Genetic relationships between internal diseases diagnosed at slaughter and carcass traits in Japanese Black cattle

The objective of this paper was to estimate the genetic parameters of certain internal diseases (multifocal necrosis in the liver [MNL], bovine abdominal fat necrosis [BFN], and inflammation of the large intestine [ILI]) and to investigate relationships between the internal diseases and carcass traits (carcass weight [CW], rib eye area [REA], rib thickness [RT], subcutaneous fat thickness, and beef marbling score [BMS]). Records of the internal diseases and the carcass traits of 5,788 Japanese Black cattle were used for this study. The data for all the diseases were recorded as binary data as to whether the disease was observed (1) or not (0). Genetic parameters were estimated using linear and threshold animal models. The prevalence rates of MNL, BFN, and ILI were 16.1, 23.0, and 6.8%, respectively, and heritability estimates ± posterior SD were 0.18 ± 0.06, 0.28 ± 0.06, and 0.18 ± 0.06, respectively. The genetic correlations of MNL with BFN and ILI were -0.23 (P = 0.19) and -0.49 (P < 0.05), respectively. In contrast, the correlation between BFN and ILI was positive and high (0.96; < 0.05). The phenotypic correlations of the internal diseases with the carcass traits were weak and not different from 0 except for those of BFN and ILI with CW, REA, and RT, which were all negative (P < 0.05) and ranged from -0.21 (ILI and CW) to -0.05 (BFN and RT). The genetic correlations of MNL with the carcass traits were all weak and not significant. In contrast, the genetic correlations of BFN and ILI with CW, REA, and RT were all negative and significant (P < 0.05) between BFN and CW (-0.36) and between BFN and RT (-0.33). However, the genetic correlations for BFN and ILI with BMS were all positive at 0.21 P( = 0.16) and 0.39 (P < 0.05), respectively. The estimated heritability of the internal diseases suggests that they can be genetically improved. Genetic relationships of BFN and ILI with meat quantity traits were favorable for beef cattle breeding, because lower disease liabilities were associated with improved CW, REA, and RT for BFN and ILI. However, rather strong and unfavorable genetic relationships were found between BFN or ILI and BMS, which is related to meat quality. This suggests that selection for animals with superior BMS would increasingly lead to animals with higher liability to the internal diseases.