Effects of indigenous browse-tree leaves supplementation on growth performance and carcass characteristics of sheep

Hagos H Abraham

Department of Animal Production and Technology, Adigrat University, P.O.BOX 50 Adigrat, Tigray, Ethiopia
hagsabr@gmail.com

Abstract

Primary source of animal feed in the developing world including Ethiopia is natural pasture and crop residue, which are typically low in nitrogen and high in fibre mainly during the dry season. Protein source supplement with concentrate mixtures under farmers’ level is difficult due to their unavailability and high cost. One of the viable solutions to the shortage of protein source feeds is supplementation with accessible browse-tree leaves. The study investigated the effects of African wild olive (OL) and Acacia lahai (AL) dried leaves supplementation on dry matter (DM) intake, digestibility, body weight change, carcass parameters and economic profits using sheep. Twenty-five yearling intact rams (nearly 16.7±2.1kg initial body weight; means ±SD) were assigned into five treatments in randomized complete block design. The treatment feeds included: CONTROL=grass hay ad libitum; OTL100=CONTROL+300g (100% OTL: 0% AL); OTL65=CONTROL300g (65% OTL: 35% AL); OTL35=CONTROL+300g (35% OTL: 65% AL); OTL0=CONTROL+300g (0% OTL: 100% AL). Grass hay, water and salt were free choice. Body weight changes were taken every 2 weeks. The feeding trial lasted 90 days followed by 7 days of digestibility trial. Partial budget analysis and carcass evaluation was conducted at the end of digestibility trial. Results obtained indicated that supplementation of the browse-tree leaves significantly (p<0.05) improved daily DM intake, digestibility, body weight change, feed conversion efficiency and carcass traits (slaughter weight, hot carcass weight, dressing percentage based on slaughter, rib-eye muscle area). In general, results of the study indicated that the multipurpose browse-tree leaves are good supplements and correspondingly increased the net income from the sale of sheep at the end of the feeding trial. Thus, smallholder farmers, in areas where these trees are amply found, should be advised to conserve and use them as the dry season feed supplement.

Keywords: protein source, intake, digestibility, body weight change, partial budget, sheep

Introduction

Ethiopia (3 -15 N, 33 -48 E, 110-4600 m above sea level) is landlocked country situated in the northeastern part of the horn of Africa. Ethiopia is the second most populous country in Africa (Ayele and Raga, 2023), with nearly 80% of the population residing in rural areas, and 31% lives below purchasing power parity (PPP) US$1.90 day^-1 (World Bank, 2021). Ethiopia’s economy is principally based on agriculture (crop, livestock and fishery, natural resources). The sub-sector livestock production is vigorous in terms of its contributions to both agricultural value-added and Gross Domestic Product (GDP). Meanwhile, recent reports suggest the sub-sector is estimated to provide 12-20% of the national GDP, 26-35% of the agricultural GDP, 60-70% of the Ethiopian population’s livelihood, 15-18% of the export earnings (leather and leather products only without live animals as well as other products export) and 30% of the agricultural employment (Gelan et al 2012; FAO, 2016; World Bank, 2017; Tegegne and Legese, 2020).

Ethiopia has one of the largest livestock inventories in Africa with a national herd size about 70 million cattle, 57 million chickens, 96 million small ruminants, 13 million equines in addition to 8 million camels estimated in the year 2021 (CSA, 2021). The livestock population is commonly local type and has not been fully characterized and documented (CSA, 2017). Despite the large livestock population is found in the country and its importance to smallholder breeders and to the national economy, the sub-sector has remained underdeveloped and underutilized because of a number of production constraints.

Among the major restrictive factors, low nutritional status (both in quantity and quality) is the most series problem in the country mainly during the dry season. Babayemi (2007) indicated the dry season is the most challenging limitation, which is characterized by insufficient feed of poor quality. Livestock in Ethiopia derive most of their feed from natural pasture and crop residues (CSA, 2017). These feedstuffs are unfavorably deficit in important nutrients such as protein and minerals, and low in nitrogen and high in fibre essentially during the dry season (Okoruwa and Ikhimioya, 2020). Hence, high levels of production cannot be attained only from such feeds that hardly meet even the maintenance requirement of animals, typically during the dry season. This show improving the existing feed resources by identifying alternative and nutritious feeds, which have been the interest of animal nutritionists to bridge the gap between the requirement as well as availability of nutrients.

Protein source supplement with concentrate mixtures in small-scale livestock production system is difficult owing to their unavailability and high cost. One of the viable solutions to the shortage of protein source supplements is supplementation with browse-tree leaves, which are cheap and easily accessible by smallholder farmers. According to Ansah et al (2016), leaves of trees serve as important sources of nutrients for ruminants in most tropical countries due to their abundance and accessibility. They bridge the gap created by decline in the nutritive potentials of roughages as brows-tree leaves are able to retain their green leaves and relative nutrient content during the dry season (Adane and Anjulom, 2023). The ability of most browse-trees to remain green longer time, which is because of their deep roots that enable them to extract water and nutrient sources from deep soil profile, is one of the characteristics that attracted the use of browse-trees as the dry season supplementary feed. Most browse-trees have high crude protein (CP) content, ranging from 10 to exceeding 25% on dry matter (DM) basis (Okoli et al 2003) and they are degraded amply in rumen to make the protein available to the animal and non-toxic (Leng, 1997). So, the global interest in brose-trees as forage and feed supplement for ruminants has increased research on their nutritive value (Okoruwa and Ikhimioya, 2020).

Indigenous browse-trees in Ethiopia are well known to poor farmers and are better adapted to the environments than the exotic ones (Haile and Tolemariam, 2008). Indigenous browse-trees are used as animal feed in many parts of the country although not on scientific knowledge based manner. In the study area, African wild olive (Olea africana) and Red thorn (Acacia lahai) are the most often used indigenous brows-trees as a source of animal feed. Hence, it is imperative that these brows-trees should be evaluated for their feed value. Likewise, reports are not readily available on ruminant animals’ growth performance and carcass with supplementation of such indigenous brows-trees. The study was, thus, designed to evaluate effects of supplementation with air dried leaves of the local trees solely and/or mixing at different proportion on intake, digestibility, body weight change and carcass traits of sheep fed grass hay in the northeastern part of Ethiopia.

Materials and methods

Description of the study area

The study was conducted in eastern zone of Tigray National Regional State. The area is located in northernmost part of Ethiopia at about 890km north of Addis Ababa (capital city of Ethiopia), at an altitude ranging between 900 and 3200m above sea level. Geographical location of the area is 13 41'-13 48' north latitude and 39 21'-39 48' east longitude. The study area is characterized by rain-fed production system of a wide‐range of cereals and pulses, and livestock husbandry practices. According to the available metrological data, the area receives average annual rainfall ranging between 140 and 600mm with the minimum and maximum annual temperatures of 10 and 30 , respectively. Eastern Tigray has bimodal rainfall pattern namely long rainfall and short rainfall. The long rainfall starts by the mid of June and lasts by the beginning of September, but the short rainfall extends from March to May. The pattern of rainfall in any given year is with a high degree of variation. The eastern margin of the study area borders the western margin of the Great East African Rift.

Experimental animals and their management

Twenty-five yearling intact ram lambs with an approximate average initial body weight of 16.7±2.1kg (mean ±standard deviation (SD)) were purchased from local markets. The age of the experimental animals was determined based on dentition and information obtained from owners. Immediately after purchase, they were ear-tagged, de-wormed against internal (flat and round worms) and sprayed for external (tick and mange mites) parasites with albendazole bolus and diazole, respectively and quarantined for nearly 2 weeks. The animals were vaccinated against common diseases in the study area (pasturellosis, anthrax, sheep and goats small-pox). Following the quarantine period, initial body weights of all animals were measured. They were kept in well ventilated individual pens equipped with individual feeding and watering troughs. Overall, the experimental animals were closely observed for the incidence of any ill health and disorders during the experimental period.

Feed collection and preparation

Grass hay was purchased from farmers of the surrounding area, which was harvested from own and communal grazing areas and then transported to the experimental site. The grass hay was chopped manually into short lengths in order to minimize refusals. Mature fresh leaves from the native browse trees viz. African wild olive (Olea africana)and Red thorn acacia (Acacia lahai)were harvested by hand stripping from communal grazing areas and closures. After harvesting, the leaves were dried under shade by spreading on plastic sheet for 12 days to ensure consistency for moisture contents and safe storage until feeding. All the estimated quantity of air-dried leaves meals required for the whole experimental period was collected, mixed and stored in sacks. At each feeding the proportion of leaves meals required daily as per the treatment were weighed separately, mixed and offered to animals accordingly. Samples for chemical analysis were taken from each sack during the experiment at the time when a new sack was opened for feeding.

Experimental design and treatments

Before commencement of formal feeding trial, the experimental animals were allowed 2 weeks adaptation period for adjusting to housing and experimental diet plans and the initial body weight of each animal was taken on the last day of the adaptation period. They were blocked into five blocks of five animals based on their initial body weight and randomly assigned to one of the five treatment diets within a block. Randomized Complete Block Design (RCBD) was used. The treatment diets were: CONTROL=grass hay ad libitum; OTL100=CONTROL+300g (100% OTL: 0% AL); OTL65=CONTROL300g (65% OTL: 35% AL); OTL35=CONTROL+300g (35% OTL: 65% AL); OTL0=CONTROL+300g (0% OTL: 100% AL) (for details see Table 1 below).

Procedures and measurements

Feed intake

All experimental animals offered grass hay ad libitumas a basal diet (at 20% refusal rate). The daily offer of the basal diet was weighed early in the morning and kept in separate plastic bags for each animal. From the plastic bags, the feed was offered twice daily in the morning as well as afternoon. Basal feed offered was adjusted every 10 days ensuring a refusal of 20% based on the previous days’ intake of an individual animal. Animals in the supplemented group were fed the supplements in the morning at 8:00 am daily. Clean water and mineral salt lick were available to all experimental animals’ free choice. Feed refused was collected every morning before fresh feed was offered, weighed individually for each animal, recorded and pooled per treatment. The daily average DM intake of individual animal was then determined as a difference between the feed offered and feed refused.

Digestible organic matter (DOM) intake of the treatment diets was estimated by multiplying the organic matter (OM) intake by its apparent digestibility coefficient. Estimated metabolizable energy (EME) content of the treatment diets was then estimated from the DOM contents of the feeds using McDonald et al(2002) equation as fellows: EME (MJ/kg DM)=0.016×DOM; where EME=estimated metabolizable energy; MJ=mega joule; kg=kilogram; DOM=gram of digestible organic matter per kilogram of dry matter and DM=dry matter.

Body weight change

The experimental animals were weighed individually using a suspended spring balance having 50kg capacity with 200g precision during the feeding trial initially at 10 days interval, in the morning after overnight (12 hours) fasting. This was done before offering basal and supplements feeds. Body weight change of each animal was calculated as a difference between the final and initial body weight of individual animal while average daily body weight gain was calculated as ratio of body weight change to the total number of feeding days.

Feed conversion efficiency

Feed conversion efficiency (FCE) was calculated by dividing average daily body weight gain by daily total DM intake. As shown below, substitution rate (SR) was calculated as the difference between basal diet intake of the control and supplemented treatments divided by the amount of supplement offered (McDonald et al 2002).

Digestibility

After completion of the 90 days of feeding trial, a digestibility trial was carried out with the same animals and the same rations of the feeding trial. The experimental animals were weighed and all of them were fitted with harness for 3 days for adaptation to carrying of the fecal collecting bags. This was followed by total collection of feces for 7 consecutive days, during which daily intake of basal and supplementary diets were recorded. Samples of feed offered, feed refused and feces were recorded every day in the morning. Feces in the harness were weighed and recorded every morning separately for each animal, mixed and 20% of representative samples were taken and kept frozen in deep freezer at a temperature of –20 , and pooled over the collection period for each animal. The fecal samples were then oven dried at 60 for 72 hours. The dried feces were milled using a laboratory mill through 1mm sieve and bagged for later analysis. The apparent digestibility coefficient of DM and nutrients (OM, CP, NDF, ADF, and ADL) was determined by the following equations;

Where; DM = dry matter and DMI = dry matter intake

Carcass evaluation

At the end of the feeding and digestibility trials, 4 sheep from each treatment, a total of 20 sheep (leaving block three animals across the treatment) were taken and fasted over night to determine the effect of treatments on carcass traits. Slaughter weight (SW) was recorded and animals were slaughtered following the standard procedures. After the processes of slaughtering and flaying skin were completed; skin (with ears and by removing legs below the fetlock joints), head, tongue and feet were weighed independently. This was followed by weighing the components of the alimentary canal viz. esophagus, reticulorumen, omaso-abomasum, small and large intestines with and without contents separately. Internal main organs such as lung with trachea, heart, liver with gall bladder, spleen and kidney and other parts such as total fat (omental and kidney), penis, testicles, tail and empty body weight (EBW) were weighed and recorded independently for each animal. EBW was determined by subtracting weight of gut fill from the SW.

Categorization of non-carcass offal components as edible and/or non-edible was done based on eating habit and culture of the people in the surrounding areas where this study was conducted. Total edible offal components (TEOC) were recorded as the sum total weight of the following: blood, head, tongue, heart, liver, gall bladder, kidney, small and large intestines, reticulorumen, omaso-abomasum, tail, omental fat and kidney fat, while usable products were taken as the sum total weight of TEOC components, skin and hot carcass weight (HCW). HCW was measured by subtracting weight of skin, head, thoracic, abdominal and pelvic cavity contents and legs below the hook and knee joints. Non-edible offal components (NEOC) were considered as the sum total of the weight of lung with trachea, skin, penis, testicles, spleen, feet and gut fill.

Eventually, carcass weight was taken to assess dressing percentage both on SW and EBW bases. Rib eye muscle area (cm²) was measured by dissecting the carcass between the 11^th and 12^th ribs after cutting perpendicular to the back bone (Galal et al 1979). The left and right rib eye muscle area was traced on a transparent water proof paper and the area was measured using planimeter. Mean of the right and left cross sectional areas were then taken as a rib eye area measurement.

At the end of the feeding trial, partial budget analysis was carried out for the determination of the economic profitability of the leaf’s meals supplementation. Analysis was made following Upton (1979) procedures. Purchasing and selling prices of animals, purchasing price of basal diet (grass hay) and labor cost for supplementary feed (collector (s) of leaves of native browse-trees) were recorded. Other expenses for example transport (animals and feed), labor (feeder) and veterinary services were not considered as they remain common for all treatments.

Five well-experienced sheep market dealers in the surrounding were invited to estimate selling price of each animal. The difference of sheep price in each treatment, before (purchasing price) and after (selling price) the experiment was considered as total return (TR). Net income (NI) was calculated by subtracting total variable cost (TVC) from the total return (TR);

NI = TR–TVC

Change in net income (∆NI) was calculated as the difference between the change in total return (∆TR) and the change in total variable cost (∆TVC), and calculated as;

∆NI = ∆TR–∆TVC

Marginal rate of return (MRR), to measure the increase in net income with each additional unit -expenditure was calculated as;

Chemical analysis

Chemical analysis of feeds offered, refusals and feces were conducted after taking sub samples at Mekelle University, Animal Nutrition Lab, Tigray, Ethiopia. Partially dried fecal samples (60⁰C for 72 hours) and feed samples (offered and refusal) were milled to pass through 1mm screen for chemical analysis. The samples of feeds and feces were analyzed for DM, ash and CP according to the procedure of AOAC (1990). DM of feeds and feces was determined after oven drying at 105⁰C for 12 hours and ash was determined by combusting the samples at 550°C for 5 hours. N content was determined by the Kjeldahl method and then CP was estimated as N×6.25. Neutral detergent fiber (NDF), acid detergent fiber (ADF) and acid detergent lignin (ADL) contents were analyzed according to the procedure of Van Soest et al (1991) method of analysis.

Statistical analysis

Data were subjected to analysis of variance (ANOVA) using the general linear model procedure of SAS Version 9.2 (Statistical Analysis System, SAS Institute Inc, Cary, NC, USA). Individual animal served as the random experimental units for all of the data and the browse-tree leaves served as fixed effect. Statistical differences between the treatments means were tested by using least significant difference (LSD) test.

The linear model used for the analysis was as follows:

Y _ij = µ + T _i + B _j + _ij. Where; Y _ij = response variable, µ = overall mean, T _i = treatment effect, B _j = block effect and _ij. = random error.

Results and discussion

Chemical composition of treatment feeds

Approximate laboratory results for chemical composition of the treatment feeds and hay refusals are presented in Table 2. The DM content of the grass hay used in this study was lower than the DM content of 94.6, 93.4 and 92.4% recorded by Gebru et al (2017), Bishaw and Melaku (2008) and Adane and Anjulo (2023), respectively, however, it is comparable with 89.0 and 90.0% DM reported by Abera et al (2021) and Hailecherkos et al (2021), respectively. The OM content of the grass hay was comparable to the findings of Abera et al (2021) and Gebru et al (2017) that reported 89.7 and 89.3% OM, respectively while lower than the OM of 93.0 and 92.7% recorded by Bishaw and Melaku (2008) and Arefaine and Melaku (2017), respectively. The CP content of the grass hay used in the current study was above the maintenance requirement of sheep (7-7.5%, Van Soest, 1982). This might be due to the good environmental condition in which the grass hay was grown, storage as well as early time of harvesting. Evidently, early harvested hay gave high % CP than delayed harvest. Of the factors affecting the nutritional value as well as the chemical composition of pastures is forage maturity at harvesting time. Advance in maturity of pasture was reported to be associated with low CP and high cell wall contents (McDonald et al 2002). The CP content of the grass hay in the study was higher than the values of 3.2, 3.6 and 5.2% found by Bekele et al (2022), Bishaw and Melaku (2008), and Arefaine and Melaku (2017), respectively. But, it was comparable with the CP of 11.4% (Hailecherkos et al 2021) and 9.7% (Mengistu and Assefa, 2022).

The DM content of the African wild olive tree leaves (OL) is lower than that documented by Lee et al (2021) (94.59%), and the DM content of Acacia lahai (AL) is lower than 94.50% (Ali et al 2020). The CP content of OL (9.85%) is similar with 10.87% reported by Lee et al (2021) for air dried leaves. Molina-Alcaide and Ya´nez-Ruizhe (2008) indicated that OL composition varies depending on its origin, proportion of branches, storage conditions, climatic conditions, moisture content and degree of contamination with soil and oils. However, the CP content of AL fall within the range of 7-43% CP reported for 31 different acacia species (ILRI, 2008). As can be seen in Table 2, the browse-tree leaves used in the study had relatively similar CP contents.

NDF portion of feed is only partially digestible by any species of animals though can be used to greater extent by such animals as ruminants, which depend on microbial digestion for utilization of most fibrous plant components (Pond et al 2004). Feeds that contain lower proportion of ADF have better availability of nutrients due to the fact that ADF is negatively correlated with feed digestibility (McDonald et al 2002). In the present study, NDF content of the grass hay is relatively comparable with the value of the previous finding noted by Chufa et al (2022): 72.1, 70.9 and 71.1% in the highland, midland and lowland agro-ecological zones of southwest of Ethiopia, respectively, but lower than 87.8% reported by Gebru et al (2017). The ADF content of grass hay used in this study is lower than 55.4% recorded by Gebru et al (2017) although it is comparable to 40.9% (Alemu et al 2014).

The CP composition of the refusals of the basal diet (grass hay) of the present study was lower by 31.2, 30.9, 34.5, 32.4 and 36.0% in treatments Control OTL0, respectively than in the feed offered. This leads to the conclusion that feed refusals are mainly characterized by low CP contents and high contents of cell wall fiber (NDF). This shows the ability of sheep in selecting feed materials with better nutritive values.

Feed and nutrient intake

Table 3 shows the mean daily DM and nutrient intake during the feeding trial. The DM intake of the basal diet was significantly (p<0.001) higher in the control treatment (Control) when compared to leave supplemented ones although non-significance (p>0.05) difference was observed among the supplemented groups. The current result is in agreement with the reports of Alemu et al (2014) who recorded higher basal diet DM intake in non-supplemented Washera sheep fed grass hay supplemented with Millettia ferruginea (Birbra) foliage. Likewise, Arefaine and Melaku (2017) recorded higher hay DM intake in non-supplemented Adilo sheep than the group supplemented with sole or mixtures of moringa stenopetala leaf meal and wheat bran. In reality, these results revealed that supplementation reduces intake of basal diet. On the contrary, significantly higher intake of basal diet by the control group is reasonable. This is as roughage feeds in general are poor in protein and energy content, and the control animals consume more basal diet (roughage feeds) to fulfill their nutrient requirements.

However, the total DM intake under the control group was significantly (p<0.01) lower than the supplemented groups. This could be attributed to the poor quality of the roughage as well as its low digestibility, which limits digesta flow rate. Furthermore, the reason for increased total DM intake in the supplemented group could be due to the positive effect of supplementation by tree leaves on quality and digestibility of the diet. The increase in total DM intake in this study is in line with the previous results reported by Bekele et al (2022) and Bishaw and Melaku (2008). Nonetheless, there were non-significant (p>0.05) differences in total DM intakes among the supplemented animals. This might be attributable to the comparable nutritional composition of supplement feeds. Correspondingly, significant difference was observed between the control and supplemented treatments in daily total DM intake per unit of metabolic body weight (g/kg W^0.75) and as per cent of body weight. These could be because of variations in body weight change and efficiency of feed utilization of the experimental animals. The total DM intake as per cent of body weight in the current study (3.2-3.6%) is within the range of 2-6% recommended by ARC (1980).

The CP intake was statistically (p<0.001) higher in supplemented sheep as compared to non-supplemented sheep. Sheep supplemented with OTL35 had statistically (p<0.001) higher CP intake than sheep supplemented with OTL100. The intake of fiber (NDF, ADF) was similar in both control and supplemented sheep even though significantly (p<0.001) higher OM intake was recorded in the supplemented sheep, which is in line with the results of Alemu et al (2014) and Hailecherkos et al (2021).

Dry matter and nutrient digestibility

The apparent digestibility coefficients of DM, OM, CP, NDF and ADF values are given in Table 4. CP digestibility of leaves supplemented sheep was significantly (p<0.001) higher as compared to the non-supplemented sheep, however, there was no significant (p>0.05) difference among supplemented sheep. The higher CP digestibility in the supplemented than the control group could be due to the higher CP supply in the former ones. This agrees with findings of Ash and Norton (1987) which revealed that feeding high protein diet to goats significantly improved N digestibility when compared to low protein diet. However, there were no statistically significant (p>0.05) changes in nutrient (DM, OM, NDF, ADF) digestibility between the supplemented and control groups in the current study. This indicated that supplementation with air dried leaves of African wild olive and Acacia lahai did not play role in digestibility of these nutrients in this study. In accordance with the study, Mackrae and Armstrong (1969) noted that supplementation had little or no effect on digestibility of NDF and ADF despite the depression of fractional digestion. Except for CP, there was a statistical correspondence (p>0.05) in nutrient digestibility among treatments which is in good agreement with findings of Abera et al (2021) reported that non-significant differences among the supplemented and control treatments in Arsi-Bale sheep fed grass hay basal diet and supplemented with Vetch (Vicia villosa).

Body weight change and feed conversion efficiency
Body weight change

The mean initial body weight, daily body weight gain, final body weight and feed conversion efficiency (FCE) are given in Table 5. Sheep supplemented with sole or mixture of the tree leaves had significantly higher average daily body weight gain (ADG) (p<0.001) and final body weight (p<0.01) than the non-supplemented sheep. These could be due to lower nutrient intake and lower nutrient digestibility in the non-supplemented group as compared to the supplemented groups. However, there was non-significant (p>0.05) difference in ADG and final body weight among the supplemented sheep. This indicated that 300g sole or mixtures of the browse-tree leaves supplementation consisted comparable nutritive value. Results of the study revealed that supplementation increased ADG and final body weight, which is in agreement with the results of Asmare et al (2008), Alemu et al (2014), Abera et al (2021) and Hailecherkos et al (2021), who indicated that supplementation with protein and energy source feeds improved growth performance of sheep.

The ADG for the supplemented sheep (36.7-41.8g/day) in this study is higher than values of -8.0 to -6.0g/day reported by Alemu et al (2014) in Washera sheep supplemented with Millettia ferruginea (Birbra) leaves. Likewise, ADG of 15.0-16.1g/day in Djallonké rams supplemented with tanniferous browse plant was reported by Ansah et al (2016). Besides, Gebru et al (2017) found ADG in the range of 28.8-36.8g/day for sheep supplemented with indigenous browse-tree pods. The trend in all experiments revealed that browse leaves generally have positive effect on animal performance although ADG of animals in different experiments differ due to differences in species, breed, and stage of growth or level of feeding.

The positive average live daily body weight gain observed in the non-supplemented sheep is attributed to the good quality of the grass hay (9.9% CP). Similar to the present study, Ansah et al (2016) and Okoruwa and Ikhimioya (2020) reported 12.7 and 83.6g/day mean daily body weight gain in control group of sheep and goats, respectively, which were offered grass hay.

The body weight change across time is shown in Figure 1. As can be observed from this figure, the body weight change of supplemented and un-supplemented sheep increased throughout the experimental period although growth rate variation was being greater for the supplemented than the non-supplemented sheep. This was due to the fact that all animals received sufficient amount of CP above their maintenance requirement.

Figure 1. Body weight change of sheep fed grass hay and supplemented with 300g sole or mixtures of air dried leaves of African wild olive and Red thorn

The regression analysis result (Figure 2) between the dependant variable body weight gain (ADG) and the indipendant variable total CP intake (TCPI) revealed that as the intake of CP increased, daily body weight gain also progressively increased. The higher body weight gain in the present study might be the result of high CP intake, which increased feed intake and improved nutrient digestion.

Figure 2. Regression of total CP intake on body weight gain of sheep fed grass hay and supplemented with 300g sole or mixtures of air dried leaves of African wild olive and Red thorn

Feed conversion efficiency

Diets that promote a high rate of gain will usually result in a greater efficiency than diets that do not allow rapid gain because the rapidly gaining animals utilize less of the total feed intake for maintenance and more of it for live weight gain (Pond et al 1995). In this study, supplemented animals had statistically (p<0.001) higher feed conversion efficiency than the non-supplemented animals. Nonetheless, there were non-significant (p>0.05) differences among the supplemented groups. This shows that all of the supplemented animals utilized almost comparable amount of nutrients for a unit of body weight gain. The results of the current study are in line with previous findings (Gebru et al 2017; Abera et al 2021).

Correlation between nutrients intake, digestibility and daily body weight gain

The correlation analysis results between nutrient intake, digestibility and average daily body weight gain of sheep is given in Table 6. Total DMI was positively and significantly (p<0.001) correlated with CPD, ADFD and ADG. The positive associations among these parameters reflect the improved fermentation and passage rate, which lead to improved intake that resulted in daily body weight gain. This could be come from the positive effect of supplementation on nutrients intake and digestibility. Melaku et al (2004) indicated that supplementation with mixtures of multipurpose trees at 1.5% body weight to Menz sheep fed teff straw promoted higher intake of DM and OM, higher feed consumption efficiency and higher ADG at the increasing level of CP.

In this study, CPI was significantly (p<0.01) and positively correlated with OMD, however, non-significantly (p>0.05) and positively correlated with DMD. Likewise, CPD was significantly (p<0.001) and positively correlated with DMI and OMI. However, CPD was non-significantly (p>0.05) and negatively correlated with NDFI and NDFD. ADG of sheep is strongly (p<0.001) and positively correlated with CPI, CPD, DMI and OMI. Nonetheless, it is negatively and non-significantly correlated with NDFI.

Carcass Characteristics
Slaughter weight, hot carcass weight and dressing percentage

Values for SW, EBW, HCW, dressing percentage (slaughter and empty body weights bases) and rib eye muscle area of the experimental sheep are given in Table 7. Animals supplemented with air dried leaves of the sole or mixtures of the browse-trees had higher SW and HCW (p<0.01), and EBW (p<0.001) than non-supplemented ones though the supplemented treatments were not statistically (p>0.05) different among themselves.

Dressing percentage is both a yield and value determining factor, and is therefore, an important parameter in assessing performance of meat producing animals (Mtenga et al 2007). Most research works on small ruminants’ carcass assessments in Ethiopia includes dressing percentage as a major parameter to determine meat production and its efficiency. In the present study, supplementation value-added dressing percentage as calculated on slaughter weight (p<0.001) basis; however, there was no difference (p>0.05) among the supplemented groups. On the other hand, no significant (p>0.05) difference was observed between the supplemented and non-supplemented groups in dressing percentage as calculated on empty body weight basis. 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 significantly heavier in non-supplemented animals. In agreement with the present study, previous studies revealed that dressing percentage calculated on empty body weight basis did not differ between supplemented and non-supplemented individuals. For instance, values of dressing percentage calculated on empty body weight basis obtained by Abera et al (2021) did not statistically differ between supplemented and non-supplemented animals.

Rib eye muscle area

Rib-eye (longissmus dorsi)muscle area, which is an indirect estimate of body musculature, or lean meat of the body, indicates the musculature development of the animal (Galal et al 1979). In this regard, supplemented sheep had significantly (p<0.001) higher rib-eye muscle area as compared to the non-supplemented sheep, indicating the development of more lean flesh in the supplemented groups. The present result was in agreement with other previous findings (Tesfay et al 2017). Nevertheless, there was no statistically significant (p>0.05) difference among the supplemented groups. This indicated that sheep supplemented with 300g sole or mixtures of the brows-tree leaves were able to accommodate better lean flesh.

Edible and non-edible offal components

Data on edible and non-edible offal components are shown in Tables 8 and 9, respectively. The results of the present study indicated that supplementation has a positive effect on most of the edible offal components (Table 8). Among the edible offal components tongue (p<0.001), liver with gall bladder and tail (p<0.01), total fat and omaso-abomasum (p<0.05) were significantly heavier in the supplemented sheep when compared to the non-supplemented sheep. But, heart was heavier (p<0.5) in OTL65 and OTL35 whereas heavier omaso-abomasum was recorded in OTL65. The remaining edible offal components viz. blood, head, kidney, esophagus, reticulo-rumen, small and large intestines) were not affected by supplementation.

The TNEOC for example feet, lung with trachea, spleen and penis did not differ significantly (p>0.05) between the control and supplemented sheep. But, statistically (p<0.01) heavier skin and testicles were recorded for sheep in OTL65 and OTL35 than the non-supplemented group. Gut fill was heavier in un-supplemented sheep, but significant difference was not recorded among the supplemented groups. The significantly (p<0.01) heavier gut fill in the control group could be due to the higher consumption of roughage feed (basal feed), which is characterized by low digestibility and increased amount of digesta in the rumen. Van Soest (1994) and Pond et al (1995) noted that non supplemented animals fill their gut with less digestible roughage which is retained in the gut for long time to be degraded by rumen microorganisms. Apart from this, supplemented sheep had statistically higher (p<0.01) total edible offal components (TEOC) and (p<0.001) total usable products (TUP) because of the positive effect of supplementation on the weight of most organs.

Conclusion

Results of the study revealed that supplementation of air dried leaves of the indigenous browse species and their mixtures to the basal diet grass hay improved TDMI, FCE, CPI and CPD. It also improved the growth performance of all supplemented animals. Thus, from biological point of view, sheep keepers can use sole or mixture of the browse-tree leaves to attain better sheep productivity.

Acknowledgement

I would like to acknowledge all persons who were involved in this activity for their contribution in different aspects.

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