Feeding Forage Cowpea: Goats Performed Well with High Nutrient Digestibility and Nitrogen Retention

Abstract

This chapter deals with the utilization and performance of Red Sokoto goats fed varieties of forage cowpea (Vigna unguiculata). It contains information for use right from keeping to precision production of goats. Background information is given on cowpea history and distribution, cowpea varieties and forage yields of cowpea (mainly in Africa and precisely Nigeria). Cowpea haulm nutritional value, mineral contents as well as anti-nutritional factors like tannins, saponins, oxalate, phytate and phenols are then detailed. The final sections highlight the performance of Red Sokoto goats in terms of nutrient digestibility and nitrogen retention when fed with two cowpea haulm varieties for optimum performance under smallholder production system.

1. Introduction

The role of livestock in providing protein is essential in human nutrition, and it is increasingly being recognized. This necessitates immediate concern in development programs for improvement of livestock productivity, through improved nutrition. Animal productivity could be increased by the introduction of low-cost technologies such as feeding systems that are simple, consistently practical and within the limits of the farmer’s resources [1]. One of such feeding systems is the use of forage legume that supplies protein in fodder for livestock [2, 3]. Feeding of forage legumes has been found easily adoptable, but farmers do not pay particular attention to the planting of pure forage legume stands rather greater emphasis is on the cultivation of food crops. In Nigeria, the planting of cowpea is gaining popularity due to its huge economic returns on sales of grains and haulms, respectively. About 10.6 million ha of cowpea was estimated to be produced in West Africa, particularly in Niger and Nigeria [4].

Cowpea haulm is the above-ground part of cowpea without the pods which contains the grains [5]. The haulms contain about 45–65% stems and 35–50% leaves and sometimes roots [6], and are an important by-product in Sub-Saharan Africa [7].

Cowpea haulm addition improves nutrient supply and growth of livestock over the use of low-quality forages alone [8]. Previous studies by Osafo et al. [9] observed improved intake and digestibility of poor quality fodder with supplementation of cowpea haulm. The incorporation of promising legumes fodder such as cowpea haulms for livestock production will help to overcome the feed shortages. The Institute for Agricultural Research (IAR), Zaria-Nigeria, with other collaborating institutes has bred and released new cowpea varieties overtime with focus mostly on higher grain yield, while forage yield and quality is rarely a priority [10]. SAMPEA 14 and 15 varieties of cowpea are high yielding, striga-resistant and tolerant to heat and drought with maturity period of 70–78 days [11]. Considering the good qualities of this legume crop in the tropical savanna, the knowledge of its nutritive value will be very important. This chapter will provide information on the supplementation of two cowpea haulm varieties in concentrate diets for improved nutrient digestibility and nitrogen balance in Red Sokoto bucks.

2. Background information

Cowpea is gradually attaining economic importance in Nigeria, even though the bulk of the production is done in the semi-arid zone of Nigeria [12]. In Nigeria, the production trend of cowpea has experienced about 44.1% increase in area planted and 41% increase in yield from 1961 to 1995 [13]. The appreciating economic importance may be due to its food value and supplementary source of protein for animal use. Inaizume et al. [5] observed several factors that account for the impressive significant advances made by International Institution of Tropical Agriculture (IITA) over the last two decades in improving cowpea productivity in Sub-Saharan Africa. Singh et al. [14] also indicated that a number of varieties have been developed which combine diverse plant type, different maturity period and resistance to several disease, insect pest and parasite as well as good agronomic traits. The leaves, vines and some portions of the roots (haulms) serve are often stored for use during the dry season as animal feed. The sale of the haulms as animal feed during the dry season when there is a feed shortage and during festive season were livestock such as goats are slaughtered, thereby providing a vital income for farmers [15]. In this chapter, the background information is given on cowpea history and distribution, varieties and forage yields, nutritional value, anti-nutritional factors as well as nutrient digestibility and nitrogen retention when fed with two cowpea haulm varieties.

2.1 History and distribution of cowpea

Cowpea is one of the most ancient crops known to man. Cowpea (Vigna unguiculata L. Walp) is a member of the family Fabaceae and tribe phaseoleae [16]. Morphological features and geographical distribution are used in determining the origin of cowpea [17]. Early observations showed that the cowpeas present in Asia are very diverse and morphologically different from those growing in Africa, suggesting that both Asia and Africa could be independent centres of origin for the crop. Cowpea has been cultivated in southern Europe at least since the eighth century BC and prehistoric times [18]. However, Asia has been questioned as a centre of origin due to the lack of wild ancestors [19]. A lack of archaeological evidence has resulted in contradicting views supporting Africa, Asia and South America as its origin [20].

Carbon dating of cowpea (or wild cowpea remains) has been carried out by Flight [21]. The author reported that the oldest archaeological evidence of cowpea was found in Africa in the Kintampo rock shelter remains in Central Ghana dating about 1450–1000 BC, suggesting Africa as centre of origin. One view is that cowpea was introduced from Africa to the Indian subcontinent approximately 2000 to 3500 years ago [11]. Duke [22] based his conclusions on West Africa as the centre of cultivated cowpea. Kitch et al. [23] also reported that the species unguiculata is thought to be West African Neolithic domesticated.

Cowpea is now widely adapted and grown throughout the world, extensively in 16 African countries with the continent producing two-thirds of the world total [24]. The centre of maximum diversity of cultivated cowpea is found in West Africa, in an area encompassing the savannah region of Nigeria, southern Niger, part of Burkina Faso, northern Benin, Togo and the north western part of Cameroon [19]. V. unguiculata is known by different names throughout the world. In the United States, the crop is called black-eye peas or southern peas [19] and the English-speaking people in Africa refer to it as cowpea. In Nigeria, it is called “wake” [25]. Cowpea was now grown on an estimated 12.3 million ha in Africa in 2014 with the bulk of production occurring on 10.6 million ha in West Africa, particularly in Niger, Nigeria, Burkina Faso, Mali and Senegal [4].

2.2 Cowpea varieties in Nigeria

The International Institute for Tropical Agriculture (IITA) in Ibadan, Nigeria, is the centre for worldwide collection and testing of cowpea germplasm. The Institute for Agricultural Research-Zaria with other collaborating Institutes (i.e. IITA) has a cowpea breeding programmes that releases new varieties (such as SAMPEA 14 and 15) over a time with focus mostly on higher grain yields, while crop residue quality is rarely a priority [10, 26]. The Institute developed high yielding, short season and multiple disease-resistant varieties with varying maturity periods (that are ready for harvest in 60–70 days), as well as different seed colours, and adapted to various Nigerian agro-ecological zones. Several of these varieties have also been released in Nigeria and are being promoted by the State Agricultural Development Projects (ADPs), farmers’ groups and seed companies [10]. Considerations in variety selection should either be on growth pattern, maturity, market value, seed size and colour and resistance to the prevailing biotic and abiotic stresses in the areas to be planted. Generally, varieties differ in their adaptation to new ecology, in yield potential, maturity periods and canopy architecture [27]. Sampea 14 and 15 varieties of cowpea were chosen for the trial because of their relative promising performance in the Nigerian Savanna [11].

2.2.1 Sampea 14 and 15 varieties of cowpea

Sampea 14 is a semi-erect variety of seed that is characterized by small-sized and white colour seed. It has brown eye, rough seed coat and long peduncles that carries pod above canopy. The cowpea variety thieves well in Sudan and Sahelian agro-ecologies. It is an early maturing variety (70–75 days) with high seed yield (1.3 t/ha), producing 12–15 seed per pod. It is resistant to pod damage by striga/Alectra and also tolerant to heat and drought [11]. Sampea 15 is a creeping variety of seed that is characterized by small-sized and white colour seed. It has black eye, rough seed coat and long peduncles that carries pod above canopy. The cowpea variety thieves well in Sudan and Sahelian agro-ecologies. It is an early maturing variety (73–78 days) with high seed yield (1.3 t/ha), producing 12–15 seed per pod. It is resistant to pod damage by striga/Alectra and also tolerant to heat and drought [11].

2.3 Forage yields of cowpea

The annual production is high, but the average grain yield per hectare in Nigeria is only 776.31 kg/ha which though above the average yield worldwide of 521.91 Kg/ha in 2013, but is far lower than yield of 5333.33 kg/ha obtained in USA [28]. Yields of up to 8 t DM/ha have been recorded for cowpea in irrigated areas [29] and over 4 tDM/ha under favourable conditions [30]. The average fodder yield of cowpea in India is 25–45 t/ha [31]. However, the world average yield of cowpea fodder is 0.5 t/ha [32]. Farmers may harvest up to 0.4 t/ha of cowpea leaves in a few cuts with no noticeable reduction in seed yield. Cowpea crop can produce a yield of 1–2.5 t/ha fresh fodder and an intercrop cowpea can give 0.35–1 t/ha of fresh fodder. A dry forage yield of 0.23 t/ha and 2.86 t/ha forage yield from Sampea 14 variety of cowpea under rain-fed and irrigation condition, respectively, was also reported [33, 34]. In a study by Antwi et al. [35], a haulm yield of 13.35 t/has was recorded from improved dual purpose cowpea variety (IT93K-2045-93). Also, a dry cowpea fodder of 0.4–0.5 t/ha was produced at the end of the raining season under intercropping system in Sahelian and Sudan areas [36, 37]. Bundles of harvested fodder are stored on rooftops or on trees fork for use and for sale as “harawa” (feed supplement) in dry season. Singh et al. [38] reported that early and medium maturing varieties yielded higher grain but lower fodder than late maturing and fodder-type cowpea varieties which yielded 5 t/ha of fodder and less grain. However, the number of leaves and branches were positively correlated with green fodder yield [39]. Many reports have shown that higher number of leaves will allow animals to select forage with higher crude protein and digestibility [40] as leaves consist of two-third of forage feeding value [41].

2.4 Nutritional value of cowpea grains and haulms

Cowpeas are important legumes and sources of protein in livestock diets. Protein content of cowpea leaves varies within different genotypes [42]. Cowpea seed contains 25% crude protein [43, 44] with leaves containing 27–34% crude protein [45]. Protein content of cowpea leaves range from 27 to 43%, and protein concentration of the dry grain ranges from 21 to 33% [46]. The crude protein content ranges from 22 to 30% in the grain, from 6.9 to 7.1% in cowpea shell [47] and from 13 to 17% in the haulms [48] with a high digestibility and low fibre level [37]. An average crude protein of cowpea haulms (12.36%) was reported by [49] which was within the range of 8–13%, below which [50] observed that feed will not provide the required levels of ammonia for an optimum rumen microbial activities. Due to seasonal differences in the quality of haulms, care must be taken when handling to minimize loss of leaves [6]. The proximate composition of forage meal of cowpea at two stages of growth was found to be high in crude protein and either extract at flowering stage than at maturity [47].

The chemical composition of cowpeas has been shown to vary considerably according to cultivar and environmental [51] and genetic factors [52]. Dry matter digestibility of cowpea haulm is between 65 and 70% [53], and differs greatly between leaves (60–75%) and stems (50–60%). Because of this difference, the proportion of leaves and stems in the haulm affects its nutritional value [7]. Many reports have shown that higher number of leaves will allow animals to select forage with higher crude protein and digestibility [40] as leaves consist of two-third of forage feeding value [41]. As plants mature, even the leaves would become more fibrous and less digested [54]. A safe upper limit of 60% nitrogen detergent fibre (NDF) level for guaranteed forage intake by ruminant as it can be digested by ruminant animals [55]. It has also been reported that as the plant matured, photosynthetic products are more rapidly converted to structural components, thus having the effect of decreasing protein and soluble carbohydrate and increasing the structural cell wall components [56].

Sebetha et al. [57] studied the protein content of two cowpea varieties grown under different production practices in Limpopo province, Ghana. The results of the study revealed that cowpea leaf protein content ranged from 24.1 to 28.1% and 26.0 to 30.7% for Red Caloona and Pan 311, respectively. The protein content of green cowpea pods obtained from Pan 311 cowpea variety ranged from 18.8 to 25.1%, while that of Red Caloona varied between 17.9 and 20.7%. Similarly, the protein content of the fodder obtained after grain harvest varied between 9.3–9.4% and 9.9–12.3%, respectively, for Pan 311 and Red Caloona during the two seasons.

Anele et al. [58] observed that cowpea haulm can be used for sheep as a supplement to poor quality basal diets. Anele et al. [59] also observed that cowpea haulms can provide adequate protein and energy to sustain ruminant production during an extended dry season. Savadogo et al. [53] reported that the intake of cowpea haulms by sheep can reach 86 g/day as a supplement to sorghum stover. Although supplementation decreased total dry matter (DM) intake, this was compensated for by an increase in stover digestibility [53]. In sheep fed 200–400 g/day of cowpea haulms as a supplement to a basal diet of sorghum stover, the resulting average live-weight gain (80 g/day) was twice that obtained with sorghum fodder alone [60]. In male Ethiopian Highland sheep, supplementation of maize stover with cowpea haulms (150 or 300 gDM/day) improved dry matter and protein intake, organic matter (OM) digestibility, average daily gain, final live weight, carcass cold weight and dressing percentage [61].

2.4.1 Mineral contents of cowpea haulms

Mineral contents of forage species are influenced by genetic factors [52] and climatic and soil factors on which plant grows [51]. Variations in the concentrations of minerals are due to the differences in nutrient uptake from the soil [62]. Alhassan et al. [47] also revealed that the proximate and mineral composition of forage meal of cowpea at two stages of growth to higher in minerals which is fairly high in calcium (Ca), sodium (Na) and potassium (K) at flowering stage than at maturity but low in phosphorus. Deficiency of phosphorus (P) in legumes depressed the activity of nitrogen-fixing bacteria [63] for which the availability of nitrogen in root zone is also reduced. P concentration in herbage decreases with increase in maturity [64]. In a trial by Abia [64], a mean range of calcium content of 1.6–2.0% was reported for tropical legumes with a range of 0.5–1.1 g/day will be able to satisfactorily meet the daily Ca requirement of goats [65]. NRC [66] recommended 0.15 and 0.80% for of P and K, respectively, while a range of 0.71–0.21 g/100 g magnesium (Mg) was recommended for small ruminants [67].

2.4.2 Anti-nutritional factors of cowpea haulms

Anti-nutritional factors are a chemical compounds synthesized in natural food and/or feedstuffs by the normal metabolism of species. They are also known as toxic factors due to their deleterious effect when consumed by animals. Toxicity due to the consumption of various forages is very common among the farm animals. The anti-nutritional factors present in the forages are mainly responsible for this [68]. The presence of anti-nutritional substances in any of the edible legumes is of major concern. Cowpea (V. unguiculata L. Walp) has been utilized as a supplement feed to enhance feed intake and improve productivity in ruminants fed low-quality roughage diets [69]. Cowpea forage contains anti-nutritive factors, which includes, but not limited to tannins, oxalate, saponins, phytate and phenol [70]. These anti-nutritional factors are also known as “secondary metabolites” in plants and they have been shown to be highly biologically active [71].

2.4.2.1 Tannins

Cowpea forage contains tannin [70], which is a bitter plant and water-soluble phenolic compounds with the ability to precipitate protein from aqueous solution [72]. Tannins are the most widely occurring anti-nutritional factors found in plants. Tannins in feed stuffs such as pasture legumes decrease palatability and protein digestibility [73]. Hydrolysable tannins and condensed tannins are two different groups of tannins [68], differing in their nutritional and toxic effects. Smitha et al. [68] reported that tannins in forage legumes have both positive and negative effect on nutritive value. Condensed tannins containing forages have different benefits for ruminants, depending on the species of plant [74]. The condensed tannins have more profound digestibility-reducing effect than hydrolysable tannins, whereas the latter may cause varied toxic manifestations due to hydrolysis in rumen [75]. Tannins forms insoluble complexes with proteins, and the tannin protein complexes may be responsible for the anti-nutritional effects of tannin containing feeds [71]. The tannin-protein complexes are astringent and adversely affect feed intake.

The concentration of condensed tannins above 4% (40–100 g/Kg DM) has been reported to be toxic for ruminants as they are more resistant to microbial attack and are harmful to a variety of microorganisms [76] and depressed feed intake and growth in ruminants [77]. Goats are known to have a threshold capacity of 9% (90 g/kg/DM) dietary tannin [78]. Ravhuhali et al. [79] reported that some cowpea forage cultivars had high amounts of condensed tannins (0.11%, DM basis), but these did not exert negative effects on intake and digestibility. A study by Adjei-Fremah et al. [80] on analysis of phenolic content and antioxidant properties of selected cowpea varieties tested in bovine peripheral blood revealed that there was variation among leaf samples from the different cowpea varieties for condensed tannins. Low levels of condensed tannins were observed in all fresh leaves samples ranging from 0.13 to 0.22 mg/100 g compared to high condensed tannins content in dry leaves samples (0.30–0.52 mg/100 g). This may be an important consideration in the use of cowpea for animal feed either as hay or silage. However, the range of values for all the content of tannins in all varieties was below 5% DM, the critical value above which tannins interfered with intake, digestion and utilization of forages [81].

2.4.2.2 Saponins

Saponins are secondary compounds that are generally known as non-volatile, surface active which are widely distributed in nature, occurring primarily in the plant kingdom. The structural complexity of saponins results in a number of physical, chemical and biological properties, which include sweetness and bitterness, foaming and emulsifying, pharmacological and medicinal as well as antimicrobial, insecticidal activities [71]. Saponin content of the leaves is twice as much as those of the stems and declines as the plant becomes older. The tolerable level of saponin in goat is 1.5–2% [82]. Saponins are among several plant compounds which have beneficial effects. Among the various biological effects of saponins are antibacterial and antiprotozoal [83].

2.4.2.3 Oxalate

Oxalate binds with nutrients to render their availability to the animal body, thus resulting in nutritional deficiencies. Oxalate also reacts with proteins to form complexes which have an inhibitory effect in peptic digestion [84]. In ruminants, oxalic acid is of only minor significance as an anti-nutritive factor since ruminal microflora can readily metabolize soluble oxalates to its calcium salts [71, 85]. Various tropical grasses contain soluble oxalates in sufficient concentration to induce calcium deficiency in grazing animals. Oxalates react with calcium to produce insoluble calcium oxalate, reducing calcium absorption. Calcium oxalate adversely affects the absorption and utilization of calcium in the animal body [75]. Ruminants, unlike monogastric animals, can consume considerable amounts of high oxalate plants without adverse effects, principally due to microbial degradation in the rumen [71]. Plants containing about 10% oxalate on dry weight bases cause toxicity [73]. During early stages of growth, there is a rapid rise in oxalate content with concentrations as high as 6% followed by a decline in oxalate levels as the plant matures [73].

2.4.2.4 Phytate

Phytate, which is also known as inositol hexakisphosphate, is a phosphorus containing compound that binds with minerals and inhibits mineral absorption. The cause of mineral deficiency is commonly due to its low bioavailability in the diet. Phytates are generally found in feed high in fibre especially in legumes such as cowpea haulms and have been associated with reduced mineral absorption due to the structure of phytate which has high density of negatively charged phosphate groups which form very stable complexes with mineral ions causing non-availability for intestinal absorption [86].

2.4.2.5 Phenols

Cowpea contains significant amounts of phenolic compounds including phenol acids [87]. Cowpea phenol compounds have health benefits for animals due to their antioxidant [88]. The antioxidant capacity of phenols in different cowpea varieties has been reported. Phenols and their antioxidant activity function to protect cells from oxidative stress which has been implicated in the cowpea leaves and husk that have high nutritive values [89, 90]. Cowpea leafs extract showed antioxidant properties in cow blood; thus, this suggests a possible role in regulating oxidative stress in cow blood [80]. Oxidative stress plays a key role in several pathological conditions connected with animal production and reproduction [91]. Oxidative stress affects the health status of animals as well as product quality such as milk and meat [92]. Lowered antioxidant status is predominant in ruminants during mastitis, retained placenta, acidosis, ketosis and milk fever conditions [93]. The use of cowpea forage as supplement feed impacts milk and meat antioxidant capacity and the overall quality of products. Phenols also exhibit antimicrobial effect against pathogenic bacteria [94].

Mokoboki et al. [81] study sixteen cowpea forage varieties grown under similar soil and management conditions at the University of the North Experimental Farm. After harvesting, the cowpea forages were dried and then analysed for content of dry matter, crude protein, total phenols, condensed tannins, packed volume and water retention. Results revealed that cowpea varieties (TUV11424 and IT85D385) had a total phenols range of 0.75–1.96% DM which suggest no or minimal detrimental effects on protein levels adequate to promote fibre digestion in the rumen. This could reduce live weight losses in ruminant animals in rural areas during the dry season when crop residues are the main feed resource.

3. Methodology

The feeding trial and nutrient digestibility study was conducted at the Sheep and Goat Unit of College of Agriculture and Animal Science, Division of Agricultural colleges, Ahmadu Bello University, Mando-Road, Kaduna State. The farm is located at an elevation of 676 m and latitude of 10°35’N and longitude of 7°25′ E [95]. Fifteen experimental Red Sokoto bucks of an average weight of 10 kg were used for the experiment. The animals were balanced for initial weights before they were allocated to three treatment diets with five bucks per treatment in a complete randomized design. The animals were allowed 14 days to adjust to feed and confinement before the actual start of the experiment that lasted for a period of ninety days.

The three treatment diets consisted of Brachiaria decumbens hay as basal diet. Concentrate diets (14% CP) was supplemented with cowpea haulms at 0% (Control), 10% (SAMPEA 14) and 10% (SAMPEA 15). The basal forage diet was fed ad libitum after feeding the supplements in order to ensure maximum supplement consumption at the rate of 1% of body weight per head per day in the morning (08:00 am). Water and mineral salt lick were provided ad libitum for the period of 90 days. All bucks were weighed at the beginning of the experiment and fortnightly thereafter to determine the live-weight changes and to adjust the amount of feed offered in order to maintain the pre-determined level of 3% feeding of the animal’s body weight for the periods in confinement.

At the end of the feeding trial, three animals were randomly selected from each of the three treatment groups and housed in metabolic creates for total faecal and urine collection as described [96]. The bucks were maintained on the same treatment diets used in the feeding trial and were allowed 14 days adjustment period before the start of the digestibility studies. Each morning (8.000 am), feed left over, faecal output and urine output were collected and weighed for 7 days. The daily total faecal output collected form each buck was weighed and bulked, and subsample was taken for analysis. The daily urine output from each buck was collected into a plastic container containing 10 ml of 0.1 M H₂SO₄ placed under the metabolic creates to prevent nitrogen loss by volatilization. Urine collected was bulked, and about 10% of the total urine output was subsampled for each buck and stored in the refrigerator pending nitrogen determination. Feed samples offered, feed left over and faecal output were analysed for chemical compositions, and urine samples have been analysed for nitrogen using the method described by SAS [97] at the central laboratory of National Animal Production Research Institute, Shika-Nigeria. Data collected on were analysed using Analysis of Variance (ANOVA) by General Linear Model procedures [98]. Data on rumen metabolites and fortnightly weight changes were analysed using repeated measures ANOVA and trend analysis. Treatment means were separated using Dunnett’s test.

4. Nutrient digestibility and nitrogen retention: concentrate diets supplemented with two cowpea haulms varieties and B. decumbens hay basal

An on-farm experiment was conducted in Samaru-Zaria, North-Western Nigeria, by Bala et al. [99] to evaluate the effect of supplementating two cowpea haulm varieties in concentrate diets for Red Sokoto bucks as presented in Table 1. Results revealed that digestibility of dry matter, crude protein, crude fibre, ether extract and nitrogen-free extract were found to increase with inclusion of cowpea forage. The most probable explanation for this phenomenon is in the fact that diet at 10% inclusion level of Sampea 14 cowpea forage might result in high palatability, increased activity of rumen microorganisms for rapid fibre digestion in the rumen and better utilization of the nutrients by bucks. The improvement in digestibilities of nutrients in response to legume supplementation is in line with the reports of Nsahlai and Umunna [100]. Also, it may be attributed to the quality of Sampea 14 cowpea forage, which might have improved the digestibility of other poor-quality roughages. The improvement in CP digestibility due to cowpea hay supplementation could be attributed to the high CP content of the legumes as argued by Murphy and Colucci [101].

Parameter	Control (0%)	Sampea 14 (10%)	Sampea 15 (10%)
Cowpea haulm	0.00	10.00	10.00
Maize offal	35.46	27.33	31.08
Rice offal	30.00	30.00	30.00
Cottonseed cake	32.54	30.67	26.92
Bone meal	1.50	1.50	1.50
Common salt	0.50	0.50	0.50
Total	100.00	100.00	100.00
Calculated analysis:
Crude protein(%)	14.46	14.19	14.41
M.E (Kcal/kg)	3090	3059	3051

Table 1.

Ingredient composition of concentrates containing cowpea haulms supplements.

ME = Metabolizable energy.

Nitrogen retention (N) is the major indicator for accessing the protein nutritional status of ruminant livestock [102]. The N retained recorded in bucks fed 10% Sampea 14 forage inclusion levels as shown in Table 2 is in agreement with the report of Yashim et al. [103] that N depends on good digestibility of nutrients and or utilization. The low N retention for bucks given the control diet could be due to the inadequacy of the diet to maintain N equilibrium and, consequently, live-weight [104]. In the study, the significantly higher N retained and lower N loss in bucks fed 10% Sampea 14 forage inclusion levels cowpea forage indicated that it contained enough digestible nutrients to provide nutrient retention for better performance in Red Sokoto bucks. However, the better N retention in the diet supplemented with Sampea 14 cowpea haulm could be due to a higher rumen degradable protein available which reduced then total N losses. Elseed et al. [105], however, observed that supplementation of protein sources improved microbial N yield and N retention (Tables 3 and 4).

Parameters (%)	Sampea 14 haulm	Sampea 15 haulm	Brachiaria. decumbens hay
Dry matter	89.66	88.52	87.39
Crude protein	16.11	15.55	7.31
Crude fibre	27.88	28.50	28.8
Ether extract	1.83	1.55	0.93
Nitrogen-free extract	47.34	51.48	42.18
Ash	5.28	5.88	5.14
Neutral detergent fibre	59.97	61.4	62.06
Acid detergent fibre	34.03	35.3	30.76
Lignin	17.18	18.4	7.21

Table 2.

Chemical composition of the two varieties of cowpea haulm and Brachiaria decumbens hay.

	Control	Sampea 14	Sampea 15 (%)
Nutrient digestibility (%)	0	10	10	SEM
Dry matter	51.10^b	75.81^a	54.11^b	1.87
Crude protein	61.19^b	77.41^a	61.71^b	2.30
Crude fibre	63.22^c	86.08^a	72.87^b	1.31
Ether extract	26.62^b	39.17^a	27.57^b	2.49
Ash	41.72^a	32.83^b	24.94^c	3.03
Nitrogen-free extract	60.06^b	84.41^a	67.34^b	1.98

Table 3.

The effect of feeding two cowpea haulm varieties on nutrient digestibility in Red Sokoto bucks fed Brachiaria decumbens hay as basal diet.

^abc Means with different superscripts along the row differed significantly (P < 0.05).

SEM = Standard error of means.

Nitrogen balance (g/day)	Control	Sampea 14	Sampea 15 (%)
	0	10	10	SEM
Nitrogen intake	5.07	6.43	5.46	0.68
Faecal Nitrogen	3.45	2.13	3.46	0.72
Urinary Nitrogen	0.94	0.51	0.81	0.45
Total nitrogen loss	4.39^a	2.64^b	4.28^a	0.77
Nitrogen retained	0.67^b	3.79^a	1.18^b	0.62
Nitrogen absorbed	1.61	2.80	1.68	1.11

Table 4.

The effect of feeding two cowpea haulm varieties on nitrogen balance in Red Sokoto bucks fed Brachiaria decumbens hay as basal diet.

^abc Means with different superscripts along the row differed significantly (P < 0.05).

SEM = Standard Error of Mean.

5. Conclusions

Farmers could incorporate cowpea forage/haulms in concentrate diet of Red Sokoto bucks for optimum performance under smallholder production system.