Genetic and environmental influences on carcass defects of Japanese Black cattle by logistic-regression analysis

Abstract

In cases where carcass defects are found during beef carcass grading, no change in the grade of carcass is seen but could affect the carcass market price. These defects might be found at the meat distribution stage and the defected parts cannot be sold, therefore the impact of these defects on both beef producer and supplier can be substantial. However, the mechanisms of the occurrence of most of the defects are not yet clear. Therefore, this study intended to get basic knowledge of the defect occurrence factors, and investigate the influence that environmental and genetic factors have on defects occurrence by logistic-regression analysis of beef carcass grading records (n=70,171) of Japanese Black cattle in Miyazaki. The results showed low incidences of blood splash and trim loss, and that the incidences of intermuscular edema tended to be lower in recent years. Fattening farm factor had significant effects on defect occurrences but the effects of sire were not significant. On the other hand, the highest bruising odds ratio was in carcasses graded in 2008 and an increasing trend was observed. High odds ratios between sires were obtained. This suggested that differences in nature of activity and/or militancy attributed to sire genetic effects might cause the bruising considering that one of the outbreak factors of bruising is the struggle between cattle. Odds ratios within sires or fattening farm were higher for steatosis cases, suggesting that genetic and environmental factors influence steatosis outbreaks. In addition, the steatosis odds ratio of carcasses graded in March was the highest. It was thought that these fattening cattle spent initial fattening period (about 10 months of age) in high temperature and humidity during rainy seasons, because most Japanese Black fattening cattle are slaughtered from 28 to 30 months of age. For these cattle, while the energy consumption was increasing, the amount of feed intake was decreasing under the hot environment. On the contrary, the lowest odds ratio was observed in cattle fattened from the start of the winter season and slaughtered in October. This observation suggests that the drop in feed intake during the early fattening period influences steatosis outbreak. Although further investigations of feed intake level and/or temperature of environment are needed, it may be concluded that environmental factors including feed management in conjunction with differences in sensitivity due to genetic factors cause the steatosis.