## 2 Materials and Methods
### Assessing Marbling Scores and Yield Grades  
The left or right halves of the 300 carcasses were ribbed. Marbling scores and yield grades were directly estimated using the VIA-based camera system VBG 2000 (e+v, Oranienburg) at the rib-eye cut between the 10 th/11 th rib interfaces of _longissimus thoracis_. All halves were further ribbed to assess marbling scores and yield grades (including meat surface, rib fat thickness and carcass weight) at the US grading position between the 12 th/13 th rib section. The official numerical USDA (United States Department of Agriculture) marbling scores, Practically Devoid (100-199) Traces (200-299) Slight (300-399), Small (400-499), Modest (500-599), Moderate (600-699) and Slightly Abundant (700-799), were used. Assessment of the yield grades at the 12 th/13 th rib-(eye section included the parameters of hot carcass weight, measured subcutaneous fat thickness and rib-eye area using the established yield formula of VBG 2000.  
VBG 2000 was initially created to classify US beef carcasses. It is a camera-based system with special lighting to photograph the rib-eye. It is positioned at the spinal channel, the ribs and the meat surface [18]. All measurements were taken on the same flat surface. Images of each rib-eye were linked to processing software. The images erroneously included the outside area of the rib-eye _musculus spinalis_ because of its different size at the 10 th/11 th rib-eye section. Software predictors and colour values of VBG 2000 were generated for the larger 12 th/13 th rib-eye position. Therefore, it was later necessary to modify the digital estimation thresholds and colour values with the developer of VBG 2000 (e+v, Oranienburg, Germany) [18].  
The process line and the butchers were not familiar with the new cutting position and the changed size of the rib-eye, resulting in improper cuts of the meat surface. Thus, 126 of the 300 selected carcasses could not be assessed in the slaughterhouse. A correct camera assessment requires a very accurate cut but as this was not always provided, it was not possible to capture all carcasses in pictures. Consequently, with some carcasses, not all parameters could be reliably assessed. In total, complete data could be assessed for 174 carcasses.  
VBG 2000 usually includes kidney pelvic heart (KPH) fat as a yield parameter but this was not possible to assess at the 10 th rib position in the current study because there was no occasion to scan the whole carcass. Furthermore, the rib-eye size at the 10 th/11 th rib-eye position could not be determined precisely in this investigation due to the inaccurate rib-eye cut. Instead, the images were segmented into pixels of beef and fat and the ratio of beef pixels/fat pixels in the defined surface of rib-eye muscle was calculated to better determine the amount of saleable beef in the muscle (Figure 1, left image). In all cases, yield grade at the 10 th/11 th rib-eye section was assessed retrospectively with a modified formula adapted to the modified image thresholds: 25.1088 + hot carcass weight \(\times\) 0.002488168 + number of meat pixels \(\times\) \(-\)16.72879 + meat/fat ratio \(\times\)\(-\)0.4330382 + number of fat pixels 23 \(\times\) 0.01327071 + number of meat pixels \(\times\) 0.001183337+ number of fat pixels 12 \(\times\)\(-\)0.1445752. Rib fat thickness was measured at the same position as the US position (Figure 1).  
Figure 1: Visualisation of the segmentation of meat and fat pixels (**left**) and the standardized position for the assessment of the rib-eye fat thickness at the 10 th/11 th rib position (**right**).