Genetics Selection Evolution 2009, 41:36 http://www.gsejournal.org/content/41/1/36 Background Meat quality is of great importance to the beef industry where the consumer is willing to pay more for superior products [1]. Traditional trait improvement has centred on quantitative genetics, using statistical analysis of phe- notypic data to determine animals with the highest genetic merit [2]. This selection approach is most effec- tively implemented for highly heritable traits that are eas- ily recorded before reproductive age. However, meat quality traits can usually only be measured post-slaughter and often have low heritabilities [3], therefore making progress using direct measurement is difficult for these traits. Marker-assisted selection has the potential to signif- icantly increase the rate of genetic improvement in such traits [4], using markers linked to economically relevant traits, which can be used to predict the genetic merit of an animal. Several such markers have been identified in the last decade. These include markers based on polymor- phisms in the leptin (LEP) gene, involved in the control of appetite and energy metabolism, which have been shown to be associated with carcass fat [5-8], body weight [6], and growth rate [9]; polymorphisms in the μ-calpain (CAPN1) and calpastatin (CAST) genes, which are known to play a key role in post mortem tenderisation of meat and have been associated with meat tenderness [10-13]; and polymorphisms in the bovine growth hormone receptor (GHR) gene, which have been associated with drip loss [14], body weight [15,16] and marbling score [17]. Before such marker information can be used in breeding programmes, it is important that unbiased and independent validation studies in different breeds are car- ried out to establish whether observable effects are found in the breed/population under selection. The aim of this study was to test such associations between eight single nucleotide polymorphisms (SNP) from five different genes and meat quality traits in a sam- ple of Aberdeen Angus-cross animals collected in Scot- land. All the tested SNP have been previously reported to be associated with various carcass and meat quality traits in cattle or pigs and have been incorporated into commer- cially available tests for meat or milk quality. Methods Sample collection Commercial crossbred beef cattle (n = 443 animals) with purebred Aberdeen Angus sires were sourced through the Scotbeef abattoir (Bridge of Allan, Scotland). Cattle origi- nated from 14 breeder finisher farms (i.e. farms where ani- mals are bred and finished on the same farm) and were selected to be representative of British commercial cattle slaughtered for beef production, being a mix of heifers and steers ranging between 408 and 912 days old at kill, with the age differences depending largely on the farm. The 443 animals used in the experiment included 135 females and 308 males. The sires for all animals were pure-bred Aberdeen Angus whilst the dams were a mix- ture of purebreds of various breeds and crossbreeds including Aberdeen Angus, Aberdeen Angus-cross, Sim- mental-cross and Limousin-cross. Cattle were stunned by captive bolt before being slaugh- tered by exsanguination and dressed using standard com- mercial specifications. During exsanguination, 100 mL blood was collected and frozen for DNA extraction. Carcass trait measurement At slaughter, hot carcass weight was recorded and car- casses were graded by a Meat Hygiene Service assessor for muscle composition and carcass fatness according to the standard European Union beef carcass classification scale (EUROP) [18]. Conformation and fat class scores were transformed into a 7-point numerical scale [19]. Twenty- four hours after slaughter, pH and temperature were recorded in the sirloin muscle with the TESTO 205 pH meter (TESTO, Hampshire, UK) and ETI FPT thermometer (ETI Ltd. Worthing, UK), respectively. At deboning, weight of the hindquarter and sirloins were recorded. Sirloins were vacuum-packed and stored below 4°C for 21–30 d to mature, then removed from the vac- uum pack, patted dry to remove excess moisture and weighed. Three steaks were cut from the centre of the sir- loin as follows: for tenderometer testing 3–4 cm thick, for sirloin measurements 1–2 cm thick and for sensory testing 2 cm thick. For tenderometer testing, steaks were trimmed to 200– 220 g of eye muscle and placed in a water bath at 100°C until the centre of the sample reached 82°C. Samples were left to cool to 7°C then tested using a MIRINZ Tenderom- eter machine (AgResearch, Hamilton, New Zealand). A full list of analysed carcass quality traits can be found in Table 1. Taste panel selection and assessments Taste panel members were chosen among workers at the Scotbeef meat processing plant in East Kilbride, Scotland. Members of staff (n = 38) were tested using the Triangle and Matching tests [20] with 10 being discarded due to poor scores. Taste panels included six members and an average of nine samples were tested in one sitting with the addition of one blind repeat steak per panel. Participants were instructed to rinse their mouths with water before tasting began as well as between samples. They were also instructed not to eat or drink for one hour prior to the test. Prior to assessment sirloin steaks were cooked using a Lin- cat Lynx 400 electric griddle (Lincat Ltd, Lincoln, UK) Page 2 of 12 (page number not for citation purposes)