Effects of supplementation with graded levels of lablab (Lablab purpureus) hay on feed intake, digestibility, live weight change and carcass characteristics of Tikur sheep fed tef (Eragrostis tef) straw

Kassahun Shibeshi, Yayneshet Tesfaye¹ and Tassew Mohammed

Animal Science, College of Agriculture, Woldia University, Ethiopia
tassewm010@gmail.com
¹ Mekelle University, College of Dry land Agriculture and Natural Resources Department of Animal, Rangeland and Wildlife Sciences, Ethiopia

Abstract

The objective of the experiment was to evaluate the effect of graded levels of lablab supplementation of tef straw on feed intake, nutrient digestibility, body weight gain and carcass parameters of Tikur sheep. The experiment was conducted at Mersa Agricultural Technical Vocational Education and Training (ATVET) College, North Wollo, Ethiopia using twenty­ yearling intact male Tikur sheep with a mean initial body weight of 19.09 ± 1.76 kg (mean ± SD). The experiment consisted of 90 days of feeding trial and 7 days of digestibility trial followed by evaluation of carcass parameters at the end of the experiment. The experimental design was RCBD. The experimental sheep were blocked into 5 blocks of 4 animals based on initial body weight and randomly assigned to one of the four treatment diets. Dietary treatments consisted of tef straw offered ad libitum (Lp0) (used as control) and lablab hay supplement at levels of 100 (Lp100), 200 (Lp200) and 300 (Lp300) g/head/d on as fed basis. The crude protein (CP) content was higher in lablab hay, but the fiber fractions were markedly higher in tef straw. Lablab supplementation increased (P<0.001) total dry matter (DM), organic matter (OM) and crude protein (CP) intakes, whereas tef straw dry matter intake (DMI) showed no significant difference between supplemented and control treatments .Significantly higher (P<0.05) dry matter digestibility (DMD), organic matter digestibility (OMD), crude protein digestibility (CPD), neutral detergent fiber digestibility (NDFD) and acid detergent fiber digestibility (ADFD) was observed in lablab supplemented sheep than the control ones. Lablab supplementation resulted in significantly higher (P<0.01) final body weight, average daily gain (P<0.001) and feed conversion efficiency than sheep in the control treatment. Supplemented sheep had heavier slaughter weight (SBW) (P<0.001), empty body weight (EBW) and carcass weight (HCW). Sheep fed on medium and higher levels of supplementation (T3 and T4) had higher dressing percentage (DP) on slaughter weight (SW) basis (P<0.01) and larger rib-eye area than supplemented sheep. Among the different treatments, Lp200 and Lp300 resulted in better DMI, nutrient digestibility, average daily gain (ADG) and carcass characteristics.

Keyword: animal production, crop residues, feeding, legumes, sheep

Introduction

Ethiopia is the second in Africa and sixth in the world in sheep populations. In the country, there were approximately 40 million sheep. The Amhara National Regional State has 10.4 million heads of sheep which are about 26% of the national sheep populations, respectively (CSA, 2020a). The country is not only rich in livestock number, but also rich in genetic diversity that has been developed by natural selection (Galal, 1983).

Under nutrition, due to inadequate or fluctuating nutrient supply is a major constraint limiting the productivity of the livestock, leading to high mortality of animals, longer parturition intervals and substantial weight loss, particularly during the dry season extending from December to May (EARO, 1989) in most parts of Ethiopia. At this period most of the animals depend on matured herbage, aftermath grazing and crop residues, the latter two accounting for 60 to 70 percent of available basal diet in the highlands of Ethiopia and are inherently low in protein, digestible energy and minerals (Seyoum and Zinash, 1998), which may result in sub-optimal rumen fermentation and lowered animal performance. Effective methods through which utilization of low quality roughages could be improved include supplementation with energy and nitrogen sources, chemical and/or physical treatment, and selection and breeding of crops, each of which ultimately depends on the economic benefits and applicability (Ibrahim and Schiere, 1989; McDonald et al 2002). Lablab combines a great number of qualities that can be used successfully under various conditions. It is drought resistant and can be grown in a diverse range of environmental conditions worldwide. Staying green during the dry season, it has been known to provide up to six tones of dry matter/ha (Murphy and Colucci, 1999). It is a leguminous plant that can be grazed by both large and small ruminant animals (Muhammad et al 2004). Its hay is palatable as well used for making good silage. The use of forage legumes such as lablab as feed supplements has been shown to enhance intake of poor quality roughages, improve growth rates and increase production efficiency in ruminants (Orden et al 2000). Lablab can be grazed or used for hay or silage. The foliage analysis result suggests that it has high protein content (15-30%) as well as high levels of lysine and digestibility (Valenzuela and Smith, 2002). The hay is high in crude protein (>17%), ash (>8%) and digestibility (>54%) (Murungweni et al 2004).

In Ethiopia, the self- reliance of the farmer on forage legumes as the source of nitrogen, therefore, is a pre requisite to improve the efficiency of utilization of crop residues and productivity of animals. Forage legumes have been identified to contain high amounts of protein, which can improve the rumen ecosystem and thereby enhance the utilization of crop residues. However, the effects of supplementation with graded levels of lablab (Lablab purpureus) hay on performances of Tikur sheep fed tef ( Eragrostis tef) straw have not been yet studied even though the feed is a potential sources of protein. Therefore, the study is designed to evaluate the effect of graded levels of lablab hay supplementation on feed intake, digestibility, body weight gain and carcass characteristics of Tikur sheep fed tef straw.

Materials and methods

Description of the Study Area

The research was conducted at Mersa Agricultural Technical Vocational Education and Training (ATVET) College, North Wollo Administrative Zone of Amhara region, Ethiopia. It is situated at 11^°35’N latitude and 39^°38’E longitude with an elevation of 1660 m above sea level. The mean annual rainfall is 850 mm and the mean maximum and minimum temperatures are 29.5 and 13.5 ^°C, respectively, with a mean of 21.5 ^°C. In 2000, the population of the Woreda was 16,209 where 8043 were female (HARDO, 2006), and Ninety percent of the economic activity of the Woreda depends on mixed farming and 5.5% on arable farming. According to HARDO (2006), 45%, 19% 2% of the Woreda land is covered by Black, Red, Brown, and other soils respectively. The land use pattern of Habru Woreda indicates that annual crop production, sparse vegetation and grazing land constitute about 44.9 %, 27.16% and 7.18 % of the land mass of the Woreda. Only 1614 ha is covered by forest and 11207 ha is covered by shrub and bushes (HARDO, 2006).

Map 1. Map of the Study Area

Photo 1. Lablab forage (left upper corner), lablab hay (left lower corner) and Teff straw (right lower corner)

Experimental animals and their management

Tikur sheep have short fat tail; wooly undercoat; predominantly black (60%) coat; small body size; majority short semi pendulous ears and 24% rudimentary ears (Gizaw et al 2008). They are geographically distributed in North Wollo zone of Amhara region with a population of 525,300. Twenty yearling male Tikur sheep from North Wollo, with average initial weight of 19.1 ± 1.76 kg (mean ± SD), were used in the experiment. Sheep were purchased from local markets. The age of the animals was estimated by dentition. During the first 3 weeks sheep were quarantined to get them used to their new environment and to observe their health condition. Animals were vaccinated against pasteurellosis, dewormed with albendazole and sprayed against external parasite using deazinon. During this period, animals grazed natural pasture. At the end of the quarantine period, sheep were weighed and blocked into five blocks of four animals each and randomly distributed to one of the treatment feeds (Table 2). Then, sheep were fed with the respective treatment diets for 15 days to adapt to the treatment diets. The lambs were kept individually in a well-ventilated (150x 80x100cm) pen. The individual wooden pens were partially opened on the front side for easing management. The floor of the pens was concrete. Cleaning of the pens was done every morning before the placement of the daily ration. The lambs were neck belted for identification which was used for the feeding trial (90 days) as well as the digestibility trial (7days).

Feeds and feeding

Feeds used in the experiment were tef straw as a basal diet and lablab as a supplement. Lablab was harvested from Mersa ATVET College’s farm at 10% flowering and sun dried into hay on plastic sheets to minimize leaf loss. Treatment feeds (both tef straw and Lablab) were chopped before the start of the experiment at about 7-10 cm using a long knife (gegera), thoroughly mixed and stored to reduce any variation when fed during the experiment. Whole part (leaf and steam) of the supplement was included. Both feeds were then fed separately in plastic buckets and troughs for Lablab and tef straw, respectively. The chopped lablab hay was divided into two equal meals and offered in the morning at 08:00 and 15:00 hrs in the afternoon. Tef straw was offered to each animal with a refusal rate of 20% of the adaptation period intake to ensure adlibitum feeding. There was continuous access to water and salt lick for the animals.

Experimental design and treatments

The experiment was conducted using a randomized complete block design (RCBD) with four treatments. RCBD was chosen because of the blocking of body weight and the graded levels. The experimental sheep were blocked into five blocks of four animals based on initial weight with weight ranges of 16.5-17.5kg, 17.5-18.5kg, 18.5-19.5kg, 19.5-20.5kg and 20.5-21.5kg. Animals of each block were randomly allocated to one of the four treatments making five animals per treatment. Dietary treatments consisted of tef straw offered ad libitum (Lp0, control) and lablab hay supplement at levels of 100 (Lp100), 200 (Lp200) and 300 (Lp300) g per head per day on as fed basis. When expressed per unit body weight, the treatments consisted of supplementing sheep with lablab hay at 0.5%, 1.0%, or 1.5% of body weight. The minimum level of supplementation at 0.5% of body weight was set to provide animals with a crude protein (CP) intake of more than 7-8%, which is the minimum level required for proper function of rumen microorganism (Van Soest, 1995), and alleviate the decrease in intake often noted with forages of low CP. These supplement levels were also considered as optimal supplementation levels and assumed to provide CP of 87 to 109 g/d for sheep weighing 20 kg, and gaining daily weight of 50 to 100 g/d (Paul et al 2003).

Feeding and growth trial

The experimental animals were accustomed to the experimental feed for 15 days before the commencement of actual data collection.

Feed intake measurements

Amount of tef straw and lablab offered and refused were collected and recorded on per animal basis throughout the experimental period. Feed was weighed using a sensitive balance. Daily feed intake of individual sheep was recorded as the difference between feed offered and refused. The daily samples of feeds offered and refusal were collected; bulked and representative sub samples of 100g each were taken after thorough mixing for the determination of nutrient composition. Feed conversion efficiency (FCE) for each sheep was calculated as a proportion of daily body weight gain to daily feed intake.

Body weight measurement

Body weight measurements were taken using a weighing scale. Initial body weights of all sheep were recorded on the first day of the experiment and subsequent weights were taken every week after withholding feed for overnight. Average daily weight gain was calculated on a per sheep basis as total body weight gain divided by the number of feeding days. Mean of initial and final body weight were used to calculate feed intake as percent of body weight.

Digestibility trial

The digestibility study was conducted for 7 days after the feeding trial was completed using all the experimental animals. Apparent digestibility of treatment feeds was determined using total collection method. It was conducted by fitting animals with fecal bags permitting separate collection of feces. Sheep were accustomed to the fecal collection harness for three days followed by a collection period of seven days. Faecal output of the sheep was collected individually in faecal bags which were made of canvas with plastic sheet plastered inside and attached to the animal’s rectum throughout the collection period. The daily collected feces from each animal were mixed thoroughly and 20% of the total feces voided was sampled and kept in air tight container and stored in deep freeze in refrigerator till the completion of the digestibility trial (Osuji et al 1993). At the end of the digestibility trial, the seven days collected feces for each animal was pooled and 20% of composite samples were taken for chemical analysis.

The apparent digestibility of nutrients (DM, OM, CP, NDF and ADF) was determined using the following equation (Campbell et al 2003):

Slaughtering Procedures and Carcass Characteristics

At the end of the digestibility trial, all sheep from each treatment were slaughtered for determination of carcass characteristics. Slaughter weight was taken immediately before the animals were killed. The animals were slaughtered by severing the jugular vein and carotid artery with knife. The blood was drained into bucket and weighed. After the animals were decapitated, the skin was flayed cautiously to avoid adherence of fat and muscle tissue to the skin. The skin was weighed with leg below the fetlock joints. After flaying, weight of offals like head, skin and feet, heart, lungs and trachea, liver with gall bladder, spleen, testis, penis, kidneys, visceral fat, reticulo-rumen, omaso-abomasum, small and large intestine were recorded.

Empty body weight was calculated as slaughter weight less gut content. Dressing percentage was computed as proportion of hot carcass weight to slaughter weight and empty body weight.

The rib-eye muscle area of each animal was determined by tracing the cross sectional area of the 11^th and 12^th ribs after cutting perpendicular to the back bone. The left and right rib-eye muscle area was traced on a transparent water proof paper and the area was measured by using mechanical polar planimeter (model series 20).

Total edible offal component was taken as the sum of blood, heart, head, liver, kidney, tail, visceral fat and testis. The non-edible offal component was taken as the sum of skin with feet, penis, lung with trachea, spleen and gut fill. Percentage of total usable product was taken as the sum of dressing percentage and percentage of total edible offal component.

Chemical analysis

Ten percent of the feed material from each offer and refusal was sampled every day and kept in dry area on individual animal base. After thoroughly mixing, representative sub-sample of 0.5kg was taken and oven dried at 65 ⁰C to constant weight in forced draft oven for 72 hours. The dried samples were milled in a laboratory mill to pass through 1mm sieve and thoroughly mixed and stored in paper bags until chemical analysis. The feed offered, refusal and fecal samples were analyzed for DM, OM, CP, and Ash according to the procedure of AOAC (1990). Neutral detergent fiber (NDF), acid detergent fiber (ADF) and acid detergent lignin (ADL) were analyzed according to the procedures of Van Soest and Robertson (1985). Analysis for Kjeldhal nitrogen was run according to AOAC (1990) procedures. The CP content was determined by multiplying nitrogen value by a factor of 6.25. All the chemical analyses were done at Mekelle University Nutrition Laboratory except for NDF which was done, using amylase, at Holeta Research Center Nutrition Laboratory.

Statistical analysis

The data collected were subjected to analysis of variance (ANOVA) using JMP-5 software package (Business Unit of SAS, 2002). When the analysis of variance revealed the existence of significant difference among treatment means, Tukey HSD test was used to separate significant treatment means. Significant differences were declared at P<0.05

The statistical model used was Y_ijk =µ + T_i +B_j +E_ijk

Where:

Yij_k =the response variable

µ = the overall mean

T_i =the fixed effects of i^th treatment effect (1-4)

B_j =the fixed effects of j^th block effect (1-5)

E_ijk =the random error.

Results and discussion

Chemical composition of experimental feeds

The chemical composition of the treatment feeds is given in Table 2. The DM content was higher in tef straw than lablab used in the present study. The percentage composition varied also depending on feed type, in which the content of CP was higher in lablab hay, but the cell wall fractions were markedly higher in tef straw than in the supplement. For both feeds, the ADF fraction was a large proportion of the NDF, which indicated high content of cellulose and lignin, and low levels of hemicellulose.

The DM content of lablab hay in this study was slightly lower than 91.8 and 90.7% reported by Mupangwa et al (2000) and Mpairwe et al (2003) and comparable to 87.7% reported by Nsahlai et al (1996). The DM content of tef straw used in this experiment was slightly higher than 91.30 and 90.93% reported by Daniel (1988) and Solomon et al (2003) and lower than 93.3% as reported by Ahmed (2006).

The ash content in lablab hay was higher than that observed for tef straw. Mostly the mineral contents in the seeds and straws of legumes are higher as compared to that of the cereals (Ranjhan, 1980). The ash content of lablab hay in the current study was similar to 11.9% as reported by Abule et al (1995). The ash content of tef straw was comparable to ash content of tef straw reported by Kabaija and Little (1988) and by Ahmed (2006) which was 8.3 and 8.14%, respectively and slightly lower than 8.9% reported by Solomon et al (2003). Crude protein was found to be lower in tef straw, which contained 4 times less CP concentration as compared to lablab hay. The CP content of lablab hay in the present study was similar to the value of 21.5% as reported by Kenani et al (2006) and comparable to 21% reported by Nworgu (2005). The CP content of lablab hay was lower than 22.8% reported by Ajayi (2009) and 22.1% reported by Mupangwa et al (2003) but higher than 19.4% reported by Hindrichsen et al (2004) and 18.6% reported by Abule et al (1995). The higher CP content of lablab hay in the present study may be due to the younger stage of harvest, which was 14 weeks after germination.

The NDF concentration showed much variation with the highest value recorded for the tef straw. The tef straw contained 36.4% of more NDF on DM basis than lablab hay. The NDF and ADF values recorded for tef straw in the present experiment were comparable to the results of Sisay (2006) who reported values of 76-79.6% NDF and 41.6 - 46.9% ADF and lower than NDF and ADF contents of tef straw reported by Ahmed (2006). This author reported NDF and ADF values of 84.64 and 69.33%, respectively. Lower values of 72.89 and 41.24% were also reported for NDF and ADF, respectively (Solomon et al 2003). Kabaija and Little (1988) reported lower NDF (71.13%) content in tef straw than the results of the present study, but higher (49.1%) ADF content. The NDF content of tef straw obtained in this study agreed with the results of Solomon (2004) that reported NDF contents of 74.3-81.5% for crop residues. The NDF content of tef straw in the current study was more than 70%, which showed the high fiber content that could be a limiting factor for feed intake, since voluntary intake and NDF content are negatively correlated (Ensiminger et al 1990). Similarly, since digestibility of feeds and ADF content are negatively correlated (McDonald et al 2002), the relatively high ADF content of tef straw reflected its low digestibility. The NDF and ADF contents of lablab hay in the current study were lower than NDF and ADF contents of lablab hay reported by Mupangwa et al (2003) which were 45.5 and 33.1%, respectively but higher than NDF and ADF contents of lablab hay reported by Mupangwa et al (1997) which were 37.3 and 29.4%, respectively. Mupangwa et al (2000) reported higher NDF (47.3%) but lower ADF (29.4%) values while Mpairwe et al (2003) reported lower NDF (41.2%) but higher ADF (34.6%) values than the present study.The ADF fraction in tef straw was higher than that observed for lablab hay and accounted for about 59.4% of the NDF, further signifying the high content of cellulose and lignin, and low levels of hemicellulose. The lignin content of tef straw was comparable to the 8.0% reported by Sisay (2006) and higher than the values reported by Solomon et al (2003) which was 4.1%. The lignin content of lablab hay (6.1%) in this study was comparable to 6.4 and 6.7% reported by Mupangwa et al (2000) and Solomon et al (2003), respectively. The variations for all chemical compositions recorded in this study when compared to same chemical entities (DM, CP, Ash, NDF and ADF) reported for lablab in the works of Mpairwe et al (2003), Solomon et al (2003), Mupangwa et al (2000) and Abule et al (1995) could possibly arise from differences in stage of maturity at harvest, curing methods, crop management, climate and soil type (Adugna and Sundstol, 2000). The results of this study agreed with the general statement made by Preston and Leng (1986) that all cereal straws have low N content and are composed of cell wall components with little soluble cell contents. The CP content of tef straw observed in the current study was lower than the 70 g/kg DM minimum requirement for optimal microbial function in the rumen. Moreover, the fiber content of tef straw exceeded 70%, which would qualify it as a poor quality roughage feed that could affect voluntary feed intake and hence animal productivity. According to Van Soest (1965), NDF content of more that 55% limits DMI, and therefore, tef straw assessed in this study could affect feed intake of animals unless supplemented with feeds having better nutrient content.

On the other hand, lablab hay had higher CP and lower NDF concentrations relative to tef straw. The NDF of lablab was lower than 55% reported by Van Soest (1965) to limit appetite and digestibility.

Thus, in the current study, the relatively higher content of CP and lower content of NDF in lablab hay than in tef straw revealed its paramount supplementary value to augment the nutritional deficiency of ruminants fed poor quality roughages such as tef straw.

Feed and nutrient intake

The mean daily dry matter and nutrient intake of Tikur sheep fed tef straw supplemented with graded levels of lablab hay is given in Table 3 and Figure 3. Dietary treatment did not significantly (P>0.05) affect the basal feed intake of the animals, but supplementation with lablab hay caused a numerically substantial increase in tef straw DM intake for Lp100 (608.5g) over both the control (576.0g) and lablab supplemented animals (Lp200=583.6g and Lp300=573.6g). Supplementation with lablab increased (P=0.0001) total DM intake compared to the control treatment. Sheep supplemented with the highest level of lablab hay had significantly higher (P=0.0001) total DMI (835g) as compared to those offered with the lowest level of supplement (695.6g). The 200g lablab supplemented group had also a numerically higher daily total dry matter intake (757.9g) compared to 100 g lablab supplemented group (695.6g). Lablab supplementation also improved total CP and OM intake (P=0.0001), and these increased with the forage legume inclusion. The total NDF (P=0.001) and ADF (P=0.0001) intakes were lower in the control compared to the treatments with lablab. The increase in these nutrients total intake observed in diets containing lablab could be due to the combined effect of the higher total DM intake and digestibility associated with lablab intake.

The increased total DM intake with increased level of supplementation could be attributed to a more balanced intake of nutrients that led to better efficiency in the utilization of the fiber in the total diet. Moreover, increased availability of nutrients due to the supplementation of lablab might have promoted the observed higher total DM intake in the supplemented sheep. The (total) DM intake value as percentage of body weight in the present study (3.1-3.8% BW) was in agreement with the values (1.8-4.7% BW) reported by Devendra and Burns (1983) for small ruminants, particularly indigenous sheep in the tropics. The values were also in close agreement with results noted by Dawit (2008) for Arsi-Bale sheep fed urea treated barley straw supplemented with graded levels of vetch and lucerne hay. Sheep in the present study had also consumed comparable amount of total DM expressed as metabolic body weight reported by Tesfaye (2007) for Afar rams (58, 60,70.08, 75.84 and 74.25 g/kg W^0.75) when sheep were supplemented with 150–350 g concentrate mix on basal diet of tef straw. A lower value of 65 g/kg W ^0.75/d was also reported for urea treated straw supplemented with increasing levels of concentrate mix up to 400 g/d (Abebe, 2007). In all cases the observed variation was apparently believed to have emanated from the difference in the quality of supplement and basal feed materials (rumen fill, rate of passage of particulate matter and rates of degradation of experimental feeds) and animal factors (Norton and Poppi, 1995) used in each case.

The literature reports on feed intake are inconsistent with respect to the effect of forage and browse legume supplementation to poor quality roughages. Kaitho et al (1998) observed an increase in total DM intake and a decrease in basal tef straw intake with increasing level of forage legume supplementation. Adugna and Sundstol (2000) also reported that supplementation of maize stover with Desmodium intortum increased intake of total dry matter but tended to depress intake of maize stover. Other studies (Bird et al 1994; Bonsi et al 1994) showed that forage legume supplementation increased total DM intake with out any significant effect on intake of the basal, cereal straw, diet. In the current study, supplementation of lablab hay has no significant difference (P>0.05) in tef straw DM intake across the different levels considered. The variation could partly be attributed to the quality of the basal roughage. The N and NDF contents of the basal roughage have important implication on intake (Umuunna et al 1995). The supplementation of low N containing basal feeds with forage legumes will increase the N content of the diet, which likely increases feed intake and the rate of degradation of the basal diet in the rumen (Topps, 1995). However, the response obtained in the utilization of the basal roughage feed from such supplementation is variable. The extent of substitution of the basal diet by the forage legume, resulting from reduced intake of the basal diet, depends up on the level of inclusion of the supplement. Many studies have reported partial substitution of the basal ration by forage legume supplement (Adugna and Sundstol, 2000). Kaitho et al (1998) also observed substitution of basal feed DM when L. pallida was supplemented at a high level. Similarly, increasing the level of vetch and lucerne hay to 350 g DM per day resulted in partial substitution of urea treated barley straw (Dawit, 2008). Higher amount of CP intake through increased forage legume supplementation could replace part of the basal feed intake, which is related to physical limitation of the digestive tract to handle large amounts of DM. Topps (1997) reported that substitution of the basal feed usually occurs when the forage legumes make up at least 30-40% of the total DM intake. The variation could be attributed to the quality of the supplement. On the need for N supplementation, Smith et al (1989) and Masafu (2006) showed that forages with a high content of rumen degradable nitrogen (RDN) elicited greater responses in feed intake than those with a low content. Bonsi et al (1994) indicated that rapidly degrading legume forages will elicit increased intake of the basal diet by alleviating nutritional deficiencies and by disappearing faster from the rumen. Thus, the effect of forage legume on basal roughage intake is a function of their solubility, rate of degradation and rate of passage from the rumen. Forage legumes that disappear fast from the rumen are likely to induce lower substitution rates (Umunna et al 1995). In general, the amount of forage legume needed to provide effective supplementation varied with the quality of the basal diets, the rate of fermentation of the forage legume and the level of animal production expected (Osuji et al 1995). Ngwa et al (2002) indicated that a supplement should primarily provide critical nutrients lacking in the basal diet and create an environment conducive to optimizing the release and utilization of other nutrients in the basal diet. Therefore, the role of forage legumes must be to increase the efficiency of utilization of low CP containing basal feeds, such as straws at low levels of supplementation (FAO, 1997).

Apparent digestibility of dry matter and nutrients

Supplementation with lablab in tef straw based feeding of Tikur sheep increased the apparent digestibility of DM (P=0.0016), OM (P=0.0019), and CP (P=0.0001) (Table 4). Higher digestibility of NDF (P=0.0328) and ADF (P=0.0314) was observed for Lp100 compared to the control group.

Generally, feed which is rich in protein content promotes high microbial population (McDonald, 2002) which facilitates rumen fermentation.

The low level of DMD for the control group could be attributed to low N and high cell wall content of tef straw, which resulted in slow digestion, low rate of passage and hence limited voluntary intake (McDowell, 1988). On the other hand the improvement in DMD in response to lablab supplementation was due to the increased level of CP provided by the supplement, which resulted in increased digestibility. The increase in DM digestibility with increasing diet CP content in the present trial could be attributed to the innately high digestibility of protein (Tyrell, 1980), or positive effects on microbial fermentation and digestion in the rumen (Adugna and Sundstol, 2000). In agreement with Dawit (2008), the lower digestibility of CP in the tef straw as compared to the treatments with lablab might be related to the lower CP content of the basal diet.

Supplementation with legume crop residues contributes fermentable energy to the rumen in the form of available cellulose and hemicellulose which stimulates fibre digestion (Silva and Ørskov, 1985).Topps (1995) in his review stated that the positive effect of forage legume supplements on the activity of the rumen microorganisms and a concomitant increase in degradation of fibre has been recorded. Forage legumes increase the total concentration of volatile fatty acids without affecting the relative proportions and the rumen _PH, indicating that forage legumes are likely to maintain a stable fermentation pattern (Topps, 1995). The feeding of a lucerne (Ndlovu and Buchaman-Smith, 1985) and velvet bean hay supplements (Mupangwa et al 2002) were found to increase the proportion of branched chain volatile fatty acids suggesting that this increase may stimulate the growth of cellulolytic microorganisms. Dawit (2008) with an experiment on Arsi-Bale sheep fed urea treated barley straw found DMD of 62% for high levels of lucerne hay supplementation (350 g/d). Lower values of 48.3% were also reported for lambs fed corn residue supplemented with graded levels of alfalfa hay (Karsli et al 1999). Higher DMD has also been reported for low quality basal feeds supplemented with forage legumes. For example, Getahun (2006) reported DMD of 64.2% for sheep fed urea treated wheat straw supplemented with Leucaena leucocephala. Variations in the level of digestibility between the different trials can be accounted for by the difference in the type of basal diet and supplement, and breed of sheep used.

Body weight change and feed conversion efficiency

Mean initial and final body weights, average daily gain (ADG), and feed conversion efficiency (FCE) of the experimental animals on the different treatment feeds are presented in Table 5 and Figure 1. In the current study, supplementation resulted in a significant variation (P<0.001) in daily body weight gain of sheep. Sheep maintained on tef straw alone lost weight (0.04kg) and were loosing at the rate of 0.4 g/d throughout the experimental period. However, lablab supplementation improved (P<0.001) daily body weight gain of sheep (42.2g, 53.6g and 67.1g). Among the supplemented treatments, the highest level of lablab supplementation produced significantly higher (P=0.0001) ADG than the lowest level of lablab supplementation. The feed conversion efficiency (FCE) was higher (P=0.0001) for the lablab supplemented sheep compared with the control, and the highest (P>0.05) FCE was recorded at high level of supplementation (Lp300) (figure 2).

Figure 1. The regression of average daily gain (ADG) of Tikur sheep on increased levels of lablab supplementation.	Figure 2. The relationship between increased level of lablab supplementation and dry matter (DM) feed conversion efficiency of Tikur sheep
Figure 3. Regression of Intake Teff straw dry matter (TSDM) on increased levels of lablab supplementation in Tikur sheep

Trend of body weight change

The trend in weight change of sheep over the experimental period is given in Figure 4. The body weight of the experimental animals in all the supplemented treatments increased through time with more prominent increase in animals supplemented with the highest level of lablab. The mean body weights of sheep continue to increase, and by the end of the experiment, animals had gained on average 3.8, 4.82 and 6.04 kg for LP100, LP200 and LP300, respectively. The negative performance by sheep fed the control treatment could be attributed to the less nutrient density extracted from basal diet tef straw which failed to fulfill the daily requirement of the animals. The quality of protein together with energy utilization will determine growth rate (Vanes, 1997). Thus, the unbalanced nature of the nutrients that arise from digestion of tef straw seems to be the major reason for the weight loses. Abule (1994) and Getahun (2006) also observed weight loss in calves and sheep fed sole diet of tef and wheat straw. Bonsi et al (1996) and Kaitho et al (1998) reported similar weight losses of sheep fed unsupplemented tef straw diets. The highest daily body weight gain recorded for the higher level of supplementation could be due to increased nutrient density as a result of higher protein in the forage legume and a reflection of increased total fed DM and nutrient intake. It was also shown that supplementation of urea treated barley straw with graded levels of vetch and lucerne significantly improved the body weight gain of sheep (Dawit, 2008). Abule (1994) also reported higher body weight gain in calves supplemented with the forage legumes, cowpea and Dolichos lablab hay. The higher FCE recorded for lablab supplemented sheep could be due to the higher content of energy and protein in the diet of sheep in these treatments. Improved trend in FCE was observed with increased proportion of lablab that caused higher body weight gain. Similar to the present result, Dawit (2008) observed strong relationship between the body weight gain of Arsi Bale sheep and level of forage legume supplementation of urea treated barley straw.

In the present study there was linear correlation between CP intake and average daily gain with R² of 79% (figure 4). The tendency for higher daily live weight gains with increasing levels of lablab hay is a reflection of higher digestible CP intake, which was positively correlated with daily live weight gain. The regression equation is ADG= -28.38+1.17CPI. This was in agreement with (Owen and Zinn, 1988) that after reviewing a large amount of body weight data concluded that added dietary protein resulted in increased rate of weight gain over 85% of feeding trials.

Figure 4. Regression of total crude protein intake on body weight gain of Tikur sheep fed on tef straw supplemented with different levels of lablab hay

Carcass Characteristics

Carcass characteristics of Tikur sheep fed tef straw based diet and supplemented with graded levels of lablab hay are summarized in Tables 8 and 9. Carcasses were evaluated based upon slaughter weight (SBW), empty body weight (EBW), hot carcass weight (HCW), dressing percentage (DP), rib-eye area, and edible and non-edible offals.

Slaughter weight and dressing percentage

Sheep on the supplemented groups had heavier carcass, empty body weight and slaughter body weight (P<0.001) than unsupplemented group. Animals fed on tef straw alone had significantly lower (P<0.01) dressing percentage as percent of slaughter weight compared to those supplemented with the two higher levels of lablab hay. Although higher level supplemented sheep were heavier (P>0.05) at slaughter than the medium or the lower level supplemented groups, they had lower, but not significantly different (P>0.05) dressing percentage. Likewise, supplemented sheep tended to have slightly but not significantly different (P>0.05) hot carcass and empty body weights across all levels of supplementation.

The higher SBW, EBW and HCW recorded for the supplemented sheep could be explained by the better possible growth observed due to the increased intake of both energy and protein in the supplemented group than the control. According to Mtenga and Kitaly (1990), response of goats in growth rate is mainly associated with increased dietary protein intake. Almeida et al (2000) also noted significant (P<0.05) deleterious effect of under-nutrition on carcass weights. Oman et al (1999) who conducted research on the effect of breed and feeding regimen on goat carcass traits reported that, feedlot goats had heavier (P<0.05) live and carcass weights than did the carcasses of non-supplemented extensively managed goats. Similarly Abebe (2007) reported that, empty body weight (P<0.001) and hot carcass weight (P< 0.05) of supplemented groups were heavier than non-supplemented groups. Effect of supplementation and/or supplementation level on dressing percentage independent of gut fill was non-significant. The lack of significant difference in dressing percentage on empty body weight basis might be due to the exclusion of the contribution of gut fill, which was high in un-supplemented groups and in sheep maintained on the lower plane of nutrition, in the latter case. The low digestibility estimate of feed for the control sheep (ADMD=47.4) than the supplemented ones (ADMD=62.0, average of all supplemented groups) could have possibly contributed to higher gut fill and lower dressing percentage in the control sheep. It has been reported that gut fill is higher in animals that consume feeds of low digestibility or high fibre (Van Soest, 1987). Thus digestibility difference among the control and supplemented sheep in feed retention time in the gut may result in differences in gut fill when the pre-slaughter fasting period is relatively short. Consistent with the findings of this study, Karanjkar et al (2000) observed relatively higher gut contents in grazing goats due to longer retention period of feed in the alimentary tract owing to its high fiber contents. Similarly gut contents composed up to 14% of fasted body weight in sheep and goats, fasted for about 24 hours before slaughter was reported (El-Khidir et al 1998). Gibbs and Ivings (1993) reported that ingesta constitute significant proportion of the body weight even if the animals are fasted long hours. Accordingly, the pre-slaughter fasting period of 12 hours, in the present study was adequate. The fact that substantial amount of gut fill could be found even when animals fast for long hours indicate that use of body weight and/or dressing percentage as indices for carcass merit evaluation should be made with caution, particularly in roughages based production systems. Thus, carcass quality and carcass weight must be judged using slaughter records such as hot carcass weight, empty body weight and rib-eye area.

Rib-eye muscle area

Rib-eye muscle area of the carcass in sheep fed on different treatment feeds is given in Table 7. In the present study, groups fed higher level of supplement showed significantly (P=0.0011) higher rib-eye area when compared with the control, but its effect did not reach to significant level in sheep on the lowest level of supplementation. There was no significant difference (P>0.05) in rib-eye area when the control group were compared with the lower level supplemented sheep. This showed that level of supplementation had significant effect on rib-eye area only at higher level of lablab supplementation. The present study agrees with Gebregziabher et al (2003). In their study to investigate the effect of supplement on feed lot performance of Horro rams, these authors indicated that protein supplements increased loin-eye muscle area for supplemented groups when compared to non-supplemented groups. Increased rib-eye area (P<0.01) has also been reported in supplemented Croix lambs than non-supplemented controls (Hammond and Wildeus, 1993). In the present study, the rib-eye area ranged from10.9-15.9 cm² comparable to 9-14.5 cm² reported by Abebe (2007). Higher values of 26.8-35.8 cm² was also reported for Horro lambs supplemented with protein supplements (Gebregziabher et al 2003). Generally, supplemented sheep in the current study had expressed their superiority in pre- slaughter body weight, empty body weight and carcass weight over unsupplemented groups. This appears to be due to improvement in plane of feeding (Mtenga and Kitaly, 1990). Hot carcass weight in the present study is comparable with the result reported by Tesfaye (2007) for Afar rams fed tef straw supplemented with graded levels of concentrate mix that recorded values of 5.6, 7.68, 9.66 and 9.40 kg/head. Moreover, the result of this study was nearly comparable with results of FAO (2001) which reported on average carcass value of 10 kg for tropical sheep and still lower result observed when compared with the average carcass weight of sheep in the neighboring countries with values of 13, 13, 12 and 13 kg in Sudan, Somalia, Djibouti and Kenya, respectively. This might be due to the low nutrient intake or small mature weight of this breed type. As indicated by Ruvuna et al (1992) dressing percentage is an important tool for evaluating carcass merit. However, since dressing percentage is influenced by many factors such as breed, age, castration, feeding regime and fattening level (Ruvuna et al 1992) care should be taken in interpreting results. As in most developing countries, non-carcass items are consumed in Ethiopia. Therefore, in addition to the slaughter traits, such as carcass weight and dressing percentage that are usually the focus in meat animal studies, non-carcass components were also incorporated in the present study.

Edible and non-edible offal

Offals removed from the dressed carcass are shown in Table 7. The difference in slaughter weight is also reflected in the weights of offals. The offal consisted of edible (head, liver, heart, kidney, testes, tail, visceral fat and empty gut) and non-edible offals (skin + feet, spleen, lung + trachea, penis and gut contents).

The increased liver weight in supplemented sheep might be related with the storage of reserve substances such as glycogen as described by Lawrence and Amedeo (1989). Increasing trend of external offal (skin) was due to increase in sub-cutaneous layer of fat deposition on the skin. A reduction in skin thickness has been reported during restricted feeding for sheep (Lawrence and Fowler, 1997) where by the difference in alimentary tract were due to the lower daily feed intakes and negative growth of non-supplemented animals. Similarly, Fluharty and McClure (1997) reported that high protein diets of the calculated NRC requirements resulted in greater weights of liver, small intestine, and kidney compared to normal protein diets in lambs. In consistent to this, Almeida et al (2000) reported a significant (P<0.05) detrimental effect of under nutrition on heart and liver weights of Boer goat bucks.

In the current study, there was a close relationship between level of feed intake and the weight of some non-carcass components. According to Burrin et al (1990), there is a positive relationship between nutrition level, visceral organs and metabolic activity; where by the level of feed intake changes the relative proportion of visceral organs to body mass.

The proportion of the meat animal considered to be edible differs from country to country. In countries where proteins of the offal are considered edible, these offals are useable/saleable offals that add value to the carcass (Tesfaye, 2007). Due to difference in taste and in eating habits, what are edible portions in one area of a country may not be acceptable in the other parts of the country (Getahun, 2001). In many parts of Ethiopia large proportion of body weight (except skin + feet, and respiratory tract) is consumed.

Generally, medium and higher level supplemented sheep (Lp200 and Lp300) were higher (P<0.001) in total edible offal and (P<0.01) total usable products than non-supplemented sheep. The results of this experiment indicated the need to pay attention to the yield of usable products; rather than only the carcass weight and dressing percentage, particularly in cultures where offal components are traditionally consumed. These carcass traits that constitute both conventional carcass components and non-carcass yields give better picture on effect of supplementation on carcass characteristic.

Conclusions

Results of this study showed that supplementation with lablab hay increased total DM intake compared to the control treatment, where the highest result was shown in Lp300 (300 g/head/day lablab hay supplementation). Similar trends were observed for daily live weight gain results. Sheep on the supplemented groups had heavier carcass, empty body weight and slaughter body weight than unsupplemented group. Higher levels of lablab hay supplemented groups (200 and 300g/day) showed significantly higher (P<0.01) dressing percentage than the control group. The results of the study indicated that feeding tef straw to sheep by supplementing lablab hay is effective in improving straw nutrient value and the daily body weight gain of sheep. Among the different levels of supplementation, 200 and 300 g/d lablab hay resulted in better TDMI, nutrient digestibility, ADG and carcass characteristics.

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