Supplementation of graded levels of
Desmodium
intortum
hay to sheep feeding on maize stover
harvested at three stages of maturity
1. Feed intake, digestibility and body weight change
Adugna Tolera
a,b,*, Frik Sundstùl
c,1aDepartment of Animal Production and Rangeland Management, Awassa College of Agriculture,
P.O. Box 222, Awassa, Ethiopia
bDepartment of Animal Science, Agricultural University of Norway, P.O. Box 5025, N-1432 Aas, Norway cAgricultural University of Norway, Noragric, P.O. Box 5001, N-1432 Aas, Norway
Received 16 April 1999; received in revised form 15 February 2000; accepted 3 March 2000
Abstract
Feed intake, digestibility and body weight change of lambs fed basal diets of maize stover harvested at three stages of maturity and supplemented with graded levels (0, 150, 300 and 450 g per head per day) of desmodium (Desmodium intortumcv. Greenleaf) hay were studied. The maize stovers were harvested at 30, 22 and 12% grain moisture content which were designated as stages I, II and III, respectively. The crude protein (CP) content of the stovers showed a decreasing trend whereas the ®bre contents showed an increase from stages I to III. The desmodium hay had higher CP, phenolic compounds, calcium, sulphur and manganese contents and lower ®bre (neutral and acid detergent ®bres, cellulose and hemicellulose) contents than the stovers. Maize stover, total dry matter (DM) and organic matter (OM) intake showed a decreasing trend (p>0.05) with increasing stage of maturity of the stover. The CP intake was signi®cantly higher (p<0.05) in sheep fed maize stover harvested at stage I than at stages II and III. Total DM, OM and CP intake increased whereas maize stover DM intake showed a signi®cant decrease (p<0.05) with increasing level of supplementation. Desmodium hay constituted about 28, 47 and 66% of the total DM intake and, on average, there was a substitution of about 12, 21 and 37% of the stover by the desmodium hay at 150, 300 and 450 g of supplementation, respectively.
Dry matter, OM and neutral detergent ®bre (NDF) digestibilities showed a decreasing trend (p>0.05) with increasing stage of maturity. Crude protein digestibility and the intakes of digestible
85 (2000) 239±257
*Corresponding author. Tel.:251-6-200221; fax:251-6-200072.
E-mail address: aca@telecom.net.et (A. Tolera)
1Present address: SACCAR, Private Bag 00108, Gaborone, Botswana.
OM and metabolizable energy (ME) were signi®cantly higher (p<0.05) in sheep feeding on maize stover harvested at stage I than stage III and showed a general declining trend with increasing stage of maturity of the stover. Supplementation resulted in improved digestibility of the diet. There was a signi®cant increase (p<0.05) in CP digestibility, digestible OM intake, digestible organic matter in the DM (DOMD), ME concentration of the diet and ME intake with increasing level of supplementation. The body weight gain showed a signi®cant increase (p<0.05) with increasing level of supplementation whereas all sheep without supplement lost body weight. The weight loss increased with increasing stage of maturity of the stover. Considering DM intake and digestibility, 300 g of desmodium hay appears to be an optimum level of supplementation, under similar conditions to the current study.#2000 Elsevier Science B.V. All rights reserved.
Keywords:Maize stover; Stage of maturity;Desmodium intortum; Feed intake; Substitution rate; Digestibility; Body weight gain
1. Introduction
Maize produces the largest proportion of crop residues in the world compared to other crops (Kossila, 1984; Chaudhry, 1998). The quantity and quality of maize stover is very variable depending upon variety, agro-climatic conditions and management factors (Harika et al., 1995). Stage of maturity of the crop at the time of harvest is one of the management factors in¯uencing the nutritive value of crop residues and much work on this subject has been undertaken (Fleischer et al., 1989; Irlebeck et al., 1993; Harika and Sharma, 1994; Tolera et al., 1998). Based on ®eld, in sacco degradability and laboratory studies, Tolera et al. (1998) showed that early harvesting of maize after attaining its physiological maturity, followed by immediate sun drying of the grain and the stover improved quality of the stover without adversely affecting grain yield and quality.
However, the voluntary feed intake and the ef®ciency of extraction of nutrients from the feed during digestion are the most important determinants of nutritive value of a feed. Low digestibility of poor quality roughages results from their failure to provide rumen micro-organisms with all nutrient requirements. Nitrogen (N) de®ciency is the most important limiting factor in these feeds. When the N content of the diet is less than 1.2%, rumen function may be impaired, feed intake reduced and animal performance markedly reduced (Conrad and Hibbs, 1968). Fibrous crop residues, therefore, require appropriate supplementation as they cannot sustain effective animal production or even maintenance when they are fed alone. Conventional concentrate supplements are costly and in short supply in developing countries (Anderson, 1987). Thus, supplementation with leguminous forages, that can be grown on the farm, appears to be a more feasible alternative to improve the feeding value of cereal straws and stovers in most developing countries (Devendra, 1985; Mosi and Butterworth, 1985a; Yilala, 1989).
harvested at different stages of maturity and supplemented with graded levels of desmodium (Desmodium intortum cv. Greenleaf, commonly known as Greenleaf desmodium) hay were studied. This trial will aid in assessing the potential improvements that could be achieved through management of maize stover harvesting stages and forage legume supplementation.
2. Materials and methods
2.1. Animals and management
Seventy two intact male lambs of the local sheep from southern Ethiopia, with average initial live weight of 181.5 kg, were used in the experiment. The lambs were purchased from local markets, about 70±95 km northwest of the experimental site at Awassa. Before the commencement of the experiment, the lambs were accustomed to the experimental feed for about 1 month and they were drenched against internal parasites and sprayed against external parasites at the same time.
2.2. Feeds used in the experiments
Feeds used in the experiment were maize stover, harvested at three stages of maturity, as a basal diet andDesmodium intortumhay as a supplement at four levels (0, 150, 300 and 450 g per head per day on as fed basis which, on average, constituted 0, 16, 30 and 46%, respectively, of total feed offered). The maize stovers were harvested at 30, 22 and 12% grain moisture content which were designated as stages I, II and III, respectively. The maize stovers harvested during the ®rst and second stage were sun-dried in the ®eld to decrease the stem moisture content for safe storage. There was heavy rain during the ®rst and second harvests which could impact negative effects on the quality of the stover. The desmodium was harvested by hand, using a sickle, at late ¯owering stage and sun dried into hay on canvas to minimize leaf loss. The maize stover was chopped before the start of the experiment and thoroughly mixed in order to obtain a uniform material. The desmodium hay was similarly treated. Both feeds were then fed separately.
2.3. Growth experiment
During the growth experiment, which lasted for 63 days, the lambs were assigned to 12 treatments of six animals each in a factorial arrangement (three maturity stages of maize stoverfour levels of desmodium hay supplementation). They were housed and fed in individual pens provided with feed troughs. The chopped desmodium hay was divided into two portions and offered as the ®rst feed in the morning at 08:00 and at 15:00 hours in the after noon. The maize stover was offered separately ad libitum at 150% of the previous day's intake (50% refusal rate). Clean water was freely available all the time. Awash mineral lick was provided free choice at the beginning of the experiment. However, when some animals showed a tendency of consuming excess amount of the mineral due to its molasses content (5%) and loose nature, the mineral offer was ®xed at
6 g per head per day to avoid possible risk of copper toxicity as the mineral lick was high (1974 mg/kg) in copper content. Amounts of maize stover and desmodium hay offered and refused were monitored and the values used to calculate intake levels. Substitution rates were calculated as the ratio of the difference in the intake of maize stover between the unsupplemented and supplemented diets to the intake of the supplement. The lambs were weighed every 2 weeks to monitor their body weight change. Although the experiment was initially designed for 76 days of data collection, it was terminated after 63 days due to declining feed intake and progressive loss of body condition of sheep feeding on the unsupplemented stover.
2.4. Digestibility experiment
After completion of the growth experiment and a rest period of 2 weeks, three lambs from each treatment group were transferred to metabolism crates for the digestibility trial. The lambs were accustomed to the metabolism cages and to the faeces and urine collec-tion harnesses for 7 days followed by a colleccollec-tion period of 7 days. The feeding regime during the rest period and during the digestibility trial was the same as in the preceding growth experiment. Faecal output of the lambs was collected individually in faeces bags attached to the animal and 10% of the daily output was sampled and stored in a deep freezer. Separate faeces samples were dried daily at 1058C overnight to determine dry matter (DM) content of the faeces. The 7 days' samples were bulked for each individual sheep and sub-sampled at the end of the experiment for chemical analyses. Faeces samples for chemical analyses, other than N, were oven dried at 658C for 48 h, ground and stored in tightly covered sample bottles pending analyses. Metabolizable energy (ME) content (MJ/kg DM) was calculated as 0.15DOMD% (digestible organic matter in the DM) (MAFF, 1984).
2.5. Chemical analyses
Dry matter and ash contents of composite samples of feed and faeces were determined by oven drying at 1058C overnight and by igniting in a muf¯e furnace at 6008C for 6 h, respectively. Nitrogen content was determined by the micro-Kjeldahl method and crude protein (CP) was calculated as N6.25. Faeces N content was determined on fresh frozen samples. Neutral detergent ®bre (NDF), acid detergent ®bre (ADF) and acid detergent lignin (ADL) were determined according to Van Soest and Robertson (1985). Hemicellulose and cellulose were calculated as NDFÿADF and ADFÿADL, respectively. Extractable and total proanthocyanidins contents of feed offered were determined following the methods of Porter et al. (1986). Calcium, phosphorus, copper, manganese and zinc contents were analysed according to AOAC (1990) using the dry ashing method and sulphur was determined following the method of Selmer-Olsen (1986) at the Laboratory for Analytical Chemistry, Agricultural University of Norway.
2.6. Statistical analysis
the effects of stage of maturity of the stover and the levels of desmodium hay supplementation as well as their interaction on feed intake, digestibility and body weight change of the sheep. Initial body weight of the sheep was included in the model as a covariate. Statistical signi®cance of the difference between stover stage of maturity and level of desmodium hay were tested using Duncan's New Multiple Range (SAS, 1985; Montgomery, 1991). Regression analysis was carried out to ®nd the relationship of total DM intake and live weight gain with the amount of supplement offered. No statistical analysis was done on chemical composition.
3. Results and discussion
3.1. Chemical composition
The chemical composition of maize stover and desmodium hay used in the experiment is shown in Table 1. There were no differences in the DM and OM content of maize
Table 1
Chemical composition of maize stover andDesmodium intortumhay used in the experiment
Components Maize stover Desmodium
intortumhay Stage I Stage II Stage III
Dry matter (%) 93.4 93.7 93.4 89.2
In dry matter (g/kg DM)
Organic matter 926 931 931 922
Crude protein 36 33 31 138
Neutral detergent ®bre 772 790 801 533
Acid detergent ®bre 455 483 531 351
Acid detergent lignin 50 68 83 97
Cellulose 405 415 458 254
Hemicellulose 317 307 270 182
Total extractable phenolics 7.6 6.9 7.1 45.4
Total extractable tannins 1.8 1.5 1.6 34.6
Proanthocyanidins (A550 nm/g DM)
Extractable proanthocyanidins 1.1 1.1 1.2 447.6
Nitrogen:sulphur (N:S) ratio 6.2 6.1 5.7 12.3
Trace minerals (mg/kg DM)
Copper 2.0 2.0 2.1 3.3
Manganese 40.9 33.2 31.7 82.0
Zinc 32.4 28.8 31.7 26.3
stovers harvested at the three stages of maturity. The CP content showed a slight decline from stages I to III whereas the ®bre fractions (NDF, ADF, lignin and cellulose) showed an increase from stages I to III. The CP content was much higher in the desmodium hay than in the maize stovers whereas the NDF, ADF, cellulose and hemicellulose contents showed the reverse trend. On the other hand, the desmodium hay had relatively higher lignin content than the stovers. The maize stovers were characterised by low CP and high cell-wall, cellulose and hemicellulose contents, which are typical features of most cereal crop residues. Lignin and ADF are related more to digestibility than to intake, whereas the reverse is a characteristic feature of protein, cell wall, cellulose and hemicellulose contents (Van Soest, 1994). The OM, CP, NDF and lignin contents of the desmodium hay were comparable to the values reported by Said and Tolera (1993).
The concentrations of total phenolics, total tannins, extractable proanthocyanidins and total proanthocyanidins were very high in the desmodium hay whereas the values recorded for the maize stover types were very low but similar for these variables. The calcium, sulphur and manganese contents of desmodium were higher than that of the stovers. However, the three maturity stages of the stover were not different in their mineral contents. The calcium, phosphorus and sulphur contents of the stovers were comparable to the values reported by Kabaija and Little (1988) for maize stover in Ethiopia. Nitrogen and sulphur are the most critical nutrients in¯uencing the activity of rumen micro-organisms (McDonald et al., 1996) and their de®ciency and/or imbalance primarily causes decreased availability of microbial protein with consequent loss of appetite (Preston and Leng, 1987). The nitrogen:sulphur (N:S) ratio for ef®cient microbial growth in the rumen appears to lie between 10:1 and 12:1 for sheep and 14:1 and 15:1 for cattle (Bray and Till, 1975; cited by Preston and Leng, 1987). The maize stovers used in the present study had very low contents of both nitrogen and sulphur with N:S ratios varying from 5.7:1 to 6.2:1. This indicates that nitrogen de®ciency is a more critical limitation to ef®cient utilization of the stovers.
3.2. Voluntary feed intake
decreasing nutrient contents in the maize fractions (Russell, 1986; Tolera et al., 1998; Tolera and Sundstùl, 1999). The intake of maize stover is mainly affected by the nitrogen and ®bre contents and the leaf-stem ratio of the stover. The leaf components are more acceptable to animals, physically easier to chew and more digestible (Joshi et al., 1995). Total DM intake showed a signi®cant increase (p<0.05) with increasing level of desmodium hay supplementation up to 300 g per day. But there was no signi®cant difference (p>0.05) between 300 and 450 g of supplementation in total DM intake. The DM intake showed a strong quadratic relationship with the amount of desmodium hay Table 2
Dry matter (DM), organic matter and crude protein intake of sheep fed a basal diet of maize stover harvested at different stages of maturity and supplemented with graded levels ofDesmodium intortumhaya,b
Variable Level of supplement (g per head per day)
Stage of maturity of maize stover Mean S.E.
Stage I Stage II Stage III
Stover DM intake 0 46.2 44.9 38.4 43.2 a 1.5
(g/kg W0.75per day) 150 40.7 37.0 37.9 38.5 b 1.4
300 35.6 31.4 33.8 33.6 c 1.1
450 20.6 23.7 24.5 22.9 d 1.4
Mean 35.8 a 34.2 a 33.6 a
S.E. 2.3 1.9 1.6
Total DM intake 0 46.2A 44.9AB 38.4B 43.2 c 1.5
(g/kg W0.75per day) 150 55.9 52.3 53.1 53.8 b 1.4
300 65.0 60.8 63.2 63.0 a 1.0
450 64.1 67.3 67.7 66.3 a 1.1
Mean 57.8 a 56.3 a 55.6 a
S.E. 1.9 2.0 2.6
Total DM intake 0 2.3A 2.2AB 1.9B 2.1 c 0.08
(% of body weight) 150 2.7 2.5 2.6 2.6 b 0.07
300 3.1 2.9 3.0 3.0 a 0.05
450 3.1 3.2 3.2 3.2 a 0.05
Mean 2.8 a 2.7 a 2.7 a
S.E. 0.09 0.09 0.12
Organic matter intake 0 362 348 301 337 d 13
(g per head per day) 150 469 437 449 452 c 13
300 572 537 555 555 b 12
450 577 610 615 601 a 14
Mean 495 a 483 a 480 a
S.E. 22 22 27
Crude protein intake 0 14.0 12.3 10.0 12.1 d 0.6
(g per head per day) 150 31.5 29.2 28.9 29.8 c 0.5
300 48.7 46.4 46.5 47.2 b 0.5
450 62.2 62.7 62.3 62.4 a 0.5
Mean 39.1 a 37.7 b 36.9 b
S.E. 3.8 3.9 4.1
aMeans with the same letters within a row or within a column are not signi®cantly different (p>0.05). bStage of maturity means, without desmodium hay supplementation, with the same upper case letters are not signi®cantly different (p>0.05).
offered. The quadratic response of total DM intake Y (g kg0.75) to the amount of desmodium hay supplementedX(g per day) is shown by the following equation:
Y42:89 1:24 0:09 0:01Xÿ0:00008 0:00003X2
R:S:D:5:39;R20:74;p<0:0001:
On the other hand, maize stover DM intake showed a signi®cant decrease (p<0.05) with increasing level of supplementation. Desmodium hay constituted about 28, 47 and 66% of the total DM intake at 150, 300 and 450 g of supplementation, respectively. A similar pattern of increase in total DM intake and a decrease in maize stover intake with increasing levels of forage legume supplements were observed in previous studies (Smith et al., 1990; Said and Tolera, 1993).
The literature reports on feed intake are inconsistent with respect to the effects of forage and browse legume supplementation to poor quality roughages. Mosi and Butterworth (1985b) and Kaitho et al. (1998a) observed an increase in total DM intake and a decrease in basal tef straw intake with increasing level of forage legume supplementation. Umunna et al. (1995b) also reported that supplementation of oats hay with forage legumes increased intake of total DM and OM but tended to depress intake of oats hay. Veereswara Rao et al. (1993) found that supplementation of sheep with Leucaena leucocephala, Sesbania grandi¯ora and Gliricidia maculata depressed the intake of the basal feed, hybrid napier (NB-21) grass (7.1% CP), and the total DM. Supplementation of dried Gliricidia sepium leaves to sheep fed a basal diet of dried elephant grass (10.3% CP) decreased DM intake of the basal diet without any signi®cant effect on total DM intake (Mpairwe et al., 1998). Other studies (Bird et al., 1994; Bonsi et al., 1994) showed that forage legume supplementation increased total DM intake without any signi®cant effect on intake of the basal, cereal straw, diet. The variation could partly be attributed to the quality of the forage supplements and the quality of the basal roughages. The N and NDF contents of the basal roughages (Umunna et al., 1995b) and the solubility and degradation rates of the forage legume supplements have important implications on intake (Umunna et al., 1995a). Ash (1990) and Bonsi et al. (1994) indicated that rapidly degrading legume forages will elicit increased intake of the basal diet by alleviating nutritional de®ciencies and by disappearing faster from the rumen. Thus the effect of forage legume supplements on basal roughage intake is a function of their solubility, rate of degradation and rate of passage from the rumen.
maturity of the stover (Fig. 2). Pooled across the three stages of maturity, the total DM intake was 47, 57, 64 and 70% of total feed DM offer at 0, 150, 300 and 450 g of supplementation, respectively. Maize stover intake was 47, 48 and 48% of maize stover offer at 0, 150 and 300 g of supplementation, respectively, but signi®cantly decreased (p<0.05) to 44% as the level of supplementation increased to 450 g per day. On average, the total DM intake increased from 2.1 to 3.2% of body weight as the level of supplementation increased from 0 to 450 g per day (Table 2). The OM and CP intake showed a signi®cant increase (p<0.05) with increasing level of supplementation. This is consistent with the ®ndings of Goodchild and McMeniman (1994) who reported increased N and OM intake with increasing level of browse legume supplementation to a basal diet of sorghum stover. Kaitho et al. (1998a) also reported increased N and digestible OM intake with increasing level of browse legume supplementation to a basal diet of tef straw.
The increased DM, OM and CP intake with increasing level of supplementation could partly be due to desmodium having lower ®bre and higher CP and sulphur contents as well as a more favourable N:S ratio than the stovers (Table 1). High ®bre content or dietary bulk causes distension of the digestive tract with consequent limitation of feed intake (Van Soest, 1994). Nitrogen and sulphur de®ciencies and imbalance are liable to Fig. 1. Effect of graded levels ofDesmodium intortumhay supplementation on stover and total DM intake of sheep feeding on a basal diet of maize stover.
reduce feed intake due mainly to a reduction in the activity of rumen micro-organisms and hence cellulose digestibility. If the rate of digestion of feed in the rumen is decreased, intake will be decreased as a result. However, supplementary protein to diets of low nitrogen concentration can also have an effect beyond the rumen (Garnsworthy and Cole, 1990).
3.3. Substitution rate
desmodium hay at 150, 300 and 450 g of supplementation, respectively. This could be explained by the high NDF content and bulky nature of the desmodium hay. Roughage intake response to supplementation is in¯uenced by the supplement fermentation rate and bulk density (Nsahlai et al., 1996). Forage legumes that disappear fast from the rumen are likely to induce lower substitution rates (Umunna et al., 1995a). Kaitho et al. (1998a) and Mpairwe et al. (1998) observed a similar increase in substitution rate with increasing level of browse legume supplementation to basal diets of tef straw and dried elephant grass, respectively.
3.4. Digestibility
Stage of maturity of the stover did not have any signi®cant effect (p>0.05) on DM, OM and NDF digestibility (Table 4). However, the mean digestibility values across the four levels of supplementation showed a decreasing trend with increasing stage of maturity. Digestibility of CP was signi®cantly higher (p<0.05) in sheep feeding on maize stover harvested at stage I than those feeding on stage III stover. This was due to the relatively higher CP content in maize stover harvested at stage I than the stover harvested at stage III (Table 1). The negative apparent digestibility values of CP in the unsupplemented maize stover diets and the low digestibility values observed at low levels of supplementation were due to inadequate N intake coupled with high metabolic faecal N loss. Extrapolation of faecal N excretion to zero N intake showed estimated metabolic faecal N excretion of 3.4, 4.0 and 3.3 g per day in sheep fed maize stover harvested at stages I, II and III, respectively, which are close to a value of 2 g per day reported by Nsahlai et al. (1998). However, the N intake at 450 g of supplementation was excluded from the extrapolation because its inclusion could exaggerate the estimate of metabolic faecal N excretion. The excretion of faecal N increased with increasing level of supplementation up to 300 g per day followed by a signi®cant decrease as the level of supplementation further increased to 450 g per day (Tolera and Sundstùl, 2000; in preparation). Very low or negative apparent digestibility of CP can be found in cases where low CP content is associated with a small intake or large metabolic losses of nutrients.
Table 3
Substitution rate when the stover was offered ad libitum, at 150% of the previous day's intake, with or without graded levels ofDesmodium intortumhay supplementa
Variable Supplement level (g per head per day)
Stage of maturity of stover Mean S.E.
Stage I Stage II Stage III
Substitution rate (g/kg DM) 150 0.17 0.31 ÿ0.12 0.12 b 0.11
300 0.22 0.32 0.08 0.21 a, b 0.05
450 0.48 0.38 0.23 0.37 a 0.04
Mean 0.29 a 0.34 a 0.06 b
S.E. 0.09 0.05 0.07
aMeans with the same letters within a row or within a column are not signi®cantly different (p>0.05).
Supplementation resulted in improved digestibility of the diet. There was a signi®cant increase (p<0.05) in DM, OM, NDF and hemicellulose digestibilities as the level of supplementation increased. Crude protein digestibility showed a signi®cant linear increase (p<0.05) with increasing level of supplementation due to an increase in CP content of the diets. In general, the results showed a trend of increased digestibility with increasing level of supplementation which was associated with decreased ®bre content and increased CP and S contents of the diets (Table 1) with concomitant increase in microbial N supply and rumen fermentation (Tolera and Sundstùl, 2000; in preparation). However, no interaction was observed between stage of maturity of the stover and the level of desmodium hay supplementation. The improved digestibility of the diets as a result of supplementation is consistent with the ®ndings of previous studies (Mosi and Butterworth, 1985a; Goodchild and McMeniman, 1994). Alayon et al. (1998) and Kaitho et al. (1998a) observed a similar increase in DM, OM and N digestibility with increasing level of browse legume supplementation to sheep fed basal diets of star grass (Cynodon Table 4
Nutrient digestibility (%) in sheep fed a basal diet of maize stover harvested at different stages of maturity and supplemented with graded levels ofDesmodium intortumhaya
Digestibility (%) Supplement level (g per head per day)
Stage of maturity of stover Mean S.E.
Stage I Stage II Stage III
Organic matter 0 45.2 37.3 34.6 39.0 c 3.3
150 59.5 56.7 57.1 57.8 b 3.0
Neutral detergent ®bre 0 52.0 45.0 44.1 47.0 c 2.8
150 60.7 58.3 60.1 59.7 b 2.8
300 66.1 62.6 62.1 63.6 a, b 1.6
450 67.6 70.7 67.5 68.6 a 1.4
Mean 61.6 a 59.1 a 58.5 a
S.E. 2.7 3.5 3.1
nlemfuensis) hay and tef straw, respectively. However, both groups could not ®nd any signi®cant effect of level of supplementation on NDF digestibility.
3.5. Digestible OM and ME intake and body weight change
The DOMD and ME concentration of the diets showed a signi®cant decrease (p<0.05) with increasing stage of maturity of the stover (Table 5). Digestible OM and ME intake was signi®cantly higher (p<0.05) in sheep feeding on maize stover harvested at stage I
Table 5
Digestible OM and ME intake and body weight change of sheep fed a basal diet of maize stover harvested at different stages of maturity and supplemented with graded levels ofDesmodium intortumhaya,b
Variables Level of supplement (g per head per day)
Stage of maturity of maize stover Mean S.E.
Stage I Stage II Stage III
Digestible OM intake 0 161 127 102 130 d 7
(g per head per day) 150 279 246 257 207 c 8
300 379 351 332 354 b 9
450 410 440 429 426 a 10
Mean 307 a 291 a, b 280 b
S.E. 22 25 26
Digestible OM in the 0 41.2 34.1 31.6 35.6 d 1.0
DM (DOMD; %) 150 56.4 53.8 54.5 54.9 c 0.3
aMeans with the same letters within a row or within a column are not signi®cantly different (p>0.05). bStage of maturity means, without desmodium hay supplementation, with the same upper case letters are not signi®cantly different (p>0.05).
than III and showed a general declining trend with increasing stage of maturity of the stover. There was a signi®cant increase (p<0.05) in digestible OM intake, DOMD, ME concentration of the diet and ME intake with increasing level of desmodium hay supplementation. The increase in digestible OM intake with increasing level of supplementation is consistent with the ®ndings of previous studies (Goodchild and McMeniman, 1994; Chowdhury, 1997; Kaitho et al., 1998a). Chowdhury (1997) also reported increased ME intake with increasing level of Leucaena leucocephala supplementation to a basal diet of rice straw.
The stage of maturity of the stover, pooled across different levels of supplementation, did not have a signi®cant effect on body weight change of the sheep (Table 5). The lack of signi®cant difference among the different stages of maturity of the stovers in some of the variables studied could be due to the effects of rain damage at harvesting time on the stovers harvested during stages I and II. All sheep without desmodium hay supplement lost body weight during the experiment and the weight loss was signi®cantly higher (p<0.05) in sheep feeding on maize stover harvested at stage III than at stage I and it tended to be higher (p>0.05) in sheep feeding stage II than stage I stover. This indicates that the unsupplemented maize stover was a de®cient diet that could not satisfy even the maintenance requirement of the animals regardless of the stage of maturity. Similar body weight losses of sheep fed unsupplemented crop residues (tef straw) diets were reported in other studies (Bonsi et al., 1996; Kaitho et al., 1998a, b). Supplementation with 150 g of desmodium hay changed the body weight loss observed in the unsupplemented group to a slight body weight gain. In general, the body weight showed a signi®cant increase (p<0.05) with increasing level of supplementation (Table 5). The interaction between stage of maturity of the stover and level of desmodium hay supplementation was not signi®cant for body weight change (p>0.05). There was a strong quadratic relationship between live weight gainY(g per day) and the level of desmodium hay supplementX(g per day) as shown by the following regression equation.
Y ÿ31:83 2:83 0:32 0:03Xÿ0:0003 0:0001X2
R:S:D:11:99;R20:86;p<0:0001:
Similarly, Kaitho et al. (1998a) observed a signi®cant increase in live weight gain of sheep feeding on a basal diet of tef straw with increasing level of browse legume supplementation. The body weight change, expressed as percent of initial weight, showed a decrease with increasing stage of maturity of the stover (Fig. 3) and an increase with increasing level of supplementation (Fig. 4). These changes were associated with CP, digestible OM and ME intake of the animals (Tables 2 and 5).
Fig. 3. Effect of stage of maturity of maize stover, pooled across different levels ofDesmodium intortumhay supplementation, on body weight change of sheep expressed as percent of initial weight.
Fig. 4. Body weight change, expressed as percent of initial weight of sheep feeding on basal diet of maize stover at different levels ofDesmodium intortumhay supplementation.
The body weight changes observed in the current study were also re¯ections of the changes observed in DOM, ME and CP intake (Tables 2 and 5) with increasing level of supplementation.
4. Conclusion and implications
The body weight loss of the sheep fed maize stover as a sole diet indicated that unsupplemented maize stover used in the present study could not support even the maintenance requirements of the animals, irrespective of the stage of maturity at the time of harvest due to de®ciency of essential nutrients (such as nitrogen, sulphur and ME), high ®bre content, poor digestibility and very low voluntary intake. Considering DM intake and nutrient digestibility, with the exception of CP digestibility, 300 g per day appears to be an optimum level of supplementation if the basal roughage is abundant and the desmodium hay is in limited supply.
At this level of supplementation, feed resource use would be optimized and modest level of body weight gain could be achieved. Moreover, this is a useful strategy to overcome the problems of undernutrition and malnutrition in areas where livestock depend on cereal crop residues and other poor quality roughages during the dry season. However, if the availability of desmodium hay is not a limiting factor, the level of supplementation could be increased up to 450 g per day to further enhance animal performance (body weight gain). The ultimate decision on the optimum level of supplementation depends on the relative cost and availability of the stover and desmodium hay and on the level of animal production expected.
Acknowledgements
We would like to thank the Norwegian Universities Committee for Development Research and Education (NUFU) for ®nancial support. The assistance of Alemayehu Kidane, Tadesse Bokore, Fiseha Gebre and all the barn attendants is duly appreciated.
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