Sheep is a vital ruminant farm animal of Bangladesh. It plays an important role regarding the income and food supply, as well as the socio-economic status of poor farmers . The sheep in Bangladesh are less profitable because of lower birth weight, average daily gain (ADG) and slaughter weight. The profitability of lamb farming in Bangladesh is associated with inadequate and poor quality feeds . Concentrate supplementation plays a vital role on the growth and lamb performance [3–5]. There is alternatives way to mitigate this problem by supplementing high-energy concentrate feeds before marketing of lambs. Indigenous lambs are resistance to high ambient temperature in tropical and sub-tropical environment . The production performances of lamb, carcass and meat quality depends on feedlot conditions. Various factors enhance the production performances such as breed and age of lamb, types of feed supplied as well as the period of feeding . Concentrate feed supplementation in adult sheep increased the marbling and the tenderness of mutton .
The energy and protein play a crucial role on affecting meat production in small ruminants by including dietary nutrients . The ADG of Jamuna basin lamb was found 51–54 g upto slaughter age at 9–12 months and the body weight (wt) was found 17–20 kg at that time . Several researchers studied on sheep rearing systems particularly grazing with different levels of concentrate supplementation on the meat quality of lambs [11,12]. They found a positive result of concentrate supplementation on intramuscular fat depositionin lamb compared to only grazed lamb. The natural antioxidants are present in green grass resulting in the effect of grazing system to minimize meat oxidation . The influences of green grass on sensory attributes, meat instrumental color values and texture had been studied by another author with different findings . There were many previous studies which compared pasture grazing with concentrate supplementation on growth performance and meat quality , color , sensory attributes  and water holding capacity (WHC) . The lambs having only grazing leads leaner carcasses with lower dressing% whereas, lambs with concentrate feeding performed higher growth rates, better carcass traits, and lower ultimate pH . The instrumental color of mutton influences the consumer purchasing decisions . The red color is treated by consumers as good quality whereas pale, discolored meat is treated as poor quality meat . The consumers choose lamb meat due to its better color but market fails due to the lacking of standardization and quality when it reaches to the consumers .
Only limited information on growth, carcass & meat quality of lambs through different levels of concentrate were available in Bangladesh. The carcass traits and meat quality such as nutritional, physicochemical, sensory and meat color of lamb meat have not been studied yet in Bangladesh. The production of lamb in Bangladesh is practised through traditional feeding and its genetic potential is lower . Therefore, it needs to identify the growth performances, carcass & meat quality of finished lambs at different ages & body weights with different concentrate feeds supplementation with normal grazing. Supplementation can help to improve the quality of feed resources through enhancing the activity of rumen microbes . Concentrate supplementation levels are responsible for fluctuating the carcass traits, meat quality and fat deposition . From different literatures it was found that 1% to 6% concentrate supplementations used to increase carcass and meat quality of lamb according to size and body weight. Only limited research is reported of different levels of concentrate supplementation in lambs and kids to identify slaughter age and meat quality in Bangladesh [26,27]. Bangladesh Livestock Research Institute (BLRI) conducted a basic research suppying 1%, 1.5% and 2% concentrate feed to enhance the lamb production performances in their own research station . From this point of view, 1%, 1.5% and 2% of concentrate feeds were used to validate this research work at rural farming condition in Bangladesh. Hence, the study was undertaken to evaluate the production performances, carcass & meat quality of marketing age and live weights with concentrate supplementation for Jamuna basin lambs in Bangladesh.
MATERIALS AND METHODS
The study was carried out forty (40) castrated Jamuna basin lambs with same management, feeding and vaccination under four treatments such as T0 (Control), T1 (1% concentrate), T2 (1.5% concentrate) and T3 (2% concentrate) having ten lambs in each group. The lambs were grazed at 6–7 h in an open grazing field at the day time and kept in the shed at night. The supplied feed was uniform in all four treatments. Sufficient green grass and fresh water were supplied with 1%, 1.5%, and 2% concentrate feed that contain 18% crude protein (CP) and 12 MJME/kg dry matter (DM). The ingredients of the formulated diet were crushed wheat (68%), soybean meal (30%), di-calcium phosphate (DCP) (0.5%), vitamin-mineral premix (0.5%) and iodine salt (1%) which were supplied to the lambs twice a day.
Forty castrated lambs were fasted and slaughtered with Halal or Muslim method for laboratory analyses after end of the growth & feeding trial. The fasted body weights of the lambs were recorded before slaughtering and individual hot carcass weights were recorded immediately after flaying and evisceration. Non-carcass components such as skin, head, liver, lung, spleen, heart, kidneys, shank, and viscera were removed and measured their respective weights to indentify dressing percentage and other carcass parts. The rumen ingesta and other gut contents and the post-ruminal tracts were removed and weighed. The obtained dressing percentage was calculated as hot carcass basis or without chilling. Finally, 100–120 g sample was taken from Longissimus dorsi (LD) muscle for analyses of proximate component, physiocochemical traits, instrumental meat color and sensory evaluation.
After slaughtering, complete bleeding was practiced. The following parameters viz. live wt, carcass wt, dressing percentage, blood wt, skin wt, viscera wt, head wt, half carcass wt, pluck wt, neck wt, shoulder wt, rack wt, loin wt, kidney wt, liver wt, heart wt, lung wt, spleen wt and shank weight were measured. Then, the weight of hot carcass was taken with a balance to calculate dressing percentage.
Similarly, the weight of liver, heart, lungs, kidney, and spleen were taken to determine the percentage of these organs accordingly.
The proximate components of lamb meat such as DM, CP, ether extract (EE), and ash were analysed according to AOAC .
Different sensory attributes of Jamuna Basin lamb were performed in this study. All meat samples were examined by skilled 8-members evaluation panel. The sensory parameters were measured on a 5 point scale for the attributes such as tenderness, juiciness, color, flavor, and overall acceptability. There were eight training sessions were conducted for the judges to familiarize themselves with the attributes for evaluation [30,31]. All panelists participated in orientation sessions prior to sample evaluation might be due to familiarize with the scale attributes. All lamb samples were served in the petri dishes prior to evaluation.
Drip loss was measured according to the principle followed by Rahman et al. . For drip loss measurement approximately 30 g sample was hung with a wire and kept in an air tight plastic container for 24 h. After 24 h, the sample was weighed and calculated the difference. It was expressed as percentage.
For cooking loss % measurement, thirty (30) g lamb meat sample was taken in a poly bag and put it into a water bath having 71°C temperatures. Then lamb meat was removed from the water bath after 30 minutes cooking and soaked its moisture with white tissue paper. Weight loss of the sample was measured through deducting the moisture loss during cooking of lamb meat. The cooking loss was calculated using the following formula:
Lamb meat pH was measured after 24 h of slaughtering (ultimate pH) using a pH meter (Hanna HI 99163, Hanna, Woonsocket, RI, USA). The pH was measured by inserting the electrode at three different locations of the lamb meat which was calibrated prior to use at pH 7.0. Triplicate measurements of pH were taken from on the medial portion of the lamb meat at one cm depth to get an average value.
The lamb meat samples were cooked at 71°C for 30 minutes and then the meat samples were taken out from the water bath. After cooling the samples, the pH was measured as described in the same procedure as of raw meat samples.
The WHC of lamb meat was measured according to the principle described by Choi et al. . One g thawed sample was wrapped by absorbent cotton and put it into a 1.5 mL eppendorf tube. The tubes with samples were then centrifuged in a centrifuge separator (H1650-W Tabletop high speed micro centrifuge, LABO-HUB, Shanghai, China) at 10,000 rpm for 10 min at 4°C temperature. After then the samples were weighed and calculated the WHC%. The WHC% of the sample was measured through the following formula:
Instrumental color was measured from longissimus muscle of lamb carcass. Color was measured from the chilled muscles kept at 4°C temperature after 24 h of slaughtering using a Konica Minolta Chroma Meter (CR 410, Konica Minolta Sensing, Osaka, Japan). A Miniscan Spectro colorimeter programmed with the International Commission on Illumination (CIE) Lab (International Commission on Illumination, France) was used to measure the value of CIE L*, a*, and b*, where L* represents lightness, a* redness and b* yellowness . The values were determined from the medial surface of the lamb meat just after 24 h of post-mortem .
RESULTS AND DISCUSSION
Level of concentrate feeding showed a significant difference (p < 0.01) on the final body weight and ADG in different treatments. A higher ADG was found in T2 and T3 but there was no statistical difference. It was found from the study that 1.5% concentrate feed (T2 group) showed the highest ADG (58.85 g/d) and dressing weight (51.35%) than all other treatments (Table 1). Concentrate feed digested easily and utilized properly in ruminal environment that results higher muscle growth as well as meat quality. Tadesse et al.  stated that the ADG was higher in small ruminant at higher level of concentrate supplements. A similar ADG was found in the results of Hashem et al.  and Hossain et al.  in growing Jamuna basin lambs. Yirdaw et al.  also found a similar ADG and dressing % in bagait sheep through cottonseed meal feeding. Dressing percentage was found significantly higher (p < 0.05) in T2 compared to T0, T1 and T3 treatments. Similar results were stated by Ayrle et al.  and Worku et al.  in case of dressing percentage. Costa also found a significant (p > 0.05) effect of hot carcass and dressing percentage which was very much similar with this study . Gashu et al.  stated that the sheep consuming higher level of concentrate supplements had significant heavier carcass than lower level of concentrate feed. These results supported the present study. The heavier carcass weight reported in T3 might be reflacted the effect of higher feed consumption in that treatment. The hot carcass weight of lambs (6.36–7.73 kg) in this study was not higher to the Ethiopian indigenous sheep breeds might be due to the breed variation . Moniruzzaman et al. showed that the age of animal had significant influence on dressing percentage and the quality of meat . In case of head weight, no difference was found in T0 and T1 but there was a significant difference (p < 0.05) was detected with T2 and T3 treatment. The leg weight was similar in T0, T1 and T2 but found a significant different (p < 0.05) with T3. A similar neck weight was found in T0 and T1 which had significant different (p < 0.05) with T2 and T3 treatment. The loin weight was significantly different at different treatments of concentrate suppementation along with control group. Heart and spleen weight were found significantly heavier (p < 0.001) in T1, T2, and T3 treatments, respectively but lungs didn’t. Liver weight had significantly (p < 0.05) increased with increasing concentrate feeds. Weight of edible by-products such as liver, heart, spleen weight was similar and the kidney weight was not similar with the findings of Adem et al. .
The CP and EE percentage were 21.46, 22.41, 24.16, 25.57 and 0.97, 1.94, 3.56 and 6.58, respectively in T0, T1, T2 and T3 treatments (Table 2) which were significantly increased (p < 0.001) with the increasing of concentrate supplementation. Ash percentage found significantly lower (p < 0.001) in four treatments compared to control group. The amount of CP, EE and ash of lamb meat was found significantly higher (p < 0.001) at different treatments (T1, T2 and T3) than in T0 treatment. The CP and EE percentage were found significantly higher (p < 0.001) in concentrate supplemented groups and the increasing was proportional to the level of concentrate feed. Worku et al.  found higher CP and EE percentage with increasing level of concentrate feed for Washera sheep where CP percentage was not increased significantly (p > 0.05) but the EE percentage was increased significantly (p < 0.05). On the contrary, sheep fed higher concentrate showed the higher meat fat . The higher rate of concentrate supplementation showed a positive result on the fat deposition in meat. These findings were very much similar with this present study. Supplementation of concentrate results a greater feed intake and growth as compared to the control group lambs grazed on low quality forages in this current study. Some other researcher also reported that there was a positive effect on the protein intake and the digestibility of feed ingredients . Gashu et al.  reported a lower fat deposition in Washera sheep (2.61%–2.62%) might be due to lower concentrate supplementation. Good quality of lamb meat contains 70% moisture and 18.5%–23.40% protein along with sufficient marbling and subcuteneous fat content . Ash percentage of their study was higher up to 2.00 for concentrate feed which was significantly different (p < 0.001). The result of ash content was similar with the results of Tadesse et al.  where they showed a non significant (p > 0.05) effect of ash with the increasing levels of concentrate feed.
The values of cooked pH, ultimate pH, cooking loss, drip loss and the WHC at different treatments are shown in Table 3. The ultimate pH was found optimum level (5.95) in T2 treatment as compared to T0, T1 and T3 treatments which showed significantly different results (p < 0.001). Hossain et al.  reported that ultimate pH was 5.95 which were very similar with the present study. The ultimate pH values of T2 lamb meat in the present study ranges within the acceptable international values of meat pH (5.5–5.9) for international trade. The muscle glycogen is responsible to produce lactic acid results a lower pH that improve the shelf life of meat . The optimum pH value observed in this study indicated that lambs were in sound health status that ensured enough glycogen reserve during slaughtering. The higher glycogen levels in the muscle help to developed optimum level of lactic acid resulting the reduced pH that improve the shelf life of meat . Higher ultimate pH was found in T0, T1 and T3 treatment groups as compared with T2 treatment. Live lambs were transported to Bangladesh Agricultural University market before slaughtering from a 90 kilometer distant place might be the cause of higher pH. There was a reduced muscle glycogen resulting from longer time feed withdrawl and transportation stress. The symultaneous effect of feed withdrawl and transportation stress decreased the amount of glycogen in muscle during slaughtering. Cooked pH was significantly lower (p < 0.001) in T2 as compared with other treatment groups. Lower cooking loss and drip loss percentages were found in T2 as compared with T0, T1 and T3 treatments in which cooking loss and drip loss had significant effect (p < 0.05 and p < 0.001, respectively). A lower cooking loss value (20.33–21.63) and higher drip loss (3.80–4.89) was also reported by Costa et al.  which were not similar with this study might be due to the stress condition of the slaughterd lamb. The cooking loss values of meat of small ruminants showed an acceptable range (14%–41%) which was corroborated with the present study . The drip loss percentage from the present study was found within the optimum ranges (0%–4%) with increasing levels of concentrate feeds. The WHC% was detected significantly higher (p < 0.001) in T2 as compared with T0, T1 and T3 treatments. Drip loss is an important indicator of WHC of fresh meat which is resulted by the gravity force. The WHC percentage of the present study was not in accordance with the results of Costa et al.  where they showed that the WHC% was 72.55.
The values for color, flavor, tenderness, juiciness and overall acceptability at different treatments were 3.85 to 4.51, 4.06 to 4.46, 4.25 to 4.63, 4.25 to 4.63 and 4.17 to 4.46, respectively (Table 4). The color and tenderness were observed significantly higher (p < 0.001) in T2 compared with other treatments. In case of flavor, there was no difference in T0 and T1 but there was a significant superior flavor (p < 0.05) was detected with T2 and T3 treatment. Juiciness and the overall acceptability were also detected significantly higher (p < 0.05) in T2 compared to T0, T1 and T3 treatments. The average score of flavor (4.42 in T2 treatment) and juiciness (4.63 in T2 treatments) of the present study were higher than the results of Zanzibar Chulayo and Muchenji for flavor (3.33) and juiciness (3.47) in sheep . The flavor was significantly higher (p < 0.001) in T3 and overall acceptability also significantly higher (p < 0.05) in T2 treatment compared with other treatments. The reason of higher flavor in lamb’s meat might be due to increase of fat deposition with increasing concentrate feeds for lambs. Worku et al.  found significantly higher (p < 0.001) flavor, tenderness, juiciness and overall acceptability with increasing concentrate feeds which was supported by the present study.
According to CIE the values of L*, a*, b*, hue angle and saturation index at different treatments were ranged at 42.03–51.81, 15.83–18.15, 9.27–12.71, 20.75–26.11 and 16.78–22.65, respectively at different treatments (Table 5). Color value is an important criterion of meat quality evaluation of lambs. This color value was observed variation in age, sex, breed, geographical location and management condition of lambs. The L* value was observed significantly higher (p < 0.001) in T0 compared to T1, T2 and T3 treatments. The higher L* value in T2 was due to the distribution of more intramuscular fat deposition which made the luminous of meat . Muscle from heavier lambs showed lighter/higher (L*) color than that of higher/lighter weight lambs. A significant higher (p < 0.05) a* value was found in T2 compared with T0, T1 and T3 treatments. Lower b* value was also found in T2 compared with T0, T1 and T3 treatments which was significantly different (p < 0.001). Worku et al.  found a non-significant higher CIE L*, a* and b* results at higher levels of concentrate feeds. These results were not similar with the present study. Costa et al.  found that the CIE L*, a* and b* values of unweaned lambs and supplemented weaned lambs were 41.67 & 43.17, 15.23 & 15.98 and 6.34 & 6.55, respectively. These values were much lower than the present stydy. The bright red color of meat is an important characteristic for meat quality that influenced the consumer’s perception that indicates the freshness and wholesomeness of meat . The higher hue angle and saturation index were found in control group than treatment groups. The higher hue angle and saturation index were detected significantly difference (p < 0.01) among the all treatments groups. The hue angle and saturation index values were not influenced by the higher concentrate supplemented groups  which were not supported the present study.
The correlations in different variables of carcass traits are shown in Table 6. There was found a strong positive correlation association (r > 0.80) between initial body weight and the final body weight. Strong positive correlation (r > 0.85) was found between final body weight and hot carcass. High positive correlation association (r > 0.83) was also observed between liver, shoulder and rack weight. Also, a stronger positive correlation associations (r > 0.80) were observed between spleen & heart, skin & head and heart & head weight, respectively. A comperative higher positive correlation association (r > 0.79) was observed between shoulder and rack weight. Olawumi et al.  stated that all the carcass traits were good indicators of live weight which was similar with the present study . The correlation of ADG and hot carcass between live weight was significantly differed (p < 0.01 and p < 0.05), respectively. The hot carcass yield was strongly correlated (r = 0.90) with the chilled carcass yield; therefore, with a high hot carcass yield and low losses during the chilling of the carcass, the chilled carcass yield increased. The correlation of these two variables permits estimations of the characteristics of the carcasses and the meat when specific and accurate equipment were not available [51,52]. The correlation between final body weight and hot carcass was significantly different (p < 0.05). The correlation between spleen and heart, shoulder and rack withl iver were significantly different (p < 0.01). The correlation between initial and final body weight, skin and head weight were also found significantly different (p < 0.01). Costa observed a positive correlation between body condition and dressing% in lamb meat which was significantly (p < 0.05) different .
A, initial weight (kg); B, final weight (kg); C, average daily gain (g/d); D, hot carcass wt.; E, dressing %; F, blood %; G, skin %; H, viscera %; I, head %; J, leg%; K, half carcass %; L, pluck %; M, neck %; N, shoulder %; O, rack %; P, loin %; Q, kidney %; R, liver %; S, heart %; T, lung %; U, spleen %; V, shank %.
The correlation between proximate component and sensory attributes of meat traits is presented in Table 7. There was found positive correlation association (r > 0.60–0.79) between CP and EE, CP and flavor. Positive correlation association (r > 0.50–0.56) was observed between EE and ash, EE and flavor, EE and tenderness, respectively. The positive correlation of fat content (EE) and flavor between CP was found significantly differed (p < 0.01). The positive correlation of ash, flavor and tenderness between EE was found significantly differed (p < 0.01). Yalcintan et al.  found significant positive correlation (p < 0.01) on juiciness and overall acceptability between tenderness. These results were in accordance with the present study. They also found significantly different (p < 0.01) of positive correlation between juiciness and overall acceptability. These findings did not corroborate with the present study.
The correlation between physiocochemical traits and color values of meat traits is presented in Table 8. Positive correlation association (r > 0.71) was observed between cooked pH and ultimate pH. Positive correlation association (r > 0.50–0.70) was observed between b* value and ultimate pH, b* value and cooked pH, respectively. On the contrary, negative correlation association (r > -0.51) was found between L* and ultimate pH. The positive correlation between ultimate pH and cooked pH was found significantly differed (p < 0.01). The positive correlation between b* and ultimate pH, b* and the cooked pH was found significantly different (p < 0.01). The negative correlation between L* and ultimate pH was found significantly differed (p < 0.01). Rahman et al.  found positive and significant (p < 0.01) correlation of ultimate pH and drip loss between L* values. Their results were not similar with the present study.
The ADG is presented in Table 9. The mean square of initial live weight was 15.51, F-value 0.54 which was non-significant. The mean square of level of concentrate feed was 1680.78, F-value 58.53 which was significantly different (p < 0.001). The root sqaure was 0.83 and adjusted root square was 0.82. The total sum of square was 92071.66 and degree of freedom 40. The corrected total was 6047.89 and degree of freedom was 39.
The following analysis of variance (ANOVA) model was used to justify the analysis of covariance of different levels of concentrate feeds on ADG:
D2= 1 for 0% concentrate = 0 otherwise
D3= 1 for 1% concentrate = 0 otherwise
D4= 1 for 1.5% concentrate = 0 otherwise
The estimated regression model has been presented below:
F= 59.10** R sqrare = 0.82
To identify which feed is contributing mostly for ADG, the following ANOVA model has been estimated. Feeds 0 and 1% concentrate were found to have significantly negative impact on the increase of ADG and they were significantly different from other feeds. However, 1.5% and 2% concentrate feeds were found to have positive impact of increasing ADG and there was no different impacts of 1.5% concentrate feed as compared to 2% concentrate feed. That is, 1.5% and 2% concentrate feeds were significantly (p < 0.001) better compared to control and 1% concentrates feed. A significant F value suggests that the model is well fitted to the data. The adjusted R square shows that 82% variation of ADG could be happened due to supplementation of concentrate feeds of Jamuna basin lambs.
It is concluded from the study that the 1.5% concentrate supplementation in Jamuna basin lamb up to 12 months of age showed better productive and meat quality on the basis of carcass traits, nutritional, physicochemical, sensory and instrumental color values. Further research is required to deterrmine the detail nutritional contents like omega-3, omega-6, amino acid profile, fatty acid profile and consumer’s acceptablity of lamb meat.