ABSTRACT

We evaluated performance, non-carcass components, and carcass characteristics of crossbred Texel lambs in different categories of residual intake and gain (RIG). We assessed 77 crossbred (¼ Pantaneira and ¾ Texel) non-castrated animals in two study phases. The first phase included 47 lambs with an initial average weight of 29.9±5.5 kg, and the second phase included 30 lambs with initial average weight of 22.4±3.3 kg. Dry matter intake (DMI) and average daily gain (ADG) were evaluated for 70 days. Animals were divided into three groups in terms of efficiency: efficient (high RIG), intermediate (medium RIG), or inefficient (low RIG), based on the standard deviation of the mean for the RIG variable. We measured the yield of non-carcass components, carcass characteristics, and yield of meat cuts. Efficiency group had no association with DMI, nor with initial and final body weights of the animals. The ADG of efficient (0.310 kg day⁻¹) and intermediate (0.290 kg day⁻¹) animals was greater than observed in inefficient (0.260 kg day⁻¹) animals. Lambs in the efficient and intermediate groups had significantly higher levels of all efficiency indicators evaluated. Efficient and intermediate animals yielded significantly more wool/skin in comparison with lambs in the inefficient group. Animals with high RIG also had lower relative weight of testicles/scrotal sac in comparison with inefficient animals. Fat deposition in the omentum and mesentery as well as total fat were decreased in efficient animals. No significant differences occurred among groups regarding carcass characteristics and yield of meat cuts. The RIG index allows for the identification of lambs with higher growth rates and greater wool/skin yield and lower proportion of visceral fat.

Keywords:
feedlot; residual feed intake; sheep; tissue composition; visceral fat

Introduction

Intensive production systems and use of feed concentrates constitute some of the strategies used to avoid the exposure of lambs to verminoses and sanitary problems associated with pastures (Fernandes et al., 2011Fernandes, A. R. M.; Orrico Junior, M. A. P.; Orrico, A. C. A.; Vargas Junior, F. M. and Oliveira, A. B. M. 2011. Desempenho e características qualitativas da carcaça e da carne de cordeiros terminados em confinamento alimentados com dietas contendo soja grão ou gordura protegida. Revista Brasileira de Zootecnia 40:1822-1829. https://doi.org/10.1590/S1516-35982011000800028
https://doi.org/10.1590/S1516-3598201100... ). These strategies also boost animal performance, reducing production cycles and improving the financial viability of farms. However, intensive systems have more elevated feed costs (Pacheco et al., 2014Pacheco, P. S.; Restle, J.; Valença, K. G.; Lemes, D. B.; Menezes, F. R. and Machado, G. K. G. 2014. Análise econômica determinística da terminação em confinamento de novilhos abatidos com distintos pesos. Ciência Animal Brasileira 15:420-427. https://doi.org/10.1590/1089-6891v15i425747
https://doi.org/10.1590/1089-6891v15i425... ). The identification of lamb breeds that convert feed into body mass more efficiently can thus further reduce costs and shorten production cycles (Lima et al., 2013Lima, L. D.; Rêgo, F. C. A. R.; Koetz Junior, C.; Ribeiro, E. L. A.; Constantino, C.; Belan, L.; Gasparine, M. J.; Sanchez, A. F. and Zundt, M. 2013. Interferência da dieta de alto grão sobre as características da carcaça e carne de cordeiros Texel. Semina: Ciências Agrárias 34(6 supl 2):4053-4064.).

Several efficiency indicators exist, including feed conversion ratio (FCR), gross feed efficiency (GFE), residual feed intake, and residual body weight gain (Archer et al., 1999Archer, J. A.; Richardson, E. C.; Herd, R. M. and Arthur, P. F. 1999. Potential for selection to improve efficiency of feed use in beef cattle: a review. Australian Journal of Agricultural Research 50:147-162. https://doi.org/10.1071/A98075
https://doi.org/10.1071/A98075... ). However, animal selection based on such indices may result in excessive body weight (BW) gain, increases in adult body size, alterations to carcass composition, or increases in feed intake. Thus, Berry and Crowley (2012)Berry, D. P. and Crowley, J. J. 2012. Residual intake and gain: A new measure of efficiency in growing cattle. Journal of Animal Science 90:109-115. https://doi.org/10.2527/jas.2011-4245
https://doi.org/10.2527/jas.2011-4245... proposed a new indicator named residual intake and gain (RIG) specifically designed to identify animals that display a better BW gain:feed intake ratio. The use of RIG, which has no phenotypical dependence on BW, may improve feed efficiency, reduce confinement time, and allow for slaughter at an early stage with no elevation in the adult size of lambs.

The study of variations in feed efficiency unveils differences in responses of efficient and inefficient animals. Previous work has shown that efficient animals display different BW gain patterns, including reduced fat thickness during finishing, smaller visceral fat depots, and reduced non-carcass weight (Gomes et al., 2012Gomes, R. C.; Sainz, R. D.; Silva, S. L.; César, M. C.; Bonin, M. N and Leme, P. R. 2012. Feedlot performance, feed efficiency reranking, carcass traits, body composition, energy requirements, meat quality and calpain system activity in Nellore steers with low and high residual feed intake. Livestock Science 150:265-273. https://doi.org/10.1016/j.livsci.2012.09.012
https://doi.org/10.1016/j.livsci.2012.09... ; Redden et al., 2013Redden, R. R.; Surber, L. M. M.; Grove, A. V. and Kott, R. W. 2013. Growth efficiency of ewe lambs classified into residual feed intake groups and pen fed a restricted amount of feed. Small Ruminant Research 114:214-219. https://doi.org/10.1016/j.smallrumres.2013.07.002
https://doi.org/10.1016/j.smallrumres.20... ; Nascimento et al., 2016Nascimento, M. L.; Souza, A. R. D. L.; Chaves, A. S.; Cesar, A. S. M.; Tulio, R. R.; Medeiros, S. R.; Mourão, G. B.; Rosa, A. N.; Feijó, G. L. D.; Alencar, M. M. and Lanna, D. P. D. 2016. Feed efficiency indexes and their relationships with carcass, non-carcass and meat quality traits in Nellore steers. Meat Science 116:78-85. https://doi.org/10.1016/j.meatsci.2016.01.012
https://doi.org/10.1016/j.meatsci.2016.0... ; Moraes et al., 2017Moraes, G. F.; Abreu, L. R. A.; Ferreira, I. C. and Pereira, I. G. 2017. Genetic analysis of residual feed intake adjusted for fat and carcass and performance traits in a Nellore herd. Ciência Rural 47:e20151505. https://doi.org/10.1590/0103-8478cr20151505
https://doi.org/10.1590/0103-8478cr20151... ).

In addition to higher performance, efficient lambs should also have satisfactory quality and carcass yield. A few previous studies have attempted to correlate performance and carcass characteristics with RIG levels in bovine animals. However, data regarding sheep breeds remain scant. Thus, we assessed performance, non-carcass components, and carcass characteristics of crossbred Texel lambs segregated into three groups according to RIG.

Material and Methods

Experiments were conducted in two phases in Campo Grande, Mato Grosso do Sul, Brazil (20°26'34"S, 54°38'47" W, 532 m). The first phase took place between September and December of 2015, and the second phase between July and October of 2016. The Commission for the Ethical Use of Animals approved all procedures (case number 632/2014 – CEUA).

Animals used in this study were purchased from a farm located in the city of Ribas do Rio Pardo, Mato Grosso do Sul, Brazil. The farm is specialized in the production of lambs in the weaning phase in extensive system and aims at the marketing of lambs for rearing and finishing. During the first phase, 47 crossbred Texel lambs ($\mathrm{¼}\text{Pantaneira and}\mathrm{¾}\text{Texel}$) were used. All animals were non-castrated males at an age of 132±14 days and average initial weight of 29.9±5.5 kg. The second phase included 30 non-castrated male lambs of the same crossbreed, at an age of 106±16 days and initial average weight of 22.4±3.3 kg. During the two phases, animals received identification tags and were randomly distributed into 2.5-m² individual stalls, with slatted suspended floors and individual feeding and watering equipment.

Lambs were allowed to adapt to diet, handling, and stalls for 25 days. Feces samples were collected from all animals on the day after landing for evaluation of parasite load. All animals were weighed and treated against ectoparasites and endoparasites (active principle: Closantel, Levamisole hydrochloride, Toltrazuril, and Moxidectin). After 10 days of deworming, feces were collected again to verify if there was reduction of the parasitic load. For animals that still had infestation, the second dose was applied. During the 25 days of adaptation, each animal was provided with corn silage and gradually increasing dosage of concentrate up to the level set for diet. After adaptation, lambs were confined for 70 days.

The experimental diet was formulated according to NRC (2007) recommendations, for weight gain of 200 g day⁻¹. Silage made with the aerial part of corn was used as roughage, and the concentrate included cracked corn, soybean meal, mineral mixture, urea, and supplements. The roughage:concentrate ratio was 40:60 (Table 1). Lambs were fed twice daily, at 07:30 and 14:30 h. The amount of feed provided was adjusted daily to allow for 100 g kg⁻¹ leftovers. Water was provided ad libitum.

Samples of silage, concentrate, and leftovers were collected from each stall every 14 days and kept frozen at −20 °C until analysis. Levels of dry matter (method number 967.03), gross protein (GP) (method number 981.10), mineral matter (MM) (method number 942.05), and ether extract (EE) (method number 920.29) were determined according to the AOAC (1995)AOAC - Association of Official Analytical Chemistry. 1995. Official methods of analysis. 16th ed. AOAC International, Arlington, VA..

The analyses of neutral detergent fiber (NDF), acid detergent fiber (ADF), and lignin were conducted as per Van Soest (1991)Van Soest, P. J.; Robertson, J. B. and Lewis, B. A. 1991. Symposium: carbohydrate methodology, metabolism, and nutritional implications in dairy cattle. Journal of Dairy Science 74:3583-3597.. Levels of NDF and ADF were corrected for protein content (NDFp and ADFp). The concentration of non-fiber carbohydrates (NFC) in roughage was estimated as described by Sniffen et al. (1992)Sniffen, C. J.; Connor, J. D.; Van Soest, P.; Fox, D. G. and Russel, J. B. 1992. A net carbohydrate and protein system for evalution cattle diets. II. Carboydrate and protein availability. Journal of Animal Science 70:3562-3577.: $\text{NFC}=100-(\text{GP}+\text{MM}+\text{NDFp}+\text{EE})$. Levels of NFC in concentrate were determined according to Hall (2000)Hall, M. B. 2000. Calculation of non-structural carbohydrate content of feeds that contain non-protein nitrogen. University of Florida No. 339. A25-A32, Gainesville, FL.: $\text{NFC}=100-[(\text{GP}-\text{GP derived from urea}+\text{inclusion of urea})+\text{MM}+\text{NDFp}+\text{EE}]$. Total digestible nutrients (TDN) were calculated from the equation proposed by Cappelle et al. (2001)Cappelle, E. R.; Valadares Filho, S. C.; Silva, J. F. C and Cecon, P. R. 2001. Estimativas do valor energético a partir de características químicas e bromatológicas dos alimentos. Revista Brasileira de Zootecnia 30:1837-1856. https://doi.org/10.1590/S1516-35982001000700022
https://doi.org/10.1590/S1516-3598200100... : $91.0246-(0.571588\times \text{NDF})$.

Initial empty body weight (EBWi, kg) and final empty body weight (EBWf, kg) of the feed efficiency evaluation period were measured following 16 h of food and water fasting. The mid-test metabolic BW (MMBW) was calculated as the mean between EBWi and EBWf.

Initial body weight (BWi, kg) and final body weight (BWf, kg) were obtained before feeding to minimize differences in animal gut fill but with no food and water restriction. Lambs were weighed every 14 days without fasting for the calculation of the observed average daily gain (ADG, kg day⁻¹), which was calculated by regression between individual BW and days on feedlot using PROC REG (Statistical Analysis System, version 9.2.), in which the slope represents growth rate.

The observed dry matter intake (DMI, kg day⁻¹) was calculated as the difference between the amount of dry matter provided to each lamb and the amount of dry matter in leftover. Feed conversion ratio was calculated as the ratio between DMI and ADG, and GFE, its inverse (ADG:DMI).

Residual feed intake (RFI, kg day⁻¹) was determined from the equation proposed by Koch et al. (1963)Koch, R. M.; Swiger, L. A.; Chambers, D. and Gregory, K. E. 1963. Efficiency of feed use in beef cattle. Journal of Animal Science 22:486-494. https://doi.org/10.2527/jas1963.222486x
https://doi.org/10.2527/jas1963.222486x... : $\text{RFI}=\text{DMI}-\text{DMIp}$, in which DMIp is the predicted DMI. This one was calculated from the regression of DMI as a function of MMBW and ADG, using the MIXED procedure of the SAS, resulting in these equations for phase 1 (1) and phase 2 (2):

and

in which ε is the model error.

Residual gain (RG, kg day⁻¹) was also obtained from Koch's equation: $\text{RG}=\text{ADG}-\text{ADGp}$, in which ADGp is the predicted ADG. This one was determined from the regression of ADG as a function of MMBW and DMI, using the MIXED procedure of SAS, resulting in these equations for phase 1 (3) and phase 2 (4):

and

The RIG (kg day⁻¹) was determined from the equation proposed by Berry and Crowley (2012)Berry, D. P. and Crowley, J. J. 2012. Residual intake and gain: A new measure of efficiency in growing cattle. Journal of Animal Science 90:109-115. https://doi.org/10.2527/jas.2011-4245
https://doi.org/10.2527/jas.2011-4245... : $\text{RIG}=-1\times \text{RFI}+\text{RG}$. Both RFI and RG were previously standardized to a variance of 1, and other effects considered in the estimates of RFI and RG were ignored, because they had already been considered in the calculation of these indicators.

After 70 days in evaluation, lambs were taken to a slaughterhouse in Campo Grande, Mato Grosso do Sul. After fasting from food and water for 16 h to obtain slaughter BW (SBW), lambs were desensitized by cerebral concussion and slaughtered. Blood was collected in a recipient and weighed. Animals were skinned and eviscerated. Non-carcass components were separated and weighed, including external components (skin/wool, hooves, head, tail, and testicles/scrotal sac), organs (tongue/trachea/esophagus, heart, lungs, spleen, liver/gall bladder/diaphragm, kidneys, reproductive/urinary organs, stomachs, and small and large intestines), and visceral fat depots (cardiac, omental, mesenteric, perirenal, and inguinal). Total fat was calculated as the sum of all fat depots. Components of the gastrointestinal tract (GIT) were weighed before and after emptying of contents, for the determination of empty GIT weight.

Hot carcass weight (HCW) was measured, and hot carcass yield (HCY) calculated as $\text{HCY}=\text{HCW/SBW}\times 100$. After a 24-h cooling period at 2 °C, cold carcass weight (CCW) was also obtained, and yield was calculated as $\text{CCY}=\text{CCW/SBW}\times 100$. These variables were used in the calculation of weight loss by cooling: $\text{WLC}=(\text{HCW}-\text{CCW/HCW})\times 100$.

Cooled carcasses were cut longitudinally along the mid line with an electric saw. The left half-carcass was used in the evaluation of the following biometric indicators: external carcass length, internal carcass length (ICL), leg length, leg thickness, and maximum thoracic depth. Carcass compactness index (CCI) was calculated as $\text{CCI}=\text{CCW/ICL}$.

Loin eye area (LEA) was obtained with the exposure of the longissimus lumborum through a cut across the carcass, between the 12th and 13th thoracic vertebrae. The area exposed was drawn on tracing paper, scanned, cropped, and measured with a leaf area measuring device Li-Cor (model 3100). Subcutaneous fat thickness (SFT) was measured in the terminal third of the longissimus lumborum with a caliper (Osório and Osório, 2005Osório, J. C. S. and Osório, M. T. M. 2005. Produção de carne ovina: Técnicas de avaliação “in vivo” e na carcaça. 2.ed. Universidade Federal de Pelotas, Pelotas, RS.).

The left half-carcass was divided into eight anatomical regions [shoulder, leg, rib, loin, breast, rack, neck, and HH section (between the 9th and 11th ribs)], which were separately weighed for the determination of absolute weights and weights as a percentage of cooled half-carcass weight. Rib, loin, breast, rack, and HH section were grouped and considered a sole rib cut.

Tissue composition was determined from a sample taken from the HH section of each animal. Samples were marked, conditioned in plastic bags, and stored at −20 °C until analysis. Frozen HH section samples were thawed at 4 °C, weighed, and dissected with a scalp and surgical tweezers for the separation of muscle, fat, and bones. Tissue components were individually weighed, and percentage contribution to the total thawed HH section weight was estimated as (g of tissue/g of HH section) × 100 (Hankins and Howe, 1946Hankins, O. G. and Howe, P. E. 1946. Estimation of the composition of beef carcasses and cuts. United Sates Department of Agriculture No. 926. Washington, D.C., USA.). We also obtained the of muscle:bone and muscle:fat ratios. The proportions of muscle, fat, and bone in the carcasses were estimated with the equations proposed by Morais et al. (2016)Morais, M. G.; Menezes, B. B.; Ribeiro, C. B.; Walker, C. C.; Fernandes, H. J.; Souza, A. R. D. L.; Ítavo, C. C. B. F. and Feijó, G. L. D. 2016. Models predict the proportion of bone, muscle, and fat in ewe lamb carcasses from in vivo measurements of the 9th to 11th rib section and of the 12th rib. Semina: Ciências Agrárias 37:1081-1090..

We calculated RIG for each lamb, and three groups of animals were established during each of the two study phases as follows: animals with RIG equal to or greater than 0.5 standard deviations above the average were grouped as efficient (high RIG); those with RIG equal to or greater than 0.5 standard deviations below the average were grouped as inefficient (low RIG); and animals between these two groups were classified as intermediate (medium RIG).

Data from the two study phases were grouped and analyzed according to a completely randomized design, considering the fixed effect of RIG groups and random effect of assays, in which each animal represented an experimental unit, according to the statistical model described below (5):

in which μ is the fixed overall mean effect; βi is fixed RIG effect; γj is the random effect of assays, in which each animal represented an experimental unit; and eij is the random residual error associated with Yij.

Data were also analyzed for the presence of outliers and considered statistically significant when P<0.05, using the PROC MIXED of SAS.

Results

Among the animals evaluated, 22 (29%) were classified as inefficient (low RIG), 20 (26%) as efficient (high RIG), and 35 (45%) were placed in the intermediate group (medium RIG). The mean, maximum value, minimum value, and standard deviation for RIG in the study population were 0.00, 5.11, −4.06, and 1.78 kg day⁻¹, respectively. No significant differences for BWi, BWf, DMI, and TDN intake in absolute terms (kg day⁻¹) and as relative of BW (g kg⁻¹ day⁻¹ of BW) were observed among RIG groups (P>0.05; Table 2).

We observed a significant difference (P<0.0001) in ADG among RIG groups. Efficient and intermediate animals had ADG of 0.310 and 0.290 kg day⁻¹, respectively, which differed from inefficient animals (0.260 kg day⁻¹). Animals with high RIG were also more efficient than those with medium and low RIG (P<0.0001) in terms of FCR, GFE, RFI, and RG (Table 2). In comparison with inefficient animals, the efficient group had 27.6% lower FCR, 23.1% higher GFE, 0.150 kg day⁻¹ lower RFI, and 0.060 kg day⁻¹ greater RG (P<0.05; Table 2).

No differences were found among RIG groups in the relative weights of total non-carcass components, blood, head, hooves, tail, organs, and filled and emptied GIT (P>0.05; Table 3). Efficient and intermediate animals yielded more wool/skin (mean of 12.3 kg/100 kg of SBW) than inefficient lambs (mean of 11.0 kg/100 kg of SBW). However, the relative weight of testicles/scrotum was lower in efficient animals in comparison with inefficient animals (1.13 versus 1.33 kg/100 kg of SBW, respectively; P<0.05; Table 3). Similarly, the relative weights of omental, mesenteric, and total fat depots were greater in inefficient animals in comparison with efficient and intermediate animals (P<0.05).

No differences among groups were observed regarding SBW (46.6 kg), HCW (23.1 kg), CCW (22.5 kg), HCY (49.4 kg/100 kg of SBW), CCY (48.1 kg/100 kg of SBW), WLC (2.57 g/100 g), and carcass biometric indicators (P>0.05; Table 4).

Average shoulder, neck, rib, and leg yields were, respectively, 18.2, 7.49, 44.0, and 30.3 kg/100 kg of CCW; we found no differences among groups (P>0.05; Table 5).

Animals in different RIG groups had similar proportions of tissue components (muscle, fat, bone, muscle:fat ratio, and muscle:bone ratio) estimated from HH section samples (9th to 11th ribs; P>0.05; Table 6).

Discussion

The lack of difference for BWi and BWf among animals (P>0.05; Table 2) may result from the inclusion of RFI and RG in the model, which, in turn, were derived from MMBW. The method makes RIG phenotypically independent from BW (Koch et al., 1963Koch, R. M.; Swiger, L. A.; Chambers, D. and Gregory, K. E. 1963. Efficiency of feed use in beef cattle. Journal of Animal Science 22:486-494. https://doi.org/10.2527/jas1963.222486x
https://doi.org/10.2527/jas1963.222486x... ; Berry and Crowley, 2012Berry, D. P. and Crowley, J. J. 2012. Residual intake and gain: A new measure of efficiency in growing cattle. Journal of Animal Science 90:109-115. https://doi.org/10.2527/jas.2011-4245
https://doi.org/10.2527/jas.2011-4245... ). These results agree with previous reports by Berry and Crowley (2012)Berry, D. P. and Crowley, J. J. 2012. Residual intake and gain: A new measure of efficiency in growing cattle. Journal of Animal Science 90:109-115. https://doi.org/10.2527/jas.2011-4245
https://doi.org/10.2527/jas.2011-4245... and Nascimento et al. (2016)Nascimento, M. L.; Souza, A. R. D. L.; Chaves, A. S.; Cesar, A. S. M.; Tulio, R. R.; Medeiros, S. R.; Mourão, G. B.; Rosa, A. N.; Feijó, G. L. D.; Alencar, M. M. and Lanna, D. P. D. 2016. Feed efficiency indexes and their relationships with carcass, non-carcass and meat quality traits in Nellore steers. Meat Science 116:78-85. https://doi.org/10.1016/j.meatsci.2016.01.012
https://doi.org/10.1016/j.meatsci.2016.0... , who evaluated calves and found similar BW across groups with different RIG levels. Thus, RIG provides a good indicator of efficiency for lambs – selection with this indicator does not elevate BWf; thus, it probably does not produce increases in the adult size of the animal, which may lead to increased nutritional requirements.

The 16.1% higher ADG observed in efficient lambs may have resulted from lower maintenance energy requirements – not evaluated in the present study. Changes to energy partition in the animals may have occurred, because TDN intake through the diet was similar in all groups (Table 2). Available energy may have been directed in greater proportion to net requirements related to gain, translating into the improved performance observed in efficient animals. These results resemble those reported by Berry and Crowley (2012)Berry, D. P. and Crowley, J. J. 2012. Residual intake and gain: A new measure of efficiency in growing cattle. Journal of Animal Science 90:109-115. https://doi.org/10.2527/jas.2011-4245
https://doi.org/10.2527/jas.2011-4245... and Nascimento et al. (2016)Nascimento, M. L.; Souza, A. R. D. L.; Chaves, A. S.; Cesar, A. S. M.; Tulio, R. R.; Medeiros, S. R.; Mourão, G. B.; Rosa, A. N.; Feijó, G. L. D.; Alencar, M. M. and Lanna, D. P. D. 2016. Feed efficiency indexes and their relationships with carcass, non-carcass and meat quality traits in Nellore steers. Meat Science 116:78-85. https://doi.org/10.1016/j.meatsci.2016.01.012
https://doi.org/10.1016/j.meatsci.2016.0... , who observed that high-RIG bovine animals had, respectively, 17.7 and 20.4% greater BW gain than low-RIG animals.

The comparison of efficient and inefficient lambs shows that RIG provides a good indicator that will allow for reduced time in confinement, because accelerated growth is associated with early finishing (Leme and Gomes, 2007Leme, P. R. and Gomes, R. C. 2007. Características de carcaça de novilhos Nelore com diferente consumo alimentar residual. p.453. In: XX Reunión de la Asociación Latinoamericana de Producción Animal. Asociación Latinoamericana de Producción Animal, Cuzco, Peru.). Reduction of production cycle has a direct impact on feed costs, which represent approximately 70% of finishing stage costs (Pacheco et al., 2014Pacheco, P. S.; Restle, J.; Valença, K. G.; Lemes, D. B.; Menezes, F. R. and Machado, G. K. G. 2014. Análise econômica determinística da terminação em confinamento de novilhos abatidos com distintos pesos. Ciência Animal Brasileira 15:420-427. https://doi.org/10.1590/1089-6891v15i425747
https://doi.org/10.1590/1089-6891v15i425... ).

The similar DMI and TDN intake observed among RIG groups in the present study differ from those published by Berry and Crowley (2012)Berry, D. P. and Crowley, J. J. 2012. Residual intake and gain: A new measure of efficiency in growing cattle. Journal of Animal Science 90:109-115. https://doi.org/10.2527/jas.2011-4245
https://doi.org/10.2527/jas.2011-4245... , who observed that high-RIG calves had 5.45% lower DMI than inefficient animals. Nascimento et al. (2016)Nascimento, M. L.; Souza, A. R. D. L.; Chaves, A. S.; Cesar, A. S. M.; Tulio, R. R.; Medeiros, S. R.; Mourão, G. B.; Rosa, A. N.; Feijó, G. L. D.; Alencar, M. M. and Lanna, D. P. D. 2016. Feed efficiency indexes and their relationships with carcass, non-carcass and meat quality traits in Nellore steers. Meat Science 116:78-85. https://doi.org/10.1016/j.meatsci.2016.01.012
https://doi.org/10.1016/j.meatsci.2016.0... also reported lower DMI (9.6%) and TDN intake (10.5%) in efficient Nellore calves than in inefficient animals.

Differences observed for FCR and GFE (Table 2) were expected, because animals had similar DMI and different ADG levels. Average FCR and GFE were better among efficient animals. However, these indicators must be used with caution because of their close correlation to ADG (Archer et al., 1999Archer, J. A.; Richardson, E. C.; Herd, R. M. and Arthur, P. F. 1999. Potential for selection to improve efficiency of feed use in beef cattle: a review. Australian Journal of Agricultural Research 50:147-162. https://doi.org/10.1071/A98075
https://doi.org/10.1071/A98075... ), which could result in increases in the adult size of animals.

Total non-carcass components represented, on average, 40.6 kg/100 kg of SBW, value close to that obtained by Pompeu et al. (2013)Pompeu, R. C. F. F.; Beserra, L. T.; Cândido, M. J. D.; Bomfim, M. A. D.; Vieira, M. M. M. and Andrade, R. R. 2013. Características da carcaça e dos componentes não-carcaça de ovinos alimentados com dietas contendo casca de mamona. Revista Brasileira de Saúde e Produção Animal 14:490-507. https://doi.org/10.1590/S1519-99402013000300011
https://doi.org/10.1590/S1519-9940201300... . Wool and skin represent the most valuable non-carcass components, making up 10 to 20% of total animal value (Camilo et al., 2012Camilo, D. A.; Pereira, E. S.; Pimentel, P. G.; Costa, M. R. G. F.; Mizubuti, I. Y.; Ribeiro, E. L. A.; Campos, A. C. N.; Pinto, A. P. and Moreno, G. M. B. 2012. Peso e rendimento dos componentes não-carcaça de ovinos Morada Nova alimentados com diferentes níveis de energia metabolizável. Semina: Ciências Agrárias 33:2429-2440.; Pompeu et al., 2013Pompeu, R. C. F. F.; Beserra, L. T.; Cândido, M. J. D.; Bomfim, M. A. D.; Vieira, M. M. M. and Andrade, R. R. 2013. Características da carcaça e dos componentes não-carcaça de ovinos alimentados com dietas contendo casca de mamona. Revista Brasileira de Saúde e Produção Animal 14:490-507. https://doi.org/10.1590/S1519-99402013000300011
https://doi.org/10.1590/S1519-9940201300... ). This important source of revenue leads producers to improve herd sanitary conditions, thus increasing product quality (Santos et al., 2015Santos, C. P.; Ferreira, A. C. D.; Valença, R. L. V.; Silva, B. C. D.; Bomfim, L. E. L. M. and Silva, M. C. 2015. Componentes do peso vivo e características da carne de cordeiros alimentados com silagem de bagaço de laranja. Archives of Veterinary Science 20:21-29. https://doi.org/10.5380/avs.v20i3.37837
https://doi.org/10.5380/avs.v20i3.37837... ).

Inefficient animals had higher mean testicle/scrotal sac weight than efficient and intermediate lambs. We did not measure the separate weights of testicles and scrotal sac. However, our results likely reflect greater fat deposition in the scrotal sac of inefficient animals, which had larger visceral fat depots (P<0.05; Table 3). Furthermore, these results may be associated with the precocious sexual development of inefficient animals, because scrotal circumference is an indicator of early puberty (Kealey et al., 2006Kealey, C. G.; MacNeil, M. D.; Tess, M. W.; Geary, T. W. and Bellows, R. A. 2006. Genetic parameter estimates for scrotal circumference and semen characteristics of Line 1 Hereford bulls. Journal of Animal Science 84:283-290. https://doi.org/10.2527/2006.842283x
https://doi.org/10.2527/2006.842283x... ). We did not measure scrotal circumference in the present study. However, a strong correlation exists between the weight of testicles/scrotal sac and scrotal circumference (0.60; Santos et al., 2016aSantos, R. A.; Vargas Junior, F. M.; Seno, L. O.; Orrico, A. C. A.; Bottini Filho, F. D. E.; Senegalhe, F. B. D.; Cansian, K. and Longo, M. L. 2016a. Biometria testicular de ovinos Pantaneiros alimentados com níveis crescentes de glicerina bruta na dieta. Revista Brasileira de Saúde e Produção Animal 17:311-321. https://doi.org/10.1590/S1519-99402016000200018
https://doi.org/10.1590/S1519-9940201600... ). Thus, animals with heavier testicles would likely have larger scrotal circumference. However, more studies are needed to relate RIG to reproductive traits.

As observed with testicles/scrotal sac, relative weights of omental, mesenteric, and total fat depots were greater in inefficient animals, in comparison with efficient and intermediate animals (Table 3). These results resemble those reported by Gomes et al. (2012)Gomes, R. C.; Sainz, R. D.; Silva, S. L.; César, M. C.; Bonin, M. N and Leme, P. R. 2012. Feedlot performance, feed efficiency reranking, carcass traits, body composition, energy requirements, meat quality and calpain system activity in Nellore steers with low and high residual feed intake. Livestock Science 150:265-273. https://doi.org/10.1016/j.livsci.2012.09.012
https://doi.org/10.1016/j.livsci.2012.09... , who evaluated Nellore calves divided into groups according to RIG levels and found 21.5% lower fat deposition in the GIT of efficient animals.

The discrepancies between weight gain and visceral fat deposition observed in efficient versus inefficient animals may result from different energy partition into muscle and adipose tissues. Lambs synthetize muscle more efficiently than they do adipose tissue. For each kilogram of BW gain, the animal requires 1.2 Mcal of metabolic energy for the deposition of water and protein and 8.0 Mcal for the deposition of fat (NRC, 2007). Thus, internal fat displays a wider range of variation, and its deposition requires a larger amount of maintenance energy (Redden et al., 2013Redden, R. R.; Surber, L. M. M.; Grove, A. V. and Kott, R. W. 2013. Growth efficiency of ewe lambs classified into residual feed intake groups and pen fed a restricted amount of feed. Small Ruminant Research 114:214-219. https://doi.org/10.1016/j.smallrumres.2013.07.002
https://doi.org/10.1016/j.smallrumres.20... ). Indeed, visceral fat deposition is among the causes for inefficient energy use by farm animals (Redden et al., 2013Redden, R. R.; Surber, L. M. M.; Grove, A. V. and Kott, R. W. 2013. Growth efficiency of ewe lambs classified into residual feed intake groups and pen fed a restricted amount of feed. Small Ruminant Research 114:214-219. https://doi.org/10.1016/j.smallrumres.2013.07.002
https://doi.org/10.1016/j.smallrumres.20... ; Moreno et al., 2014Moreno, G. M. B.; Borba, H.; Araújo, G. G. L.; Voltolini, T. V.; Souza, R. A.; Silva Sobrinho, A. G.; Buzanskas, M. E.; Lima Júnior, D. M. and Alvarenga, T. I. R. C. 2014. Rendimentos de carcaça, cortes comerciais e não-componentes da carcaça de cordeiros Santa Inês alimentados com feno de erva-sal e concentrado. Revista Brasileira de Saúde e Produção Animal 15:192-205. https://doi.org/10.1590/S1519-99402014000100017
https://doi.org/10.1590/S1519-9940201400... ). Energy ingestion and the relative weight of organs were similar across the different RIG groups (Table 2). Therefore, the higher ADG of efficient animals may have resulted from lower maintenance energy expenditure in fat tissue synthesis. Lamb internal fat has no use for human consumption; thus, fat deposition directs energy away from the production of components with commercial value (Carvalho and Medeiros, 2010Carvalho, S. and Medeiros, L. M. 2010. Características de carcaça e composição da carne de cordeiros terminados em confinamento com dietas com diferentes níveis de energia. Revista Brasileira de Zootecnia 39:1295-1302. https://doi.org/10.1590/S1516-35982010000600019
https://doi.org/10.1590/S1516-3598201000... ; Moreno et al., 2014Moreno, G. M. B.; Borba, H.; Araújo, G. G. L.; Voltolini, T. V.; Souza, R. A.; Silva Sobrinho, A. G.; Buzanskas, M. E.; Lima Júnior, D. M. and Alvarenga, T. I. R. C. 2014. Rendimentos de carcaça, cortes comerciais e não-componentes da carcaça de cordeiros Santa Inês alimentados com feno de erva-sal e concentrado. Revista Brasileira de Saúde e Produção Animal 15:192-205. https://doi.org/10.1590/S1519-99402014000100017
https://doi.org/10.1590/S1519-9940201400... ).

The lack of effect on carcass characteristics among efficiency groups was expected, because animals were slaughtered with similar BW (P>0.05). Weight, yield, and size of animals at slaughter have a positive correlation with carcass characteristics (Cyrillo et al., 2012Cyrillo, J. N. S. G.; Nardon, R. F.; Mercadante, M. E. Z.; Bonilha, S. F. M. and Arnandes, R. H. B. 2012. Relações entre medidas biométricas, características de carcaça e cortes cárneos comerciais em bovinos Zebu e Caracu. Boletim de Indústria Animal 69:71-77.; Santos et al., 2016bSantos, N. P. S.; Guimarães, F. F.; Sarmento, J. L. R.; Sousa Júnior, A.; Rego Neto, A. A.; Sena, L. S. and Santos, G. V. 2016b. Estrutura de covariância para características de carcaça e tamanho corporal com medidas repetidas em ovinos de diferentes grupos genéticos. Revista Brasileira de Saúde e Produção Animal 17:652-665. https://doi.org/10.1590/s1519-99402016000400009
https://doi.org/10.1590/s1519-9940201600... ). Our results corroborate previous findings by Nascimento et al. (2016)Nascimento, M. L.; Souza, A. R. D. L.; Chaves, A. S.; Cesar, A. S. M.; Tulio, R. R.; Medeiros, S. R.; Mourão, G. B.; Rosa, A. N.; Feijó, G. L. D.; Alencar, M. M. and Lanna, D. P. D. 2016. Feed efficiency indexes and their relationships with carcass, non-carcass and meat quality traits in Nellore steers. Meat Science 116:78-85. https://doi.org/10.1016/j.meatsci.2016.01.012
https://doi.org/10.1016/j.meatsci.2016.0... , who evaluated HCW and HCY of Nellore calves and found no significant differences among RIG groups. Reis et al. (2015)Reis, S. F.; Fausto, D. A.; Medeiros, S. R.; Paulino, P. V. R.; Valadares Filho, S. C. and Torres Júnior, R. A. A. 2015. Feed efficiency and meat quality of crossbred beef heifers classified according to residual feed intake. Revista Brasileira de Saúde e Produção Animal 16:632-642. https://doi.org/10.1590/S1519-99402015000300014
https://doi.org/10.1590/S1519-9940201500... also found no significant differences in SBW and HCW in heifers with different RIG levels.

The average HCY (49.4 kg/100 kg SBW) found for non-castrated male lambs ($\mathrm{¾}\text{Texel}+\mathrm{¼}\text{Pantaneiro}$) in our study was higher than that reported by Carvalho and Medeiros (2010)Carvalho, S. and Medeiros, L. M. 2010. Características de carcaça e composição da carne de cordeiros terminados em confinamento com dietas com diferentes níveis de energia. Revista Brasileira de Zootecnia 39:1295-1302. https://doi.org/10.1590/S1516-35982010000600019
https://doi.org/10.1590/S1516-3598201000... for non-castrated male lambs ($\mathrm{½}\text{Texel}+\mathrm{½}\text{underfined}$; 47.4 kg/100 kg SBW). Lima et al. (2013)Lima, L. D.; Rêgo, F. C. A. R.; Koetz Junior, C.; Ribeiro, E. L. A.; Constantino, C.; Belan, L.; Gasparine, M. J.; Sanchez, A. F. and Zundt, M. 2013. Interferência da dieta de alto grão sobre as características da carcaça e carne de cordeiros Texel. Semina: Ciências Agrárias 34(6 supl 2):4053-4064. also published HCY (48.7 kg/100 kg SBW) and CCY (47.2 kg/100 kg SBW) for male Texel lambs that were lower than those found in the present work. Thus, we found good HCY (49.4 kg/100 kg SBW) and CCY (48.1 kg/100 kg SBW) that fell within the ideal range of 40 to 50 kg/100 kg SBW established for meat-producing sheep breeds, such as Texel (Silva Sobrinho, 2006Silva Sobrinho, A. G. 2006. Criação de ovinos. 3.ed. FUNEP, Jaboticabal.).

Weight loss by cooling did not vary significantly across RIG groups. The level of WLC observed was adequate (2.57 g/100 g), falling within the previously reported range of 1 to 7 g/100 g for sheep (Martins et al., 2000Martins, R. R. C.; Oliveira, N. M.; Osório, J. C. S. and Osório, M. T. M. 2000. Peso vivo ao abate como indicador do peso e das características quantitativas e qualitativas das carcaças em ovinos jovens da raça Ideal. Embrapa Pecuária Sul No. 21. Bagé, RS.). This indicator varies with the uniformity of fat layer on the carcass, sex, SBW, temperature, and relative humidity of the cold chamber.

Carcass biometric indicators may have reflected the observed lack of variation in SBW, because biometric indicators are associated with SBW (Pinheiro and Jorge, 2010Pinheiro, R. S. B. and Jorge, A. M. 2010. Medidas biométricas obtidas in vivo e na carcaça de ovelhas de descarte em diferentes estágios fisiológicos. Revista Brasileira de Zootecnia 39:440-445. https://doi.org/10.1590/S1516-35982010000200030
https://doi.org/10.1590/S1516-3598201000... ; Cyrillo et al., 2012Cyrillo, J. N. S. G.; Nardon, R. F.; Mercadante, M. E. Z.; Bonilha, S. F. M. and Arnandes, R. H. B. 2012. Relações entre medidas biométricas, características de carcaça e cortes cárneos comerciais em bovinos Zebu e Caracu. Boletim de Indústria Animal 69:71-77.). Similarly, Nascimento et al. (2016)Nascimento, M. L.; Souza, A. R. D. L.; Chaves, A. S.; Cesar, A. S. M.; Tulio, R. R.; Medeiros, S. R.; Mourão, G. B.; Rosa, A. N.; Feijó, G. L. D.; Alencar, M. M. and Lanna, D. P. D. 2016. Feed efficiency indexes and their relationships with carcass, non-carcass and meat quality traits in Nellore steers. Meat Science 116:78-85. https://doi.org/10.1016/j.meatsci.2016.01.012
https://doi.org/10.1016/j.meatsci.2016.0... could not find differences in carcass depth and internal length when assessing Nellore calves segregated according to RIG level. Basarab et al. (2003)Basarab, J. A.; Price, M. A.; Aalhus, J. L.; Okine, E. K.; Snelling, W. M. and Lyle, K. L. 2003. Residual feed intake and body composition in young growing cattle. Canadian Journal of Animal Science 83:189-204. https://doi.org/10.4141/A02-065
https://doi.org/10.4141/A02-065... evaluated the carcasses of bovine animals within different RIG groups and did not observe differences in internal and external carcass length, thoracic depth, and leg length and thickness. These measurements provide a good indicator of carcass and meat cut yields (Cyrillo et al., 2012Cyrillo, J. N. S. G.; Nardon, R. F.; Mercadante, M. E. Z.; Bonilha, S. F. M. and Arnandes, R. H. B. 2012. Relações entre medidas biométricas, características de carcaça e cortes cárneos comerciais em bovinos Zebu e Caracu. Boletim de Indústria Animal 69:71-77.). They also constitute an important data set for the evaluation of carcasses according to sheep carcass classification systems (União Europeia, 2008União Europeia. 2008. Regulamento (CE) N.° 22/2008 da Comissão, de 11 de janeiro de 2008, que estabelece as regras de execução da grelha comunitária de classificação das carcaças de ovinos. Jornal Oficial, n° L 9 de 12/01/2008.).

A few indicators assess the quality of the final commercial product (Souza et al., 2014Souza, D. S.; Silva, H. P.; Carvalho, J. M. P.; Melo, W. O.; Monteiro, B. M. and Oliveira, D. R. 2014. Desenvolvimento corporal e relação entre biometria e peso de cordeiros lactantes da raça Santa Inês criados na Amazônia. Arquivo Brasileiro de Medicina Veterinária e Zootecnia 66:1787-1794. https://doi.org/10.1590/1678-7364
https://doi.org/10.1590/1678-7364... ), such as carcass compactness index, which had an average of 0.35 kg/cm in the present study. Variations in RIG level did not correspond to changes in LEA and SFT assessed through cuts to the longissimus lumborum muscle (P>0.05). According to Silva Sobrinho and Osório (2008), the SFT reported here (5.58 mm) falls within the adequate range for animals in the finishing stage (5 to 10 mm). This fat layer may have contributed to a relatively low WLC (2.57 g/100 g), because fat protects carcasses against water loss during the cooling process (Silva et al., 2014Silva, R. M.; Restle, J.; Missio, R. L.; Lage, M. E.; Pacheco, P. S.; Bilego, U. O.; Pádua, J. T. and Fausto, D. A. 2014. Perfil de ácidos graxos da carne de novilhos europeus e zebuínos alimentados com milheto. Pesquisa Agropecuária Brasileira 49:63-70. https://doi.org/10.1590/S0100-204X2014000100009
https://doi.org/10.1590/S0100-204X201400... ).

Gomes et al. (2012)Gomes, R. C.; Sainz, R. D.; Silva, S. L.; César, M. C.; Bonin, M. N and Leme, P. R. 2012. Feedlot performance, feed efficiency reranking, carcass traits, body composition, energy requirements, meat quality and calpain system activity in Nellore steers with low and high residual feed intake. Livestock Science 150:265-273. https://doi.org/10.1016/j.livsci.2012.09.012
https://doi.org/10.1016/j.livsci.2012.09... as well as Reis et al. (2015)Reis, S. F.; Fausto, D. A.; Medeiros, S. R.; Paulino, P. V. R.; Valadares Filho, S. C. and Torres Júnior, R. A. A. 2015. Feed efficiency and meat quality of crossbred beef heifers classified according to residual feed intake. Revista Brasileira de Saúde e Produção Animal 16:632-642. https://doi.org/10.1590/S1519-99402015000300014
https://doi.org/10.1590/S1519-9940201500... reported similar results and found no differences in LEA and SFT in the carcass of calves that had been grouped according to RFI level. Nascimento et al. (2016)Nascimento, M. L.; Souza, A. R. D. L.; Chaves, A. S.; Cesar, A. S. M.; Tulio, R. R.; Medeiros, S. R.; Mourão, G. B.; Rosa, A. N.; Feijó, G. L. D.; Alencar, M. M. and Lanna, D. P. D. 2016. Feed efficiency indexes and their relationships with carcass, non-carcass and meat quality traits in Nellore steers. Meat Science 116:78-85. https://doi.org/10.1016/j.meatsci.2016.01.012
https://doi.org/10.1016/j.meatsci.2016.0... also did not observe differences in SFT when evaluating the longissimus lumborum of calves with varying levels of RFI and RIG. However, these authors detected larger LEA in animals with higher RFI and RIG, suggesting that the animals had greater muscle deposition. In contrast, Leme and Gomes (2007)Leme, P. R. and Gomes, R. C. 2007. Características de carcaça de novilhos Nelore com diferente consumo alimentar residual. p.453. In: XX Reunión de la Asociación Latinoamericana de Producción Animal. Asociación Latinoamericana de Producción Animal, Cuzco, Peru. reported lower SFT in bovine animals classified as efficient according to RFI.

Despite divergent results regarding RFI, a few studies suggest that the use of this indicator may produce carcasses with decreased fat finishing. The fat layer has a direct association with qualitative aspects of carcasses (Yamamoto et al., 2013Yamamoto, S. M.; Silva Sobrinho, A. G.; Pinheiro, R. S. B.; Leão, A. G. and Castro, D. P. V. 2013. Inclusão de grãos de girassol na ração de cordeiros sobre as características quantitativas da carcaça e qualitativas da carne. Semina: Ciências Agrárias 34:1925-1934.). Thus, losses during finishing can negatively affect carcass value. Moreover, animals with less subcutaneous fat deposition are late developers that need more time in confinement, which, increase production costs. The association of RIG and SFT may eliminate the problem of insufficient fat at slaughter, because RIG identifies animals with elevated growth rates and adequate finishing.

The similar yield of meat cuts observed in all RIG groups reflects the similar SBW and carcass sizes of animals in different groups. Previous works provided evidence of moderate to high correlation among BW, carcass yield, and yield of meat cuts in sheep (Pinheiro and Jorge, 2010Pinheiro, R. S. B. and Jorge, A. M. 2010. Medidas biométricas obtidas in vivo e na carcaça de ovelhas de descarte em diferentes estágios fisiológicos. Revista Brasileira de Zootecnia 39:440-445. https://doi.org/10.1590/S1516-35982010000200030
https://doi.org/10.1590/S1516-3598201000... ; Souza et al., 2014Souza, D. S.; Silva, H. P.; Carvalho, J. M. P.; Melo, W. O.; Monteiro, B. M. and Oliveira, D. R. 2014. Desenvolvimento corporal e relação entre biometria e peso de cordeiros lactantes da raça Santa Inês criados na Amazônia. Arquivo Brasileiro de Medicina Veterinária e Zootecnia 66:1787-1794. https://doi.org/10.1590/1678-7364
https://doi.org/10.1590/1678-7364... ). According to Fernandes et al. (2011)Fernandes, A. R. M.; Orrico Junior, M. A. P.; Orrico, A. C. A.; Vargas Junior, F. M. and Oliveira, A. B. M. 2011. Desempenho e características qualitativas da carcaça e da carne de cordeiros terminados em confinamento alimentados com dietas contendo soja grão ou gordura protegida. Revista Brasileira de Zootecnia 40:1822-1829. https://doi.org/10.1590/S1516-35982011000800028
https://doi.org/10.1590/S1516-3598201100... , when animals of the same breed have equivalent body conformation, their carcass weight, carcass yield, and relative weight of meat cuts are also similar.

Lima et al. (2013)Lima, L. D.; Rêgo, F. C. A. R.; Koetz Junior, C.; Ribeiro, E. L. A.; Constantino, C.; Belan, L.; Gasparine, M. J.; Sanchez, A. F. and Zundt, M. 2013. Interferência da dieta de alto grão sobre as características da carcaça e carne de cordeiros Texel. Semina: Ciências Agrárias 34(6 supl 2):4053-4064. assessed Texel lambs with SBW of 40.6 kg and found shoulder, neck, rib, and leg yields of 19.3, 5.72, 41.4, and 32.6 kg/100 kg of CCW, respectively, values that closely match those reported here. Cutting the carcass into specific parts that suit different consumers optimizes yield, avoids waste, and allows for adequate pricing (Silva Sobrinho and Silva, 2000Silva Sobrinho, A. G. and Silva, A. M. A. 2000. Produção de carne ovina – Parte II. Revista Nacional da Carne 286:30-36.). Such process represents an important step in the production of lamb meat.

The mean proportions of carcass muscle (52.8 kg/100 kg of CCW) and bone (14.8 kg/100 kg of CCW) were lower than those reported by Rosa et al. (2002)Rosa, G. T.; Pires, C. C.; Silva, J. H. S.; Motta, O. S. and Colomé, L. M. 2002. Composição tecidual da carcaça e de seus cortes e crescimento alométrico do osso, músculo e gordura da carcaça de cordeiros da raça Texel. Acta Scientiarum 24:1107-1111., who studied non-castrated male Texel lambs and found proportions of 61.9 and 19.4 kg/100 kg of CCW for muscle and bone tissue, respectively. We found 29.5 kg/100 kg of CCW fat in comparison with 18.1 kg/100 kg of CCW reported by these authors. In the present work, mean values of muscle:fat and muscle:bone were 1.82 and 3.62, respectively.

Diverging results such as these, regarding muscle and fat percentages, may reflect differences in SBW and age at slaughter in other studies. Increasing SBW and age reduce the muscle:fat ratio, because each tissue reaches physiological maturity in different life phases of lambs (Lemes et al., 2014Lemes, J. S.; Osório, M. T. M.; Osório, J. C. S.; Gonzaga, S. S.; Martins, L. S.; Esteves, R. M. G. and Lehmen, R. I. 2014. Características da carcaça e da carne de cordeiros Corriedale manejados em duas alturas de milheto. Archivos de Zootecnia 63:161-170. https://doi.org/10.21071/az.v63i241.573
https://doi.org/10.21071/az.v63i241.573... ). Fat deposition is greater in more mature animals with higher SBW (Owens et al., 1995Owens, F. N.; Gill, D. R.; Secrist, D. S. and Coleman, S. W. 1995. Review of some aspects of growth and development of feedlot cattle. Journal of Animal Science 73:3152-3172. https://doi.org/10.2527/1995.73103152x
https://doi.org/10.2527/1995.73103152x... ). The weight of mature Texel lambs is 37.0 kg (Malhado et al., 2008Malhado, C. H. M.; Carneiro, P. L. S.; Santos, P. F.; Azevedo, D. M. M.; Souza, J. C. and Affonso, R. M. 2008. Curva de crescimento em ovinos mestiços Santa Inês x Texel criados no Sudoeste do Estado da Bahia. Revista Brasileira de Saúde e Produção Animal 9:210-218.). However, lambs in the present study had a mean SBW of 46.6 kg, whereas in the previous study (Rosa et al., 2002Rosa, G. T.; Pires, C. C.; Silva, J. H. S.; Motta, O. S. and Colomé, L. M. 2002. Composição tecidual da carcaça e de seus cortes e crescimento alométrico do osso, músculo e gordura da carcaça de cordeiros da raça Texel. Acta Scientiarum 24:1107-1111.), lambs were slaughtered with weights ranging between 25 and 33 kg, providing a possible explanation for the different proportions of muscle.

Efficient and inefficient animals often have different body compositions. These differences often represent a limitation of the use of efficiency indicators: efficient animals likely display lower fat deposition and have smaller body reserves (Leme and Gomes, 2007Leme, P. R. and Gomes, R. C. 2007. Características de carcaça de novilhos Nelore com diferente consumo alimentar residual. p.453. In: XX Reunión de la Asociación Latinoamericana de Producción Animal. Asociación Latinoamericana de Producción Animal, Cuzco, Peru.). This premise is aligned with previous findings (Basarab et al., 2003Basarab, J. A.; Price, M. A.; Aalhus, J. L.; Okine, E. K.; Snelling, W. M. and Lyle, K. L. 2003. Residual feed intake and body composition in young growing cattle. Canadian Journal of Animal Science 83:189-204. https://doi.org/10.4141/A02-065
https://doi.org/10.4141/A02-065... ) indicating decreased fat deposition in efficient animals grouped by RFI level. Nevertheless, Reis et al. (2015)Reis, S. F.; Fausto, D. A.; Medeiros, S. R.; Paulino, P. V. R.; Valadares Filho, S. C. and Torres Júnior, R. A. A. 2015. Feed efficiency and meat quality of crossbred beef heifers classified according to residual feed intake. Revista Brasileira de Saúde e Produção Animal 16:632-642. https://doi.org/10.1590/S1519-99402015000300014
https://doi.org/10.1590/S1519-9940201500... evaluated HH section carcass composition of calves grouped according to RFI and found no significant differences among groups.

In general, carcasses produced during the current study had good muscle composition and fat finishing within the adequate range for commercial cuts. The Texel breed and its crossbreeds are known for producing lean meat with a better muscle:bone ratio (Mendonça et al., 2008Mendonça, G.; Osório, J. C. S.; Osório, M. T. M.; Silveira, I. D. B.; Gonçalves, M. and Rocha, A. 2008. Época de nascimento sobre a composição regional e tecidual da carcaça de cordeiros da raça Texel. Revista Brasileira de Zootecnia 37:1072-1078. https://doi.org/10.1590/S1516-35982008000600018
https://doi.org/10.1590/S1516-3598200800... ). The diet used in our study allowed animals to perform at their fullest potential, with ADG values above the expected in every RIG group. The higher growth rate of efficient animals and adequate finishing indicate that the appropriate use of RIG as indicator might reduce the production cycle.

Conclusions

As an indicator, residual intake and gain index allows for the identification of crossbred Texel lambs with higher growth rates, greater wool and skin yield, and lower proportion of undesirable non-carcass components such as visceral fat, without impairing carcass characteristics and yield of meat cuts.

Acknowledgments

We greatly thank the Fundação de Apoio ao Desenvolvimento do Ensino, Ciência e Tecnologia do Estado de Mato Grosso do Sul (FUNDECT; grant no. 23/200.308/2014) and Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES), for financial support and fellowships granted. We also thank the Universidade Federal de Mato Grosso do Sul (UFMS), for assistance in performing the experiment; Empresa Brasileira de Pesquisa Agropecuária (EMBRAPA Beef Cattle), for the infrastructure and material provided for slaughter and carcass processing; and Macal Nutrição Animal company, for the donation of the concentrate supplement used in the experiment.

References

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