animals were weighed at 7:00 am after 12 hours of fasting using a weight scale (50 kg ± 100 g) before receiving their diet. Average daily gains (ADGs) were calculated every two weeks as well as the consumption index (CI, amount of dry matter ingested per unit of average daily gain).

Statistical analysis
The dry matter intake (DMI), ADG, and CI were analyzed with the one-way analysis of variance (ANOVA) with R software (R Core Team Development, 2017) to test the effects of supplementation on animal performances (with significant differences when p < 0.05). Multiple comparison of means was performed with Tukey test (with significant differences when p < 0.05).

Economic evaluation methods
Economic efficiency has been evaluated through the calculation of the gross margin (GM) and direct cost margin (Boehlje and Eidman 1984;Kiéma et al., 2008) per animal and per diet. GM is the difference between the total revenue from the sale of animals and the operational cost (costs of acquiring animals, feeds and veterinary products). The direct expense margin is the difference between GM and the depreciation of the equipment specific to the activity.

Chemical composition and nutritional value of feeds
Soybean pulp was richer in CF and ADF than cottonseed cake (Table II). Conversely, NDF and MM contents in cottonseed cake were higher than those in soybean pulp. Soybean pulp and cottonseed cake had similar PDIE and PDIN contents, and energy (UFV). Considering these properties, the diets had almost the same energy and protein content (Table II).

Dry matter intake and growth performance
DMI, CI, and ADG are presented in Table III. DMI was different (p < 0.0001) between groups. The highest DMI (482 ± 18 g/day) was obtained with R1 lambs, and R2 and R3 lambs had similar values with 448 ± 12 g/day and 441 ± 14 g/day, respectively. The high intake in R1 lambs compared to R2 and R3 lambs was due to the high palatability of CSC. With regard to the feed consumption index, no significant difference (p > 0.05) was observed between groups. These CI values were lower than those of 4.48 to 5.79 obtained by El Fadili (2012) in Morocco in sheep of the same age as ours, but supplemented with a concentrate composed of barley and triticale grains (40%), sunflower meal (14%), minerals and vitamins (1%), and a commercial pelted feed (45%). The difference between our results and those of this author could be related to the ration.
The type of diet had no effects (p > 0.05) on ADG or the final live weight. The ADGs obtained were 77.50, 73.13 and 70.21 g/day for diets R1, R2 and R3, respectively (Table III). These ADGs were lower than those of 92.60 and 95.70 g/day reported by Simitzis et al. (2008) in lambs of the same age as those in our study. The 92.60 g/day value was obtained in lambs fed a diet containing a concentrated feed and alfalfa hay, whereas 95.70 g/day was obtained in lambs fed the same diet, the only difference being that the concentrated feed was uniformly sprayed with oregano essential oil (1 ml/kg). Otherwise, the ADGs obtained in our study were higher than those of 18.33, 41.11, 57.67 and 58 g/day reported by Montcho et al. (2016) on the complementation of West African Dwarf lambs with multi-nutritional blocks. The differences between our results and those of these authors could be related to the ration. The evolution of the ADGs at 2-week intervals (Figure 1) was not identical in the three groups. During the first and second fortnight, R1 and R2 had a higher ADG (p < 0.05) than R3. Then, the ADG of the lambs in R3 increased to reach ADGs similar to those in R1 and R2 (p > 0.05).

Economic profitability of fattening
The production cost of one kilogram of each ration was determined based on ingredient costs according to their proportion in the diet. P. maximum was harvested from a one hectare fodder plot. The price of this feed was estimated at 50 FCFA/kg. On the market, corn bran and cottonseed cake cost 30 and 150 FCFA/kg, respectively, and soybean pulp 50 FCFA/kg (during the trial period). On this basis, one kilogram of rations in R1, R2 and R3 cost 68, 58 and 48 FCFA,

Conflicts of interest
The study was carried without any conflict of interest.
respectively. During the 60 days of the experiment, the lambs in R1, R2 and R3 ingested 36.50, 34 and 33.50 kg of fresh material, respectively.
Thus, the feeding cost per lamb was estimated at 2482, 1972 and 1608 FCFA for R1, R2 and R3, respectively. The cost of veterinary care per animal was approximately 425 FCFA. The lick block cost 550 FCFA/animal. The economic results of the fattening of the lambs (Table IV) showed that the production cost of one kilogram of feed was not identical for the three groups. This cost was higher in diet R1 than in the other diets, and lowest in R3, mainly because of the low price of soybean pulp compared to cottonseed cake. All the diets were economically profitable. R3 generated the best net margin with 6042 FCFA (vs 5613 FCFA in R1 and 5728 FCFA in R2). The substitution of cottonseed cake by soy pulp therefore allowed a reduction in the cost of feed and an increase in the farmer's income.

■ CONCLUSION
This study showed that locally available feed resources could help reduce the constraints (high costs, access problems) related to zootechnical input markets. Il also showed that there were opportunities for fattening at a lower cost and higher net profits than with cottonseed cake. Partial or total substitution of cottonseed cake by soybean pulp can achieve these results. This resource is locally abundant in rural and urban areas of Benin. Overall, the enhancement of locally available feed resources in the development of improved meat production techniques is an alternative for intensifying production in developing countries. Their adoption should contribute to improve the development of fattening.

Author contributions statement
YI and ASA participated in the conception and design of the study; JAA collected data and drafted the first version of the manuscript; HSSW and BGCA participated in the design; YI and ASA performed statistical analyses; IAT critically reviewed the manuscript. Mots-clés : ovin, alimentation des agneaux, gain de poids, tourteau de coton, produit à base de soja, Bénin