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Interest in genetic improvement of carcass and tenderness traits of beef cattle using genome-based selection (GS) and marker-assisted management programs is increasing. The success of such a program depends on the presence of linkage disequilibrium between the observed markers and the underlying QTL as well as on the relationship between the discovery, validation, and target populations. For molecular breeding values (MBV) predicted for a target population using SNP markers, reliabilities of these MBV can be obtained from validation analyses conducted in an independent population distinct from the discovery set. The objective of this study was to test MBV predicted for carcass and tenderness traits of beef cattle in a Canadian-based validation population that is largely independent of a United States-based discovery set. The discovery data set comprised of genotypes and phenotypes from > 2,900 multibreed beef cattle while the validation population consisted of 802 crossbred feeder heifers and steers. A bivariate animal model that fitted actual phenotype and MBV was used for validation analyses. The reliability of MBV was defined as square of the genetic correlation (R-g(2)) that represents the proportion of the additive genetic variance explained by the SNP markers. Several scenarios involving different starting marker panels (384, 3K, 7K, and 50K) and different sets of SNP selected to compute MBV (50, 100, 200, 375, 400, 600, and 800) were investigated. Validation results showed that the most reliable MBV (R-g(2)) were 0.34 for HCW, 0.36 for back fat thickness, 0.28 for rib eye area, 0.30 for marbling score, 0.25 for yield grade, and 0.38 for Warner-Bratzler shear force across the different scenarios explored. The results indicate that smaller SNP panels can be developed for use in genetic improvement of beef carcass and tenderness traits to exploit GS benefits.

4 páginas, 2 tablas.- Trabajo presentado al 58th International Congress of Meat Science and Technology (Montreal, Canadá, Aug. 12-17, 2012)., The objective of this study was to test the potential of near infrared reflectance spectroscopy (NIRS) to estimate the proportion of polyunsaturated fatty acids (FA) and their biohydrogenation products in perirenal adipose tissue (PrFat) from cattle fed sunflower or flaxseed. PrFat from 63 steers was collected immediately after skinning, scanned at 37 °C over a NIR spectral range from 400 to 2498 nm on benchtop equipment, and analysed for FA composition. NIR calibrations, tested by cross-validation, showed high predictability for most of the total n-3, conjugated linolenic acids, t,t-conjugated linoleic acids (CLA), non-CLA dienes and trans-monounsaturated FA, with R2 and root mean square error of crossvalidation (RMSECV, %) of 0.95 (0.07-0.08), 0.86- 0.89 (0.01-0.09), 0.93 (0.07), 0.89 (0.46) and 0.92-0.93 (0.87-1.29), respectively. The results show NIRS to be a useful technique for the early, fast and relatively inexpensive estimation of proportion of FA with potential human health effects.

Trabajo presentado en el 58th International Congress of Meat Science and Technology, celebrado en Montreal (Canadá) del 08 al 12 de octubre de 2012.

1 página.-- Proceedings of the Canadian Meat Science Association Technical Symposium (Halifax, Canadá, 6-7 octubre de 2011), Today, consumers are interested in fat composition as scientific evidence suggests that diets high in saturated fat are associated with an increased risk of cardiovascular disease. Techniques to quantify fatty acids (FA) in meat are costly and time-consuming. Near infrared reflectance spectroscopy (NIRS) is a rapid and non destructive method. The aim of this study was to examine the ability of NIRS to estimate the concentration of polyunsaturated FA and their biohydrogenation products in subcutaneous fat from cows fed flaxseed. Subcutaneous fat samples at the 12th rib of 62 cows were collected and stored at -80ºC. After thawing, 32 spectra from each intact sample were collected, then averaged, over a NIR spectral range from 400 to 2498 nm at 31ºC (warm samples) and 2ºC (cold samples), and then analyzed for FA profiles. NIRS calibrations on warm samples, tested by cross-validation, showed high predictability for most of the n-3 (R2: 0.81- 0.86; RMSECV: 0.11-1.56 mg·g-1 fat) and linolenic acid biohydrogenation products such as conjugated linolenic acids, conjugated linoleic acids (CLA), non-CLA dienes and trans-monounsaturated FA with R2 (RMSECV, mg·g-1 fat) of 0.85-0.85 (0.16-0.37), 0.84-0.90 (0.21-2.58), 0.90 (5.49) and 0.84-0.90 (4.24-8.83), respectively. When spectra were obtained from cold samples NIRS predictability was lower than that for warm samples, probably due to a less homogeneous distribution of fat throughout the cells and more air bubbles, or to reduced molecular vibration due to the cooler temperature. NIRS could discriminate 100% of subcutaneous fat samples from cows fed different diets (with or without flaxseed). These data support that NIRS has the potential to be used as a fast and accurate predictor of content of linolenic acid and its biohydrogenation products in subcutaneous fat of beef cows. Nevertheless, further studies are required to test its ability during on-line operations in an abattoir.

This study aimed to evaluate quality and sensory properties of 6 and 21 days aged beef (steaks and ground beef) from animals with different tissue levels of ?-tocopherol. A total of 56 feedlot steers were fed a barley-based finisher diet with four vitamin E supplementation levels (340, 690, 1040 and 1740 IU dl-?-tocopheryl acetate.animal-1.day-1) for 120 days. The animals were then grouped based on their ?-tocopherol (?g.g meat-1) levels (5 or high). Longissimus lumborum muscle and overlying subcutaneous fat were aged 6 days and then used to prepare steaks and 75/25 ground beef. Steaks aged for 21 days were also analysed. Although the increase in fatty acid oxidation over time was smaller (P0.05) pH, proximate analysis, drip and cooking losses, and shear force of steaks. Similarly, ?-tocopherol tissue levels had no effect (P>0.05) on sensory characteristics of 6 days aged steaks and ground beef. No effect of tissue ?-tocopherol levels was found over the 6 days retail evaluation period for steaks, but with 21 days of ageing, a delay in formation of metmyoglobin (P=0.008) was observed with higher tissue levels of ?-tocopherol. Similar results were found for ground beef (25% fat) prepared from 6 days aged meat. Higher ?-tocopherol tissue levels protected ground beef ad long-aged steaks from discolouration and lipid oxidation.