1. Introduction
Feeding livestock animals plays a crucial role in animal production, and there is growing concern regarding feed raw materials (availabilities and costs) and their direct impacts on livestock productivity and efficiency, which can substantially contribute to the profitability of the livestock industry [
1,
2,
3,
4]. Feedstuffs and nutrition play an important role in the livestock production chain (e.g., a link between crop yield, animal products, and the processing). A higher demand and competition regarding supplies result in stressed market conditions in which feedstuff operators and producers need to continuously balance activities, considering animal performance and consumer demand. Since animal feed contributes to up to 70% of the total operating productivity costs in animal production, and the profits in the chain are dynamic and usually under pressure, improvements in feed quality and feeding management have received much attention in order to optimize productivity and efficiency [
4,
5,
6,
7].
In arid and semi-arid regions, sheep are raised under harsh conditions in terms of shortages in natural resources, lower forage availability, higher feed, and energy costs. Under these conditions, three main feeding systems are used for feeding livestock: cereals plus forages (mainly barley and alfalfa hay), concentrate pellets plus forages, or complete pelleted diets [
7,
8]. Moreover, the quantity and quality of feeds are mainly dependent on the type, proportion, and availability of the feedstuffs that are used, as well as the feed processing, all of which can directly affect the changes in growth rate, carcass yield, meat quality, and composition [
4,
9,
10,
11]. Therefore, the objectives of the study were to investigate the effects of different feeding regimes on productive performance, carcass characteristics, meat quality, and fatty acid contents in growing lambs.
2. Materials and Methods
2.1. Animal Welfare and Ethics Clearance
The research experiment was carried out at King Saud University in Riyadh, Saudi Arabia. All animals and procedures used in this experiment followed to the Animal Welfare Act of Practice for the Care and Use of Animals for Scientific Purposes, with approval from the King Saud University Research Ethics Committee (REC-KSU; Ethics Reference No: KSU-SE-22-26).
2.2. Animals and Management Practices
A total of 75 growing Awassi lambs with average initial body weights of 23.5 ± 2.0 kg, ages of 3 months, and a good healt condition were used in an 84-day trial. The lambs were purchased from a local livestock market 14 days before the beginning of the experiment, and then they were transported using an animal transport truck to the Experimental Station of Animal Production Department, King Saud University. On the day of arrival, the animals were immediately ear tagged, weighed, immunized against comment infections, and treated for both internal and external parasites of sheep. Thereafter, lambs were allocated randomly into 15 replicates of 5 lambs each and housed in shaded group pens (4.0 m long by 3.0 m wide); each pen was provided with a feed trough and water bucket. Lambs were given a two-week adaptation period in these pens. On day 1, lambs were randomly assigned to 1 of 3 dietary treatments (5 groups in each treatment), which were as follows: (1) whole barley grain (60%) plus alfalfa hay (40%; GB-AH; the basal diet); (2) a concentrate pelleted diet plus alfalfa hay (CP-AH); and (3) a complete pelleted diet (CPD). All three feeds were formulated (
Table 1) in order to meet the nutritional requirements for growing lambs according to NRC [
12].
2.3. Feed Analyses
Samples of feed were collecetd frequently every month from each treatment and then pooled (5%) at the end of the study for nutrient composition determination. Feed samples were dried in an oven at 100 °C for 4 h for determination of dry matter (DM) and then incinerated in a muffle furnace at 550 °C for 3 h in order to determine ash content. The crude protein (CD) contained in each sample was measured by using an elemental analyzer. The samples containing neutral and acid detergent fibers (NDF and ADF, respectively) were measured following the methodologies described by Van Soest et al. [
13] and the AOAC [
14], respectively. The fatty acids compositions in feed samples were determined according to the methods described by Barros et al. [
15].
2.4. Growth Rate and Feed Efficiency
All lambs were weighted, using an electronic small-animal scale, on day 1, and then every 2 weeks, to calculate the initial body weight, changes in body weight, and average daily gain. Feed intake for each pen was recorded weekly by measuring the difference between feed offered and feed refused. The feed conversion ratio (FCR) was calculated by dividing the amount of daily intake on average daily gain, and then expressed as kg of DMI to kg BW.
2.5. Blood Sample Processing and Analysis
On days 1, 40, and 84, blood samples (10 mL) were taken from all lambs through jugular venipuncture. Aliquots of 10 mL of blood were placed in 2 Vacutainer tubes devoid of additives in order to obtain serum. The serum concentrations of glucose, non-esterified fatty acid (NEFA), total protein, albumin, urea, creatinine, total cholesterol, high-density lipoprotein (HDL), low-density lipoprotein (LDL), triglyceride (TG), creatine kinase (CK), aspartate aminotransferase (AST), alanine aminotransferase (ALT), and β-hydroxybutyrate were determined according to the manufacturer’s instructions. Commercial kits (Randox Laboratories, Antrim, United Kingdom) and a microplate reader (Multiskan EX, Thermo Fisher Scientific Inc., Waltham, MA, USA) were used for analysis.
2.6. Carcass Characteristics and Meat Quality
On day 84, lambs (13 animals per treatment) were firstly deprived of the diets for 16 h and then slaughtered following the Islamic slaughtering method. During the slaughtering processes, the live body weight, empty and hot carcass, organs (including heart, liver, stomach, kidneys, and tail) were weighted and then stored at 4 °C. After 24 h of slaughter, the carcasses were weighed again to determine cold carcass weight, dressing percentage, and chilling losses for each carcass. Thereafter, the 6th–13th ribs were separated (right side). Then, pH values of meat were determined by using a pH meter. The back fat thickness above the 6th and 10th ribs was recorded by using a digital ruler. The 12th rib from each carcass was used to measure the longissimus thoracis muscle and to determine the meat color value by using a Minolta Chroma Meter (Konica Minolta, CR-400-Japan) with a CIELAB Color System for the color values (L * = lightness; a * = redness; and b * = yellowness). An approximately 300 g sample of muscle (2.5 cm thick) was used to determine the myofibril fragmentation index (MFI) [
16], water-holding capacity (WHC) [
17], and cooking loss (CL) [
18]. A texture analyzer (TA. HD, Stable Micro Systems, Surrey, UK), with a compression-plate attachment was used to determine the meat chewiness, hardness, springiness, and cohesiveness.
2.7. Fatty Acid Analysis
Using the procedure described by Barros et al. [
15], samples of subcutaneous fat were obtained from the ribs and longissimus thoracis muscle of each carcass to evaluate fatty acid contents. In summary, 3 gm of dry meat was thoroughly homogenized in a 60 mL mixture of chloroform and methanol (2:1), followed by filtering by (#4 filter paper, >20 to 25 μm) and an addition of 12 mL of a 0.88% KCl solution. This was centrifuged at 2000×
g for 30 min at room temperature before being transferred to a reaction vial and nitrogen-dried. The dry samples received 0.5 mL of (0.5 N) NaOH in methanol, which was then heated in a heating block for 5 min at 100 °C before being cooled to room temperature. Total fat (g/100 g muscle) was calculated at the end of this process. The extract received 0.5 mL of boron trifluoride in methanol. The extracts were then heated for 5 min at 100 °C before being cooled to room temperature. A total of 0.5 mL of hexane and 1 mL of saturated NaCl were added, and the mixture was centrifuged at 1500×
g for 5 min. The methyl esters of fatty acids found in the upper phase were isolated. The capillary column SP-2340 was then fused in silica using gas chromatography–mass spectrometry (GC–MS) with a flame-ionization detector under the following conditions: initial temperature, 150 °C; initial isotherm, 5 min; the temperature was increased 1 °C per minute up to 160 °C; intermediate isotherm, 11 min, followed by a temperature increase of 7 °C per minute up to 230 °C; final isotherm, 9 min; injector temperature, 200 °C; and detector temperature, 250 °C. The carrier gas was helium (1.5 mL/min). A combination of standard fatty acids was used to identify the fatty-acid peaks (Larodan Fine Chemicals AB). Fatty acids (FAs) were computed and calculated as a proportion of identified fatty-acid methyl esters using chromatogram peak regions.
2.8. Statistical Analyses
All data were analyzed by using a complete randomized design with general linear model procedures of statistical analysis software (SAS Institute Inc., Cary, NC, USA). The statistical model included the type of diet (feeding regime), collection day and animal within treatment, carcass and meat quality characteristics, and fatty acid composition data for the GLM model of SAS. Data are reported with the least square mean (±SE), and the differences between them are significantly considered at p < 0.05.
4. Discussion
In the current study, providing alfalfa hay with concentrate pellets increased feed intake by 14.2% compared with the total mixed ratio diet in pellet diets. The addition of roughage to concentrate pellets improves rumen fermentation and feed intake in fattening animals [
6,
19]. The consumption of roughages with concentrate pellets can encourage rumen motility, increase size and muscular development, and promote rumination [
20,
21]. It is generally accepted that an increased fiber intake results in the physical filling of the rumen and, thus, regulates intake [
22,
23,
24,
25].
Previous studies on productive performance in lambs have indicated that growth rate is increased by feeding ruminant animals total mixed ration diets in a pellet form, rather than concentrate or complete feeds [
26,
27,
28,
29]. This beneficial effect on growth rate is supported by the results of Atti and Mahouachi [
30], who observed an 18.3% increase in body-weight gains in lambs fed high-concentrate pellets compared with that of lambs fed grain-feeding pastures. Similarly, feeding growing lambs pellet diets in the current study resulted in increases in body weight gain (24.2%; 20.25 vs. 16.3 kg) and average daily gain (23.3%; 240.5 vs. 195.0 g/d) compared with lambs fed barley grain and alfalfa hay. The mechanism by which a concentrate pellet diet improves growth rate is mainly increasing the daily feed intake or improving feed efficiency regarding the majority of animals’ nutritional requirements, particularly the micronutrients, which, in turn, have a positive effect on feed efficiency and growth rate.
Although all serum concentrations of biochemical and enzymatic parameters were within the reference ranges of serum metabolic concentrations for sheep reported by Aiello [
31], increases were observed in the glucose and urea concentrations in serum in lambs fed concentrate pellet and alfalfa hay in the current study. There is evidence of alterations in the extent and pathways of utilization for these processed forages [
32,
33]. These increases in circulating glucose and urea to the rumen as metabolic pathways (protein and carbohydrate digestibility) can be caused by feeding livestock animals a long alfalfa hay [
27,
34].
Evidence from previous studies indicates that the quality and quantity of the feeding system can directly and indirectly affect the carcass characteristics and meat quality of ruminants, causing significant improvements by increasing growth rate, providing the nutritional requirements, quickly achieving the target weights, and causing alterations in enzymatic and hormonal secretions, or improvements in immune and health status [
1,
4,
19,
35]. Feeding lambs concentrate pellets increased the carcass variables (including the slaughter weights, weights of wholesale cuts and organs, and linear measurements of carcass and fatness scores) when compared with lambs fed grains [
1,
27,
28,
36]. Similarly, lambs fed pellet diets (either concentrate or complete pellets) in the current study showed increases in slaughter weight (9.4%), hot carcass weight (11.1%), shoulder (10.8%), backfat thickness (16.9%), and the area of longissimus thoracis muscle (16.8%), all of which can be considered as improvements in feed efficiency and growth rate.
Meat quality is a multidimensional concept encompassing organoleptic, nutritional, and microbiological characteristics, which, in turn, can be regulated by a variety of factors that are intrinsic and extrinsic to ruminant animals. Fatty acids content has a vital role in the nutritional value and organoleptic characteristics of meat [
37]. Numerous meat science studies have observed that alterations in fatty acid profile in the meat of livestock animals mainly depend on the type of feed and ingredients used [
4,
6,
30,
36]. For instance, feeding fattening lambs concentrate pellets instead of barley resulted in an increase from 35.0% to 35.9% in the MUFA proportion in the longissimus thoracis muscle [
28]. In addition, the main fatty acids in the longissimus thoracis muscle of lambs were oleic, palmitic, and stearic acids [
28,
38,
39,
40].
Despite the ω-6/ω-3 ratio being only one factor of the pathogenesis of cardiovascular and other diseases, its lower value seems to decrease the risk of chronic diseases [
41,
42]. These results are consistent with the results obtained by the current study that feeding lambs concentrate diets instead of whole cereals causes an increase in unsaturated fatty acids (MUFA and PUFA), and reductions in SFA, AI, and TI, all of which have a positive effect for meat consumers.
5. Conclusions
Under the conditions of this study, the results indicate that feeding growing lambs concentrate pellets instead of whole barley grain improved their growth rate, traits, meat quality, and fatty acid profile, which have important implications for productivity, efficiency, and profitability in the livestock industry. In addition, these results can have beneficial contributions to human health. Therefore, it is better for lamb producers to use concentrate pellets in terms of productive quantities and qualities as well as economic efficiency.