Different Grass Availabilities of Tropical Pasture on Performances and Carcasses of Lambs

This study aimed to identify the best green-leaf offerings of Urochloa brizantha cv. Marandu for pasture-finished lambs receiving protein-energy supplementation at the rate of 1.6% of their body weights (BW). The animals were assigned into four treatments, which consisted of varied green-leaf offerings, namely, 105, 90, 75, or 60 g of dry matter/kg of body weight (BW). Sixty-eight contemporary Texel × mixed-breed lambs with an average initial BW of 22.6 kg were used over two years of experiment. The experiment was set up in a completely randomized design, the data were evaluated by analysis of variance and the means were compared by Tukey’s test at the 0.05 significance level. There was no significant effect of year neither interaction of year with green-leaf offer. There were significant effects of leaf offer on dry matter intake (DMI) with behavior of positively linear (p<0.05). There were significant effects of green-leaf offer on final BW and average daily gain, and lambs receiving of 75 g/kg green-leaf offer showed the highest ADG (179 g/d). There were no significant differences in the carcass, meat, and primal cuts between the groups of lambs receiving different herbage offerings. There were significant effects of leaf offer on slaughter weight, hot carcass weight, and subcutaneous fat thickness. Lambs receiving of 75 g/kg leaf offer showed the highest SFT (5.8 mm). Slaughter weight and hot carcass weight averaged 41.52 kg and 20.07 kg, respectively. We recommend the treatment with leaves offer of 75 g/kg BW of Marandu pasture for the finishing of lambs supplemented at 1.6% of BW.


INTRODUCTION
Urochloa spp. (Syn. Brachiaria) is the most widely used pasture in the Brazilian cerrado biome regions by virtue of its hardiness and little need for fertilizer (Euclides et al., 2019). In those regions, productions of animals are mostly finished on pasture. However, this type of system is known to possibly result in the reduced or worsened carcass composition (Euclides et al., 2018). manding when purchasing it. Some of the first aspects considered in choosing meat at the time of purchasing are color and smell, and later, flavor and tenderness (Osório et al., 2012). The nutritional quality of the diet supplied to the animal as well as management and slaughter procedures directly influence these characteristics.
In searching for alternatives strategy to improve the composition of carcass and meat of animals reared on pasture, the producers started to adopt a supplementation technique to improve the final animal product and make the system profitable, since the other options for finishing these animals would be the feedlot, which is a rather costly practice. However, the tropical pasturebased sheep finishing system is not yet well elucidated due to the lack of information and studies investigating the ideal herbage offering for sheep to optimize performance and final-product characteristics.
In this scenario, with a view to reduce costs but to maintain a good carcass and meat qualities, also to combine animal production with pasture quality, the present study was designed to examine the performance, carcass characteristics, and meat characteristics of lambs on Urochloa brizantha cv. Marandu pasture, under varied green-leaf offerings during the finishing stage.

Location, Animals, and Diets
The experiment was conducted in the Sheep Farming Section at teaching farm (20º26'34.31''S 54º50'27.86''W; 530.7 m altitude) belonging to the Faculty of Veterinary Medicine and Animal Science (FAMEZ) at UFMS, in Terenos -MS, Brazil. All experimental procedures were approved by the Ethics Committee on Animal Use at the Federal University of Mato Grosso do Sul (UFMS) (approval no. 481/2012).
Lambs, male, contemporary (60 days old on average) Texel × mixed breed, with an initial average weight of 22.6 kg, from a pre-weaning system with slow feeding, were used for two consecutive years. The experimental period in the first year used 33 lambs and, in the second year, used 35 lambs. The animals were evaluated in the pasture after weaning at 60 days. All animals were slaughtered at six months of age (180 days old) by the end of the finishing stage.
After weighing at weaning, the 60 lambs were distributed with 12 animals per treatment. The treatments consisted of 4 offers of green leaves, namely: 105, 90, 75, and 60 g DM/kg of body weight. The supply of leaves was adjusted every 28 days, according to the variation of the animal weight and the pasture structure. The animals were weighed at the start of the experimental period and continued every 28 days to measure body weight gain and average daily gain. Body condition score (BCS) (Russel et al., 1969) and degree of anemia (Famacha ® method) were also measured, and feces were collected every 28 days to count the number of eggs per gram of feces (EPG) (Gordon & Whitlock, 1939).
Lambs were allocated to Urochloa brizantha cv. Marandu paddocks, where they grazed in a continuous grazing system with a variable stocking rate. Put-andtake animals were used whenever necessary to adjust herbage availability. All paddocks were equipped with a drinker and a trough for mineral supplementation, with unrestricted access. The supplement was provided at a rate of 1.6% of BW. The supplement was formulated according to NRC (2007), based on corn, soybean meal, and minerals, to provide a daily weight gain of 150 g/d. Its nutritional composition included 909.0 g/kg dry matter, 21% crude protein, and 3.1 Mcal ME/kg DM. The same supplement was used for all treatments during the two years of experimental periods. For calculating supplement consumption per treatment, the value of daily head, and the consumption of supplements in the trial period was considered.
Herbage dry matter was measured every 28 days by the total sampling method, which consisted of harvesting six samples per paddock near the soil level (Euclides et al., 2019). The material was collected from within 0.5 × 0.5 m metal frames that were cast over random points representative of each paddock. Areas near roads, spots of fecal accumulation, areas near troughs and drinkers, and areas with sparse herbage were avoided. After weighing and identification steps, composite samples per paddock were taken to the Laboratory of Applied Nutrition where the total aerial part was weighed, which was followed by a morphological separation to obtain the percentages of leaf, stem + sheath, and dead material (leaves and stems with progressive yellowing, darkening, and visible drying, characterizing the plant senescence stage). The amount of herbage available in each paddock (whose sizes were varied) and the percentage of the green leaf was calculated to adjust the stocking rate. Based on this calculation, it was possible to determine how many kilograms each paddock could carry according to each treatment (60, 75, 90, or 105 g/kg BW).

Forage Sampling and Analysis
Grazing simulation was performed by analyzing the way an animal was fed and the grazing site was monitored in order to obtain a representative sample of its natural and behavioral grazing habits. Monthly samples were collected manually without using scissors (Costa et al., 2019). Fecal sampling and grazing simulation were performed to obtain a sample composed of animal/treatment. After drying in an oven at 55 o C, the samples were processed in a sieve mill with sieves of 1 mm for subsequent laboratory analysis.   Internal indicator (iNDF) on forage and feces were determined using 0.5 g of samples packed in TNT bags (cut and sealed to a size of 5 × 5 cm with the porosity of 100 microns), previously dried, weighed, and incubated for 144 hours to represent the indigestible portion of the food (Costa et al., 2019), in the in vitro incubator for degradability testing (MA443 Marconi®). Next, 1600 mL of buffer solution and 400 mL of rumen inoculum were added and CO 2 was purged to maintain anaerobic conditions. After 144 h of inoculation, the bags were removed and washed in running water until fully bleached, dried, weighed then boiled for 1 hour in neutral detergent solution (Van Soest & Robertson, 1985), washed with hot water (80°C for 3 × 10 min) and acetone (10 min), dried, and weighed; this residue was considered as iNDF. Estimates of dry matter intake (DMI) was calculated, according to Lippke (2002).

Slaughter
The lambs were sent for slaughter at six months of age, after a solid-feed deprivation of 18 h. Prior to slaughtering, their body condition scores (BCS) were determined by palpating the lumbar region and assigning scores of 1.00 to 5.00 (1.00 being the worst and 5.00 was the best) (Russel et al., 1969). Additionally, in vivo measurements of body length, heart girth, rump height, rump width, chest width, and height at the withers were also taken.
The lambs were slaughtered at an abattoir under inspection in Campo Grande -MS, Brazil. Lambs were stunned and then bled by sectioning their carotid arteries and jugular veins, following the techniques proposed in the Regulation of Industrial and Sanitary Inspection of Animal Products (RIISPOA, 1997). After the slaughtering and evisceration procedures, the carcasses were weighed (hot carcass weight -HCW) and moved to a cold room where they were kept over 24 h, at 2 o C, hung by the Achilles tendons on appropriate hooks so that the tarsometatarsal joints were kept 17 cm apart. At the end of this period, cold carcass weight (CCW) was determined by calculating the percentage of chilling loss and the dressing percentage (ratio between cold carcass weight and slaughter weight).

Carcass
The colors of fat and muscle in the lamb carcasses were evaluated using a portable colorimeter (D65, 10º viewing angle) operating in the CIELab system, in which L* represents the lightness spectrum in the fat/ muscle, a* represents the color variation from green (-) to red (+), and b* defines the color variation from blue (-) to yellow (+). The carcass pH was determined using a digital pH meter by inserting the electrode directly into the muscle. The color and pH evaluations were performed on the longissimus muscle in the region between the 12th and 13th ribs.
Internal and external carcass lengths, chest depth, and leg circumference were measured (Osório et al., 1996a;Osório et al., 1996b). Subsequently, the carcass was sectioned in two parts, and the left half was weighed and sub-divided into seven anatomical regions, which were weighed individually. The percentages of these regions relative to the whole carcass were determined, as follows: loin, leg, flank, neck, ribs (anatomical base at the eight last thoracic vertebrae, along with the upper half of the corresponding ribs), rack (region whose osseous base are the five dorsal vertebrae along with the upper half of the corresponding ribs), and shoulder (Trindade et al., 2018).
The longissimus muscle area was measured transversely between the 12th and 13th ribs using transparency. Loin-eye area (LEA) was determined using AUTOCAD ® computer software. Subcutaneous fat thickness (SFT) was measured using a caliper ruler in the same longissimus section.

Meat
The samples were weighed and stored in a refrigerator for 24 h at 5 o C. After this period, they were weighed again to determine thawing losses by weight difference. Longissimus dorsi muscle samples of a 2.5-cm thickness (frozen at -20 o C) were extracted from each sample perpendicularly to the direction of the muscle fibers. Next, the muscle samples were cooked in an oven at 170 o C until they reached an internal temperature of 71 o C to determine cooking loss by difference. After the sample (longissimus muscle) was chilled and reached the temperature of 28 o C, four sub-samples of 1.23-cm thickness were sectioned in the direction of the muscle fibers to determine the shear force, using a texture analyzer (TA. XTPlus was Texture Analyzer with a Warner-Bratzler Blade probe; Texture Expert Exponent software was Stable Micro Systems, Ltd, in Godalming Surrey UK. SMS). The result corresponded to the force required to cut each meat sample. Shear force value was calculated from all samples.

Economic Analysis
The economic data involved in all proposed treatments were recorded and organized as revenue obtained from the sale of lambs and nutritional costs with supplementation. Supplement costs were calculated per day, per animal, and per hectare (30 g/d of mineral supplement/animal), and revenues were calculated as US$ 3.29 per kilogram of CCW of a slaughtered lamb.

Statistical Analysis
The experiment was set up as a completely randomized design with four levels of herbage offering, according to the following statistical model: Y= m + Of + Y + Of × Y + e, where: Y was the observed value of the evaluated variable; m was the overall constant; Of was the effect of green-leaf offering (1, 2, 3, and 4); Y was the different years (1, 2); Of × Y was the interaction effect between green-leaf offering and year; and e was the random error associated with each observation. The data were evaluated by analysis of variance and means were compared by Tukey's test at the 0.05 significance level.

RESULTS
There was no significant effect of year neither interaction of year with the green-leaf offer on all parameters measured. The average herbage mass supplied was 4779.69 kg DM/ha. This quantity consisted of 21.7% leaves, 27.7% stems, and 50.6% senescent material. There were significant effects of leaf offers on total and forage dry matter intakes (DMI) with positive linear behavior and negative linear behavior for DMI of supplement (Figure 1). Performance There were significant effects of leaf offer on final BW and average daily gain (g/d) of lambs ( Table 2). The in vivo pre-slaughter analysis of the lambs, which included final weight, body condition score, body length, chest girth, rump height, rump width, chest width, and height at the withers, revealed no significant effects of green-leaf offering in the finishing stage (Table 3).

Carcass and Meat
Herbage offering did not affect HCW, CCW, pH, internal length, external length, leg length, chest depth, leg circumference, LEA, or the color of muscle and fat (L*, a*, b*). The mean values for the respective variables were 20.07 kg, 18.55 kg, 5.82, 62.02 cm, 91.67 cm, 38.73 cm, 18.16 cm, 40.55 cm, 13.85 cm², 38.55, 15.38, 8.92, 82.83, 0.96, and 9.01, respectively. However, there was    a significant effect of leaf offering on subcutaneous fat thickness (SFT). The lambs receiving 75 g/kg offer showed the highest SFT (5.8 mm). There were no significant effects of treatments on cooking loss or shear force (p>0.05) (Table 4), which averaged 10.27 kg and 4.32 kg, respectively. In the analysis of primal cuts, there was no significant difference for the weights of loin, leg, flank, neck, rib, rack, or shoulder among the green-leaf offerings (60, 75, 90, and 105 g/kg BW) (p>0.05) ( Table 5).

Economic Analysis
The highest individual revenue per slaughtered lamb (US$66.00) was obtained in lamb, receiving a green-leaf offering of 60 g/kg BW. The best revenue per hectare (US$ 563.00) was achieved with the treatment with a leaf offering of 75 g/kg BW. The treatment with a leaf offering of 90 g/kg BW resulted in the highest cost per hectare (US$ 208.86), but which was similar to that obtained with the leaf offering of 75 g/kg BW (US$ 207.43). Lastly, the highest and best profit per hectare (US$ 356.30) was obtained by the group treated with 75 g/kg BW (Table 6).

Performance
Because there were significant effects of leaf offer for final BW and average daily gain of lambs, being the highest results in lambs receiving 75 g/kg of leaf-offer, this offer was able to meet the animal requirements just as well as the highest offering (105 g/kg BW) despite total and forage DMI were positively linear behavior and negatively linear for DMI of supplement, once the supplement was formulated according to NRC (2007), together with forage intake to meet a daily gain of 150 g/d. According to Silva (2016a), supplementation at the rate of 1.6% BW for lambs on pasture is sufficient to minimize the negative effects of low herbage quality. Note: HCW= Hot carcass weight; CCW= Cold carcass weight; SFT= Subcutaneous fat thickness; LEA= Loin-eye area; Ma= muscle color ranging from green (-) to red (+); Mb= muscle color ranging from blue (-) to yellow (+); Fa= fat color ranging from green (-) to red (+); Fb= fat color ranging from blue (-) to yellow (+); BW= body weight. Means in the same row with different superscripts differ significantly (p<0.05). In this way, the animals manage to achieve satisfactory performance, which would be similar to that of feedlotfinished lambs. Oliveira et al. (2016) stated in which the animals received 40, 80, or 120 g DM/kg of pasture, found a total weight gain of 16.85 kg/animal during the same period of this research. This value is lower than the average of 18.7 kg per animal observed in the treatment of 75 g/kg (Table 2), which shows that the performance of the production of supplemented animals can be affected when they receive varied pasture offers, as they fully meet nutritional requirements.

Carcass Characteristics
The similarity for most carcass measurements may be linked to the compensatory effect observed in food intake, and the animals that had higher leaf offerings showed less supplement intake and greater forage intake. In contrast, the animals that had less leaf supply consumed more supplements and less forage. This compensatory mechanism was not sufficient to level the nutrient intake, given the difference observed for the animals 'weight gain. However, the difference of three kg in the animals' final weight was not enough to change the weight and carcass and commercial cuts.
In commercial terms, the producer is mostly concerned with hot carcass yield (HCY), calculated as HCW divided by slaughter weight (Rezende et al., 2019). In the present study, the average carcass yield was 48.3%, higher than the 38.9% found by Trindade et al., (2018) in Santa Ines sheep finished in tropical pastures receiving supplementation at a rate of 1.38% of body weight. Several factors may have contributed to these results, from the management of rearing, weight, and age of weaning to the type of pasture used, sex, and mainly, quantity, and quality of pasture offered to the finishing lambs. Oliveira et al. (2016) analyzed the performance and carcass characteristics of mixed-breed sheep raised on pastures of two Buffel-grass cultivars, under varied herbage offerings (40, 80, and 120 g total DM/kg BW), and found respective HCW values of 18.62, 16.52, and 17.19 kg, which were lower than the average of 20.07 kg obtained by all treatments in the present experiment. It can be understood that these differences are due to the quality of herbage offered to the animals, since the quantity supplied was similar, on average. The minimum SFT to protect the carcass during chilling is 1.4 mm (Pearce et al., 2017). The average SFT observed in the treatments with herbage offerings of 60, 75, 90, and 105 g/kg BW in the present study were 3.07, 5.79, 3.52, and 4.91 mm, respectively, which meet the criteria for protection. Silva (2016b) supplemented lambs on pasture during the finishing stage at the rate of 1.6% BW and observed a fat thickness of 1.6 mm in the carcass. Oliveira et al. (2017) finished ewes in a feedlot and obtained a respective FTS value of 1.56 mm, the value that was much lower than those described in Table 4. Therefore, it is believed that supplementation is maintained at 1.6% of body weight; it was favorable to the fat of the animals under varied forage offerings. In addition, the fact that the animals were fed fluently during the pre-weaning phase may explain these high values of FTS, which a pasture-only regime would not be allowed.
Supplementation emerges in this scenario as a mean of meeting the lamb's nutritional requirements, besides directly contributing to the finishing process for slaughter. Souza et al. (2010) evaluated different supplementation levels for grazing sheep (0, 0.6, 1.3, and 2.0% BW) and found that increasing supplementation levels led to the increases in external carcass length, rump width, chest depth, rump circumference, and leg circumference. However, even more important than supplementation is an adequate herbage offering. We found no difference among leaf-offering in in vivo pre-slaughter analysis of lambs finished on Marandu pasture slaughtered at 6 months old receiving supplementation of 1.6%BW.
The rib eye area was an average of 13.85 cm², higher than the 11.95 cm² reported by Silva (2016b) in sheep supplemented with 1.6% BW in pastures of Urochloa spp. The present results are also higher than the 9.03 cm² found by Urbano et al. (2015) in sheep finished in confinement, both works were developed in experimental periods similar to this work. These differences are probably due to varying body size, body weight, and age at slaughter. The average slaughter weight in the present study was 41.5 kg, while Urbano et al. (2015) found an average of 29.5 kg.
As stated by Ítavo et al. (2019) and Silva et al. (2019), fat was the carcass component that most varied in terms of thickness, color, flavor, and quantity. In this regard, Osório et al. (2012) described the importance of fat for meat, as it gave flavor and aroma and protected it during the chilling period. Despite these assertions, there were no significant differences in the color of fat or muscle between the leaf-offering tested in the present study.

Meat Quality
No significant differences were observed for primal cuts, which may be because the animals received the same type of herbage and supplement, extracting the ideal amount of nutrients from them. In doing so, they met their requirements and achieved optimum body conditions.
Physical characteristics of meat, such as tenderness, color, and lightness, are important attributes at the time of purchase (Gois et al., 2017). In the present study, these variables did not show significant differences, because, regardless of the amount of forage or supplement consumed, the finishing system was the same. The feeding and finishing systems to which the sheep are subjected can alter the quality of their meats . The shear force was 3.5 kgf, presenting an aspect of intermediate mercies . Costa et al. (2018) obtained 7.52 kg/cm² in supplemented grazing sheep. This better softness value in this research may be due to the animal breed and, mainly, to the age of slaughtering. Younger animals of meat breeds produce softer meat when compared to animals of mixed breeds, such as those used in the present study.
The pH of meat (5.59) did not differ between the leaf offering treatments. This result suggests that the finishing system does not interfere with the quality of the final product, considering that all animals consumed the same type of herbage and received the same amount of supplement (1.6% BW). Similar findings were reported by Silva (2016b) (average pH: 5.74) and Costa et al. (2018) (average pH: 5.85), in experiments with grazing lambs.

Economic Analysis
The highest profit per slaughtered animal was achieved between the leaf-offerings of 60g/kg BW, while the highest profit per hectare was obtained in the treatment with leaf offering of 75 g DM/kg BW. Therefore, despite the lack of significant differences (p>0.05) for in vivo measurements, carcass characteristics, and meat quality variables in lambs finished on Marandu pasture and receiving supplementation at 1.6% BW, the profit can be an extremely important factor of great interest to sheep producers and consumers. We observed better profits (total, individual, and by area) in leaf offering of 75 g DM/kg BW.

CONCLUSION
We recommend 75 g/kg of BW of leaf offering of Marandu pasture for finishing lambs when aiming at the increased performance and total profit without alterations in carcass characteristics, or meat characteristics.

CONFLICT OF INTEREST
We certify that there is no conflict of interest with any financial, personal, or other relationships with other people or organizations related to the material discussed in the manuscript.