2.1. Treatments and Animals
The work was conducted in accordance with requirements of the Chilean Law 20,380 on Animal Protection and with the approval of the INIA Bioethics Committee. A total of 45 male Corriedale lambs were raised to weaning with their dams on a typical sheep farm, representative of the main range farming area, located in the Aysén region of Western Patagonia. Ewes and lambs were grazed together on extensive rangeland, where the vegetation was dominated by
Festuca pallescens,
Poa dussenni,
Puccinellia sp. and
Trifolium repens. Weaning occurred on a single day when lambs averaged 27 kg live weight (LW) and 90 d of age. The lambs were then randomly allocated into three groups on the basis of their live weight (LW) and condition score [
9]. The first group of 15 lambs was transported directly to a commercial abattoir, and their carcass characteristics at weaning (W) are presented in
Table 1.
The remaining 30 lambs were transported to the Instituto de Investigaciones Agropecuarias, INIA Tamel Aike research station (45°45′ S, 72°02′ W, 480 m a.s.l.), located in Simpson Valley, Western Patagonia, Chile.
Lambs were assigned to two feeding groups: grazing on a legume-based pasture of alfalfa (Medicago sativa), (AG), n = 15, and grazing on improved permanent pasture, (PPG), n = 15. Improved permanent pasture was based on cocksfoot (Dactylis glomerata) and white clover (Trifolium repens). Animals were allocated to treatment groups based on LW. A rotational grazing was imposed which was controlled by an electric net fence. Lambs were shifted and weighed weekly during the experiment. Pasture was abundant (4700 and 3200 kg dry matter (DM) ha−1 on average for alfalfa and permanent pasture, respectively); net fence was moved when the residual was approximately 2500 and 1600 kg DM ha−1 for alfalfa and permanent pasture, respectively. There was a 7 d pre-experimental period to accustom animals to the two grazing systems and management conditions. No attempt was made to measure DM intake. At the beginning of the experiment, the lambs were treated with Fenbendazol 100mg (Panacur® 10%), at 6 mg per kg, against liver, lung and intestinal parasites. Free access to watering was provided at all time. The experiment ranged from 21 January 2016 to 28 March 2016 (68 d) and lambs were slaughtered thereafter.
The botanical composition and chemical characteristics of improved permanent pasture and alfalfa consumed after weaning during the grazing period are shown in
Table 2. For botanical composition, pasture samples from three 0.5 m
2 frames were bulked and the proportions of botanical groups (grasses, legumes and herbs) as well as plant species within these groups were determined. Statistical evaluation of botanical analysis of pasture samples results was not performed as only an average (
n = 3) pasture sample was available. For chemical characteristics, simulated grazed pasture samples were collected in polythene plastic bags from the allowance pasture strips. All the feed samples were transported under refrigeration to the laboratory and were dried for 48 h at 60 °C for chemical analyses. The chemical content of the feed samples was analyzed at the INIA Remehue Animal Nutrition and Environment Laboratory in Osorno, Chile.
The dry matter (DM), crude protein (CP), and ash were measured with the methods described by the AOAC [
10]. The metabolizable energy (ME), in vitro digestibility (IVD) analysis and the neutral detergent fiber (NDF) were determined according to Sadzawka et al. [
11].
2.2. Lamb Carcass Evaluation
In all cases, slaughter took place at the same local commercial abattoir, with pre slaughter live weights being recorded after 18 h of fasting. Lambs were stunned, and the carcasses were eviscerated and skinned according to normal commercial practices, weighed hot and held at 5 °C for 8 h. The hot carcass weight (HCW) included kidney-pelvic fat. The day after slaughter, cold carcasses were weighed (CCW) and graded for conformation using a four-point scale to represent very good, good, average or poor muscling, according to the Chilean standard for lamb carcasses [
12]. Further slaughter data consisted of fat grade and kidney knob and channel fat grade (KKCF), using a three-point scale to represent deficient, normal or excessive fat covering. Carcass length from the last sacral vertebra to the first cervical (atlas) vertebra was also recorded.
Carcasses were split with a band saw between the 12th and 13th ribs and the fat depth over the eye muscle (
Longissimus dorsi) was measured (mm) on both sides of the carcass with a sharpened steel ruler. Tissue depth (grade rule—GR) was also measured, as described by Kirton and Johnson [
13]. Carcasses were then divided into commercial cuts according to the Chilean standard jointing procedure for lambs [
14]. Commercial cuts were prepared and trimmed by experienced butchers and the trimmed cuts and trimmings were weighed.
Longissimus muscles were vacuum packaged and transported to the meat laboratory of INIA-Remehue, Chile and kept frozen at −18 °C until analyses.
2.3. Color, pH and Texture
The Longissimus muscle samples were thawed for analysis for 48 h at 4 ± 2 °C, after which instrumental color was measured. The samples were then kept at room temperature for 30 min before measuring pH levels with a pH meter (HI 99163, Hanna Instruments, Madrid, Spain) with a penetration electrode (FC 232, Hanna Instruments). To analyze shear force, samples were cut into 3 cm samples and the external fat was removed. The samples were cooked in an oven at 170 °C until reaching a central temperature of 73 ± 1 °C (approximately 15 min). After being cooked, the samples were chilled at 4 ± 2 °C for 24 h. Some 6 to 10 1.3 cm circular specimens were extracted with a hollow punch to measure shear force with a texture analyzer (TA-XT2i, Stable Micro Systems, Godalming, UK) using the Warner–Bratzler method (WBSF) at a crosshead speed of 1 mm s−1, yielding the shear force (kgf).
2.4. Fatty Acid Composition
Samples of 10 g were used for the fatty acid analyses of meat, at the Animal Nutrition and Environment Laboratory of INIA Remehue in Osorno, Chile. Fat extraction method was performed according to Lumley and Colwell [
15]. In the case of the meat, the trans methylation was done in accordance with Ichihara et al. [
16]. After phase separation, the supernatant was collected and analyzed by gas chromatography. The FA profile was determined in a gas chromatograph (GC-2010 plus Shimadzu, Kyoto, Japan) equipped with a flame ionization detector. A capillary column SP-2560 (Sigma-Aldrich, Bellefonte, Pennsylvania, USA) of 100 m × 0.25 mm × 0.25 µm film was used. Helium was used as the carrier gas at 1.0 mL min
−1 with an inlet pressure of 15 psi, using the split injection method (100:1). The injector temperature was fixed at 250 °C and the detector temperature at 260 °C. The injected sample volume was 1.0 µL and the oven temperature was programmed to increase from 140 (held for 5 min) to 240 °C (held for 15 min) at 4 °C min
−1. Fatty acids were identified by comparing the retention times of the chromatograph peaks to those of the methyl esters from a mixture prepared with a 37-component FAME mix standard (Standard: 47885-U, Sigma-Aldrich Co, St. Louis, MI, USA), C18:1 t-11 methyl ester standard (Standard: 46905-U, Sigma-Aldrich) and c-9, t-11 octadecadienoic conjugated methyl acid (Standard: 10-1823-7, Larodan AB, Malmo, Sweden).
2.6. Statistical Procedures
The data were subjected to ANOVA to examine the effect of grazing group (two treatments after weaning) on lamb performance, carcass characteristics and meat cut characteristics. For the chemical and physical characteristics and FA composition of meat, comparisons were made between the three production systems (including the “at weaning” treatment). Comparisons of discrete variables (KKCF grade, fat grade and conformation classification) were performed using Kruskal–Wallis non parametric test. These data were analyzed using the General ANOVA procedure in InfoStat Software (Facultad de Ciencias Agropecuarias, Universidad Nacional de Córdoba, Argentina), considering a completely randomized design, treatment differences were tested for significance at the 0.05 probability level based on the Fisher’s least significant difference (LSD) method. The ANOVA for sensory data (tenderness, juiciness and flavor) were performed with the General Linear Model (GLM) procedure of the SAS system (SAS Inst. Inc., Cary, NC, USA). Treatments were used as fixed effects and differences among effects were tested using Tukey’s test.