Abstract
A total of 21 fat-tail Barbarine lambs were divided into three groups. Two groups were conducted on feedlot (FL). The daily diet was oat hay and 800 g of concentrate/lamb for control feedlot group (CFL) and control plus 200 g of aromatic plant (AP) of pasture for the second group (APFL). The last group was conducted on a natural pasture (NPG – natural pasture grazing group) rich with APs; sheep received daily 400 g/lamb of the same concentrate. At the end of the experiment, 70 days, all lambs were slaughtered. The average daily gain was 161 ± 11 g, and the slaughter body weight was 43 kg for all groups. Also, daily muscle and fat gains were similar for all groups. The initial pH was significantly higher for NPG than for both the FL ones. The use of AP increased a* and b* values for both rearing modes (16.4 vs. 15.5 and 7.3 vs. 5.8, respectively) but lightness value only for NPG group (L* = 37.3). Meat from NPG and APFL groups was more tender than that of FL one. However, meat juiciness was lower for grazing than for both the FL groups. In conclusion, with the half quantity of concentrate grazing natural pasture system resulted in the same growth rate as FL. The use of APs in natural pasture or in FL system leads to the same growth rate and tends to improve carcass traits. Furthermore, this use resulted in an increase in meat tenderness and lightness.
1. Introduction
In the Mediterranean area, sheep feeding is based on natural resources, range land, fallow, and stubble with small concentrate amounts, while the lamb's fattening ration in feedlot (FL) is generally based on hay and concentrate offered ad libitum (Atti et al. Citation2003). The concentrate is often expensive without guarantee for consumers concerning meat value appreciation. However, and particularly in well-watered years, grazing is available in whole land parts during a period of 3–5 months in spring. It was shown that grazing natural fallow lambs reached slaughter age with a higher weight and less carcass adiposity FL ones (Atti & Abdouli Citation2001). This production system improved the quality aspects of products (Demeyer Citation1992), with a reduction of expensive concentrate feeds cost. On the other hand, in almost all regions in the world, people believe that meat of sheep and beef produced on grassland and natural pasture has a superior quality (Ådnøy et al. Citation2005; Resconi et al. Citation2010) and could result in additional market values (Cox et al. Citation2006). In the South Mediterranean Region, the grassland is limited, but natural land with shrubs and annual species are well extended and mostly rich in aromatic plants (AP). In the people's mind, the AP naturally consumed by animals in pasture could originate the typical meat taste and carcass quality. These plants could improve animal's product quality via their essential oils. Finishing lambs on a spring natural grazing pasture could be an alternative and cheap solution to the classic hay-concentrate ration.
The objective of this work was to study the growth and eating quality of one-year old lambs finished at natural grazing pasture or receiving pasture AP in FL as alternative to classic hay-concentrate ration in FL.
2. Material and methods
2.1. Experimental design
The experiment was conducted at Ouesslatia, experimental farm of the National Institute of Agricultural Research of Tunisia (INRAT). A plot of 0.75 ha of natural pasture with presence of APs and dominance of Artemisia herba-alba and Rosmarinus officinalis, known for the content of essential oils, was used. A total of 21 fat-tail Barbarine lambs, 12-months-old and 35 ± 1.1 kg average body weight (BW) were divided into three equal groups according to BW and initial muscle and fat weights calculated according to Atti and Ben Hamouda (Citation2004) equations for fat-breeds.
One group grazed on NPG for 6 h per day and received a daily supplementation of 400 g/lamb of concentrate. The two other groups were conducted on FL with oat hay ad libitum. Animals of control FL (CFL) group received 800 g of the same concentrate. Animals of the last group received 800 g of concentrate plus 200 g of fresh foliage of dominant aromatic plants (APFL) of pasture (Artemisia and rosemary). Animals of all groups had free access to water. At the end of the growth trial, 14 days adaptation and 56 days experiment duration (March–May), all animals were slaughtered at an average BW of 43 kg.
2.2. Biomass estimation
The biomass availability in the grazed field was estimated from cut and weighed grass within a square of 1 m2 thrown six times randomly in different parts of the parcel. This operation was repeated on three occasions during the period of the experiment (early March, early April, and beginning May). Thus, the daily amount available during the period of grazing was determined by dividing the amount of available grass by the number of lambs and the number of grazing days. This quantity was estimated in two periods; the first corresponds to the average biomass of the early and mid-test and the second to the average biomass at middle and end of test.
2.3. Experimental measurements
Sheep were weekly weighed just prior to feed distribution. Indoor, quantities of feeds offered were daily recorded. Fat-tail circumference, width, and depth were recorded at the beginning and at the end of experiment in order to calculate muscle and adipose tissue contents at these stages. At the end of the growth trial, all animals were slaughtered at an average BW of 43.8 ± 1.37 kg.
Before slaughter, lambs’ BW were recorded; then weights of the different components of offal were determined. All fractions of the digestive tract were weighed full, then empty after hand rinsing in order to determine the weight of the digestive contents. Warm carcass weight (WCW) was recorded, and then the carcasses were stored during 24 h at +4°C. Cold carcass weight (CCW) was recorded. Fat color (white, yellowish, or yellow) and persistence (hard, tender, or oily) and lean color (red or rosy) were assessed visually. The fat tail was removed, and the carcass was split longitudinally into two halves. The left half-carcass was cut into six joints (leg, lumbar region, flank, thoracic region, neck, and shoulder), following the procedures of Colomer-Rocher et al. (Citation1972). Every joint was weighed and dissected in fat, muscles, and bones. The longissimus dorsi (LD) muscles were taken. Samples of these muscles of which subcutaneous fat was removed were separated and conserved at –20°C until meat quality evaluation, and other samples of LD were taken for sensorial quality determination.
2.4. Meat laboratory analysis
The pH was measured on LD muscle at slaughter (initial) and 24-h postmortem (ultimate) with a penetrating electrode connected to a pH 330i SET (WTW, Germany) after calibration with two buffers (7.00 and 4.01).
A Minolta Chromameter CR 400 (Minolta, Japan) was used to measure color parameters in the CIE–L*, a*, b* system (where L* measures relative lightness, a* relative redness, and b* relative yellowness), with the mean of two measurements taken across the same section of muscle. The chromameter was calibrated with a standard white tile before measuring color.
For cooking loss determination, meat samples of LD muscle were weighed (Wi) and held in plastic bags and then immersed in a water-bath at 75°C and heated for 30 min until the internal temperature reached 75°C, which was monitored with a thermocouple. Then the bags were cooled under running tap water for 30 min and blotted dry with paper towels. The cooked meat was weighed again (final weight, Wf) and cooking loss was calculated as 1000 × (Wi−Wf)/Wi.
2.5. Meat sensory evaluation
For sensory analysis, not salt samples of LD were roasted in aluminum paper in a preheated oven at 180°C. Samples were then presented to seven trained panelists to evaluate each sample for the tenderness (scale 1–10; 1 = extremely tough, 10 = extremely tender), juiciness (scale 1–10; 1 = extremely dry, 10 = extremely juicy), and flavor (scale 1–10; 1 = very poor, 10 = very good). The analysis occurred in a big room where each panelist had its own table and was separate from the others by a white cardboard plaque.
Each cooked sample had been cut into seven pieces of 1 × 1 cm and each piece was coded. Bread and water were provided for each panelist to freshen their mouth between each two samples.
2.6. Statistical analysis
Statistical analysis was performed by analysis of variance using the general linear model (GLM) procedure of SAS (Citation1989; The SAS Institute, Cary, NC, USA). The effects of dietary treatment on sheep growth, carcass composition and meat characteristics were analyzed according to the following model:
The following contrasts were used to compare the effects of the different diets:
3. Results and discussion
3.1. Fed intake, biomass production, and availability
For both FL groups, mean daily dry matter (DM) intake was 0.9 kg of hay and 0.750 kg of concentrate. The evolution of biomass production during the different stages of the experiment was illustrated in the . The experimental year was well-watered, and the plot production permits an availability of fodder for the grazing animals of about 5 kg for the first period and remains almost the same during the other periods, which shows that the vegetal production is diversified and well developed. Referring to the whole FL intake (1.650 kg DM) and considering lower compactness of the grazed species, sheep can reach an intake of 2–2.5 kg of DM in pasture. Hence, intake did not exceed the half of the grass availability. From where it will be possible to at least double the loading and reach 15–18 lambs per ha in similar watering conditions.
Table 1. Grass production and availability.
3.2. Growth performance and carcass characteristics
At the beginning of the experiment, animals of different groups had an average BW of 34.8 ± 1.14 kg. The final BW and average daily gain (ADG) of NPG group, receiving the smaller amounts of concentrate, were slightly higher than both FL groups, although the effect of diet on the weight change was not significant (). It was shown that Barbarine lambs realized the best growth performance on pasture (Sarson et al. Citation1971; Atti & Haj Taieb Citation1989; Atti & Abdouli Citation2001). The intake of small quantity (200 g) of AP in FL system remained without effect on lamb's growth, and the C3 was not significant, and this is in disagreement with results of Devant et al. (Citation2006). These authors showed that a mixture of AP incorporation in young Holstein bulls feeding had a positive effect on animal's growth.
Table 2. Effect of rearing system and aromatic plants incorporation on lamb‘s growth, offal and carcass characteristics.
The carcass weight and the dressing percentage were higher for NPG group than both FL ones (), although there was the similarity of slaughter BW (42.7 kg). So with the halve concentrate quantity, grazing lambs had similar growth performances but higher carcass weight than FL ones, which confirmed other findings on better efficiency of grazing system (Atti & Abdouli Citation2001; Nuernberg et al. Citation2005). Also, the intake of large amount of AP in pasture would originate the observed changes in the fermentation profile in the rumen, gut importance, and consequently, on carcasses weight (Devant et al. Citation2006). However, for the current study, gut and red organ's importance was similar for all groups, but digestive contents were lower for NPG than CFL and APFL groups (), which partially explained the higher dressing percentage and carcass weight for NPG animals.
Fat consistency and lean color as visually assessed were not affected by diet treatments. In all carcasses, the fat was white and tender, and the lean was rose. These characteristics were appreciated by the Mediterranean consumers (Priolo et al. Citation2002).
3.3. Carcass composition
3.3.1. Carcass joints
As proportions of the carcass, the main joints represented 34.5%, 16.8%, and 17.2% of the half-carcass for the leg, shoulder, and thoracic region, respectively (). These proportions were within the range of earlier reported results for lambs (Atti et al. Citation2003; Karim et al. Citation2007). The thoracic region had similar values for all diet treatments. While leg and shoulder proportions were higher for NPG than other groups, the contrast C1, reflecting the grazing effect, was significant. However, the C3 was not significant eliminating the effect of AP in FL. This result is inconsistent with the constancy of joint proportions in the carcass according to the anatomical harmony established by Boccard and Dumont (Citation1960) and confirmed by several authors (Sents et al. Citation1982; Atti et al. Citation2003; Rodríguez et al. Citation2008). The sum of the main cuts averaged 65.9%, 69.0%, and 70.5% of the half carcass for CFL, APFL, and NPG group, respectively. This global proportion was also higher for NPG and APFL groups and the contrasts C1 and C3 were significant. It could be concluded that the grazing pasture system resulted in higher proportion of preferred joints.
Table 3. Effect of rearing system and aromatic plants incorporation on carcass composition.
3.3.2. Tissular composition
Data related to carcass dissection were shown in , and those related to estimation of initial and final muscle and fat weight in . Carcass composition was similar for all regimens; they had the same proportion of muscle (59.8 ± 3.19%) and bone (20.9 ± 2.04%) which confirmed the result of Johnson and McGowan (Citation1998), who did not register differences in muscle proportion for grazing and FL animals. Bone growth is considered more a function of age than of nutrition, so it is less affected by diet (Murray et al. Citation1974; Kamalzadeh et al. Citation1998; Atti et al. Citation2003). Also, final muscle weight and muscle proportion were similar for all diet treatments; as a tissue with an intermediate maturity, muscle depends, namely, on slaughter BW (Sents et al. Citation1982; Atti & Khaldi Citation1988; Aziz et al. Citation1992), which was practically the same for all groups.
Table 4. Effect of rearing system and APs incorporation on estimated muscle and fat importance.
Final fat weight, fat proportion, and average daily accretion were similar for all groups. It was shown that fat proportion increased with BW increasing (Macit Citation2002; Atti et al. Citation2003), while lambs from the current study had the same BW slaughter. However, in an earlier experiment on the same breed, Atti and Mehouachi (Citation2009) showed that FL lambs deposited much more fat than did the grazing animals. In both studies, the global ADG was similar for grazing and FL lambs, and the energy availability should be the same for lambs on both rearing systems. However, the climatic conditions, particularly temperature which could explain the difference in fat deposition, were different. The mentioned study (Citation2009) occurred in June–July. The grazing sheep used energy to cover supplemental requirements related to climatic conditions (Christopherson & Kennedy Citation1983; Morand-Fehr & Doreau Citation1998), the temperature is high in June–July in semi-arid areas, while FL lambs which were sheltered from the sun, used energy to deposit fat. For the current study, the temperature was fresh, and the biomass availability was high (), so grazing animals did not accomplish a lot of displacement to find food, and they did not demand more energy to cover walking and climatic conditions requirements. Although in this situation, the grazing system tends to increase muscle daily gain (63 vs. 56 g) in comparison to FL system (). Grazing animals showed a trend to increase muscle gain proportion (59% vs. 55%) and decrease fat one (41% vs. 44%), this tendency confirmed the results of other authors who found higher fat percentage for FL lambs compared to grazing ones (Atti & Abdouli Citation2001; Priolo et al. Citation2001).
3.4. Meat physical characteristics
Meat physical characteristics were shown in . As a color parameter, the lightness (L*) was not significantly affected by the feeding system, although the higher value for grazing animals. L* values for all groups remained in the range of acceptability, and meat with a lightness value equal to or exceeding 34 was on an average acceptable (Khliji et al. Citation2010). The feeding system had no significant effect on the redness (a*) parameter; however, the contrast 1 (grazing effect) was significant for this parameter, grazing animals had higher a* values than CFL and AP-FL ones which had similar values, and C3 was not significant. It was shown that animals conducted on pasture had darker meat than those of FL (Vestergaard et al. Citation2000; Priolo et al. Citation2001; Yang et al. Citation2002); this difference could be related to the different level of physical activity. The APs affected neither L* nor a* parameter. However, the b* parameter was significantly higher with AP presence in both rearing systems (grazing and FL); the contrast 2, reflecting the global effect of aromatic species, was significant for this parameter.
Table 5. Effect of rearing system and APs incorporation on meat physical characteristics.
The ultimate pH was not affected by the feeding treatment, and contrasts were not significant. However, the initial pH was significantly higher (p < 0.05) for NPG than for CFL and APFL groups, and the two contrasts (C1 and C2) were significant: the grazing system has increasing pH meat and the global effect of aromatic species has shown a positive effect on pH meat (7.07 vs. 6.94). These results corroborate with those of Priolo et al. (Citation2001), which suggest that lambs grazing grass had a higher pH than FL regimen (5.62 vs. 5.5). This can be explained by the lack of energy (glycogen) in animal's tissues related to the diet and also to locomotion.
Cooking loss from muscle was in the range of 8–11%. The higher value was detected for the grazing group (11.1 vs. 8.9); also the use of AP tends to increase this parameter (10.3 vs. 8.2). But the C1 and C2 were not significant which is consistent with other results (Mandell et al. Citation1998; French et al. Citation2001).
3.5. Meat sensory evaluation
Sensory evaluation was used to discriminate between meats from three rearing systems, given this test could discriminate between sources, genotypes, or nutritional system (Hernández-Castellano et al. Citation2013). The tenderness score varied between 6.3 and 7.6 (), and for this interval, meat was considered tender for all groups. The difference between grazing and FL groups was not significant. French et al. (Citation2001) found similar score shear force for grazing and FL cattle. The presence of APs (NPG and APFL) increased meat tenderness; the contrast 2 was significant.
Table 6. Effect of rearing system and APs incorporation on sensory attributes of roasted meat (Longissimus dorsi muscle).
The juiciness ranged from 5.6 to 6.8; meat of grazing group was less juicy and C1, reflecting the grazing effect, was significant (p < 0.05) confirming the results of Priolo et al. (Citation2002) which showed that meat of FL fattened lambs was juicier compared to meat taken from grazing lambs. Juiciness was negatively correlated with weight loss during cooking; NPG group had higher cooking loss, resulting in less juiciness (Sheridan et al. Citation2003). In the current study, the meat was considered juicy which can be explained by the low loss during cooking (). Curiously and unlike the popular belief, the flavor was not affected by the AP presence in the FL rearing system or grazing one; its average value was 7.1 for all groups. However, Mandell et al. (Citation1998) and Young et al. (Citation1999) showed that the flavor of the meat depends on the rearing mode, and they had shown that meat of animals finished on concentrate was more popular than that of animals finished on grass, while Priolo et al. (Citation2001) agree that the flavor of the meat is considered more acceptable when the animals are finished on pasture. This is the dominant popular believe in South Mediterranean area.
4. Conclusions
During the favorable seasons, grazing NPG system offers the same body gain using half the quantity of concentrate used in FL system with a tendency to gain more muscle and less fat. Incorporation of APs in diets tends to ameliorate meat sensory parameter, and it could have an important role in improving the carcass quality, but the use of small quantity did not allow concluding on this aspect. Further, research (ruminal changes) with use of APs adequate quantity or their active principle, like essential oils, is needed.
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