Effects of castration and zeranol on fatty acid composition and cholesterol content of hair lamb meat

Abstract

Hair lambs (n=72, crosses of Blackbelly, Dorper, and Katahdin breeds) with an average age of 90 days (21.4±2.3 kg of BW) were used to investigate the effects of sex class (CLASS: ram vs. wether) and zeranol implant (IMP: control vs. 12 mg) on fat and cholesterol content, and fatty acids (FAs) composition of intramuscular longissimus dorsi (LD) and biceps femoris (BF) and subcutaneous fat (SBC) depots of the loin area. Animals were assigned to one of four treatments with a factorial arrangement (n=18): (1) rams (R), (2) rams implanted with 12 mg zeranol (IR), (3) wether lambs (W), and (4) wether lambs implanted with 12 mg zeranol (IW). FAs C12:0 and C15:0 FAs were significantly higher in the wether's LD. The amount of C22:1 n-9 and C24:1 in rams’ LD was higher than those of wethers. Wethers had a higher content of C18:1 cis 9 than R group, and the content of this cis isomer was significantly lower in the implanted group. LD of rams contained a higher amount of polyunsaturated fatty acid (PUFA) and a higher PUFA/saturated fatty acid ratio. Cholesterol content in the three tissues (LD, BF, and SBC) was affected significantly by the CLASS×IMP interaction and was higher in wethers without implant. The sex class was the most important factor affecting lipid composition in hair lambs. The higher PUFA content in meat from rams may suggest a nutritional advantage in comparison to meat from wethers.

Keywords:

• sex condition
• implants
• fatty acids
• cholesterol
• hair lambs

1. Introduction

Lipid composition influences both the nutritional value and sensorial characteristics of meat (McGuire & McGuire 2000). Ovine meat fat composition, same as in other ruminant species, has been criticized and avoided by some nutritionally conscious consumers, due to its low content of polyunsaturated fatty acids (PUFAs) and high content of saturated fatty acids (SFAs). Some human chronic diseases have been linked to the amount and type of fat consumed in a regular diet. Diets with high SFA can contribute to increase low-density lipoprotein (LDL)-cholesterol levels in blood, which have been related to incidences of cardiovascular diseases (Kris-Etherton & Yu 1997). Conversely, some monounsaturated fatty acids (MUFAs) and PUFAs, especially the n-3 long-chain fatty acids (FAs), have been associated with beneficial effects on human health (Sacks & Katana 2002).

A decrease in SFA levels and/or a concomitant increase in the MUFA and PUFA contents of ruminant meat may confer benefits for human health and may provide a basis for marketing claims. By other hand, the atherogenicity index (AI), which measures the potential risk of a food to cause clogged arteries, is estimated from the ratio of SFA C12:0, C14:0 and C16:0, respect to the total unsaturated FAs (Ulbricht & Southgate 1991). This index has been estimated at meat obtained under different production systems (Oliveira et al. 2011; Hernández-Castellano et al. 2013). Any production strategy that results in a decrease of AI contributes in obtaining a healthier meat for the consumer.

Recent research has evaluated factors that may cause changes in lipid composition, starting at the level of animal production. Breed, sex, feed regime (Gattellier et al. 2005; Moreno-Indias et al. 2011; Hernández-Castellano et al. 2013) and slaughter endpoint in ruminants (Okeudo & Moss 2007) can affect both the fat content and the FA profile. A comparison of sex classes in lambs has shown that rams have a higher PUFA percentage in loin intramuscular fat than wethers, while wethers have a higher SFA percentage (Solomon et al. 1990). Duckett and Andrae (2001) indicated that aggressive implant regimes may cause a reduction of both subcutaneous and intramuscular fat. However, to our knowledge, no reports have addressed the effect of sex class under less aggressive implant regimes in ovine FA profile. This information might be very important for animal production and marketing, particularly in Mexico. Therefore, this study evaluated the effects of sex class and zeranol implant in the intramuscular fat content, FA profile and cholesterol content of subcutaneous (SBC) fat and muscle tissues from the round (biceps femoris) and loin (longissimus dorsi) of hair lambs produced in northern Mexico.

2. Materials and methods

2.1. Animals and treatments

The experiment included 72 crossbred hair lambs (Dorper×Blackbelly), 90 days old, with an initial live weight of 21.4±2.3 kg. In the feedlot performance trial, lambs were fed with a ration composed of 20% alfalfa hay and 80% concentrate. Feed was formulated with 19% of crude protein and 11.76 MJ/kg dry matter of metabolizable energy, in order to have a 220 g average daily gain, in accordance with the nutritional requirements for 20 kg live weight lambs by the NRC (2007). Animals, individually identified with an ear tag, were randomly allotted to one of the four following treatments (n = 18 per group): (1) rams (R); (2) rams implanted with 12 mg zeranol (IR); (3) wethers (W); and (4) wethers implanted with 12-mg zeranol (IW). Wethers were castrated with an elastic band. Animals from each treatment group were divided into three pens (corresponding to replicates) of six lambs each. The performance trial was conducted in the Sheep Production Unit of the Facultad de Zootecnia y Ecología of the Universidad Autónoma de Chihuahua (Mexico).

Upon reaching the slaughter weight (40±3 kg), animals were slaughtered at the Meat Lab of the Facultad de Zootecnia y Ecología of the Universidad Autónoma de Chihuahua (Mexico) following conventional procedures legislated by the Mexican government (NOM-033-ZOO-1995). At 24-h postmortem, m. longissimus dorsi (LD), m. biceps femoris (BF), and loin SBCs were removed from the left side of each carcass. Samples were vacuum packed and stored at −20°C until further analyses at the Research Laboratory of Meat Products located in CIAD AC (Centro de Investigación en Alimentación y Desarrollo AC) at Hermosillo, Sonora, México.

2.2. Intramuscular fat content

Intramuscular fat content was measured following the method 960.39 of AOAC (2007).

2.3. Lipid extraction for FA determination

Lipid fraction of each sample was recovered using an adaptation of the method described by Bligh and Dyer (1959). Approximately 20 g (rounded to the nearest 1 mg) of frozen-dried ground meat or SBC samples was added to a beaker with 40 mL of a 2:1 (v/v) chloroform:methanol solution. Afterward, this mixture was filtrated (Whatman No. 541) and the filtrate was recovered. The extraction procedure was repeated twice, and both filtrates were combined. Then, 20 mL of 0.37% KCl was added to the pooled filtrates. After 8 h, the top (aqueous) layer was decanted, and the organic layer was transferred to a volumetric flask. Chloroform:methanol solution was added to the organic layer to a total final volume of 100 mL.

2.4. Methylation of FAs

Fatty acid methylation was performed according to the next methodology: First, 5–10 mL of the lipid extraction was dried at 40°C in a rotary evaporator under vacuum. The lipid residue was washed in a glass vial using 10 mL of heptane, and 0.5 mL of 2 M methanolic KOH solution was added. The vial was gently mixed and allowed to stand for approximately 4 min. Then, the upper layer with the fatty acid methyl esters (FAMEs) was removed for determination by gas chromatography. The FA proportions of phospholipids and triglycerides were not measured as separate fractions.

2.5. Fatty acids profile analysis

The FAME composition was analyzed by gas chromatography using a Hewlett Packard 6890 chromatograph equipped with a Supelco SP2560 (0.25 mm×100 m, 0.20 µm film width) melted capillary, silicon-based column and with a flame ionization detector and a 6890 auto-sampler. The temperature of the injection port was held at 250°C and the detector at 300°C. The chromatograms were recorded and downloaded using ChemStation software. Tridecanoic acid (C13:0 Sigma-Aldrich, MO, USA) was used as an internal standard. FAME identification was performed comparing the retention time and elution patterns with those of a standard fatty mix. FAs were expressed as percentage of total detected FA. Total amounts of SFA, MUFA and PUFA were calculated, and the MUFA/SFA and the PUFA/SFA ratios were determined. The AI was calculated with the following equation: AI=(C12:0 + 4×C14:0 + C16:0)/(Σ MUFA+Σ PUFA) in accordance with Ulbricht and Southgate (1991).

2.6. Cholesterol extraction

Extraction and quantification of cholesterol were done using the technique originally reported by Thompson and Merola (1993) with slight modifications: first, 5–8 mL of the lipid extract was vaporized in a water bath at a temperature below 40°C. The residue was weighed until it reached 100±0.05 mg fat. Then, 200 µl of a 1 mg/1 mL coprostane internal standard in ethanol was added to this residue, followed by 8 mL of 3% ethanol pyrogallol and 0.5 mL of KOH (1.5 g/mL). After cooling to room temperature, 12 mL of water and 20 mL of cyclohexane were added. Then, 17 mL of the upper layer was removed and dissolved in 500 mL of the derivatizing agent (bis-trimethylsilyl-trifluoride acetamide), and 100 µl aliquots were removed. To obtain a diluted sample (with a 2.5 dilution factor) for further analysis, 150 µl of cyclohexane was added.

2.7. Cholesterol determination

Cholesterol content was quantified by gas chromatography using a Hewlett Packard 6890 Series chromatographer with a 6890 auto-sampler. A cyanopropyl-phenyl-methyl-polysiloxane capillary silicon-based column was used at 6% (Hewlett Packard 19091; 0.25 mm×30 m, 0.15 µm film). The temperature of the injector port was 260°C, whilst the detector was kept at 330°C. The chromatograms were recorded using ChemStation software.

A standard curve was constructed to quantify cholesterol concentration using a 10 mg/10 mL ethanol stock cholesterol solution; 0.2, 0.4, 0.6, 0.8, 1.0 or 1.2 mL were added to tubes, which were placed in a water bath at a temperature between 35°C and 40°C. Then, 0.5 mL of derivatizing agent and 150 µl of cyclohexane were added to each sample. The samples were then injected into the chromatograph. Chromatograms for each dilution were obtained, and the cholesterol content was reported as mg of cholesterol/100 g fresh tissue.

2.8. Statistical analysis

A completely randomized design using a factorial 2×2 arrangement was used for FA profile and cholesterol data, where sex class (CLASS: ram or wether) and zeranol treatment (IMP: control or 12 mg implant) were the main factors of the model. Analysis of variance (ANOVA) was performed with the PROC MIXED procedure of SAS (2001). The ANOVA model included CLASS, IMP, and their interaction as fixed effects, and the pen and individual lamb as random effects, and slaughter weight as covariate. Significances were estimated at a 0.05 probability level in error type I. Mean comparisons were performed by the LSMEANS/PDIFF procedure of SAS.

3. Results and discussion

The intramuscular fat content for LD and BF muscles of each treatment is shown in Tables 1 and 2, respectively. In LD, fat content was affected by CLASS (P<0.05) being higher in wethers with respect to ram lambs (3.25 vs. 2.24%, respectively). The BF muscle of wethers had 17% more fat than ram lambs (P < 0.05), and also, animals implanted showed 24% more fat than those not implanted (P < 0.05). These results were in accordance with those reported by Morris et al. (1995) who stated that as a result of sexual earlier maturity, with the same chronological age, wethers presented higher fat content than the intact lambs. In addition, values found in this study are consistent with several studies performed in confined sheep which reported that meat from intact animals or implanted is leaner than in wethers (Solomon et al. 1990; Wood et al. 2008). In beef systems, this was due to the effect of natural androgenic hormones or to the lipolytic effect of hormone implants (Wood et al. 2008).

Table 1. Intramuscular fat, fatty acid composition and cholesterol (mg/100 g muscle) of longissimus dorsi muscle from hair lambs according to sex class and zeranol implant treatment.

	Sex class and implant					Significance level
	R	IR	W	IW	SEM	CLASS	IMP	CLASS×IMP
Fat content (%)	1.98	2.50	3.66	2.83	0.23	0.04	0.51	0.17
Fatty acid (%)
C10:0	0.411	0.400	0.328	0.367	0.05	0.58	0.89	0.81
C12:0	0.261	0.352	0.104	0.169	0.04	0.02	0.28	0.85
C14:0	3.03^b	3.19^b	2.41^a	3.19^b	0.11	0.19	0.04	0.04
C15:0	0.447	0.478	0.346	0.314	0.03	0.05	0.99	0.64
C16:0	24.70	25.06	23.76	25.31	0.28	0.55	0.10	0.30
C17:0	1.08	1.21	1.10	1.16	0.06	0.85	0.43	0.76
C18:0	13.49	13.57	13.96	14.17	0.59	0.65	0.90	0.95
C22:0	0.258	0.162	0.136	0.229	0.02	0.57	0.98	0.06
C14:1	0.122	0.435	1.30	0.303	0.27	0.35	0.54	0.24
C15:1	0.988	0.108	0.784	0.763	0.06	0.04	077	0.65
C16:1	1.76	1.87	1.61	1.88	0.07	0.53	0.25	0.71
C17:1	0.729	0.974	0.743	0.817	0.06	0.60	0.24	0.53
C18:1 n-9 trans	4.08	5.08	3.64	4.06	0.27	0.19	0.20	0.60
C18:1 n-9 cis	35.56	33.39	40.47	37.03	0.57	0.001	0.02	0.58
C22:1 n-9	2.55	2.40	1.84	1.80	0.11	0.001	0.69	0.81
C24:1	0.519	0.394	0.245	0.261	0.03	0.001	0.42	0.30
C18:2 n-6	9.07	8.85	6.33	7.18	0.27	0.001	0.57	0.35
C18:3 n-3	0.032	0.123	0.049	0.024	0.01	0.16	0.27	0.06
C22:6, n-3	0.012	0.011	0.004	0.00	0.004	0.28	0.74	0.85
CLA	0.640	0.735	0.853	0.742	0.03	0.13	0.91	0.16
∑ SFA	43.92	44.63	42.38	45.17	0.48	0.60	0.07	0.28
∑ MUFA	46.31^a	45.65^a	50.37^b	46.79^a	0.51	0.001	0.01	0.05
∑ PUFA	9.759	9.71	7.24	8.02	0.28	0.001	0.52	0.47
MUFA/SFA ratio	1.05	1.02	1.20	1.03	0.023	0.11	0.04	0.16
PUFA/SFA ratio	0.222	0.217	0.172	0.179	0.007	0.004	0.95	0.69
Atherogenicity index	0.664	0.691	0.583	0.70	0.02	0.22	0.012	0.14
Cholesterol	53.8^a	60.3^a	103.4^b	76.8^a	3.7	0.001	0.14	0.02

R: rams, IR: rams + 12-mg zeranol implant, W: wether, IW: wether + 12-mg zeranol implant, SEM: standard error of mean, CLASS: sex condition, IMP: zeranol implant; CLASS×IMP: interaction. ∑ SFA: total of saturated fatty acids: C10:0–C22:0. ∑ MUFA: total of monounsaturated fatty acids: C14:1–C24:1. ∑ AGP: total of polyunsaturated fatty acids: C18:2, c6 + C18:3 + C22:6, n-3 + CLA. Atherogenicity index: (C12:0 + 4×C14:0 + C16:0/MUFA + PUFA). Means in the same row with different superscripts are significantly different (P<0.05).

Table 2. Intramuscular fat, fatty acid composition and cholesterol (mg/100 g muscle) of biceps femoris muscle from hair lambs according to sex class and zeranol implant treatment.

	Sex class and implant					Significance level
	R	IR	W	IW	SEM	CLASS	IMP	CLASS×IMP
Fat content (%)	2.40	2.92	3.48	2.76	0.10	0.04	0.009	0.64
Fatty acid (%)
C10:0	0.323	0.308	0.230	0.263	0.01	0.06	0.80	0.50
C12:0	0.309	0.265	0.260	0.244	0.04	0.61	0.68	0.83
C14:0	3.53	3.22	2.86	3.49	0.18	0.59	0.67	0.21
C15:0	0.564	0.430	0.450	0.489	0.03	0.65	0.44	0.16
C16:0	24.46	22.24	22.03	23.69	0.57	0.62	0.78	0.06
C17:0	1.34	1.12	1.19	1.25	0.06	0.95	0.51	0.21
C18:0	11.96	10.90	11.75	11.22	0.39	0.93	0.27	0.69
C22:0	0.161	0.134	0.166	0.220	0.02	0.39	0.79	0.43
C14:1	0.589^b	0.226^a	0.157^a	0.207^a	0.04	0.01	0.08	0.02
C15:1	0.668	0.646	0.990	0.864	0.12	0.22	0.73	0.80
C16:1	1.80	2.21	2.70	2.29	0.18	0.13	0.98	0.20
C17:1	1.27	1.13	1.02	1.04	0.10	0.35	0.74	0.65
C18:1 n-9 trans	4.19	5.36	3.64	3.59	0.23	0.001	0.18	0.13
C18:1 n-9 cis	36.47	36.73	41.29	38.32	1.00	0.08	0.48	0.35
C22:1 n-9	2.84	2.19	2.08	2.48	0.24	0.57	0.77	0.22
C24:1	0.533	0.412	0.353	0.401	0.04	0.22	0.64	0.27
C18:2 n-6	8.38	7.79	6.38	7.72	0.52	0.27	0.69	0.29
C18:3 n-3	0.080	0.07	0.00	0.05	0.03	0.46	0.73	0.67
CLA	0.885	0.808	1.01	0.633	0.07	0.85	0.10	0.25
∑ SFA	42.92	38.50	39.23	40.15	1.04	0.57	0.36	0.15
∑ MUFA	48.36	53.77	53.39	53.04	1.82	0.14	0.12	0.07
∑ PUFA	9.37	8.69	7.40	8.45	0.49	0.21	0.83	0.31
MUFA/SFA ratio	1.11	1.54	1.44	1.39	0.09	0.39	0.16	0.08
PUFA/SFA ratio	0. 217	0.233	0. 192	0. 214	0.01	0.34	0.43	0.89
Atherogenicity index	0.872	0.602	0.577	0.675	0.07	0.32	0.43	0.10
Cholesterol	50.1^a	59.0^a	51.7^a	84.6^b	2.5	0.001	0.01	0.03

R: rams, IR: rams + implant, W: wether, IW: lambs + implant, SEM: standard error of mean; CLASS: sex condition; IMP: implant; CLASS×IMP: interaction. ∑ SFA: total of saturated fatty acids: C10:0–C22:0. ∑ MUFA: total of monounsaturated fatty acids: C14:1–C24:1. ∑ AGP: total of polyunsaturated fatty acids: C18:2, c6 + C18:3 + C22:6, n-3 + CLA. Atherogenicity index: (C12:0 + 4×C14:0 + C16:0/MUFA + PUFA). Means in the same row with different superscripts are significantly different (P<0.05).

Fat content of both muscles in all treatments was relatively low and similar to those reported by Okeudo and Moss (2007) for lambs under similar feeding conditions. Moreover, these values were within an acceptable range for intramuscular fat without detriment to sensory acceptability by consumers (Troy & Kerry 2010).

The profile of FAs in LD and BF muscles and SBC is shown in Tables 1–3, respectively. The predominant FA in all three tissues was oleic acid (C18:1 n9 cis, 32.13–41.29% of total FA determined), palmitic acid (C16:0, 20.88–25.31%), and stearic acid (C18:0, 10.90–18.48%).

Table 3. Fatty acid composition and cholesterol (mg/ 100 g tissue) of subcutaneous fat from hair lambs of different sex class and zeranol implant treatment.

	Sex class and implant					Significance level
	R	IR	W	IW	SEM	CLASS	IMP	CLASS×IMP
Fatty acid (%)
C10:0	0.356	0.221	0.172	0.129	0.04	0.07	0.23	0.52
C12:0	0.065^a	0.165^b	0.109^ab	0.07^a	0.01	0.21	0.10	0.001
C14:0	2.55	3.06	2.58	2.42	0.14	0.23	0.48	0.17
C15:0	1.32	1.12	0.66	0.81	0.06	0.001	0.85	0.11
C16:0	21.27	22.38	20.88	21.56	0.56	0.52	0.34	0.81
C17:0	3.24^b	2.49^a	2.25^a	2.77^ab	0.16	0.21	0.66	0.02
C18:0	13.05	16.12	17.96	18.48	0.58	0.001	0.07	0.19
C22:0	0.05	0.04	0.03	0.03	0.01	0.39	0.74	0.74
C14:1	1.64^b	0.87^a	0.469^a	0.576^a	0.10	0.01	0.01	0.01
C15:1	0.306	0.290	0.147	0.166	0.01	0.001	0.95	0.48
C16:1	3.50	2.88	2.13	2.12	0.16	0.001	0.25	0.25
C17:1	2.36^b	1.41^a	1.01^a	0.97^a	0.12	0.01	0.01	0.02
C18:1 n-9 trans	7.88	8.10	7.85	6.72	0.42	0.33	0.52	0.34
C18:1 n-9 cis	36.02	35.43	38.02	32.13	1.48	0.79	0.20	0.28
C22:1 n-9	0.96	0.73	0.19	2.05	1.66	0.23	0.35	0.39
C18:2 n-6	5.01	4.64	4.04	4.27	0.17	0.03	0.81	0.31
C18:3 n-3	0.178	0.182	0.149	0.130	0.01	0.12	0.75	0.63
C22:6n-3	1.9	0.01	0.01	0.01	0.03	0.31	0.18	0.35
ConjuCLA	1.14	1.09	1.20	1.03	0.08	0.98	0.45	0.67
∑ SFA	42.01	45.72	44.75	46.37	0.71	0.17	0.03	0.38
∑ MUFA	50.74	48.35	49.88	48.46	0.73	0.76	0.13	0.68
∑ PUFA	6.44	5.90	5.40	5.41	0.18	0.02	0.42	0.38
MUFA/SFA ratio	1.21	1.08	1.12	1.05	0.03	0.32	0.11	0.64
PUFA/SFA ratio	0.152	0.133	0.121	0.117	0.005	0.01	0.16	0.37
Atherogenicity index	0.547	0.647	0.577	0.581	0.02	0.61	0.15	0.20
Cholesterol	109.0^a	143.2^b	86.7^a	75.9^a	5.64	0.001	0.01	0.05

R: rams; IR: intact rams + implant; W: wether, IW: wether + implant, SEM: standard error of the mean, CLASS: sex condition, IMP: implant, CLASS×IMP: interaction. ∑ SFA: total of saturated fatty acids: C10:0–C22:0. ∑ MUFA: total of monounsaturated fatty acids: C14:1–C22:1. ∑ AGP: total of polyunsaturated fatty acids: C18:2, c6 + C18:3 + C22:6, n-3 + CLA. Atherogenicity index: (C12:0 + 4×C14:0 + C16:0/MUFA + PUFA). Means in the same row with different superscripts are significantly different (P<0.05).

SFA content in LD fluctuated between 42.38 and 45.17% of the total FA and was not affected (P > 0.05) by the factors under study; nonetheless, some individual SFA exhibited significant variations. Although the content of lauric (C12:0) and pentadecanoic (C15:0) acids was low, they varied by CLASS with higher concentrations (P < 0.05) observed in rams. Myristic acid (C14:0) also varied due to the implant treatment and the CLASS×IMP interaction. In rams, content was similar (P > 0.05) for IR and R group (3.19 vs. 3.03%, respectively), but in wethers C14:0 content was 32% higher in IW than in W (3.19 vs. 2.41%).

Total SFA in BF muscle did not vary (P > 0.05) by CLASS or IMP and ranged between 38.5 and 42.92%. SFA content in SBC fat was affected by CLASS; wethers had a higher content of total SFA than rams (P < 0.05). Composition of individual SFAs in SBC was also affected by evaluated factors. C15:0 was present in lower levels in wethers, and C17:0 was affected by the CLASS×IMP interaction; rams had a higher concentration of this FA (P < 0.05) in comparison to IR, W and IW.

MUFA content of LD was affected by CLASS×IMP interaction. MUFA levels in rams were not affected (P > 0.05) by IMP; however, in wethers, MUFA proportion was reduced by 7% (P < 0.05) with zeranol implant (46.79 vs. 50.37% for IW and W, respectively). Individual MUFAs were affected by CLASS. Higher proportions (P<0.05) of C15:1, C24:1, C22:1 n-9 were observed in ram tissues than in wethers. Proportion of oleic acid (C18:1 n-9 cis), the predominant MUFA, was affected by CLASS and IMP. Tissues from wethers had a higher proportion (P<0.05) of C18:1 n-9 cis than those from rams. Similarly, tissues from nonimplanted animals (R+W) had a higher oleic acid concentration (P<0.05) than those from implanted groups (IR + IW).

Total MUFA content in BF was not affected by CLASS nor IMP (P > 0.05). Oleic acid varied by CLASS (P < 0.05), with rams having higher content than wethers. Interaction of CLASS×IMP caused a significant difference (P<0.05) in C14:1 level. Group R had 150% more C14:1 than IR, while no differences were observed for W and IW. Total MUFA percentage of SBC fat had no variation (P > 0.05) due to the factors under study. Nonetheless, C15:1 and C16:1 were affected by CLASS (P < 0.05); rams had higher values, for both FAs, than wethers. C14:1 and C17:1 differed (P < 0.05) by CLASS×IMP interaction; both FAs were higher in R group compared to IR, and wether animals were not affected by implantation.

Total PUFA concentration was higher (P<0.05) in rams LD compared to wethers. Linoleic acid (C18:2 n-6), the predominant PUFA, was affected by CLASS, where higher concentrations (P < 0.05) were present in ram LD muscles. The remaining PUFAs were detected in small concentrations and nonexhibited significant differences. Conjugated linoleic acid (CLA) content fluctuated between 0.65 and 0.85%.

Total changes of PUFA in BF were not significant (P > 0.05) and ranged between 7.40 and 9.37%. CLA was not affected by the studied factors (P > 0.05), and concentrations were similar to those observed in LD. Rams had the highest (P < 0.05) total PUFA and C18:2 n-6 content in SBC fat.

MUFA/SFA ratio in LD was significantly affected by implant treatment. More elevated concentrations (P < 0.05) were detected in nonimplanted (1.12) than in zeranol-implanted groups (1.02). PUFA/SFA ratio was affected by CLASS and was higher (P < 0.05) in rams. MUFA/SFA ratio in BF was higher (P < 0.05) for IR, W, and IW treatments compared to R, and this ratio was higher than that observed in LD. PUFA/SFA ratio in SBC fat was higher in rams (P < 0.05).

In general, intramuscular FA profile presented here is in accordance with those of previous reports (Díaz et al. 2005; Vasta et al. 2009) performed in lambs on high-concentrate feeding regimes. Our results were consistent with those reported by Okeudo and Moss (2007) for rams and wethers of Texel breed, and for hair lambs intensively fattened in Mexico (Ramírez et al. 2007; Valenzuela-Grijalva et al. 2012).

The increased percentages of some unsaturated FAs with the concomitant decrease of some SFAs, found in this study in ram muscle tissues, were consistent with previous reports (Okeudo & Moss 2007; Cividini et al. 2008). This observation has also been reported for cattle (Ruiz et al. 2005), where bulls had lower C16:0 and C18:0 content, higher C16:1, C18:2, and C18:3 concentration, and higher proportions of other branched chain FA in their SBC and intramuscular tissues compared to steers and heifers. The effect of CLASS on total content of PUFAs in this study was similar to the effect reported by Solomon et al. (1990) who found that rams had a significantly higher percentage of PUFA in LD than wethers. Conversely, Okeudo and Moss (2007) did not observe differences in total PUFA content between rams and wethers and reported values 50% lower than those observed in our study. According to Solomon et al. (1990), variations in FA composition due to CLASS may be caused by inherent differences in the lean:fat ratio between rams and wethers, as a direct result of hormonal influence on body growth (decreased fat deposition and increased muscle development).

Proportion of unsaturated FAs has been reported to increase at the expense of SFA proportion when maturity or slaughter weight differs (Tejeda et al. 2008). Huerta-Leidenz et al. (1996) found that the FA profile of growing cattle (calves) was affected during accelerated deposition of fat in the fattening stage.

Horcada (1996) studied the effect of growth rate on FA composition in Spanish lambs (Lacha and Aragonesa) and reported that young lower-weight animals had fewer odd-chained FA than branched-chain FA, because in this breeds the weaning-to-slaughter period is very short. However, in older or heavier animals, the unsaturated FA content was higher because of the increased deposition of adipose tissue during fattening. Excluding the compositional variations observed in total SFA and C16:0 in BF, the observations of Horcada (1996) were not confirmed in the present study.

Similar to our results, Valenzuela-Grijalva et al. (2012) reported a significant effect of zeranol implantation on the proportion C18:1 n-9 cis, and MUFA content; where implanted animals had a lower proportion. PUFA/SFA ratio in humans is an important risk factor for cardiovascular diseases (Kris-Etherton & Yu 1997; Simopoulos 1999), therefore, it is relevant from a human health standpoint. PUFA/SFA ratio has been used to calculate the risk factor of foods. According to Wood et al. (2008), the recommended value is at least 0.4. However, Hoffman et al. (2003) have suggested that the minimum PUFA/SFA ratio is 0.12. In the present study, PUFA/SFA ratios for all treatments, in the three studied tissues, were slightly higher than the recommended level by Hoffman et al. (2003), except in SBC of IW group. Nevertheless, the highest PUFA/SFA ratios were present in rams, suggesting that their meat tissues might be healthier for human consumption. In general, PUFA/SFA values observed in our study were lower than values reported by Costa et al. (2009) in crossbred Brazilian lambs. CLA content in the three evaluated tissues was consistent with values reported by Wynn et al. (2006) for lambs fed with high-concentrate diets.

The AI of BF and SBC tissues was not affected by factors. Conversely, in LD a higher AI (P<0.05) was observed in zeranol-implanted animals in comparison with no implanted. Overall, meat of all treatments showed low AI values (range 0.50–0.80), which from a human health point of view, indicate a low risk of cardiovascular disease (Ulbricht & Southgate 1991).

Cholesterol content of LD, BF and SBC is shown in Tables 1–3, respectively. Cholesterol content was significantly affected by CLASS×IMP interaction (P < 0.05) in all the three tissues. In LD, cholesterol content was similar (P > 0.05) between R and IR group; however, W (103.4 mg) had a higher cholesterol content (P < 0.05) as compared to that of IW (76.8 mg). Cholesterol was higher (P < 0.05) in BF of IW when compared to R, IR and W groups (84.6 mg vs. 50.1, 59.0 and 51.7 mg, respectively). SBC from IR had higher cholesterol content (P < 0.05) than R, W and IW groups (143.2 mg vs. 109.0, 86.7 and 75.9 mg, respectively). Generally, the cholesterol content was higher in SBC fat than in both studied muscles.

The cholesterol values observed in intramuscular fat were similar to those reported in other studies (Baranowski et al. 2007; Costa et al. 2009) for different ovine breed types fed with high-concentrate diets. The above mentioned studies were unable to detect an effect of CLASS on the intramuscular content of total cholesterol, but they did observe a higher concentration of cholesterol in the SBC fat. Costa et al. (2009) reported that no variations in cholesterol were induced by genotype.

The results of the present study indicate that implantation with zeranol caused a significant reduction of cholesterol content alone in LD muscle. Accordingly, Valenzuela-Grijalva et al. (2012) in their study with hair lambs observed a reduction of 78% in the cholesterol content of LD muscle due to implantation with zeranol respect to control group.

4. Conclusion

The relatively higher cholesterol content found in the both muscles (LD and BF) of wethers could be considered to be a disadvantage to promote its nutritional attributes in consumer segments concerned with diet/health issues. Conversely, the relatively high value of PUFA/SFA ratio in ram tissues, which was within the desirable range recommended by at least one study, suggests that the consumption of ram meat may be healthier than meat from wethers. Overall CLASS was the single, most important factor contributing to variation in FA profile observed in this group of hair lambs. Therefore, implant treatment is considered to be of lesser importance.

Acknowledgments

This research was supported by Fondos Mixtos Chihuahua-CONACYT (Project 23246). We thank Q. Thalia Islava Lagarda for technical assistance with FAs determinations.