Proceedings, 10 th World Congress of Genetics Applied to Livestock Production Evaluation of the protein change in the meat of Nellore beef cattle with contrasting shear force M. E. Carvalho 1 , G. Gasparin 2 , J. P. Eler 1 , J. C. C. Balieiro 3 , L. C. A. Regitano 4 , J. B. S. Ferraz 1 , L. L. Coutinho 2 . 1 Dep. of Veterinary Medicine, Faculty of Animal Science and Food Engineering, University of São Paulo, Pirassununga, SP, Brazil, 2 Dep. of Animal Science, “Luiz de Queiroz” College of Agriculture, University of São Paulo, Piracicaba, SP, Brazil, 3 Dep. of Basic Science, Faculty of Animal Science and Food Engineering, University of São Paulo, Pirassununga, SP, Brazil, 4 Embrapa Southeast Livestock, São Carlos, SP, Brazil ABSTRACT: Nellore beef cattle, a Bos indicus breed, is well adapted to tropical conditions and has allowed Brazil to become one of the world’s largest beef producers. Never- theless, Bos indicus breeds are reported to have less tender meat than Bos taurus. A group of 138 animals was evaluat- ed for Longissimus thoracis muscle shear force (SF). Six animals with the highest and lowest SF were then selected for protein abundance studies. Samples were subjected to two-dimensional gel electrophoresis (2-DE) to identify differentially expressed proteins associated with SF. Eight differentially expressed spots were observed (p < 0.05). These spots were submitted to a multiple regression anal- yses and three of them (41, 42 and 72) appeared in the best models for tenderness prediction in the three meat aging times: 24 h, 7 and 14 days. New approaches are needed to identify the protein spots and their corresponding genes. Keywords: Bos indicus; Proteomics; Tenderness Introduction The Nellore breed (Bos indicus) and their crosses are predominant in Brazil, accounting for 80% of the Bra- zilian herd, due to its productivity, disease resistance and heat tolerance. However, restrictions have been attributed to B. indicus breeds regarding meat tenderness (Crouse, et al. 1989). Proteomic studies have improved the understanding of complex biological processes in all areas of science (Bendixen, et. al. 2011). Proteome analysis can show pro- tein abundance, gene functions and their interactions, as well as explain genetic and environmental factors that can control cellular functions and physiological characteristics of living organisms. Comparison of extreme phenotypes was successfully used to identify proteins associated with meat tenderness (Picard et al., 2010). Although it is possible to identify numerous markers associated with tenderness, they are often specific to a certain type of animal (bull or steer), breed, environmental condition (Hocquette, et. al. 2007), or even a given muscle tissue. (Guillemin, et. al. 2011). Bouley, et al. (2004) found different potential ten- derness markers among Charolais, Limousin and Salers breeds. Considering the importance of B. indicus breeds and their crosses for the meat industry, and the fact that there are no previous studies in the Nellore breed, the present study aimed to improve the knowledge of the mechanisms responsible for meat tenderization and to identify proteins that may act as biomarkers for meat tenderness. Materials and Methods Animals and sample collection The experimental population used in this study consisted of 138 Nellore ani- mals, male progenies of 18 bulls. The number of progeny per bull ranged from 2 to 14, with an average of 7.6. Unre- lated bulls were selected to represent different Nellore lines from the Brazilian herd. Animals were raised at Embrapa Southeast Livestock Center in São Carlos, São Paulo, Bra- zil. Animals were pasture-fed until approximately 23 months of age, when they were moved to a feedlot and fed a finishing diet based on corn silage, corn grain and soy- bean hulls, and slaughtered after they reached 5 mm subcu- taneous fat (approximately 90 to 110 days). Immediately after slaughter, samples for proteomic analysis were col- lected with a puncher from the Longissimus thoracis muscle between the 12 th and 13 th ribs on the right half-carcass and stored in liquid nitrogen. Carcasses were chilled overnight at 2 °C. At 24 h post mortem, the L. thoracis muscle from the left side of the carcass was cut between the 12 th and 13 th rib in the caudal direction and 2.5 cm steaks were removed for shear force (SF) analysis. Shear force analysis For meat tenderness analy- sis, one of the three steaks collected was analyzed approxi- mately 24 h after slaughter. The other two steaks were kept for seven and 14 days in a cold chamber at 0 and 2 °C and subsequently analyzed in accordance with protocol AMSA (1995). Full peak shear force was recorded and maximum shear force was calculated as the average of the eight cores. Two-dimensional electrophoresis (2-DE). The analysis of two-dimensional electrophoresis for separation of proteins and to obtain samples of protein spots to be relatively quantified and related with meat tenderness were performed in accordance with Carvalho et. al. (2014). “In silico” map analysis. The 2-DE gels were scanned with ImageScanner Powerlook 1120 (Amersham Biosciences) and analyzed with ImageMaster Platinum software (Amersham Biosciences) to detect and infer the volume of spots, also called the intensity of the normalized expression volume (IVEN). To obtain this volume, back- ground stain was removed from gel images using software tools so that only protein spots were analyzed. To identify corresponding spots on different gels, images in triplicate for each sample were overlaid with markers in common