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ANIMAL GENETICS |
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* Department of Animal Science, Texas A&M University, College Station 77843-2471;
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Instituto de Zootecnia, Agência Paulista de Tecnologia dos Agronegócios, Sertãozinho, SP 14.160-900, Brazil;
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Departamento de Zootecnia, Universidade de São Paulo/Escola Superior de Agricultura "Luiz de Queiroz" (ESALQ), Piracicaba, SP 13.418-900, Brazil;
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Instituto de Zootecnia, Agência Paulista de Tecnologia dos Agronegócios, Sertãozinho, SP 14.160-900, Brazil;
and
# Instituto de Zootecnia, Agência Paulista de Tecnologia dos Agronegócios, Nova Odessa, SP 13.460-000, Brazil; and
|| PRDTA Alta Mogiana, Agência Paulista de Tecnologia dos Agronegócios, Colina, SP 14.770-000, Brazil
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Abstract |
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 Top Abstract INTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONLITERATURE CITED |
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Key Words: Caracu • Gir • growth • Guzerah • Nellore • selection
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INTRODUCTION |
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TopAbstractINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONLITERATURE CITED |
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; McKenna et al., 2002). Thus, several segments of the beef industry are striving to increase product quality, productivity, and economic returns. Once animal nutritional and health requirements are met, productivity of beef cattle herds depends on herd genetic merit (Owens et al., 1995).
Bos indicus breeds are used in several countries, including the United States (Paschal et al., 1995; Amen et al., 2007), Europe (Mateus et al., 2004), Australia (Bortolussi et al., 2005), South Africa (Van der Westhuizen et al., 2004), and India (Chakurkar et al., 2007). The historical development (Sanders, 1980) and research applications (Cartwright, 1980) of B. indicus breeds have been documented, with emphasis on their genetic potential to improve production systems in the United States (Franke, 1980; Koger, 1980; Turner, 1980). Brazil has the world’s largest commercial beef cattle herd, and the B. indicus Nellore is its most important breed, representing more than 80% of the country’s beef cattle herd (FAO, 2005).
An experimental program of selection based on postweaning growth performance of B. indicus and tropically adapted Bos taurus breeds was established in São Paulo, Brazil, to determine the response to selection for heavier BW of breeds of interest in the tropics (Razook et al., 2002a). Progress has been made to improve the growth performance of the experimental herds (Packer et al., 1986; Razook et al., 1998; Razook et al., 2002b). However, carcass characteristics and meat quality were not thoroughly evaluated in earlier studies.
The objective of this study was to evaluate the impact of selection for postweaning performance on carcass characteristics and meat quality of selected and control herds of B. indicus Nellore, Guzerah, and Gir and B. taurus Caracu breeds by using meta-analysis methodology.
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MATERIALS AND METHODS |
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TopAbstractINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONLITERATURE CITED |
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Selection Procedure
A genetic selection program has been conducted by the Instituto de Zootecnia research unit at the Sertãozinho Experimental Station, São Paulo, Brazil, since 1976 with B. indicus breeds (Nellore, Guzerah, and Gir) and a tropically adapted B. taurus breed (Caracu). In 1980, control and selected lines were established for the Nellore with bulls born in 1977 and 1978, 6 of which had a high selection differential for yearling weight. Another 4 bulls were used to form the control line. They had a selection differential for yearling weight near zero. Cows and heifers available for breeding were randomly assigned to either the control Nellore group (NeC) or the selected Nellore group (NeS). In contrast, the Guzerah (GuS), Gir (GiS), and Caracu (CaS) bulls mated to most of the cows and heifers available for breeding had a high selection differential for yearling weight. Control groups were not established for these herds.
Natural mating in multiple-sire herds was adopted, with 50% of the bulls being 2 yr old (first mating) and 50% being 3 yr old (second and last mating). Bulls were selected, within herd x year, for yearling weight corrected to 378 d, which was obtained at the end of a 168-d feeding performance test conducted under feedlot conditions. Replacement heifers in the selected herds were selected for high BW corrected to 550 d on pasture. In general, 50% of the heifers were retained, resulting in an annual culling rate of 20% of the mature cows. Mature cows were culled on the basis of age, reproductive efficiency, and calf BW. From the selected herds, males and females with higher corrected yearling BW were selected, whereas males and females with a selection differential near zero were allocated to the NeC herd.
Carcass characteristic measurements were part of the selection project to evaluate correlated responses. Samples of males from the calf crops born from 1992 to 2000 were finished after the feeding performance test and slaughtered for evaluation of carcass characteristics and meat quality. Evaluated animals represented the average BW of each herd obtained at the end of the feeding performance test, adjusted to 378 d of age. In this study, 9 calf crops of NeC, NeS, and CaS; 8 calf crops of GuS; and 4 calf crops of GiS herds were evaluated as described below.
Experiment and Progeny Descriptions
The 12th, 13th, and 14th calf crops (i.e., those born in 1992, 1993, and 1994, respectively) were represented by 12 yearling bulls/year randomly selected from the NeS, NeC, GuS, and CaS herds, totaling 144 bulls. In each calf crop, 12 yearling bulls from each herd were allocated across 3 slaughter groups. Bulls were slaughtered when bulls of the first, second, and third group reached an average of 385, 465, and 550 kg of BW, respectively, as described by Nardon et al. (2001).
The 15th calf crop was born in 1995 and was represented by 8 GuS bulls and 9 bulls/herd for the NeS, NeC, GiS, and CaS herds. Bulls were finished in a feedlot for 118 d and harvested at an average BW of 480 kg as described by Razook et al. (2001).
The 16th calf crop was born in 1996 and 11 NeS bulls and 10 bulls/breed for NeC, GuS, and CaS were sampled. They were finished on pastures of Brachiaria brizantha, Panicum maximum (Jacq) cv Tanzania, and Panicum maximum (Jacq). Bulls received mineral and energy supplementation and were harvested at an average BW of 508 kg (approximately 824 d of age) as described by Razook et al. (2002b).
The 17th calf crop was born in 1997 and 15 NeS, 12 NeC, 11 CaS, 10 GuS, and 8 GiS bulls were sampled. They were divided in 2 groups and finished in a feedlot. One group received a diet composed of 60% concentrate and 40% roughage, whereas the second group received a diet composed of 40% concentrate and 60% roughage. Bulls were slaughtered at an average BW of 517 kg, when they individually reached 4 mm of fat thickness, measured at the longissimus dorsi muscle between the 12th and 13th ribs by ultrasound equipment (PIE Medical Scanner 200 VET, Esaote Europe B.V., Maastricht, the Netherlands) as described by Resende et al. (2001).
The 18th calf crop was born in 1998 and was represented by 16 NeS, 14 CaS, 19 GuS, 12 NeC, and 12 GiS bulls. They were divided into 2 groups: one group was castrated at 15 mo of age, whereas the second group was left intact. Both groups were finished in a feedlot under the same conditions and received the same diet. Animals were slaughtered (BW of 471 kg) when they individually reached 4 mm of fat thickness, measured at the longissimus dorsi muscle between the 12th and 13th ribs by ultrasound equipment, as described by Vittori et al. (2006).
The 19th calf crop was born in 1999 and was randomly allocated to 3 experimental groups: baseline, restricted feeding group (AR), and ad libitum feeding group (AL). The baseline group had 4 bulls for each genetic group (NeS, CaS, and NeC), whereas the AR and AL groups had 8 NeS and 8 CaS bulls/group, and 6 NeC bulls/group. After the 28-d adaptation period, bulls in the baseline group were slaughtered and bulls in the AR and AL groups commenced the feeding period. Bulls in the AL group were slaughtered when 4 mm of fat thickness was individually measured by ultrasound between the 12th and 13th ribs. When a bull of the AL group reached the desired fat thickness, one bull from the AR group was also harvested. Each AL and AR bull was previously matched pairwise based on BW and BCS at the beginning of the experiment (Bonilha et al., 2007). The average slaughter BW of the bulls was 460 kg.
The 20th calf crop was born in 2000 and was represented by 18 NeS, 12 NeC, 16 CaS, 19 GuS, and 10 GiS bulls. Bulls were allocated into 3 groups. Each group was slaughtered when, on average, they reached at least 3, 5, and 7 mm of fat thickness, respectively, as determined by ultrasound of the longissimus dorsi muscle between the 12th and 13th ribs. The average slaughter BW of the bulls was 494 kg, as described by Faria (2004).
Data Collection and Analysis
Feeding Performance Test. All animals were fed for 168 d under feedlot conditions before using selected bulls for breeding. The diet was adjusted to simulate the nutritional value of tropical pastures. Average daily gain and BW were measured each 28 d. Body weight, BCS (scale 1 to 9), and hip height were measured at the end of the feeding performance test. Body weight values were corrected to 378 d of age.
Slaughter Procedures. Shrunk BW was measured 16 h after feed and water were withdrawn before slaughter. At slaughter, animals were stunned with a captive bolt gun and killed by exsanguination by using conventional humane procedures. Blood was collected and weighed. The body was separated into individual components, which were weighed separately. Carcasses were not electrically stimulated. The liver, KPH fat, and digestive tract were weighed separately. The remaining internal organs were weighed collectively. The digestive tract was cleaned by emptying and flushing with water. Empty BW (EBW) was computed as the sum of HCW, hide, head, feet, tail, blood, cleaned gastrointestinal organs, and internal organs.
Commercial Cuts.
The hot carcass was split into 2 identical longitudinal halves, which were chilled at 2°C for 24 h and then divided into forequarter (with 5 ribs), hindquarter, and spare ribs. These were deboned and separated into commercial cuts: blade, neck, chuck, brisket, hump, shank, striploin, tenderloin, rump, knuckle, topside, flat, eye-round, flank steak, leg-end, and beef plate (Yokoo et al., 2003). Commercial cuts were individually weighed. Bones and shavings of forequarter, hindquarter, and spare ribs were weighed separately.
Meat Quality Analysis.
Samples of the longissimus dorsi muscle (2.5 cm thick) were obtained from the 12th rib and vacuum-packed and frozen to interrupt the enzyme activity and halt the aging process. Samples were subsequently thawed for 12 h inside a 2°C chilling chamber and analyzed for tenderness and cooking losses. Steaks were baked in an oven, using individual thermometers placed in the geometric center of each steak. When the internal temperature reached 70°C, the samples were removed from the oven and kept at ambient temperature. Evaporation and drip losses were determined as described by the American Meat Science Association (1978). For tenderness analysis, 6 cylindrical samples parallel to muscle fibers were removed. Shear force was determined by a 25-kg capacity Warner-Bratzler shear force instrument (Shear 2000 D, G-R Manufacturing Co., Manhattan, KS) as described by the American Meat Science Association (1978).
Data Calculation
Animal ranking is not an easy task because several carcass traits depend on different slaughter end points (age, carcass weight, fat thickness, fat trim percentage; (Koch et al., 1979; Wheeler et al., 1996). Furthermore, if growth, fattening rates, or both differ among breeds, the comparison of breeds at different levels of a physiological end point could result in an undesirable reranking of animals or changes in the magnitude of the differences. For this reason, either maturity degree or initial BW was used as a covariate.
Maturity Degree. The maturity degree (u) for each animal was computed based on slaughter BW, body composition, and mature BW. Mature BW was assumed to be at 22% empty body fat (EBF). Specific equations were used to estimate the amount of carcass fat for animals from the 1995 to 2000 calf crops. The amount of carcass fat was physically measured in animals from the 1992, 1993, and 1994 calf crops.
Equations published in the literature were used to compute carcass fat (CF) from carcass traits. Most of these equations used the physical fat analyses of the Hankins and Howe (1946) rib section separation. Nardon (1998) published equations to compute CF for the NeS (Eq. 1), NeC (Eq. 2), CaS (Eq. 3), and GuS (Eq. 4) breeds. Jorge et al. (2000) published an equation to compute CF for the GiS breed (Eq. 5):
 | [1] |
 | [2] |
 | [3] |
 | [4] |
 | [5] |
where CF is carcass fat (kg); EBW is empty BW (kg); REA is rib-eye area (cm2); FHH is fat of the Hankins and Howe (1946) rib section (kg); FT is fat thickness (mm); MHH is muscle of the Hankins and Howe (1946) rib section (kg); FBW is final BW (kg); BHH is bones of the Hankins and Howe (1946) rib section (kg); CFp is percentage of carcass fat (%); and FHHp is percentage of fat of the Hankins and Howe (1946) rib section (%).
For all breeds, EBF was computed from CF based on Garrett and Hinman (1969) (Eq. 6), developed from implanted (30 mg of diethylstilbestrol) beef steers predominantly of the Hereford breed:
 | [6] |
where EBFp is empty body fat (%) and CFp is carcass fat (%).
On the basis of information provided by Tedeschi et al. (2002), it was considered that B. indicus and B. taurus breeds of this study are usually slaughtered when EBF is approximately 22%. Therefore, the adjusted final EBW (AFEBW) was assumed to be at 22% EBF. The AFEBW of each animal was computed by using Eq. 7, assuming the same linear relationship between EBW and EBF reported by Guiroy et al. (2001) of 14.26 kg/% of EBF:
 | [7] |
where EBFp is observed empty body fat at the slaughter BW (%) and EBW is empty BW at slaughter (kg).
Maturity degree for each animal was estimated as the average of the initial and final maturity degrees. The initial maturity degree was the ratio of initial EBW (EBW at the beginning of the experiment) and AFEBW, whereas final maturity degree was the ratio of final EBW (EBW at slaughter) and AFEBW.
Statistical Analysis
Statistical analyses were performed with PROC MIXED (SAS Inst. Inc., Cary, NC) by using a random coefficients model, considering herd as fixed and treatments within year and year as random effects (Littell et al., 2006). Either maturity degree or initial BW was used as a covariate. When the maturity degree covariate effect was not significant (P > 0.05), initial BW was the covariate adopted. The interaction between the covariate and genetic group (breed) was tested and removed from the statistical model if not significant at P < 0.05. The least squares means were used in a multiple comparison analysis. The statistical model is shown in Eq. 8:
 | [8] |
where µ is overall average; trt(yr)i(j) is the ith treatment within the jth year of study; yrj is the jth year of study; herdk is the kth genetic group of study; βi is the covariate slope; xil is either u or iBW for the ith treatment and the lth value; 
.. is the average of the covariate; and 
ijkl is the uncontrolled, random error.
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RESULTS AND DISCUSSION |
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TopAbstractINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONLITERATURE CITED |
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Table 1 shows the comparison of measured variables used to estimate body composition (Eq. 1 to 6), predicted CF and EBF, AFBW predicted by Eq. 7, and maturity degree for the 5 genetic groups. Selected Caracu had reduced CF (P < 0.001), EBF (P < 0.001), and degree of maturity (P < 0.001) relative to the B. indicus breeds, indicating it was generically the leanest group.
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Table 2 shows the growth performance information without adjustments, whereas Table 3 shows the same values adjusted for covariates. The interaction between the genetic groups and the covariate maturity degree (u) was significant (P = 0.038) for initial BW (iBW) in the feeding performance test (Table 3). The adjustment to covariates (either iBW or u) did not change the ranking and significance of the variables among genetic groups shown in Table 2 compared with those in Table 3. No significant differences (P = 0.599) were detected in BCS at the end of the feeding performance test, indicating that animals of all genetic groups reached similar BCS. Hip height was different among genetic groups (P < 0.001), with NeS being tallest, NeC and GuS being of intermediate height, and GiS and CaS being shortest. Differences among body sizes of the genetic groups during the feeding performance test were better characterized by iBW, final BW (fBW), and corrected BW to 378 d of age (BW378d; Tables 2 and 3). Although CaS were shorter than the other genetic groups, they had the heaviest iBW (P = 0.047), fBW (P < 0.001), and BW378d (P < 0.001) at the same degree of maturity (Table 3). Selected Gir and NeC were consistently lighter at iBW, fBW, and BW378d adjusted for the same degree of maturity as CaS animals. Selected Nellore were lighter at the beginning (P = 0.004) and end (P = 0.005) of the feeding performance test than CaS, but were heavier than GuS, GiS, and NeC at the beginning (P = 0.047) and end (P < 0.001) of the feeding performance test. Consequently, CaS, NeS, and GuS animals grew faster (P < 0.001) during the feeding performance test than GiS and NeC animals, without (Table 2) and with (Table 3) adjustments for covariates. Selection for postweaning weight (PWW) in Nellore cattle (NeS vs. NeC) increased body size after 20 consecutive years of selection. Selected Nellore had increased iBW, fBW, BW378d, hip height, and ADG compared with NeC (Tables 2 and 3), consistent with the findings of Razook et al. (1998), who indicated that the estimated genetic gain for Nellore BW378d was approximately 1.1%, on average, for each year of selection.
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compared carcass merit within and among family groups of B. indicus crossbreds (three-fourths Angus/one-fourth Nellore and three-fourths Nellore/one-fourth Angus) and reported that breed type did not affect ADG, fBW, dressing percentage (DP), carcass weight, adjusted fat thickness, KPH, or carcass maturity, but families within breed types differed with regard to all traits measured. They concluded there was an opportunity to improve these traits by selecting within specific family lines. Performance and Carcass Characteristics at Feeding Trials
Carcass characteristics of animals are shown in Table 4 (unadjusted values) and Table 5 (adjusted for covariates). The interaction between genetic groups and the covariate u was significant for the iBW (P < 0.001), suggesting iBW and degree of maturity had different relationships among studies. There were no significant interactions (P > 0.05) between genetic group and covariates for the other variables in the study. Adjustment for either iBW or u resulted in reranking of carcass trait values of genetic groups, with KPH values being the most affected. This result reinforces the importance of adjusting to the same degree of maturity when comparing animal performance and carcass characteristics of different breeds. Selected Nellore had greater iBW (P < 0.001), fBW (P = 0.005), ADG (P = 0.043), empty BW (EBW; P = 0.018), liver weight (P = 0.040), HCW (P = 0.018), cold carcass weight (CCW; P = 0.018), and carcass length (CL; P = 0.001) than NeC animals (Table 4). These differences reflect the direct and correlated responses to selection for PWW. No differences were observed in KPH (P = 0.094) or DP (P = 0.998) between the NeS and NeC genetic groups.
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compared 5 B. indicus breeds (Grey Brahman, Gir, Nellore, Indo-Brazilian, and Red Brahman) for birth weight, growth, and carcass characteristics. They detected that among these breeds, on average, Gir had the lowest birth, weaning, and yearling weights, similar to the results in this study.
In the program conducted at the Experimental Station of Sertãozinho, BW378d is used as the selection criterion for males. Razook et al. (1998) showed that the estimated genetic gain for Nellore BW378d was approximately 1.1% of BW378d, on average, per year of selection. Hence, from 1992 to 2000, there is an average accumulated selection period of 16 yr [from 1980 (beginning of selection program) to 1996 (average of this study period)]. The accumulated difference in BW378d was expected to be approximately 17.6% (16 yr x 1.1%/yr) between NeS and NeC. In this study, the meta-analysis of BW378d of NeS and NeC lines showed an accumulated gain in BW378d of approximately 15%. For GuS, Razook et al. (1998) showed a reduced genetic gain at around 0.8% of BW378d, on average, per year. An accumulated difference of 12.8% in BW378d was therefore expected between GuS and NeC. In this study, the meta-analysis showed an accumulated gain in BW378d of approximately 13%. Some variation between expected and actual values for GuS can be explained by breed effects, because the reference control group was NeC.
Burrow and Prayaga (2004) studied genetic selection for growth in tropical beef cattle and reported that as ADG increased, increases in BW, period weight gains, and direct and maternal genetic components of weights were observed. However, mature cow BW was not affected. These authors also found that selection for greater ADG increased the body size of the animals, without affecting male or female fertility traits and carcass and meat quality attributes. Similar results were detected by Mercadante et al. (2003) when studying Nellore cows of the same genetic selection program as used in this study.
Commercial Meat Cuts
Tables 6 and 7 show unadjusted and adjusted (for either iBW or u) values of commercial meat cuts, respectively. The interaction between genetic groups and the covariate iBW was significant for hump (P < 0.001), shank (P = 0.027), and hindquarter bones (P = 0.003; Table 7). For all other variables, no significant (P > 0.05) interactions between genetic group and the covariates were found. The covariate adjustment changed the average values and decreased the differences among genetic groups. Animals had different iBW, degrees of maturity, or both. Therefore, a direct comparison would not be valid because animals would have different body composition.
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, studying the Nellore and Caracu breeds, found similar results for hump weight. Table 6
indicated a significant difference between GiS and NeC (P = 0.047) for hump weight.
Significant differences (P = 0.001) were detected among genetic groups for hindquarter weight, the higher priced carcass quarter (Table 7). Selected Nellore and CaS had the heaviest hindquarters, indicating their carcasses have higher commercial values. The hindquarter weights of NeC, CaS, GuS, and GiS did not differ. Significant differences were found for specialized meat cuts in the hindquarter (Table 7). Selected Caracu had the heaviest striploin (P < 0.001), likely because it also had the longest carcass; both variables are strongly correlated (Luchiari Filho et al., 1985). Significant differences (P < 0.001) were found among genetic groups for tenderloin (an important meat cut because of its tenderness and commercial value): CaS and NeS had similar (P = 0.993) tenderloin weights and the other genetic groups had lighter values (P = 0.024). Selected Nellore had the heaviest rump (P = 0.010), knuckle (P < 0.001), topside (P < 0.001), flat (P < 0.001), and eye-round (P < 0.001). Although carcass (P = 0.985), forequarter (P = 0.999), and hindquarter (P = 0.086) weights were similar between CaS and NeS, CaS had less meat in the leg region compared with other genetic groups. This means that for some of the higher priced hindquarter meat cuts, NeS was superior to CaS, even though they had the same total hindquarter weights. These results are in agreement with those reported by Nardon et al. (2001) and Bonilha et al. (2007), who also detected similar carcass and quarter weights for NeS and CaS, and reduced retail weights for the leg region cuts. Selected Caracu had the heaviest spare ribs (P < 0.001) and beef plate (P = 0.013), as was expected from the strong correlation with CL (Luchiari Filho et al., 1985). Selected Caracu had the greatest (P < 0.001) value for CL (Tables 4 and 5).
Carcass Quality Characteristics
Table 8 shows unadjusted values and Table 9 adjusted values for carcass quality characteristics. The interaction between genetic group and the covariate u was significant (P = 0.011) for rib-eye area (REA). Selected Caracu and NeS had greater REA values than GuS, GiS, and NeC animals. The REA values are regarded as good indicators of carcass muscle (Morris et al., 1993). In this study, genetic groups with greater body sizes and carcass weights also had greater REA values (Tables 5 and 9). The direct comparison between NeS and NeC indicated that selection for PWW from 1992 to 2000 increased REA by approximately 4 cm2, improving the carcass muscle in Nellore. In contrast, Morris et al. (1993) compared selected (for 17 yr) versus control Angus and reported no significant difference in REA. No significant differences among genetic groups in this study were found for fat thickness (P = 0.059), likely because the data were adjusted for iBW. When data were not adjusted, significant differences (P < 0.001) were detected (Table 8). Selected Caracu had the least fat (P < 0.001), indicating this was the leanest genetic group. Differences between B. taurus (CaS) and B. indicus (NeS, NeC, GuS, and GiS) breeds were detected (P = 0.001) for shear force, with CaS having the lowest (most tender) shear force value. Bos indicus breeds usually have higher and more variable values for shear force (Morgan et al., 1991). Although B. indicus breeds had greater values for shear force than CaS, the shear force values were acceptable for meat that was not aged (below 5.0 kg; Nardon et al., 2001). No significant differences among genetic groups were found for evaporation losses (P = 0.336), drip losses (P = 0.763), or total losses (P = 0.790).
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indicated that geographic areas with a higher proportion of B. indicus breeding usually have greater and more variable values for shear force than areas with lower B. indicus influence. Early research indicated that meat from B. indicus cattle was tougher because of lower levels of intramuscular fat and higher connective tissue content when compared with B. taurus. Wheeler et al. (1990) showed that B. indicus cattle had lower levels of µ-calpain and higher levels of calpastatin and they concluded that calpain activity, as modulated by calpastatin, played a major role in the inherent tenderness differences among groups. After 20 yr of selection, our meta-analysis indicated that selection for PWW had an indirect effect on carcass characteristics of the selected progeny groups when compared with nonselected progeny groups. Differences found in this study in carcass characteristics between the NeS and NeC groups were likely caused by the selection, because animals originated from the same base population. Although the selection process started at the same time for the CaS, GuS, and GiS groups, most of the differences found reflect differences among breeds, mainly those related to body size.
Information obtained in this meta-analysis suggests that after adjusting some indicative body size traits for degree of maturity, selection has increased body size, carcass weight, and weight of important meat cuts of the Nellore breed without affecting body fat and carcass yield. Other authors (Razook et al., 2001; Resende et al., 2001; Vittori et al., 2006) reported similar results for body size when comparing selected and nonselected Nellore groups.
Selection for postweaning weight in Nellore increased body size, carcass weight, and meat retail cuts without altering the dressing percentage and body fat content. For the other genetic groups (Caracu, Gir, Guzerah), differences may reflect differences among breeds. The NeS and CaS groups had heavier carcasses and meat retail cuts. The GuS had intermediate body size, whereas the NeC and GiS had lighter carcasses and meat retail cuts. The CaS, a B. taurus breed adapted to the tropics, had lower shear force values, indicating more tender meat.
1 Corresponding author: luis.tedeschi{at}tamu.edu
Received for publication August 8, 2007. Accepted for publication April 9, 2008.
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TopAbstractINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONLITERATURE CITED |
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