# Intrinsic and Extrinsic Factors Affecting the Color of Fresh Beef Meat--Comprehensive Review
## 3 Results and Discussion
### Extrinsic Factors
#### 3.2.2 Pre-Mortem Stress
Extended lairage times in poor conditions (temperature > 18 \({}^{\circ}\)C and RH > 70%) increased the risk of producing DFD carcass from less than 1% to around 40% when animals had to spend more than 19 h before slaughtering, instead of only 7 h [97]. Similarly, lairage times higher than 16 h doubled the probability of obtaining DFD meat when compared to 8 h of lairage [67]. Another study reported that animals staying in lairage for more than 72 h without extra feeding had an 85% probability of producing DFD carcass [23]. It was also determined that for every extra hour animals spent in lairage, the ultimate pH in meat increased by around 0.013 points [98]. It was also documented that regardless of transportation times, animals kept long holding periods were more susceptible to producing bruises and lesions due to more frequent aggressive reactions [62]. On the other hand, it was suggested that short lairage times (3 h) produced more stressed animals and higher pH values in meat when compared with animals kept overnight (15 h) due to recovery of glycogen stores after a quiet night of rest [55]. It was also observed that after long transportation distances (approximately 1800 km), the incidence of obtaining DFD meat was 40% when cattle spent 72 h in lairage, instead of 90% when lairage time was 24 h or 60% for 48 h resting time [94]. Another study determined that 48 h of lairage was the best treatment for cattle to replenish their glycogen stores after a long trip of approximately 18 h [99]. It was also suggested that lairage time higher than 17 h contributed to glycogen restoration in muscle and reduced the risk of obtaining DFD meat [31]. Another manuscript claimed that reducing lairage time from 18 h to 3 h in cattle that traveled less than 6 h and with no signs of exhaustion had no effect on the meat's ultimate pH [100]. It has been reported that there were no significant differences in meat pH values when cattle were not stunned, electrically stunned, or percussively stunned, even if glycogen concentrations were different between treatments [101]. Another publication mentioned that animals stunned more than once had higher cortisol levels resulting in lower lactic acid production and DFD-related problems [102]. Similarly, it was determined that when incorrect desensitizing of the animals occurs, the probability of obtaining dark-cutting meat increases by 10% [97]. Random mixing of the animals during transportation and lairage might increase the probability of obtaining DFD carcass, whereas maintaining the animals in the same social groups in which they were grown might enhance the color of their meat. Long transportation and extended lairage times might drastically reduce the glycogen reserves of cattle and generate lower L*, a*, and b* values in the meat of those animals. However, long and quiet lairage with enough food is recommended if animals need to be transported for long distances so that glycogen reserves can be replenished before slaughtering and the incidence of DFD problems can be reduced to a minimum. A simple and continuous training program about animal handling should also be provided to the workers with direct contact with cattle to optimize slaughterhouse operations, animal welfare, and meat color. Additionally, stunning needs to be precise and performed only by trained personnel to reduce the risk of DFD carcass.