Performance of West African dwarf goats fed Guinea grass–Verano stylo mixture, N-fertilized and unfertilized Guinea grass

Small Ruminant Research 39 (2001) 145±152

Performance of West African dwarf goats fed Guinea grass±Verano stylo mixture, N-fertilized and unfertilized Guinea grass M.A. Bamikolea,1, I. Ezenwab,*, A.O. Akinsoyinua, M.O. Arigbedec, O.J. Babayemia a

Department of Animal Science, University of Ibadan, Ibadan, Nigeria b Department of Agronomy, University of Ibadan, Ibadan, Nigeria c Department of Pasture and Range Management, University of Agriculture, Abeokuta, Nigeria Accepted 23 June 2000

Abstract The supplementary values of Verano stylo in a mixed Guinea grass (Panicum maximum cv. Ntchisi)±Verano stylo (Stylosanthes hamata cv. Verano) diet from a sown grass±legume mixture and N fertilized grass were compared in West African dwarf (WAD) goats. Liveweight (LW) gain, feed intake, digestibility and N utilization were determined using 15 goats in two trials lasting for 98 days. Goats were fed Guinea grass±Verano stylo mixture (GSM), N-fertilized (NFG) and unfertilized grass (UFG). The goats were divided into three groups of ®ve animals each and randomly allocated to the dietary treatments in a randomized complete block design. Total DM and OM intakes of the goats did not vary signi®cantly among the forage diets and averaged 55.1 and 50.4 g kgÿ1 W0.75 per day, respectively. CP intake (g kgÿ1 W0.75 per day) was highest with NFG (5.6) followed by GSM (4.8) and the UFG (3.5). Total N excreted followed the same trend as the CP intake. There was no signi®cant difference between N-retention of GSM and NFG (28.5 and 26.7%), but goats on UFG had a negative N balance (ÿ9.16%). Animals on GSM had signi®cantly higher liveweight gain (31.9 g per day) than those of NFG (25.1 g per day) and UFG (21.9 g per day) which also differed signi®cantly. The digestibilities of total DM, OM, CP, NDF were higher with GSM than NFG or UFG. It is concluded that growing Verano stylo in mixture with Guinea grass is a better option for improving the feed quality of forage diets for goats than direct application of inorganic fertilizer at 200 kg N haÿ1 to the pure grass. # 2001 Elsevier Science B.V. All rights reserved. Keywords: Digestibility; Goats; Guinea grass; N utilization; Verano stylo

1. Introduction * Corresponding author. Present address: Department of Grassland Management, National Grassland Research Institute, Senbonmatsu 768, Nishinasuno, Tochigi 329-2793, Japan. Tel.: ‡81-287-37-7209; fax: ‡81-287-36-6629. E-mail address: [email protected] (I. Ezenwa). 1 Present address: Department of Animal Science, University of Benin, Benin City, Nigeria.

Sheep and goats are an important component of the farming system of southern Nigeria where they play an important religious and cultural roles and are a ¯exible ®nancial reserve for the rural population. Under the traditional free-range system of management, the animals (average of three to four per household)

0921-4488/01/$ ± see front matter # 2001 Elsevier Science B.V. All rights reserved. PII: S 0 9 2 1 - 4 4 8 8 ( 0 0 ) 0 0 1 8 2 - 6

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subsist on low quality unimproved natural grass pastures and household scraps (Sumberg and Mack, 1985). Available evidence, however, indicates that the small ruminant industry in Nigeria would bene®t, if the animals received optimal nutrition (Osuagwuh, 1992). Forage research in this area has focussed on developing strategies for improving the nutritive value of forages to enhance the productivity of these animals. These effort have been directed at use of sown improved grasses, N fertilization of pure grass stands as well as incorporation of adapted herbaceous and tree legumes into grass pastures (Ezenwa et al., 1995; Ezenwa and Aken'Ova, 1998; Bamikole and Ezenwa, 1999). Many adapted and highly productive forage grasses and legumes of high nutritive value, and appropriate agronomic management practices to achieve these targets, are now available in southern Nigeria. Among these options, sown Guinea grass±Verano stylo mixture managed under a 6-weekly cutting regime in the rainy season is the best bet in terms of high DM yield and chemical composition (Ezenwa and Aken'Ova, 1998). However, forage quality and overall potential are best measured in terms of animal productivity. The positive response of tropical grasses to inorganic N fertilization is well reported. However, reliance on high N fertilizer application (up to 200 kg N haÿ1) to achieve optimum yields is unlikely to be of practical importance to the low-input farmers in southern Nigeria, for whom small ruminant production is an adjunct to arable cropping. Only a few studies have addressed the direct impact of fertilization of grass on ruminant nutrition (Zhang et al., 1995; Delagarde et al., 1997; Peyraud and Astigarraga, 1998). Most studies in southern Nigeria have dealt almost exclusively on browse plants as the main option for improving the utilization of poor quality grass diets. However, good results have been obtained elsewhere with forages of herbaceous legumes as supplements for ruminants on low quality diets (Said and Tolera, 1993; Abule et al., 1995; Kariuki et al., 1999). It has been established that grass±legume mixtures are as productive as N fertilized grass stands and the legumes can signi®cantly contribute to the quality of the total forage (Ezenwa and Aken'Ova, 1998). The purpose of this study was to compare inorganic N fertilizer applied on Guinea grass and Verano stylo grown, and fed as a mixture with grass as ways of

improving the utilization ef®ciency of the grass and eliciting better performance in West African dwarf (WAD) goats. We determined liveweight (LW) gain, intake, digestibility and N utilization in WAD goats fed N-fertilized Guinea grass, Guinea grass±Verano mixture and unfertilized grass. 2. Materials and methods 2.1. Site The experiment was conducted at the Goat Unit of the Teaching and Research Farm of the University of Ibadan, Ibadan (78200 N, 38500 E; altitude about 200 m above sea level). The climate is humid tropical with average annual rainfall of 1150±1250 mm. The temperature and relative humidity ranges during the study were 28±348C and 70±80%, respectively. 2.2. Forages The forages were obtained from sown pastures established in a 40 m  45 m plot near the goat unit. Guinea grass (Panicum maximum cv. Ntchisi)±Verano stylo (Stylosanthes hamata cv. Verano) (GSM), N fertilized (NFG) and unfertilized Guinea grass (UFG) swards were grown in three separate adjoining blocks of 40 m  15 m each. The plots were established in July 1996. Guinea grass was established from crown splits at 0:5 m  1 m spacing in the three swards. In the GSM plot, scari®ed seed of Verano stylo was drilled in the 1-m wide inter-rows of the grass. Nitrogen was supplied to the grass in NFG plot at the rate of 200 kg N haÿ1 per year. Daily supply of 6 weeks old fresh forages throughout the study was made possible by dividing each of the pastures into 42 strips and using a staggered cutting strategy that is suitable for small-scale small ruminant production (Bamikole et al., 1998). The forages were harvested every morning and afternoon, just before feeding, to mimic traditional local practice, and chopped into 3±5 cm pieces before feeding to the animals. 2.3. Animals Fifteen male West African dwarf goats (WAD) (mean weight ˆ 5:43 kg, S:E: ˆ 0:39 kg, age ˆ 5ÿ6

M.A. Bamikole et al. / Small Ruminant Research 39 (2001) 145±152

months) were purchased from villages in the neighbourhood of the University campus. The animals underwent standard quarantine procedures. They were given i.m. injection of vitamins and antibiotics and treated against internal and external parasites for 28 days before the trial commenced. During the adaptation period the animals received the experimental diets daily. The goats were housed in individual pens in an open-sided type house with half walls that permitted cross-ventilation, and with corrugated aluminium sheet roo®ng and concrete ¯oor. 2.4. Feeding trial and experimental design The goats were balanced for weight and randomly allocated to the three experimental diets: N-fertilized Guinea grass (NFG), Guinea grass±Verano stylo mixture (GSM) and unfertilized Guinea grass (UFG) in a randomized complete block design with ®ve animals per treatment. The forages were offered twice a day, at 08:00 and 16:00 h, in equal proportions, allowing 20% increase of the DM consumed the previous day. For animals on GSM, Verano stylo was offered in the same feeder as grass and at the same time, but at the level of 40% of the amount of grass offered. All the animals had ad libitum access to water. This trial lasted for 84 days. During this period, the uneaten feed was removed, weighed and sampled before the morning feed (08:00 h) to determine the intake of the previous day. The goats were weighed every week, before morning feeding. Samples of the forages offered and the refusals were taken every morning for DM determination by drying in an oven at 1008C for 48 h. 2.5. Digestibility and N balance trial The feeding trial was followed by a 14-day digestibility trial. All the animals were put into metabolism cages, which allowed complete separation and recovery of faeces and urine. They were allowed 7 days to adapt to the cages. Complete collection of faeces and urine followed. During the digestibility trial, forages, feed refusals and faeces were sampled daily for determination of DM and chemical analysis. Samples of the faeces and urine (10% of daily production) were pooled for each animal for the 7-day period, and subsampled. The urine was collected in plastic containers containing 20 ml of 10% sulphuric acid

147

(H2SO4) to prevent loss of N by volatilization. The samples were later frozen pending chemical analysis. 2.6. Chemical analysis Dried (in an oven at 608C) forages and faeces were ground and analysed for their contents of Mg, K, Na, OM and CP (N  6:25) according to the methods of AOAC (1990). Nitrogen in the urine was also determined. Neutral detergent ®bre was analysed using the method of Van Soest and Robertson (1985). 2.7. Statistical analysis Data were analysed by the analysis of variance and regression procedures of SAS (SAS, 1988). Statistical differences between means were compared using the Duncan Multiple Range Test at P < 0:05. 3. Results 3.1. Chemical composition of the forages The chemical composition of the forages during the feeding and digestibility trials is presented in Table 1. All the forages had similar values of OM and Na contents. Verano stylo (VS) had the highest CP concentration. Nitrogen fertilization increased the CP contents of the pure grass (NFG) over those of the Table 1 Average chemical composition (g kgÿ1 DM) of forages fed to West Africa dwarf goats during the feeding and digestibility trials Compositiona

N CP NDF OM Mg K Na a

Forageb NFG

GGVS

VS

UFG

15.1 94.0 698.0 908.0 4.2 22.8 0.2

11.0 68.9 618.6 859.4 4.3 29.0 0.2

19.2 120.4 530.7 933.2 3.9 14.2 0.2

10.2 64.0 683.0 897.0 3.8 26.5 0.2

Values are means of two determinations from two harvests. NFG: N-fertilized grass; GGVS: Guinea grass in the grass± Verano stylo mixture; VS: Verano stylo; UFG: unfertilized Guinea grass. b

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unfertilized grass (UFG) and the grass grown in the mixture with Verano stylo (GGVS). NFG and UFG had relatively higher levels of NDF than VS and GGVS. UFG and GGVS had similar CP contents. The Mg contents of the forages were similar whereas VS contained the least amount of K. 3.2. Feed intake and liveweight gain Intake of forages and liveweight gain of goats during the feeding trial are shown in Table 2. The animals on grass only diets (NFG and UFG) consumed twice as much grass as animals on mixed grass± legume diet. However, in terms of total DM intake, there were no signi®cant differences among the diets. The total OM intake followed a similar pattern as the total DM intake. Total CP intake varied signi®cantly: NFG > GSM > UFG. Intake of NDF by animals on the grass-only diets (NFG and UFG) was not signi®cantly different but signi®cantly higher than that of the animals on GSM. Animals that were fed GSM gained signi®cantly more weight than did those on NFG, which in turn gained signi®cantly more weight than those on UFG did.

Table 2 Performance characteristics of West African dwarf goats fed Guinea grass±Verano stylo mixture, N-fertilized and unfertilized Guinea grass a

Variable

Diets NFG

GSM

5.64 2.26c 26.90c

Intake (g DM per day) Guinea grass Verano stylo

244.1 ±

111.5 96.8

220.6 ±

Total

244.1b

208.3b

220.6b

18.22

per day) 58.5b 53.3b 5.6b 41.1b

52.3b 47.2b 4.8c 30.5c

54.4b 50.6b 3.5d 37.8b

3.24 3.76 0.27 2.34

Intake (g kg DM OM CP NDF

0.75

LW

5.56 1.83d 21.78d

S.E.

Initial LW (kg) Liveweight gain (kg) Growth rate (g per day)

ÿ1

5.08 2.58b 30.71b

UFG

0.100 1.405

a NFG: N-fertilized grass; GSM: Guinea grass±Verano stylo mixture; UFG: unfertilized grass. b,c,d Means in a row followed by the same letter are not signi®cantly different …P > 0:05†.

3.3. Feed intake, digestibility and nitrogen metabolism Intakes of DM, OM, CP and NDF during the digestibility trial varied signi®cantly: NFG > GSM > UFG (Table 3). For digestibilities, higher values were obtained with GSM than NFG and UFG, which did not differ signi®cantly. Estimated DOM was higher in GSM that in NFG and UFG, which had similar values. The digestible and metabolizable energy values of GSM were 9±11% higher than those of NFG and UFG. Animals on NFG had signi®cantly higher N intake than the animals on GSM, which in turn had higher values than animals on UFG (Table 4). Faecal and urinary N excretion differed signi®cantly among the diets. Animals on UFG had lower values of faecal N excretion than did those on NFG and GSM. Animals on NFG excreted 21% more N in the urine than those on GSM, which had similar values as animals on UFG. Total N excreted was NFG > GSM > UFG. Nitrogen Table 3 Nutrient intake and digestibility of West African dwarf goats fed Guinea grass±Verano stylo mixture, N-fertilized and unfertilized Guinea grass Dietsa

Variable

NFG ÿ1

0.75

Intake (g kg LW DM DM (g kgÿ1LW) OM CP NDF

GSM

UFG

S.E.

per day) 60.0b 35.9b 54.0b 5.4b 41.8b

53.5c 32.1c 49.0c 5.0c 32.0c

48.5d 29.9c 43.8d 3.0d 33.7c

2.05 1.27 1.86 0.15 1.41

Apparent digestibility (g kgÿ1) DM 671.6c OM 668.5c CP 670.4c NDF 689.6c Digestible OM (%)e 60.87

749.4b 765.2b 723.4b 797.9b 66.34

665.7c 666.1c 666.1c 714.7c 59.62

9.74 15.20 10.82 10.60 NDg

Energy concentration (MJ kgÿ1 DM) Digestible energyf 11.6 12.6 Metabolizable energye 9.1 9.9

11.3 8.9

ND ND

a NFG: N-fertilized grass; GSM: Guinea grass±Verano stylo mixture; UFG: unfertilized grass. b,c,d Means in a row followed by the same letter are not signi®cantly different …P > 0:05†. e Determined by MAFF (1984) equation. f Digestible energy ˆ 0:19  digestible OM in the DM %. g Not determined.

M.A. Bamikole et al. / Small Ruminant Research 39 (2001) 145±152 Table 4 Nitrogen utilization in West African dwarf goats fed Guinea grass± Verano stylo mixture, N-fertilized and unfertilized Guinea grass Variable

Dietsa NFG

Nitrogen intake (g per day) (g kgÿ1 LW0.75 per day)

GSM

UFG

S.E.

4.00b 0.86b

3.66c 0.79c

2.13d 0.48d

0.11 0.02

Nitrogen excretion (g per day) Faecal 1.07b Urinary 1.92b Total 2.99b Balance 1.01b

1.02b 1.59c 2.61c 1.05b

0.70c 1.63c 2.33d ÿ0.20c

0.06 0.07 0.09 0.13

0.23b

0.23b

ÿ0.05c

0.03

26.70b

28.50b

ÿ9.16c

3.33

Nitrogen balance (g kgÿ1 LW0.75 per day) Nitrogen retention (%) a

NFG: N-fertilized grass; GSM: Guinea grass±Verano stylo mixture; UFG: unfertilized grass. b,c,d Means in a row followed by the same letter are not signi®cantly different …P > 0:05†.

balance was similar and positive in NFG and GSM, but negative in UFG. 4. Discussion Mixed Verano stylo±Guinea grass diet improved the quality of the total diet resulting in higher nutrient digestibilities and liveweight gain than the N-fertilized and unfertilized grass diets. This ®nding is made more signi®cant by the fact that growing Verano stylo± Guinea grass mixture is within the scope of the local farmer (Ezenwa and Aken'Ova, 1998). This assertion is supported by the ®nding of Kariuki et al. (1999) that sown grass±legume mixture (Napier-desmodium) intercrop is more appealing from the farmer's point of view due to low cost. In southern Nigeria, good results have been obtained with sheep and goats feeding Leucaena leucocephala and Gliricidia sepium leaves as supplements to basal grass diets (Sumberg, 1985; Reynolds and Adediran, 1988). These and other trials established that the overall value of forage as supplement depends on its capacity to provide nutrients needed to meet animal's requirements that are de®cient in the basal diet. Although rumen ammonia concentration was not measured in the present study, it appears that

149

Verano stylo improved N supply in the rumen and insured a more ef®cient metabolism of the basal diet. This may be because legumes have higher degradation rates than grasses and this coupled with high CP content increases the rumen ammonia concentration which has positive effects on rumen microbial growth (Said and Tolera, 1993; Abule et al., 1995). In this study, intakes of DM were similar among Nfertilized grass, grass±legume diet and the unfertilized grass and within the recommended feeding levels of 30±40 g kgÿ1 of body weight (Carew, 1983; Anugwa, 1990). This was because of the relatively young age and good quality of the forages, which had higher CP contents than the minimum level of 60±70 g kgÿ1 DM below which intake is depressed (Minson, 1983). Relatively good quality forages normally result from sown pastures based on improved genotypes of forage species under appropriate agronomic management (Ezenwa and Aken'Ova, 1998). In general, however, tropical pastures have CP contents of less than 60 g kgÿ1 DM and require supplementation for optimum performance of animals on them (Gihad, 1976, Van Eys et al., 1986; Bamikole and Ezenwa, 1999). It is also evident that NFG even with comparatively greatly improved CP content did not elicit signi®cantly higher DM intake than the GSM and UFG. Peyraud and Astigarraga (1998) also reported that Nfertilization did not result in higher DM intake in sheep. Estimated energy contents of the diets show that the NFG, GSM and UFG had adequate levels of energy to support adequate growth in goats (Onwuka and Akinsoyinu, 1989; Mtenga and Shoo, 1990). Higher intakes of CP in NFG and GSM than UFG and higher intake of NDF in NFG and UFG than in GSM are re¯ections of the levels of the components in the respective diets. This agrees with other reports (Umunna et al., 1995; Alayon et al., 1998; Kariuki et al., 1999). The N-fertilized grass had the highest concentration of CP as well as NDF. The consequence of the lower concentration of NDF in GSM was increased digestibility of nutrients in the mixed diet. This and the improved N supply from the legume, which made up for the de®ciency in the basal diet (Poppi and McLennan, 1995), might have resulted in improved rumen fermentation and ef®ciency of utilization of the basal diet and thus higher liveweight gain. This observation is supported by reports of Van

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Eys et al. (1986), Ash (1990), Alayon et al. (1998) and Kaitho et al. (1998a,b). Improved liveweight gains have generally been reported with supplementation of basal grass diets with legumes, with or without increase in total DM intake (Van Eys et al., 1986; Alayon et al., 1998; Kaitho et al., 1998a). Metabolizable protein requirements of ruminants are met primarily from rumen microbial protein and from dietary protein that escapes the rumen undegraded (Robinson et al., 1991). Kaitho et al. (1998b) showed that good protein supplements by supplying moderate levels of rumen available-N make them available for microbial synthesis. Bamikole et al. (1999) have also reported that inclusion of Verano stylo in the basal grass diet augmented mineral de®ciencies in the grass. According to computations by Kariuki et al. (1999), liveweight gains resulting from mixed grass±legume diets are cheapest when the diet is obtained from the grass± legume grown together as an intercrop. Liveweight gain obtained with GSM compares well with other reports where leguminous browse leaves or concentrates were used as supplements (Ademosun et al., 1985; Mtenga and Shoo, 1990). Negative N balance obtained in goats on unsupplemented grass diets con®rms earlier results with goats (Gihad, 1976; Van Eys et al., 1986; Mtenga and Shoo, 1990) that optimum performance of animals on forage-only diets cannot be achieved without protein and/or energy supplementation. Bene®t of N-fertilization of grass on the nutrition of animals is not fully established and has been the subject of a few studies. Ezenwa and Aken'Ova (1998) showed that although tropical grasses respond well to N application in terms of increased DM yields, the effect of N fertilization is not always evident in the superior quality of the forages. In the current study, N fertilized grass had higher CP content than the unfertilized grass, but the latter also had higher content of NDF. No change in ®bre composition of bromegrass was reported by Messman et al. (1991) using 89 kg N haÿ1, whereas in another study (Panditharatne et al., 1986) where 345 kg N haÿ1 was used on orchard grass, NDF concentration was higher. In the present study, the digestibility of DM and NDF in the NFG was not signi®cantly different from that of UFG due to the higher intakes of NDF in both diets. Similarly, Messman et al. (1991) and Zhang et al.

(1995) reported that N fertilization at 89 and 112± 336 kg N haÿ1, respectively, had no effect on the digestibilities of the ®bre components and in situ disappearance of grass DM. It appears that the high N content of N-fertilized grass was not as ef®ciently utilized in the rumen as that of the mixed grass± legume diet. This is in line with the report of Van Eys et al. (1986) that Napier grass of 6±8 week regrowth and adequate CP level of 12% did not provide suf®cient protein for growing goats owing to inef®cient protein utilization. The poor ef®ciency of utilization of NFG is corroborated by the highest total N excretion by the animals on this diet. A large amount of N excreted in the urine will be lost to the environment as ammonia. Thus, the lower N loss via the urine of the animals on GSM than on NFG has implications not only for animal production but also for the environment. High losses of N in the urine of animals on N-fertilized grass has been reported in lambs (Zhang et al., 1995) and dairy cows (Astigarraga et al., 1993; Delagarde et al., 1997). The high urinary loss of N has been attributed to the characteristic ruminal loss of N during the digestion of CP in grasses (Poppi and McLennan, 1995; Zhang et al., 1995) due to imbalance between degraded protein and energy supply for optimal microbial capture of ammonia-N. Inclusion of herbaceous legumes in grass diets while increasing digestibility, rumen ammonium concentration and rumen out¯ow rate, also reduces retention time in the rumen, and lead to a synchronous supply and utilization of N and energy (Abule et al., 1995; Kariuki et al., 1999; Ondiek et al., 1999). 5. Conclusion The positive effects of inorganic N fertilization on CP content of grass did not translate to signi®cantly higher intake of DM and OM or to superior nutrient digestibility and performance of animals on it over those of the mixed grass±legume diet. The positive responses obtained with the grass±legume diet were attributed to the ability of the legume to ameliorate N de®ciency in grass and reduce NDF concentration in the total diet. This translated into higher nutrient digestibilities and N retention by ensuring a more ef®cient rumen fermentation, and consequently higher

M.A. Bamikole et al. / Small Ruminant Research 39 (2001) 145±152

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