Assessing the influence of feeding olive leaves on the productivity and economic viability of growing Awassi lambs

Abstract The goal was to assess the influence of feeding olive leaves (OL) as a roughage source on nutrient intake, nutrient digestibility, N balance, growth performance and carcass characteristics of growing Awassi lambs. Twenty-four male lambs (initial body weight (BW) = 16.82 ± 0.998 kg; age = 70 ± 1.25 days) were randomly assigned to two isonitrogenous diets; OL at 0 (CON) or 150 (OL150) g/kg of dietary dry matter (DM). Diets were fed ad libitum for a period of 60 days after 7 days of adaptation. Feed intake and refusals were recorded daily. Body weights were recorded at the beginning of the study and at biweekly intervals thereafter. Intake of DM and crude protein was similar (P ≥ 0.05) between the two diets. Feeding OL decreased (P ≤ 0.01) intake of neutral detergent fiber and acid detergent fiber whereas it increased (P = 0.001) intake of ether extract compared with the CON diet. No differences (P ≥ 0.05) were observed in the final BW, average daily gain, and total gain between diets. However, the cost of gain was lower (P = 0.05) in lambs fed the OL diet versus the CON diet. None of the carcass characteristics nor meat quality parameters differed between the two diets. In summary, feeding olive leaves at 150 g/kg did not influence growth performance and carcass characteristics and meat quality but improved the economic value of using such products in diets of growing lambs. In addition, the use of this product has a positive impact on reducing environmental pollution.


Introduction
Livestock, especially sheep, contribute greatly to the economy and food security in the world in general and in Jordan in particular.Sheep meat is an important source of high-quality protein with similar amino acid profiles needed for human consumption.The greatest challenge facing sheep producers, especially in dry and semi-arid regions such as Jordan, is the availability and price of feeds.In the past, pastures were the main source of nutrients for grazing sheep, but in recent years, due to the lack of rain, pastures were negatively affected and are no longer sufficient to supply the nutrient needs of animals.Therefore, farmers began to rely on concentrate feeds to supply the nutritional requirements of animals.Unfortunately, most of these feeds are imported into Jordan, which raises the cost of feeding.To solve part of these problems, livestock producers began to rely on alternative feeds to replace part of the forages in rations.This practice has a positive impact on the cost of feed and at the same time aids in disposing of plant or industrial residues.
Olive tree leaves are one of the good options for use as an alternative feed for feeding sheep.The olive tree is considered one of the oldest and most acclimated trees in the Middle East ecosystem, in particular (Berbel & Posadillo, 2018), and in the world at large.Jordan is one of the top 10 olive-producing countries in the world with approximately 20 million trees and an investment's value of more than $US 1.5 billion (Al Hiary, 2018; https://egyptssp.ifpri.info/2018/04/15/competitiveness-of-olive-crop-in-jordan/accessed on 22 March 2023).Therefore, large quantities of olive tree residues are available, such as olive leaves (OL), which can be introduced into the feed of sheep.Olive trees are planted to obtain olive oil, which constitutes approximately twentyfive percent of the olive fruit.By-products originating from olive harvest season and milling include olive cake (from the oil press) and branches with leaves from pruning trees (Mattioli et al., 2018).Olive cake is a by-product of the oil extraction process and it contains crushed pulp, skin, kernel, stone wall, and some oil (Obeidat, 2017).As for olive cake, many experiments have been conducted to incorporate it as an alternative ingredient in ruminant rations (Aljamal et al., 2021;Aloueedat et al., 2019;Awawdeh et al., 2019;Obeidat, 2017).Olive leaves, however, have not been studied as extensively in ruminant rations despite the fact that they contain many nutrients that may benefit these animals.Hukerdi et al. (2019) reported that OL contains 947, 131, 406, and 39 g/ kg of dry matter (DM), crude protein (CP), neutral detergent fiber (NDF), and ether extract (EE) of dietary DM, respectively.In addition, the same study reported that OL also contains reasonable amounts of phenols and flavonoids making them a good source of antioxidants (Hukerdi et al., 2019).Recently, Hukerdi et al. (2020) reported that complete replacement of alfalfa hay with OL (0, 75, or 150 g/kg of dietary DM) in goats' kids' diets did not affect DM intake, average daily gain (ADG), and final body weight.Similarly, Alomar et al. (2022a, Alomar et al., 2022b) found that nutrient intake and growth performance were comparable when OL replaced 30 or 60% of the wheat straw in the adults lambs' diets.The hypothesis of the current study was that the inclusion of OL in the diets of growing lambs would not impact the growth, whereas it would decrease the cost of gain.Therefore, the objective of this study was to evaluate the effect of introducing olive leaves at 150 g/kg of dietary dry matter on growth performance, carcass characteristics, meat quality, and the cost of diets and gain.

Lambs and experimental procedures
Twenty-four lambs were randomly selected from more than fifty available lambs in the Animal Field of the Research and Training Unit of the Faculty of Agriculture at the Jordan University of Science and Technology (JUST).The chosen lambs were distributed equally into two different diets.Diets were: 1) the control (CON) that contained 0 olive leaves (OL) or 150 g/kg OL (OL150) of dietary dry matter (DM).In order to make OL, a substitute feed that was acquired from the olive oil press, dry enough to be ground (i.e., to attain 90% dry matter), they were exposed to the sun for three to four days.The chemical compositions of the used OL were 889, 90, 296, 222, and 58 dry matter, crude protein, neutral detergent fiber, acid detergent fiber, and ether extract, respectively.When choosing the lambs, their health condition and disease-free status was confirmed by the veterinarian.Then they were injected with ivomec (Merck; Madison, New Jersey, USA) to eliminate the influences of parasites.After it was ascertained that lambs were free of any disease, they were taken to the pens for which the experiment was intended.Lambs were distributed among eight pens (4 m × 4 m) and the sheep were distributed into two groups of forage mixes, free of olive leaves, and the other contained 150 grams per kg of DM.Lambs were distributed on the pens so that each pen contained three lambs and there were four pens for each group.Each barn contained a source of water and fodder.The feed was served in plastic containers in the morning (8:00 AM and 3:00 PM), and the feed and water were supplied ad libitum during the trial.Feed was provided daily during the study period, which extended to 67 days, of which the first 7 days were used to adapt animals to feed and pens and the remaining period for data collection.The diets were formulated to meet the nutrient requirements for growing lambs according to NRC (2007) using Excel software.Samples collected during the study were analyzed at the Department of Animal Production Laboratories.

Digestion and N balance trial
Five lambs from each group were randomly selected on day 42 to assess the digestion of nutrients and the N balance.Lambs were confined in 1.05 × 0.80 m metabolic cages for 10 days (the first five days were utilized for crate adaption, and the remaining five days were used for data collection).Crates were designed to measure feed intake and collect feces and urine.During the collection period, 10 and 5% of the feces and urine, respectively, were saved daily and composite for each lamb and frozen at −20°C for further analysis.Urine samples were collected using plastic containers and filled with 50 mL of 6 N HCL to prevent the loss of ammonia.All samples were ground to pass a 1 mm screen (Brabender OHG Duisburg, Kulturstrase 51-55, type 880,845, Nr 958,084, Germany) and stored for subsequent analysis after being dried at 55°C in a forced-air oven to obtain a consistent weight.Feed, refusals, and feces were examined for DM, CP, NDF, ADF, and EE during the experiment on digestibility and N balance (AOAC, 1990).

Slaughtering procedures
Lambs were slaughtered at the conclusion of the experiment in order to assess the meat's quality and carcass characteristics.After fasting for roughly 18 hours, lambs were processed by qualified staff using standard slaughter techniques (Obeidat, 2021).After the carcasses were chilled at 4°C for 24 h and reweighed, the final live weight, fasted live weight, and hot carcass weight were collected in order to determine the dressing % (cold carcass weight/fasting live weight ratio).Immediately following the slaughter, non-carcass edible components were separated and weighed.Lungs, trachea, heart, liver, spleen, kidneys, renal fat, and testes were among the noncarcass parts.Following Obeidat's (2021) procedures, the following measurements were made on the hanging cold carcasses the following day: carcass length, leg length, gigot width, width behind shoulders, maximum shoulder width, and tissue depth.The corpses were then divided into four pieces (shoulder, rack, loin, and leg cuts).After being sliced, the loin cut was dissected, and the longissimus muscle was immediately removed, vacuum-packed, and kept at −20°C for 2 weeks until the meat quality evaluation.

Meat quality measurements
The CIE L*a*b* coordinates for color, cooking loss, water holding capacity (WHC), and shear force values were measured for meat quality characteristics.In a refrigerator set to 4°C overnight, frozen longissimus muscles that were obtained from the 12/13 rib site) were defrosted while still in their plastic bags.According to Obeidat (2021), each muscle was cut into slices of a certain thickness, and each slice was utilized for a specific meat quality measurement.The color of the meat was assessed using slices that were 15 mm thick using a colorimeter (12 MM Aperture U 59,730-30, Cole-Parameter International, Accuracy Microsensors Inc., Pittsford, NY, USA).On a polystyrene tray, slices were laid out, covered with a permeable film, and allowed to oxygenate for two hours at 4°C.Slices were then weighed before cooking, placed in plastic bags, and cooked in a water bath at 75°C for 90 minutes in order to assess cooking loss.The slices were then reweighed after cooking in order to determine the percentage of water loss.The cooked slices were kept at 4°C overnight before 6 cores with a 1 mm 3 diameter were removed to calculate the shear force measurements.For the purpose of calculating the peak force (kg) needed to shear the samples, meat cores were sheared perpendicular to the direction of the muscle fiber using a Warner-Bratzler (WB) shear blade with a triangular slot cutting edge mounted on a Salter Model 235 (Warner-Bratzler meat shear, G-R Manufacturing Co. 1317 Collins LN, Manhattan, KS 66,502, USA).Using a pH spear (large screen, waterproof pH/temperature tester, double injection, model 35634-40, Eurotech instruments, Malaysia), the pH of the homogenate was tested after thawing by homogenizing 2 g of fresh meat in 10 mL of neutralized 5-mM iodoacetate solution.Using the method outlined by Grau and Hamm (1953), 5 g of raw meat was divided into small pieces and sandwiched between two filter papers and two quartz plates.After being compressed for 5 minutes at a weight of 2500 g, the meat was removed and weighed, and the water holding capacity (WHC) was determined as a percentage of the starting weight.WHC% was equal to the initial weight divided by the final weight by 100.

Statistical analysis
Data were analyzed using the MIXED technique of SAS (version 8.1, 2000, SAS Inst.Inc., Cary, NC, USA).Lamb was the random variable, and the fixed effects included just treatment for all data.To determine the significance and differences between means at (P ≤ 0.05), least square means were utilized.

Results
The ingredients and nutrient content of the two diets are presented in Table 1.The inclusion of OL at 150 g/kg DM slightly lowered the NDF and ADF content compared with the CON diet.The cost of the OL150 diet was reduced when compared with the CON diet.
Intake of DM and CP was similar (P ≥ 0.78) between the two diets (Table 2).Feeding OL decreased (P ≤ 0.01) NDF and ADF whereas increased (P = 0.0003) intake of EE compared with the CON diet.
Between the two diets, there was no difference in nutrient digestibility or nitrogen balance (P ≥ 0.16; Table 3).Final BW, average daily gain, total gain and feed conversion ratio did not differ between diets (P ≥ 0.73; Table 4).Lambs fed the OL diet compared favorably with lambs fed the CON diet in terms of cost of gain (P = 0.05).No differences (P ≥ 0.51) were observed in fasting life weight, cold carcass weight, hot carcass weight, or other carcass characteristics between the two diets (Table 4).Carcass leaner dimensions (P ≥ 0.13) and meat quality traits (P ≥ 0.12) were similar between the two diets as shown in Tables 5  and 6, respectively.No differences were detected in the chemical composition of the meat between the two diets (Table 7).

Discussion
The use of wheat straw to feed the sheep as a source of fiber is considered not economically feasible and it does not contain appropriate levels of nutrients and is highly indigestible in Jordan and some other countries.Therefore, replacing this feed ingredient with agro-industrial byproducts could have a positive impact on the cost of feed and animal productivity.Due to the huge amount of olive trees available in the world, a tremendous amount of by-products from the processing of olives such as the OL are available for animal diets.The chemical composition of the OL indicates that this forage can replace wheat straw.Olive leaves contained greater CP (78 vs. 30 g/kg) and EE (61 vs. 2 g/kg) than wheat straw.However, NDF and ADF content was lower (29.4 and 21.9 vs. 689 and 380 g/kg) compared with wheat straw.These findings assure that the use of OL to replace part of the wheat straw, the forage ingredient in diets of growing lambs and livestock, could be done without affecting feed intake and nutrient digestibility.The authors did not pay attention to the NDF and ADF changes when replacing wheat straw by OL in the OL150 diet when compared to the CON diet.The rationale for this formulation was for the diets to be isonitrogenous.Therefore, the nutrient composition of the two diets was similar except for the NDF and ADF contents due to the lower level of NDF and ADF in the OL versus the wheat straw.Mattioli et al. (2018) reported that OL contained 923, 107, 350, 276, and 22.4 g/kg DM for DM, CP, NDF, ADF, and EE, respectively.However, Hukerdi et al. (2019) indicated that the chemical composition of the OL was 947, 131, 406, and 39 g/kg DM for DM, CP, NDF, and EE, respectively.Parallel to our findings, previous studies reported that the nutrient content of OL was variable among different research studies.This phenomenon could be due to the differences in olive tree breeds, age of trees, and source of leaves indicating that this cheap source of forage must be analyzed before it can be incorporated in the diets of ruminants.
In the current, using OL at 150 g/kg in the diet of growing lambs reduced the cost of the diet by 12 percent compared with the control diet.Such findings agreed with results obtained in our lab when the conventional ingredients were replaced by olive cake (Obeidat, 2017), black cumin meal (Obeidat, 2020), lupin grains (Ata & Obeidat, 2020), dried distillers grain with solubles (Alshdaifat & Obeidat, 2019;Hatamleh & Obeidat, 2019), sesame meal (Obeidat et al., 2019), or OL (Ismail & Obeidat, 2023).The fact that these feeds reduced the cost of diets was due to their cheaper prices compared with the conventional ingredients showing the economic advantages of using this by-product in feeding growing lambs.
In the current study, the inclusion of OL at 150 g/kg in the diet of growing lambs did not affect the intake of DM and CP.However, the intake of NDF and ADF decreased in the OL150 diet compared with the CON diet.The reason for these findings was due to the lower content of fiber in the diet of OL150.Consistent with results obtained in the current study, Hukerdi et al. (2020) reported similar DM intake when OL was fed to goat kids at 75 and 150 g/kg.Fegeros et al. (1995) reported also those lactating ewes fed ammonium-treated OL had similar DM intake compared with ewes fed alfalfa hay.Recently, Ismail and Obeidat (2023) found that nutrient intake did not differ among growing lambs fed 50 or 100 g/kg OL of dietary DM.Previous studies showed that feeding OL at different levels did not negatively impact DM and other nutrient intake (Alomar et al., 2022a;Fegeros et al., 1995;Hukerdi et al., 2020;Ismail & Obeidat, 2023).
For lambs fed the OL150 diet as opposed to the CON diet, the cost of gain was lower.The OL was presumably less expensive to obtain than wheat straw, which contributed to the cost savings.Producers of livestock should take this observation into account because it will enhance the profitability of growing sheep.Similar findings were found in other research that examined the economic effects of feeding animals agro-industrial by-products (Aloueedat et al., 2019;Alshdaifat & Obeidat, 2019;Obeidat, 2020;Obeidat et al., 2019).In addition to these beneficial effects, the use of OL and other by-products as alternative feeds in livestock diets would diminish environmental pollution (Serrapica et al., 2019), reduce the feeding costs and the cost of gain, and maximize profits (Ismail & Obeidat, 2023).
When Awassi lambs were fed diets including sun-dried olive cakes and acid-treated sun-dried olive cakes, there were no variations in digestibility and N balance, confirming our findings (Awawdeh & Obeidat, 2013).The perceived digestibility of the OL in vivo is influenced by preservation procedures and wood content (Molina-Alcaide & Yáñez-Ruiz, 2008).Delgado-Pertı ́ñez et al. (2000) reported that when OL was dried, the digestibility of DM and CP reduced.When fresh OL was treated with an ammonia solution, Fegeros et al. (1995) discovered that the apparent digestibility of the EE, CP, and NDF rises.However, total condensed tannins in OL (9.49 mg/g DM) are higher than in wheat straw (0.04 g/mg DM) (Molina-Alcaide & Yáñez-Ruiz, 2008;Silanikove et al., 1996).The modest increase in condensed tannins had no effect on digestibility or nitrogen balance.Overall, the inclusion of OL at 150 g/kg DM did not influence nutrient digestibility and N balance.
Feeding olive leaves had no effect on live weight, hot and cold carcass weights, dressing percentages, non-carcass component measurements, or carcass weight.The tissue percentages, meat-tobone ratio, and meat-to-fat ratio of dissected loin slices were all equivalent.Tissue depth and fat depth were not different between the two treatments on varied cuts.The results for ADG, nutritional intakes, and digestibilities may explain the lack of changes in carcass features, carcass cuts, loin cut tissue percentages, and carcass tissue dimension measures.However, based on earlier research on Awassi sheep, the carcasses produced in this study were thought to be of similar meat quality and features.
The dressing percentages obtained in this investigation were similar to those reported by Obeidat (2020) and Hatamleh and Obeidat (2019) for Awassi ram lambs slaughtered at identical weights.Carcass characteristics and dressing percentages were found to be extremely satisfactory at the authorized slaughter weights, according to their findings.Fat depth measurements were also consistent with our findings and within the permissible range for marketing Awassi lambs.This could be owing to differences in the age and breed of the lambs employed in their study, as well as differences in dietary ingredients, dietary crude protein content, animal production stage, and the basal level of weight gain.
The measured meat quality indicators in this study were similar among treatments.In terms of cooking loss and WHC, there were no changes among lamb samples that consumed the two treatment diets.The loss of juiciness to the palate is directly proportional to the degree of shrinking during cooking.Cooked meat contains two organoleptic components that contribute to its juiciness.The first is the sensation of wetness, which is caused by the sudden release of meat fluid; the second is the sensation of persistent juiciness, which is caused by the stimulatory action of fat on salivation (Weir, 1960).The percentage of water lost, WHC, and shear force obtained in this study were all regarded as satisfactory.Shear force levels of 3.6 kg/cm 2 or less, according to Field et al. (1971), were regarded to be within the acceptable softness range for goat and sheep meat.

Conclusion
The findings suggested that adding olive leaves to the diet of developing Awassi lambs at 0 or 150 g/ kg had no effect on nutrient intake, nutrient digestibilities, nitrogen balance, growth performance, carcass features, or meat quality.The consistency in nutrient intake and digestibility may explain the lack of difference across treatments.As a result, more research is needed to assess the impact of adding olive leaves to diets of varied quantities and compositions.The outcomes of this study will assist livestock producers in overcoming feed availability challenges and lowering production costs and as a result it could also potentially enhance the profit margin for livestock producers.