Vet Column 10-18-10 |

Vet Column 10-18-10

David L. Morris, DVM, Ph.D.
Fort Collins, Colo.

An advantage of home-raised beef is knowing exactly what went into the animal and the indirect alignment of minimizing stress to the animal during the feeding program. These attributes are also often extended to the locally raised and processed sources as well. For those familiar with junior livestock fairs, however, it is not uncommon to see the most docile of animals at home become highly excited animals when the animals are unloaded at the fairgrounds.

For those tasked with providing a uniformly and predictable beef product, does excitement just prior to harvest affect beef tenderness? Will the freezer beef from that 4-H/FFA junior market beef project be affected by potential stress at the fair? Scientists from Colorado State University recently published data from a study that evaluated the relationships of behavior and physiological markers of pre-harvest stress to beef tenderness.

Handling and transporting cattle immediately before processing elicits a broad range of response among individual animals. While many animals appear psychologically and physically unaffected by routine pre-harvest handling and transport practices, others exhibit various combinations of behaviors. This may include nervousness, balking, excitement, fear, avoidance or flight, vocalization, or aggression as well as physiological reactions that can be representative of stress.

What happens when some animals become excited? In acute responses to stress, catecholamines (epinephrine and norepinephrine) are released into the bloodstream resulting in a cascade of effects. This can include increased heart rate, increased body temperature, and increased metabolic rate. Catecholamine release also results in elevated blood glucose and lactate concentrations. As a result, post-mortem muscle pH may increase and muscle color, firmness, and water-holding capacity can be affected.

For this study, 50 percent British and 50 percent Charolais steers (77 head) and heifers (77 head) were used. They were sorted into 16 pens with nine to 11 animals per pen. A steam-flaked corn-based finishing diet was provided once daily and consumed at will. Behavioral scores were assessed during human presence in a confined area (pen score), confinement in a squeeze chute (chute score), and transportation from feedlot to packing facility (post-transportation score). The behaviors were scored as calm, restless, nervous, flighty, or aggressive.

Measurements of heart rate, respiration rate, rectal temperature, and concentrations of serum cortisol and plasma epinephrine were used as indicators of stress associated with physical handling and chute restraint. Measurements of cortisol, glucose, lactate, and creatine kinase in blood samples were used to reflect physiological reactions of animals to transportation stress.

Results from this study indicate that animals with elevated heart rate and increased rectal temperature during restraint, and increased plasma lactate at harvest were associated with less tender beef. Behavioral results demonstrated that cattle exhibiting adverse reactions to handling and chute restraint had less tender beef as well.

For those cattle showing behavioral symptoms of stress after transportation, they produced tougher steaks when compared to calm cattle. No dark cutters were noted in this trial. This study also noted that for those cattle showing behavioral symptoms of stress after transportation, a delayed response to aging occurred. Beef carcasses from excited animals following transportation should be aged at least 14 days.

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