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. 2018 Jan 29;96(2):487–497. doi: 10.1093/jas/sky024

Substituting ground woody plants for cottonseed hulls in lamb feedlot diets: carcass characteristics, adipose tissue fatty acid composition, and sensory panel traits

Christopher R Kerth 1,✉, Kayley R Wall 1, Stephen B Smith 1, Travis Raymond Whitney 2, Jessica L Glasscock 2, Jason T Sawyer 3
PMCID: PMC6140952  PMID: 29385610

Abstract

Effects of using ground woody plants in Rambouillet wether lamb (n = 48) feedlot diets on carcass characteristics, adipose tissue fatty acid composition, and sensory panel traits were evaluated. In a randomized design study with two feeding periods (period 1 = fed a 70% concentrate diet from days 0 to 27; period 2 = fed an 86% concentrate diet from days 28 to 57), lambs were individually fed six diets that differed only by roughage source (n = 8 animals/treatment; initial BW = 32.9 ± 3.2 kg): cottonseed hulls (CSH; control) or ground wood consisting of either redberry (RED), blueberry (BLUE), one-seed (ONE), or eastern red cedar (ERC) Juniperus spp., or Prosopis glandulosa (MESQ). After 57 d, the lambs were humanely harvested and after chilling (2 ± 1 oC) 24 h, carcasses were evaluated for carcass traits. At 48 h postmortem, the longissimus thoracis (LT) was removed from the left side of the carcass, and after freezing for no more than 3 mo, were thawed for 24 h, cooked, and evaluated by a trained sensory panel. Additionally, volatile aroma chemicals on the LT were determined by gas chromatograph/mass spectrometer/olfactory (GC/MS/OF, respectively) analyses. Lamb HCW was greater (P = 0.01) for lambs fed CSH compared with all other diets, but lambs had similar (P > 0.08) LM area, back fat thickness, leg circumference, and body wall. Neither adipose tissue fatty acid composition (P > 0.08) nor trained sensory panel evaluation (P > 0.18) was affected by finishing diet roughage source. Of the 81 volatile aroma compounds found in the grilled lamb chops, only seven were affected (P < 0.05) by dietary roughage source and included 1-pentanol (a sweet, pleasant aroma), heptenal (a fishy aroma), pentanal (fermented, bready aroma description), 1-(1H-pyrol-2yl)-ethanone (caramel-like), 2-heptanone (cheesy, banana, fruity aromatic), 6,7-dodecanedione (unknown aroma), and butanoic acid (a sweaty, rancid aroma). The addition of any of four species of juniper or mesquite may be substituted for CSH without negatively affecting carcass fat and muscling, fatty acid, or sensory traits.

Keywords: feedlot, juniper, lambs, mesquite, sensory, volatile aroma compounds

INTRODUCTION

Widely fluctuating costs of feed ingredients has made finding alternatives to traditional sources of feedstuffs a priority for animal producers today. Utilizing plant material that is otherwise thought a nuisance could be a good method to reduce feed costs. Juniperus and Prosopis spp. fit this description as it is invasive in pastures and can effectively be incorporated into sheep (Stewart et al., 2015; Whitney et al., 2014, 2017a), goat (Glasscock et al., 2015), and cattle (Marion, et al., 1957; Whitney et al., 2017b) feed. Furthermore, the juniper genus is widely distributed and covers more than 50 million ha in the western United States (Van Auken and Smeins, 2008).

Whitney et al. (2011) reported that substituting redberry juniper (Juniperus pinchotii) for cottonseed hulls (CSH) resulted in no impact on carcass characteristics, but a linear increase in myristic, palmitoleic, and arachidonic acids and a linear decrease in stearic acid as the amount of juniper in the diet increased. Additionally, off-flavor scores increased linearly with increasing amounts of juniper in the diet, but only a 0.2 sensory unit difference was detected. This increase in off-flavor was likely attributed to the presence of secondary compounds in the leaves of the juniper such as monoterpenoids (Bailey et al., 1994). Nevertheless, Whitney and Smith (2015) replaced up to 100% of the hay in lamb feedlot diets and found no difference in sensory off-flavor. In fact, feeding increased levels of redberry juniper in the place of hay linearly increased the juiciness, tenderness, and flavor intensity of lamb chops. To this point, no known literature exists that evaluates the influence of different species of juniper or mesquite in lamb feedlot finishing diets on carcass traits, fatty acids, or sensory properties of lamb meat. Thus, we hypothesized that feeding any of four different species of juniper or mesquite to replace CSH would not affect lamb carcass traits, fatty acids, or sensory traits.

MATERIALS AND METHODS

The experimental protocol was approved by the Texas A&M University Institutional Animal Care and Use Committee. Detailed descriptions of animals, management, woody plant harvesting and processing, nutrient analysis and composition, lamb growth performance, blood serum chemistry, and rumen fluid characteristics were reported in a companion paper (Whitney et al., 2017a).

Animals and Management

Rambouillet wether lambs (48 total lambs; approximate age = 4 mo; initial BW = 32.9 ± 3.2 kg) had previously been on pasture; thus, a 19 d feedyard adaptation period was used. Unshorn lambs received an ear tag, subcutaneous clostridial vaccine (Vision 7 with SPUR, Intervet, Inc., Omaha, NE), and an oral dose of levamisole (Prohibit, AgriLabs, St. Joseph, MO). During the first 12 d of the adaptation period, lambs were group-fed and had ad libitum access to oat hay, which was supplemented with a 60% concentrate diet. Seven days before study initiation, lambs were weighed, stratified by BW, and randomly assigned to an individual, completely covered dirt pen (2.44 × 2.97 m) with automatic watering system and feed bunk. Each lamb was also randomly assigned to a treatment diet (n = 8 lambs/diet) that differed only by roughage source: either CSH or a ground woody product consisting of either J. pinchotii (redberry juniper; RED), Juniperus ashei (blueberry juniper; BLUE), Juniperus monosperma (one-seeded juniper; ONE), Juniperus virginiana (eastern red cedar; ERC), or Prosopis glandulosa (honey mesquite; MESQ).

During period 1 (days 0 to 27), lambs were fed their respective 70% concentrate treatment diet. All mixed diets were nonagglomerated, contained 22 g of monensin/metric ton of feed (Rumensin 90, Elanco, Indianapolis, IN), and fed once daily at 0900 h with an approximate allowance of 10% refusal. Lambs were then transitioned over 4 d into period 2 (days 28 to 57), onto their respective 86% concentrate treatment diet by gradually replacing the period 1 diet with the period 2 diet.

Sample Collection and Measurements

Woody plant harvesting, feed collection, and analysis.

The entire above-ground biomass from mature Juniperus spp. (juniper; including leaves) and mature P. glandulosa (mesquite; excluding leaves) trees was harvested separately by species, chipped, and mechanically dried to approximately 93% DM in a drying trailer. Chipped material was hammermilled to pass a 4.76 mm sieve (Sentry, model 100; Mix-Mill Feed Processing Systems, Bluffton, IN), bagged, and stored under cover. Subsamples were dried to constant weight in a forced-air oven at 103 °C to determine DM concentration.

Nutritive characteristics of woody plants were evaluated using random subsamples of mechanically dried and hammermilled (4.76 mm screen) woody plants. Subsamples of CSH, sorghum grain, and dried distillers grains with solubles (DDGS) were collected six times throughout the trial; the first three and last three subsamples were combined separately by period for analysis (Table 1). Three random subsamples of treatment diets were collected during both periods, combined by period, and analyzed separately (Table 2). These samples were dried at 55 °C in a forced-air oven (model 630, NAPCO, Portland, OR) for 48 h, ground through a 1 mm screen (Wiley mill, Arthur H. Thomas Co., Philadelphia, PA), and stored at −20 °C. Nitrogen was analyzed by a standard method (Method 990.03; AOAC, 2006) and CP calculated as 6.25 × N. The NDF and ADF were analyzed according to the procedures of Van Soest et al. (1991), which were modified for an Ankom 2000 Fiber Analyzer (Ankom Technol. Corp., Fairport, NY) using α-amylase and Na sulfite. In addition, N was analyzed in residue remaining after the ADF procedure and multiplied by 6.25 to determine acid detergent insoluble CP (ADICP). Standard methods were used to analyze lignin (AOAC 973.18; AOAC, 2006), crude fat (Method 2003.05; AOAC., 2006) and ash (Method 942.05; AOAC, 2006). For individual mineral analysis, samples were first digested with a Microwave Accelerated Reaction System (MARS6) and then analyzed by a Thermo Jarrell Ash IRIS Advantage HX Inductively Coupled Plasma Radial Spectrometer (Thermo Instrument Systems, Inc., Waltham, MA). Condensed tannins in the juniper, mesquite, CSH, and sorghum grain were assayed for soluble, protein-bound, and fiber-bound fractions by methods described by Terrill et al. (1992); samples were oven dried and standards prepared for each individual ingredient as recommended by Wolfe et al. (2008).

Table 1.

Chemical composition (% DM basis) of cottonseed hulls, sorghum grain, and dried distillers grains with solubles (DDGS), and ground Juniperus spp. and P. glandulosa used in the treatment diets

Itema Ingredientb
Cottonseed hulls Sorghum grain DDGS J.pin J.ash J.mon J.vir P.glan
Nutrient composition
 DM, % 92.3 92.6 91.8 93.9 93.8 95.4 93.8 91.9
 CP, % 3.5 11.9 30.4 2.9 2.8 2.5 3.8 5.7
 ADICP, % 3.2 1.5 1.3 1.5 1.6 1.4 1.8 2.5
 aNDF, % 85.2 7.0 30.4 62.1 65.0 71.0 68.0 74.7
 ADF, % 62.1 5.3 12.9 49.4 52.1 57.9 55.8 57.8
 Lignin, % 16.4 0.9 2.9 19.4 21.2 23.2 21.7 17.9
 Crude fat, % 0.6 3.1 8.7 3.2 3.2 4.5 4.1 6.2
 Ash, % 3.6 3.6 4.7 4.9 4.8 3.4 4.4 4.3
 Ca, % 0.12 0.04 0.07 1.31 1.53 1.27 1.37 1.42
 P, % 0.04 0.21 0.88 0.04 0.04 0.03 0.06 0.03
 S, % 0.06 0.14 0.93 0.07 0.04 0.04 0.05 0.06
 K, % 0.99 0.34 1.33 0.33 0.16 0.11 0.24 0.35
 Mg, % 0.14 0.12 0.38 0.06 0.04 0.03 0.1 0.02
 Na, % 0.01 0.01 0.31 1.25 0.01 0.01 0.01 0.01
CT, % 31.1 – –
 Extractable 1.4 0 – 2.8 3.2 1.8 2.4 0.9
 Protein-bound 1.8 0 – 2.1 2.3 1.9 2.3 3.8
 Fiber-bound 0.2 0 – 0.0 0.0 0.0 0.0 0.1
 Total 3.2 0 – 4.9 5.5 3.7 4.7 4.7
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These data have previously been reported in a companion paper (Whitney et al., 2017a).

aADICP = acid detergent insoluble CP; CT = condensed tannins.

bJ.pin = Juniperus pinchotii; J.ash = J. ashei; J.mon = J. monosperma; and J.vir = J. virginiana (entire above-ground biomass); P.glan = Prosopis glandulosa (entire above-ground biomass excluding leaves); DDGS = corn–dried distillers grains with solubles produced from corn ethanol production (POET, Sioux Falls, SD).

Table 2.

Ingredient and chemical composition (% DM basis) of treatment diets

Itema Dietb
Period 1 Period 2
CSH RED BLU ONE ERC MESQ CSH RED BLU ONE ERC MESQ
Cottonseed hulls 30.0 – – – – – 14.0 – – – – –
Ground woody product – 30.0 30.0 30.0 30.0 30.0 – 14.0 14.0 14.0 14.0 14.0
DDGS 40.0 40.0 40.0 40.0 40.0 40.0 40.0 40.0 40.0 40.0 40.0 40.0
Ground sorghum grain 21.7 21.7 21.7 21.7 21.7 21.7 37.6 37.6 37.6 37.6 37.6 37.6
Molasses, cane 4.0 4.0 4.0 4.0 4.0 4.0 4.0 4.0 4.0 4.0 4.0 4.0
Limestone 2.2 2.2 2.2 2.2 2.2 2.2 2.3 2.3 2.3 2.3 2.3 2.3
Ammonium chloride 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5
Salt 0.6 0.6 0.6 0.6 0.6 0.6 0.6 0.6 0.6 0.6 0.6 0.6
Mineral premix 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0
Nutrient composition, %
 DM 91.9 90.8 90.6 91.6 91.4 91.2 90.6 89.6 89.9 90.1 90.0 89.7
 CP 18.2 18.5 18.6 17.3 18.5 18.8 19.1 19.8 19.1 18.5 19.3 19.7
 aNDF 32.6 34.8 33.2 37.9 34.6 36.6 25.4 25.7 23.1 26.3 25.6 26.6
 ADF 16.4 19.9 19.0 22.7 20.4 19.7 13.5 13.6 12.9 14.7 13.3 12.1
 Ca 1.2 1.4 1.4 1.3 1.3 1.4 1.2 1.4 1.3 1.3 1.2 1.4
 P 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5
 Ca:P 2.3 2.7 2.9 2.8 2.9 3.0 2.4 2.7 2.8 2.7 2.5 2.9
 Ash 8.1 8.0 8.5 7.7 8.5 8.4 7.8 9.1 8.3 8.0 8.1 8.5
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These data have previously been reported in a companion paper Whitney et al., 2017a).

aDDGS = dried distillers grains with solubles were a byproduct of corn ethanol production (POET, Sioux Falls, SD); Mineral premix = NaCl, KCl, S, MnO, ZnO, vitamins A, D, and E, CaCO3, cottonseed meal, cane molasses, and animal fat.

bDuring period 1 (days 0 to 27), lambs were fed a 70% concentrate diet. Lambs were transitioned over 4 d into period 2 (days 28 to 57) onto an 86% concentrate diet. Treatment diets were nonagglomerated and ingredient composition differed only by roughage source; either cottonseed hulls (CSH) or ground woody products (RED = J. pinchotii, BLUE = J. ashei, ONE = J. monosperma, ERC = J. virginiana, or MESQ = P. glandulosa). Juniperus (entire above-ground biomass) and Prosopis (entire above-ground biomass excluding leaves) species were chipped, dried, and hammermilled to pass a 4.76 mm sieve. Monensin (Rumensin 90, Elanco, Indianapolis, IN) was added to each diet at 22 g/t of feed.

Carcass characteristics and feed and adipose tissue fatty acid composition.

Lambs were harvested after a 24 h fast, shrunk BW and HCW recorded, and carcasses chilled at 2 ± 1 °C. At 48 h postmortem, each carcass was cut through the vertebrae and longissimus thoracis (LT) between the 12th and 13th ribs for carcass evaluation. Carcasses were analyzed to determine LM area, backfat thickness at the 12th rib (BF), dressing percent (HCW/shrunk BW just prior to harvest × 100), yield grade (0.4 + (10 × BF in/2.54)), body wall thickness, and circumference of both legs across the femur-acetabulum joints on the intact carcass (USDA, 1997). At 48 h postmortem, the LM was removed from the left side of each carcass by deboning the LM from the thoracic vertebrae according to procedures of the North American Meat Processors (NAMP, 1997). Five chops, 2.54 cm thick, were cut starting from the posterior end; the first chop was designated for fatty acid methyl ester (FAME) analysis, cut to straighten the LM face, vacuum-packaged separately, and stored at −80 °C until analyzed. Subsequently, four 2.54-cm-thick chops were serially cut for sensory analysis, labeled, vacuum packaged separately, and stored at −10 °C until analyzed. A subsample was collected from a cross section of the LM, including any residual intermuscular fat, and pulverized in liquid nitrogen. Total lipids were extracted by a modification of the method of Folch et al. (1957). Adipose tissue (100 mg) was extracted in chloroform:methanol (2:1, vol/vol) and FAME prepared as described by Morrison and Smith (1964), modified to include an additional saponification step (Archibeque et al., 2005). The FAMEs were analyzed using a Varian gas chromatograph (GC; model CP-3800 fixed with a CP-8200 autosampler; Varian, Inc., Walnut Creek, CA). Separation of FAME was accomplished on a fused silica capillary column CP-Sil88 (100 m long × 0.25 mm i.d.; Chrompack, Inc., Middleburg, the Netherlands; helium as carrier gas [flow rate = 1.2 mL/min]). After 32 min at 180 °C, oven temperature was increased at 20 °C/min to 225 °C and held for 13.75 min; total run time was 48 min. Injector and detector temperatures were at 270 °C and 300 °C, respectively. Individual fatty acids were identified using genuine external standards (Nu-Chek Prep, Inc., Elysian, MN).

Sensory panel evaluation.

A trained sensory panel (six members; Cross et al., 1978) evaluated chops cut from the loin section (American Meat Science Association, 1995) and completed within 1 d. Randomly selected chops were allowed to thaw for 24 h at 2 ± 1 °C and cooked on a clam-shell style grill for 7 min, resulting in a final internal temperature of 71 °C (Kerth et al., 2003). Samples were trimmed to less than 0.64 cm of outside fat and connective tissue, cut into 1.3 cm × 1.3 cm chop portions, and placed in warming pans until served to panelist. Chop samples were evaluated for initial and sustained juiciness, initial and sustained tenderness, and flavor intensity on a scale of 1 to 8, where 1 = extremely dry, tough, and bland, and 8 = extremely juicy, tender, and intense, respectively. Chops were also evaluated for off-flavor on a scale of 1 to 4, where 1 = extreme off-flavor and 4 = no off-flavor. Samples from each chop were evaluated by panelists that were secluded in partitioned booths with controlled levels of red incandescent light. A “warm-up” sample chop was served at initiation of each sensory session, followed by 6 to 8 samples per session. Panelists were instructed to cleanse their palate with a salt-free cracker and water before each sample. Panelists’ sensory scores for each trait were averaged for each animal and the average score was used for statistical analyses.

Gas chromatography/mass spectroscopy.

After steaks were cooked, all external fat was removed and each steak was cut into pieces as would be done for sensory (1.3 cm × 1.3 cm × steak thickness cubes). Twelve pieces were placed in a 473 mL glass jar with a Teflon lid and placed in a water bath held at 60 oC to approximate normal holding temperature for sensory analyses. After equilibrating for 20 min, a solid-phase microextraction Portable Field Sampler (Supelco 504831, 75 μm Carboxen/polydimethylsiloxane [PDMS], Sigma-Aldrich, St. Louis, MO) was inserted through the lid and the headspace above each meat sample in the glass jar was collected for 2 h. Upon completion of collection, the solid-phase microextraction apparatus was removed from the jar and injected into the injection port of a GC (Agilent Technologies 7920 series GC, Santa Clara, CA) where the sample was desorbed at 280 °C for 3 min. The sample was then loaded onto the multidimensional GC into the first column (30 m × 0.53 mm ID/BPX5 [5% phenyl polysilphenylene-siloxane] × 0.5 μm, SGE Analytical Sciences, Austin, TX) using helium as the carrier gas. Through the first column, the temperature started at 40 °C and increased at a rate of 7 °C/min until reaching 260 °C. Upon passing through the first column, the compounds passed on to a second column (30 m × 0.53 mm ID [BP20 − polyethylene glycol] × 0.50 μm, SGE Analytical Sciences). The GC column then went to a three-way valve split to two olfactory (OF) ports and a third to a mass spectrometer (MS; Agilent Technologies 5975 series MS, Santa Clara, CA) for quantification and identification, using the Wiley Chemical Library. Only those volatile chemical compounds present during an aroma event detected by the GC-MS and OF operator were retained for analyses.

Statistical Analysis

Data for all traits were analyzed using JMP version 13.0 (SAS Inst., Inc., Cary, NC, USA) using ANOVA for a completely randomize design with finishing diet (CSH, RED, BLUE, ONE, ERC, or MESQ) as a fixed treatment effect. Least squares means were generated and separated using Student’s t-test when a significant (P < 0.05) F-test was indicated.

RESULTS AND DISCUSSION

Carcass Characteristics

Lamb carcass characteristics are reported in Table 3. Hot carcass weight was greater (P = 0.01) for lambs that were fed CSH compared with all other diets. No other carcass traits were affected (P > 0.08) by finishing diet. These results reflect previous work that has been done using ground juniper as a roughage source. When ground oat hay was replaced by redberry juniper (Whitney and Smith, 2015), a quadratic effect was found in both shrunk BW and HCW and both of these traits were decreased when comparing juniper diets to the control DDGS finishing diet. However, Whitney et al. (2011) reported that substituting CSH with dry juniper leaves had no impact on hot carcass weight, nor any other carcass trait. Collectively, these data indicate that feeding ground juniper or mesquite in finishing diets of lambs does not have a detrimental effect on carcass traits. Additionally, all carcasses had acceptable quality and would be either acceptable or receive a premium based on a quality grid of Yield Grade 1 and 2 carcasses for the Mountain States Lamb Cooperative (Boland et al., 2007).

Table 3.

Effects of replacing cottonseed hulls with ground woody products on lamb carcass characteristics

Itema Dietb
CSH RED BLUE ONE ERC MESQ SEM P > F
Shrunk BW, kg 46.7 44.1 44.9 45.0 41.7 43.7 1.30 0.15
HCW, kg 23.4c 20.9d 21.2d 21.0d 20.0d 20.4d 0.65 0.01
LM area, cm2 15.6 16.1 16.5 16.4 14.1 15.9 0.66 0.13
Backfat, cm 0.5 0.4 0.4 0.3 0.4 0.3 0.82 0.58
Yield grade 2.5 2.0 1.8 1.8 1.8 1.7 0.32 0.58
Body wall, cm 1.3 1.2 1.2 1.3 1.1 1.0 0.12 0.45
Leg circumference, cm 44.5 45.0 45.1 43.4 43.0 45.1 0.66 0.08
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During period 1 (days 0 to 27), lambs were fed a 70% concentrate diet. Lambs were transitioned over 4 d into period 2 (days 28 to 57) onto an 86% concentrate diet. Within row means with a different superscript than the control diet (CSH) differ (P < 0.05).

aDressing % = (HCW/shrunk BW just prior to harvest) × 100; Yield grade = 0.4 + (10 × BF, cm/2.54).

bTreatment diets were nonagglomerated and ingredient composition differed only by roughage source; either cottonseed hulls (CSH) or ground woody products (RED = J. pinchotii, BLUE = J. ashei, ONE = J. monosperma, ERC = J. virginiana, or MESQ = P. glandulosa). Juniperus (entire above-ground biomass) and Prosopis (entire above-ground biomass except for leaves) species were chipped, dried, and hammermilled to pass a 4.76 mm sieve.

c,dMeans in the same row lacking a common superscript difference (P < 0.05).

Adipose tissue fatty acid composition

No individual fatty acids, nor classifications of fatty acids measured in LM chops, were affected (P > 0.08) by diet (Table 4). Numerous studies have been published that describe the manipulation of the fatty acid composition of animal meat (Nurnberg et al., 1998; Demeyer and Doreau, 1999; Wood et al., 1999). Data reported in the current study parallel to those of Whitney et al. (2011) who found that, with the exception of CLA and arachidic acid (both of which increased linearly with an increase in the amount of juniper in the diet), no other fatty acid was affected by the addition of juniper to lamb diets. Chaves et al. (2008) fed juniper essential oil to growing lamb and reported no differences in fatty acid profile in either subcutaneous fat or liver.

Table 4.

Effects of replacing cottonseed hulls with ground woody products on lamb adipose tissue fatty acid composition

Itema Dietb
CSH RED BLUE ONE ERC MESQ SEM P > F
 Myristic acid (14:0) 2.2 2.4 2.3 2.5 2.3 2.6 0.28 0.93
 Palmitic acid (16:0) 24.0 24.5 23.5 25.4 24.6 21.5 1.03 0.10
 Palmitoleic acid (16:1n-7) 0.9 1.0 0.9 1.0 1.0 0.8 0.15 0.94
 Stearic acid (18:0) 15.7 17.8 15.4 16.6 16.5 15.3 0.98 0.38
 18:1trans-11 2.7 2.6 3.0 3.2 2.9 3.6 0.43 0.51
 Oleic acid (18:1n-9) 40.5 35.4 38.2 36.7 37.9 37.0 1.67 0.31
 Cis-vaccenic acid (18:1n-7) 0.9 0.8 0.6 0.4 0.5 0.8 0.16 0.20
 Linoleic (18:2n-6) 7.1 7.5 7.9 7.0 7.4 7.9 0.67 0.85
 α-Linolenic (18:3n-3) 0.3 0.4 0.3 0.3 0.3 0.4 0.03 0.28
 Arachidonic acid (20:4n-6) 2.1 2.1 2.1 1.7 2.1 2.3 0.22 0.60
SFA, % 43.6 47.3 43.6 46.6 45.4 42.4 1.39 0.08
SFA, no 18:0, % 27.3 28.4 27.3 29.2 28.2 25.8 1.05 0.24
MUFA, % 46.2 42.0 45.2 43.4 44.0 45.7 1.61 0.37
PUFA, % 10.2 10.8 11.2 10.1 10.6 11.9 1.02 0.78
MUFA/(MUFA + SFA), % 51.9 46.9 50.8 48.3 49.2 51.9 1.58 0.15
PUFA/SFA 0.23 0.23 0.26 0.22 0.23 0.28 0.024 0.44
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During period 1 (days 0 to 27), lambs were fed a 70% concentrate diet. Lambs were transitioned over 4 d into period 2 (d 28 to 57) onto an 86% concentrate diet. Within row means with a different superscript than the control diet (CSH) differ (P < 0.05).

aFatty acids were extracted from LM; SFA = saturated fatty acids (C14:0 to C24:0); MUFA = monounsaturated fatty acids (C15:1 to C18:1); PUFA = C18:2 to C22:5; SFA, no 18:0 = SFA not including 18:0.

bTreatment diets were nonagglomerated and ingredient composition differed only by roughage source; either cottonseed hulls (CSH) or ground woody products (RED = J. pinchotii, BLUE = J. ashei, ONE = J. monosperma, ERC = J. virginiana, or MESQ = P. glandulosa). Juniperus (entire above-ground biomass) and Prosopis (entire above-ground biomass except for leaves) species were chipped, dried, and hammermilled to pass a 4.76-mm sieve.

Enser et al. (1996) reported the fatty acid content of lamb meat at retail in England. Lamb from the present study had about 2% more palmitic acid and 4.2% to 8.0% more oleic acid, but 0.3% to 2.8% less stearic acid compared with the Enser study. This may be due to United Kingdom prevalence of forage-fed lamb and oleic acid being significantly greater in lambs finished on concentrates, as would be commonplace in the United States (Fisher et al., 2000). Interestingly, Wood et al. (2008) indicated that oleic acid in the muscle tends to increase as a percentage as fat content increases in the beef carcass, indicating that oleic acid content may be an indicator for degree of finish, and that breed has a profound impact on fatty acid profile.

Sensory Panel Evaluation

Sensory traits measured in LM chops were not affected (P > 0.18) by finishing diet (Table 5). Hornstein and Crowe (1963) proposed that the meaty flavor of meat comes from the water-soluble fraction, but that species-specific flavors are located in the lipid fraction. This lack of an impact of diet on sensory panel traits is likely a reflection of the fact that fatty acids were not affected by diet; fatty acid composition often has been found to affect sensory characteristics of lamb meat (Kemp et al., 1981; Larick and Turner, 1990; Melton, 1990). Additionally, the impact of fatty acids may be due in part to whether the fatty acid differences are found in the polar or nonpolar fraction (Legako et al., 2015), whereas data presented here reflect both fractions in the total fatty acid composition. Sensory results from the current study agree with Whitney et al. (2011) who reported that up to 30% juniper leaves could be included in lamb feedlot diets without affecting sensory traits and, in fact, reported a linear increase (although only 0.2 sensory units) in off-flavor scores in lamb from animals fed juniper leaves. When Chaves et al. (2008) fed juniper essential oil to growing lambs, no differences were found for any sensory traits compared with the control diet, thus indicating that even by attempting to alter the fatty acid composition in muscle and adipose tissue with juniper essential oil was not successful in altering the sensory panel flavor characteristics.

Table 5.

Effects of replacing cottonseed hulls with ground woody products on sensory panel traits of lamb LM chops

Itema Dietb
CSH RED BLUE ONE ERC MESQ SEM P > F
Cook-loss 36.3 30.9 34.6 30.6 28.3 39.1 4.13 0.41
Initial juiciness 6.3 6.0 6.0 6.2 5.8 6.0 0.21 0.65
Sustained juiciness 6.2 6.0 5.7 6.0 5.7 5.8 0.20 0.37
Initial tenderness 6.3 5.7 5.5 5.9 5.6 5.8 0.24 0.24
Sustained tenderness 6.3 5.6 5.5 5.8 5.4 5.7 0.24 0.19
Flavor intensity 6.1 5.9 5.8 5.9 5.8 5.8 0.15 0.70
Off-flavor 4.0 4.0 4.0 4.0 4.0 3.8 0.05 0.21
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During period 1 (days 0 to 27), lambs were fed a 70% concentrate diet. Lambs were transitioned over 4 d into period 2 (days 28 to 57) onto an 86% concentrate diet. Within row means with a different superscript than the control diet (CSH) differ (P < 0.05).

aCook loss expressed as percentage of weight loss from raw weight; initial and final juiciness, initial and final tenderness, and flavor intensity scored on an 8-point scale (1 = extremely dry, tough, and bland, and 8 = extremely juicy, tender, and intense, respectively); off-flavor scored on a 4-point scale (4 = no off-flavor, 1 = extreme off-flavor).

bTreatment diets were nonagglomerated and ingredient composition differed only by roughage source; either cottonseed hulls (CSH) or ground woody products (RED = J. pinchotii, BLUE = J. ashei, ONE = J. monosperma, ERC = J. virginiana, or MESQ = P. glandulosa). Juniperus (entire above-ground biomass) and Prosopis (entire above-ground biomass except for leaves) species were chipped, dried, and hammermilled to pass a 4.76 mm sieve.

Gas Chromatography and Mass Spectroscopy

Eighty-one volatile aroma compounds were detected in the cooked lamb chops (Table 6). These aroma compounds are derivatives of both thermal lipid degradation and products of the Maillard reaction as reviewed by Kerth and Miller (2015). Of those volatile compounds detected, only seven were significantly affected by diet (P < 0.05). Volatile aroma chemical compounds classified as alkanes measured in LM chops were not affected (P > 0.32) by finishing diet. In the classification of alcohol volatiles, the total ion count of 1-pentanol (a lipid-derived, sweet and pleasant aroma; Burdock, 2010) was greater in LM chops from lambs fed CSH compared with BLUE, ERC, or MESQ and chops from lambs fed BLUE had less 1-pentanol than ONE (P = 0.045). No other alcohol volatiles were affected by finishing diet (P > 0.06). Heptenal (a lipid-derived, fishy aroma; Kerth and Miller, 2015), pentanal (fermented, bready; Kerth and Miller, 2015), and 1-(1H-pyrol-2yl)-ethanone (a Maillard-derived, caramel-like to canned beef aroma as reviewed by Flament, 2002) volatile aroma compounds were greater (P < 0.04) in LM chops from lambs fed CSH compared with all other diets. Lambs fed CSH had greater (P = 0.03) levels of 2-heptanone (cheesy, banana, fruity aroma; Kerth and Miller, 2015) than RED, BLUE, ERC, or MESQ, but CSH chops had less (P = 0.04) 6,7-dodecanedione (unidentified aroma) compared with RED or BLUE chops. Chops from lambs fed BLUE had greater (P < 0.05) levels of the lipid degradation product, butanoic acid (sweaty, rancid aroma; Kerth and Miller, 2015) compared with all other diets. No other volatile aroma compounds were affected by finishing diet (P > 0.05).

Table 6.

Effects of replacing cottonseed hulls with ground woody products on lamb volatile aroma compounds

Itema Dietb
CSH RED BLUE ONE ERC MESQ SEM P > F
Alkanes
Decane 1135 0 0 0 0 0 501 0.43
Dodecane 0 0 0 7040 0 8750 4888 0.51
Heptacosane 0 292 920 1347 1831 1360 756 0.47
Hexadecane 0 0 2086 0 1322 0 1171 0.59
Nonacosane 287 385 196 846 427 846 445 0.80
Nonadecane 0 0 2822 0 1967 1783 1851 0.74
Octacosane 1589 1257 1886 1516 1318 2380 835 0.91
Pentadecane 759 0 2849 392 0 383 1102 0.33
Alcohols
1-Decanol 0 0 518 1641 0 0 770 0.52
1-Dodecanol 0 5791 13929 11386 417 2915 7412 0.60
1-Hexanol 7985 7267 2807 17402 6998 8897 4954 0.36
1-Nonanol 2218 0 0 0 1265 4963 2647 0.63
1-Octanol 47986 41608 46236 27593 44049 66315 22146 0.85
1-Pentanol 49293c 17570c,d,e 8103e 39907c,d 11425d,e 12110d,e 11750 0.04
2-Dodecen-1-ol 213 0 0 0 0 2979 1520 0.55
2-Hexen-1-ol 807 0 0 0 0 394 338 0.35
2-Hexyloxy ethanol 1830 11838 0 0 4989 478 3875 0.21
2-Methyl-2-propen-1-ol 4892 1462 2428 0 1784 815 1932 0.49
2-Octen-1-ol 2502 0 531 1731 2345 0 1624 0.72
2-Propyl-1-heptanol 0 0 1403 1459 0 4171 2331 0.70
Heptanol 35492 18798 6031 12596 17126 28458 10846 0.33
Octen-3-ol 75460 40918 20398 76775 32990 38984 16936 0.07
Aldehydes
2-Decenal 50715 25201 31306 17485 43165 50715 16063 0.63
2-Dodecenal 0 0 0 2702 0 0 795 0.07
2-Hexenal 1210 0 0 2287 0 0 1083 0.48
2-Hydroxy-4-methyl- benzaldehyde 147 0 0 0 0 762 394 0.58
2-Octenal 24463 12818 7423 24632 13468 12615 6082 0.18
2,4-Decadienal 2574 1199 755 1016 2642 4536 1565 0.40
3-Dodecen-1-al 6255 6488 7115 5970 3469 0 3606 0.62
3-Ethyl benzaldehyde 0 313 0 0 0 180 149 0.50
3-Methyl butanal 657 1481 907 9724 564 2169 4423 0.59
Acetaldehyde 4661 3948 1944 1312 3236 0 2344 0.65
Benzaldehyde 485742 459135 396131 398340 371926 279666 81404 0.45
Benzene acetaldehyde 628 1634 936 2594 792 1286 1156 0.81
Butanal 212 1902 0 170 743 0 604 0.19
Decanal 36078 37121 57244 26799 66109 47717 15945 0.47
Dodecanal 19553 45802 39094 37596 41301 31655 16275 0.87
Heptanal 431468 200734 113318 283973 154996 138889 87268 0.07
Heptenal 12241c 1761d 1273d 2402d 1271d 3015d 2787 0.04
Hexanal 758983 326469 209579 912653 286455 232763 253539 0.16
Nonanal 694206 620287 614887 498548 682862 444686 162515 0.80
Nonenal 41442 19071 10974 21311 17299 28752 13389 0.58
Octanal 327220 205473 179979 218631 185478 143370 66437 0.39
Octadecanal 0 0 5768 818 4518 2418 3251 0.65
Phenylacetaldehyde 1920 0 554 0 833 682 971 0.70
Pentanal 26518c 7353d 8295d 6783d 6344d 10586d 4809 0.02
Tetradecanal 14442 5600 12021 34579 12298 13135 8064 0.16
Tridecanal 0 0 3216 5825 0 0 3046 0.58
Undecanal 5083 3045 6142 0 10570 19191 6442 0.26
Undecenal 30197 10387 19732 10513 31126 43542 14128 0.42
Ketones
1-(1H-pyrol-2yl)-ethanone 6227c 1379d 1219d 4049c,d 1201d 1430d 1346 0.03
1-Phenyl ethanone 3040 1676 2056 3262 1663 2698 1488 0.94
2-Butanone 4676 5826 4041 3476 7211 8733 5611 0.98
2-Decanone 5758 1452 2847 0 3594 12169 5015 0.47
2-Dodecanone 1602 913 1735 726 1145 1771 1053 0.95
2-Heptanone 11302c 2136d,e 968e 8590c,d 0e 2543d,e 2926 0.03
2-Heptadecanone 376 654 0 1872 618 189 570 0.18
2-Nonanone 4974 1505 3308 0 3336 12594 5253 0.50
2-Octanone 3025 1319 1379 0 1504 6143 3095 0.69
2-Propanone 1879 0 0 0 0 6701 2395 0.18
2,3-Octanedione 16931 8305 0 35970 7353 4542 10449 0.13
3-Hydroxy-2-butanone 2118 0 0 0 0 6037 3212 0.60
6,7-Dodecanedione 0e 7888c 5919c,d 1493d,e 0e 2163c,d,e 2167 0.04
Acetophenone 0 1487 1438 0 0 0 918 0.57
Tridecanone 602 965 3693 1686 0 2299 1249 0.26
Undecanone 3207 1658 384 0 4013 3550 2211 0.63
Acids
Benzoic acid 6338 8338 2469 1405 0 0 3039 0.24
Butanoic acid 1472d 5174c 0d 336d 1094d 185d 1189 0.03
Decanoic acid 979 0 685 2511 0 0 1238 0.61
Heptanoic acid 1176 0 0 0 1049 0 649 0.50
Hexanoic acid 19362 7771 2027 14692 728 2625 5624 0.08
Nonanoic acid 841 0 0 604 0 0 297 0.12
Petanoic acid 0 0 0 806 0 2213 943 0.35
Sulfur compounds
2-Acetyl-2-thiazoline 12224 13208 9811 10844 5409 8124 3724 0.69
Acetylthiazole 2190 4551 2692 1843 2515 0 1768 0.56
Other
2-Ethyl-3,5-dimethyl pyrazine 28960 0 1012 0 0 0 1050 0.24
2-Pentyl furan 18595 8621 4966 13406 3579 7153 3917 0.06
2,5-Dimethyl pyrazine 8356 0 900 1643 0 0 2966 0.24
d-Limonene 0 0 1657 0 0 3087 1692 0.60
Dihydro-2(3H)-furanone 809 5455 1278 3198 3785 417 2407 0.59
Methyl benzene 966 51836 1999 1647 0 8716 18808 0.33
Styrene 0 0 0 1205 0 1159 657 0.41
Open in a new tab

During period 1 (days 0 to 27), lambs were fed a 70% concentrate diet. Lambs were transitioned over 4 d into period 2 (days 28 to 57) onto an 86% concentrate diet. Within row means with a different superscript than the control diet (CSH) differ (P < 0.05).

aVolatile aroma chemical compounds expressed as the total ion count area under the curve for each peak.

bTreatment diets were nonagglomerated and ingredient composition differed only by roughage source; either cottonseed hulls (CSH) or ground woody products (RED = J. pinchotii, BLUE = J. ashei, ONE = J. monosperma, ERC = J. virginiana, or MESQ = P. glandulosa). Juniperus (entire above-ground biomass) and Prosopis (entire above-ground biomass except for leaves) species were chipped, dried, and hammermilled to pass a 4.76 mm sieve.

c,d,eMeans in the same row lacking a common superscript difference (P < 0.05).

Volatile aroma compounds from cooked meat have been studied as indicators of lamb feeding systems (Priolo et al., 2004) as well as their influence on cooked meat flavor characteristics (Young et al., 1997, 2003). Bueno et al. (2011) found eight different aroma compounds with meaty odor, which included 2-heptenal reported in the present study. Elmore et al. (2005) reported 111 volatile compounds that were quantified in lamb, and of those, 78 were significantly affected by the dietary treatment of supplemental PUFA-rich oil. In that study, they reported that many of the volatile compounds were derived in the degradation of lipids and reported that 1-pentanol and 2-heptanone were derived from the decomposition of C18:2 n-6 fatty acids. They concluded that the inclusion of PUFA in diets, while nutritionally desirable, resulted in poor sensory quality. Furthermore, when they conducted a principal component analysis of volatile compounds and trained sensory descriptors with supplemental dietary oils, principal component 1 accounted for more than 87% of the variation in the data.

CONCLUSIONS

Minimizing input costs associated with feeding livestock is important, and furthermore, utilizing raw materials that might otherwise be thought of as pastoral waste has the potential to provide an opportunity for finishing ruminants. The utilization of ground juniper and mesquite species as roughage sources in finishing diets of lambs is expected to increase, if edible products, and sensory characteristics of these products, are not negatively affected. The research reported here indicated that lambs can be finished on a diet with 30% of the diet as ground juniper or mesquite as a source of roughage without negatively affecting carcass traits, fatty acid composition, or sensory traits.

ACKNOWLEDGMENTS

This work was supported by the U.S. Department of Agriculture National Institute of Food and Agriculture Hatch Project 205866 and funded in part by the National Sheep Industry Improvement Center.

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