The experimental protocol and all procedures involving animals were reviewed and approved by the Institutional Animal Care and Use Committee of Jordan University of Science and Technology (JUST), Jordan (Protocol No. 16/04/12/216A). All animal procedures were conducted in accordance with the approved institutional protocol and the ARRIVE 2.0 guidelines. Before enrollment, the lambs underwent veterinary examination to confirm their clinical health and suitability for participation in the experiment. The animals were subsequently administered an antiparasitic treatment before allocation to the experimental groups. Throughout the study, the lambs were individually housed under natural ventilation and lighting conditions, provided their assigned diets ad libitum, and given unrestricted access to drinking water. Animal handling, blood collection, placement in metabolic cages for the digestibility and N balance experiment, transportation, fasting, and slaughter were performed in accordance with the approved experimental protocol, with appropriate measures taken to minimize unnecessary pain, distress, and discomfort. The animals were monitored throughout the experimental period, and all lambs completed the study without reported illness or mortality. Slaughter was performed humanely at the designated slaughterhouse following the experimental feeding period.

The study was conducted from October 2025 to January 2026 at the Animal Field of the Research and Training Department, JUST, Irbid, Jordan. The feeding trial lasted 73 days, comprising a 10-day adaptation period followed by 63 days of experimental data collection.

A completely randomized design was used. Twenty-four male Awassi lambs, aged 75 ± 1.5 days and with an initial body weight of 17.33 ± 0.821 kg, were stratified by body weight and randomly allocated to three dietary treatment groups (n = 8/group). The treatments consisted of a control diet without BAWA (CON), a diet containing 100 g/kg BAWA (BAWA100), and a diet containing 200 g/kg BAWA (BAWA200), on a DM basis. Each lamb was the experimental unit. The study evaluated nutrient intake, growth performance, feed efficiency, economic outcomes, nutrient digestibility, N balance, carcass characteristics, meat quality, FA composition, and blood biochemical indicators.

Before enrollment, a veterinarian examined all lambs and confirmed they were clinically healthy. They were subsequently administered Ivomec (Merck, Madison, NJ, USA) to control internal parasites and were transferred to the experimental pens. Lambs were individually housed in 1 × 1.5 m pens under natural ventilation and lighting conditions. They were offered their respective diets ad libitum twice daily at 08:00 and 15:00 and had unrestricted access to drinking water throughout the study.

The CON, BAWA100, and BAWA200 diets contained 0, 100, and 200 g/kg BAWA on a DM basis, respectively. All diets were formulated according to the NRC requirements for growing lambs [17] and were isonitrogenous, containing approximately 160 g/kg crude protein (CP). Table 1 presents the dietary ingredients, chemical composition of the experimental diets, and chemical composition of BAWA.

BAWA, consisting predominantly of bread with some cookies, was obtained from eateries on the JUST campus. To minimize variation in nutrient composition during the experiment, the quantity required for the entire study was collected as a single batch. The collected BAWA was sun-dried, ground, tested for mycotoxins, and subsequently incorporated into the experimental diets.

Feed refusals were weighed daily, and 10% of the refusals were sampled, dried at 55°C for 48 h, ground to pass through a 1-mm screen, and retained for subsequent analyses. Samples used to determine daily nutrient intake were stored in nylon bags at −20°C until analysis. Lambs were weighed before the morning feeding at the beginning of the experiment and every 2 weeks thereafter. Average daily gain (ADG) was calculated as the difference between final and initial body weights divided by the number of experimental days. Total weight gain and feed efficiency were also determined. Feed efficiency was calculated as total DM intake divided by total body weight gain.

Feed and refusal samples were analyzed according to AOAC procedures [18]. DM was determined by drying samples in a forced-air oven at 100°C for 24 h, CP was determined using the Kjeldahl method, and ether extract (EE) was determined using the Soxtec method. Neutral detergent fiber (NDF) and acid detergent fiber (ADF) were determined using an ANKOM2000 Fiber Analyzer (ANKOM Technology Corporation, Fairport, NY, USA).

Economic efficiency was assessed using diet and body weight gain costs. Diet cost was calculated from the inclusion rate and 2025 price of each dietary ingredient. Cost of gain was calculated by multiplying the feed conversion value by the cost per kilogram of diet. Other production-related costs, including labor, water, electricity, and BAWA processing, were incorporated into the diet and gain cost calculations.

On day 49 of the feeding period, five lambs were randomly selected from each dietary group (n = 5/group) and individually housed in 1.05 × 0.80 m metabolic cages to evaluate nutrient digestibility and N balance. Lambs were allowed 5 days to adapt to the metabolic cages, followed by a 5-day collection period. Daily feed intake and refusals were recorded throughout the collection period.

Feces were collected and weighed daily, and a 10% subsample was retained for subsequent analysis. Urine was collected simultaneously in plastic containers, weighed, and recorded, and a 5% subsample was retained to determine N balance, including N intake, fecal and urinary N losses, N retention (g/day), and percentage N retention. Each urine collection container contained 50 mL of 6 N HCl to minimize ammonia loss. Retained samples were stored at −20°C until analysis.

At the end of the collection period, fecal and urine samples were composited separately for each lamb. Fecal samples were dried at 50°C to constant weight, ground to pass through a 1-mm screen, and analyzed for DM, NDF, ADF, CP, and EE. Urine samples were analyzed for N content using the Kjeldahl method.

At the end of the 63-day data collection period, the lambs were fasted for approximately 18 h, and fasting live body weight was recorded before slaughter. The lambs were transported to the slaughterhouse at approximately 09:00 and humanely slaughtered. Hot carcass weight was recorded immediately after slaughter. Non-carcass components, including the heart, spleen, liver, kidneys, lungs, and trachea, were removed and weighed.

Carcasses were chilled at 4°C for 24 h, after which cold carcass weight and other carcass measurements were recorded. Dressing percentage was calculated as cold carcass weight divided by fasting live body weight × 100. Fat depth (C), eye muscle depth (B), eye muscle width (A), tissue depth (GR), rib fat depth (J), and eye muscle area were subsequently measured. The carcasses were divided into four major cuts: loin, shoulder, leg, and rack. The longissimus dorsi muscle was removed from the loin for meat quality analyses, vacuum-packaged in plastic bags, and stored at −20°C for 14 days until analysis.

After frozen storage, vacuum-packaged longissimus dorsi muscle samples were thawed overnight at 4°C. Meat pH, shear force, cooking loss (CL), water-holding capacity (WHC), and CIELAB color coordinates (L*, a*, and b*) were determined in triplicate. Samples were cut to standardized thicknesses according to the requirements of each analysis.

For pH determination, 2 g of raw meat was homogenized in 10 mL of neutralized 5 mM iodoacetate reagent, and the homogenate pH was measured using a pH/temperature tester (Model 35634-40, Eurotech Instruments, Malaysia). Meat color was measured using the CIELAB system with a Chroma Meter CR-410 (Konica Minolta) on 15-mm-thick slices placed on polystyrene trays, covered with a porous sheet, and maintained at 4°C for 2 h before measurement.

CL was determined using 25-mm-thick meat slices. Samples were weighed before cooking, sealed in plastic bags, and cooked sous vide at 75°C for 90 min. Samples were reweighed after cooking to determine weight loss. Cooked samples were subsequently refrigerated at 4°C overnight for shear force determination and divided into six 1-cm³ cores. Maximum force (kg) required to shear the cooked samples was determined using a Warner–Bratzler shear blade with a triangular slot and sharp edge (GR Manufacturing Co., Manhattan, KS, USA) and a Salter Model 235.

WHC was determined using the method of Grau and Hamm [19]. Briefly, 5 g of raw meat was subjected to a 2,500-g load between quartz plates and filter papers for 5 min. The sample was subsequently removed and weighed. WHC was calculated as follows:

WHC (%) = [(initial weight − final weight)/initial weight] × 100.

The FA composition of meat was analyzed at the Military Quality Control Laboratories, Amman, Jordan, an accredited analytical laboratory operating under standardized quality-assurance procedures. FAs were converted to FA methyl esters (FAMEs) by transesterification as described by Jawasreh et al. [20].

FAMEs were separated and quantified using a Shimadzu GC-2010 Plus gas chromatograph (GC-MS-TQ8040 NX GC-MS/MS, Kyoto, Japan) equipped with a fused-silica capillary DB-WAX column (SP-2380, 100 m × 0.25 mm; Agilent Technologies, USA). Helium was used as the carrier gas, and detection was performed using a flame-ionization detector.

Blood samples were collected from the jugular vein of each lamb on days 1, 30, and 60 before the morning feeding at 08:00. Samples were collected into Vacutainer tubes without anticoagulant for serum separation. Blood samples were centrifuged at 3000 rpm for 30 min, and the separated serum was transferred into tubes and stored at −20°C until analysis.

Serum glucose, triglycerides, cholesterol, creatinine, urea N, low-density lipoprotein (LDL), and high-density lipoprotein (HDL) concentrations were determined. Liver-associated biochemical indicators included aspartate aminotransferase (AST), alkaline phosphatase (ALP), and alanine aminotransferase (ALT). Analyses were performed using commercial kits (Biolabo S.A.S., Maizy, France) according to the manufacturer's instructions, and absorbance was measured using a JENWAY 6105 UV/Vis spectrophotometer (Jenway Ltd., Felsted, Dunmow, Essex, UK).

Data were analyzed using the MIXED procedure of SAS (version 8.1, SAS Institute Inc., Cary, NC, USA). Diet (CON, BAWA100, and BAWA200) was included as a fixed effect, and lamb was included as a random effect. The individual lamb was considered the experimental unit.

Serum biochemical data were analyzed using repeated-measures analysis of variance, with diet, sampling day, and diet × day interaction included in the model. The covariance structure was selected from compound symmetry, first-order autoregressive, and unstructured covariance structures according to the Schwarz Bayesian criterion. Because no significant diet × day interaction was detected, only the main effects were reported.

When a fixed effect was significant (p ≤ 0.05), pairwise t-tests were performed to compare least-squares means. Statistical significance was established at p ≤ 0.05.

The increasing cost of conventional feeds has intensified interest in identifying alternative feed resources that can reduce production costs while supporting livestock productivity and environmental sustainability [21]. In the present study, partial replacement of conventional concentrate ingredients with BAWA reduced dietary costs and, particularly at the 200 g/kg DM inclusion level, improved growth performance and feed efficiency without adversely affecting meat quality or most measured blood biochemical indicators. These findings support the potential use of BAWA as a practical feed resource in small-ruminant production systems where conventional feed ingredients are costly or limited.

The chemical composition of BAWA was sufficiently compatible with the conventional ingredients used in the experimental diets to maintain comparable concentrations of CP, EE, and ME across treatments, averaging 159.3 g/kg, 9.50 g/kg, and 2.36 Mcal/kg, respectively (Table 1). Nevertheless, the chemical composition of BAWA can vary considerably among sources [10, 11, 14]. This variation may reflect differences in the type and proportion of bakery products included, fat content, processing conditions, and material source [10, 11, 13]. This variability can complicate diet formulation and comparisons among studies. Therefore, chemical characterization of BAWA before dietary inclusion remains important to ensure appropriate nutrient formulation and consistency of feeding outcomes [11].

Increasing BAWA inclusion progressively reduced diet cost (Table 1). Compared with the CON diet, inclusion of BAWA at 100 and 200 g/kg DM reduced diet cost by US$34/1,000 kg (7.1%) and US$71/1,000 kg (14.9%), respectively. This finding is consistent with previous studies reporting economic benefits from replacing conventional feed ingredients with bakery or other alternative feed resources [8, 22, 23]. The lower cost observed in the present study is attributable primarily to partial replacement of more expensive conventional ingredients, particularly barley grain, and is consistent with reports that alternative feed resources can reduce feeding expenditure [15, 16, 24, 25].

Lambs fed the BAWA diets had greater DM intake than those fed the CON diet, which was accompanied by greater CP and ME intake (Table 2). ME intake averaged approximately 2.7 Mcal/day in the BAWA groups compared with 2.5 Mcal/day in the CON group. These findings indicate that inclusion of BAWA at 100 or 200 g/kg DM did not reduce diet acceptance under the conditions of the present study. Obeidat [16] similarly reported increased DM intake in growing Black goat kids fed 100 g/kg BAWA compared with controls. Haddad and Ereifej [8] also found that replacement of barley grain with bread byproduct at up to 200 g/kg of diet did not reduce DM intake in growing kids. Similarly, França et al. [11] reported that BAWA inclusion at 250, 500, 750, and 1,000 g/kg dietary DM did not significantly alter nutrient intake in sheep.

Growth performance was greatest in lambs fed BAWA200. This group had higher final body weight, total gain, and ADG than the BAWA100 and CON groups, while feed efficiency and cost of gain also improved. The greater growth response observed with BAWA200 coincided with greater nutrient and energy intake and therefore may, at least in part, reflect the increased availability of dietary nutrients. Almahdawi and Altalib [5] similarly reported higher daily and total weight gain in lambs fed diets containing dried bread residues. Salama et al. [26] also observed favorable effects on live weight gain when lambs received bakery byproducts at 125–500 g/kg DM.

However, previous studies have not reported uniform growth responses. Hindiyeh et al. [22] found reduced growth performance in Awassi lambs when BAWA replaced barley grain at 100, 200, and 300 g/kg dietary DM, whereas Afzalzadeh et al. [24] reported no significant differences in final body weight, daily gain, or total gain in Zandi lambs receiving 0–250 g/kg BAWA. Differences among studies may reflect variation in BAWA composition, dietary formulation, inclusion level, animal breed, age, and processing method. In the present study, the improved productive response at 200 g/kg DM was accompanied by lower feed cost and lower cost per kilogram of gain, indicating a favorable economic effect under the experimental conditions.

Lambs fed the BAWA200 diet had greater DM and CP digestibility than those fed the CON diet, whereas NDF, ADF, and EE digestibility did not differ among dietary treatments. These findings indicate that including BAWA at the tested levels did not impair overall nutrient utilization and that the higher inclusion level was associated with improved DM and CP digestibility. Differences in nutrient intake among treatments may have contributed to these responses.

Mahmoud [13] reported improved CP digestibility and digestible CP in growing lambs fed diets containing 300 and 600 g/kg DM bakery byproducts. Salama et al. [26] likewise reported increased DM digestibility in lambs receiving diets containing bakery byproducts. In contrast, Obeidat [16] found no change in nutrient digestibility when BAWA replaced barley grain at 50 or 100 g/kg DM. França et al. [11] also reported that BAWA inclusion did not affect DM digestibility in sheep. Similarly, Obeidat et al. [27] found no effect of bread byproduct inclusion at 100, 150, or 200 g/kg on nutrient digestibility in Awassi ewes, and Haddad and Ereifej [8] reported no effect of increasing bread byproduct inclusion on DM, organic matter, or NDF digestibility in goat kids. Collectively, these differing results suggest that digestibility responses to bakery byproducts depend on byproduct composition and overall dietary formulation.

BAWA inclusion also influenced N utilization. Lambs fed BAWA100 and BAWA200 had greater N intake, N retained, and percentage N retention than those fed the CON diet, whereas fecal and urinary N excretion did not differ significantly among treatments. The greater N retention may be related to the higher CP intake and, particularly in BAWA200, greater CP digestibility. França et al. [11] reported that BAWA could be included in sheep diets at 250–1,000 g/kg DM without adversely affecting N balance, whereas Obeidat [16] found no differences in N intake or N balance when BAWA was included at 50 or 100 g/kg DM. The present findings therefore indicate that, under the current dietary conditions, BAWA inclusion did not compromise N utilization and was associated with greater N retention.

The greater fasting live weight, hot carcass weight, cold carcass weight, and carcass cut weight observed in the BAWA200 group were consistent with the greater growth performance of these lambs. Improved nutrient intake and digestibility may have contributed to the increased carcass weights, although the present study was not designed to establish a direct mechanistic relationship. Mesenteric and intermuscular fat weights were also greater in BAWA200 than in BAWA100, which may reflect differences in energy intake and nutrient partitioning between the groups.

Obeidat [16] reported that inclusion of BAWA at 50 and 100 g/kg in diets of Black goat kids increased loin cut weight and total lean muscle weight but did not substantially alter other carcass characteristics. In finishing beef steers, Milton and Brandt [28] reported similar hot carcass weights and dressing percentages when dried bakery products replaced corn at 15% and 30% of the diet, although kidney, pelvic, and heart fat increased linearly. Guiroy et al. [29] similarly found no differences in dressing percentage or fat depth between corn-based and bread-byproduct-based diets in growing-finishing beef cattle. Obeidat et al. [27] also reported no differences in carcass weight, internal fat weight, or fat-tail weight in lambs receiving BAWA at 60–250 g/kg DM. These comparisons further indicate that carcass responses to bakery byproducts may depend on inclusion rate, dietary energy supply, species, breed, and overall feeding strategy.

Among the carcass linear measurements evaluated, only tissue depth and rib fat depth differed among treatments (Table 5). Tissue depth was greater in lambs fed BAWA200 than in those fed BAWA100 or CON, whereas rib fat depth was greatest in BAWA200, intermediate in CON, and lowest in BAWA100. These differences are compatible with the greater growth and energy intake observed in BAWA200. Diet, breed, sex, age, and energy intake are recognized factors influencing carcass fat deposition [30]. Obeidat [16] likewise observed greater rib fat depth in goat kids fed 100 g/kg BAWA than in those receiving 50 or 0 g/kg BAWA. In contrast, Milton and Brandt [28] reported only a nonsignificant increase in 12^th-rib fat thickness when bakery products were included in diets for finishing beef steers.

BAWA inclusion did not significantly affect pH, CL, WHC, shear force, or meat color coordinates (Table 6). Thus, the improvements in growth and carcass weight observed with BAWA200 were not accompanied by detectable adverse changes in the measured physicochemical characteristics of the longissimus dorsi muscle.

This finding agrees with Obeidat [16], who reported no adverse effect of BAWA inclusion on meat quality characteristics in growing goat kids. Guiroy et al. [29] similarly found that meat palatability traits were not altered when beef steers were fed a bread-byproduct-based diet. Grossi et al. [31] also reported no unfavorable effect of bakery-derived feed ingredients on carcass-related outcomes in beef cattle. Together, these findings suggest that moderate inclusion of bakery byproducts can be compatible with maintaining desirable meat quality charac-teristics, although responses may differ according to diet composition and animal production system.

Most measured serum biochemical indicators were unaffected by BAWA inclusion, including BUN, glucose, cholesterol, HDL, LDL, triglycerides, creatinine, and ALP. ALT activity was significantly lower in lambs fed BAWA100 and BAWA200 than in those fed CON, whereas AST showed a numerical reduction but did not reach the predefined significance threshold (p = 0.051; Table 7).

The lower ALT activity observed in the BAWA groups indicates a dietary effect on this biochemical indicator; however, this finding should be interpreted cautiously because serum enzyme activity alone does not establish improved hepatic health or reduced hepatocellular stress. Mahmoud [13] reported that inclusion of bakery byproducts at 30% and 60% of dietary DM did not alter AST or ALT activity in lambs. Kaltenegger et al. [32] likewise found no effect of bakery byproduct inclusion as a grain replacement on AST activity in dairy cows, and Obeidat [16] reported no change in liver-associated enzymes in growing goat kids fed BAWA. Further studies are needed to confirm whether the significantly lower ALT and the numerical reduction in AST are related to BAWA inclusion in growing lamb diets.

Dietary BAWA did not significantly affect individual FAs or the total proportions of saturated, mono-unsaturated, and polyunsaturated FAs in lamb meat (Table 8). This finding indicates that replacing part of the conventional concentrate ingredients with BAWA at 100 or 200 g/kg DM did not materially alter the measured FA profile of the longissimus dorsi muscle under the conditions of the present study.

Diet is an important determinant of meat FA composition [33,34], and the lipid sources present in bakery byproducts may vary depending on whether the original products contain dairy fats, vegetable oils, or other fat sources [35]. Nevertheless, in ruminants, extensive ruminal biohydrogenation of dietary unsaturated FAs can reduce the direct relationship between dietary and tissue FA profiles [36]. This process, together with endogenous FA synthesis, desaturation, and elongation, contributes substantially to the final FA composition of ruminant tissues [37–39]. When dietary lipid supply is moderate and broadly comparable among treatments, endogenous metabolism and ruminal biohydrogenation may attenuate diet-related differences in tissue FAs [40, 41].

The absence of significant differences in the meat FA profile is therefore consistent with the similar EE concentrations of the experimental diets and the lack of major differences in total dietary lipid supply. Importantly, the present data indicate that BAWA could partially replace conventional concentrate ingredients without compromising the measured FA composition of lamb meat. However, because BAWA can vary considerably in nutrient and ingredient composition, appropriate quality control remains essential before its use in animal diets. Particular attention should be given to variability in fat composition, salt concentration, and potential mycotoxin contamination.