Prospecting Genetic Markers Influence On Tenderness And Beef Fat And Cholesterol Content Of Nellore Cattle 1 F.M. Rezende*, J.B.S. Ferraz*, R.C.G. Silva*, M.N. Bonin*, D.C. Cucco*, T.D. Mion*, R.Q. Daroz*, J.P. Eler* Introduction A large number of single nucleotide polymorphism (SNP), associated with genes which expressions are related on meat quality traits, were described on Bos taurus animals or on Bos taurus highly influenced breeds. However, in Brazil, more than 80% of the 200 million heads herd are represented by Bos indicus animals, especially by the Nellore breed, raised on very distinct production system than where markers were described. In this context, the present research had as objective identify, on a set of 95 genetic markers, initially described on Bos taurus animals, potential markers to be used as auxiliary tools on selection for tenderness, intramuscular fat and cholesterol content on Nellore breeding programs. Material and methods Samples description. Data on 641 Nellore bulls, raised under pasture conditions until 18 months of age and, after, fed in feedlots until slaughter, with ages varying from 21 to 28 months and live weights around 560 kg, were collected. All animals were half-sibs or full- sibs of bulls selected for growth and reproductive traits. The animals were slaughtered in six different dates in a commercial slaughter plant, always in the mornings, and after, approximately, 16 hours of fastening with free access to fresh water. Four samples of Longissimus dorsi muscle of each animal were collected. Three of them were aged for 7, 14 and 21 days for tenderness evaluation and the last one, after 7 days of ageing, was frozen under -18 ⁰C till intramuscular fat and cholesterol content analysis were done. Data collection. To measure Warner-Bratzler shear force (WBSF7, WBSF14 and WBSF21, kg), steaks were cooked and sheared as described by AMSA (1995). From each steak were taken 8 sub-samples of ½” of diameter and the average of these measures in the Warner- Braztler Shear Force equipment was considered as beef tenderness. Determination of intramuscular fat (IMF, g/100g of meat) was based on methodology described by Bligh & Dyer (1959). Cholesterol extraction and quantification was made according to method described by Saldanha, Mazalli & Bragagnolo (2004), which promote cholesterol degradation by cholesterol oxidase enzyme (CHOLESTEROL, mg/100g of meat). Descriptive statistics of evaluated traits are described in Table 1. Genotyping and polymorphisms. DNA was extracted from blood samples collected using EDTA vacuum tubes and impregnated on FTA cards by NaCl extraction and precipitation method described for Olerup & Zetterquist (1992). Genotyping process was carried out on laboratories located in USA and licensed by Merial/Igenity®, company that has the licenses 1 Research partially funded by FAPESP and CNPq, Brazil * University of Sao Paulo, College of Animal Science and Food Engineering; Pirassununga, SP, Brazil, frezende@usp.br