Assessment of the variation of marbling and intramuscular fat content of beef, and validation of possible factors to increase sensory beef quality

This thesis focuses on the intramuscular fat content (IMF) or the marbling of beef as main parameters of sensory beef quality. The aim is to identify the high variability of these traits and to verify possible influences such as genetics, age, gender and feeding strategies to increase marbling. The first part of this research focuses on the variation of quality traits within a genetically homogeneous line of an endangered German beef cattle breed “Rotes Höhenvieh” (RHV). The intramuscular fat content of beef samples (n = 539) of this breed was objectively assessed, and high variations (0.2 % - 22.9 %) in this trait were found within the whole RHV population. The second part of the thesis involves the validation of Video Image Analysis (VIA) as an objective measurement and evaluation method for German beef carcasses without any destruction of the carcass within the slaughter line. The marbling level of industrial German carcasses from young bulls (n = 300) was assessed at a standardized industrial cutting position with reference to the USDA classification system, which focuses mainly on the estimation of marbling. High correlations (r = 0.82 and R = 0.64) were found, emphasizing the feasibility of an adaption of the USDA beef classification system to focus on sensory quality attributes as a determining parameter of classification of German beef carcasses. In a third step, a special feeding regime as a main influencing factor and possible strategy to increase the intramuscular fat percentage of German beef heifers was investigated and verified. Two feeding trials were conducted with Uckermärker heifers to examine the influence of high energy and starch density. Different amounts of undegradable protein (UDP) were fed to a group of 122 heifers during the finishing fattening period and the other group of 190 heifers were fed during the marbling window with two different high energy and low energy diets and then received 3 different UDP diets in the late fattening period. Carcasses of all these animals were graded according to VIA marbling scores and subcutaneous back fat thickness after slaughtering. Results showed that the purposive feeding strategy combining a high energy and starch diet during the early fattening period with a high UDP Diet in the finishing fattening period might lead to increased marbling scores. Overall, variation of marbling and intramuscular fat content emerged in all studies. Results illustrate the need for an objective assessment of marbling or intramuscular fat content in German beef carcasses to compare the actual quality level of beef, and in another step, to verify the success or failure of different management or feeding strategies that might influence marbling and intramuscular fat content and therefore increase beef quality in the long run.