Meat Quality of Turkeys Affected by Heat Stress and Immune Challenge Conditions, and the Relationship Between Meat Quality and the Social Index
Heat stress (HS) and immune challenges (IC) are just two of the many stressors poultry can experience in commercial settings that can have an effect on bird welfare and final product quality after harvest. Individual animals vary greatly in their responses to stressors, which can further influence product quality. The overall goal of this study was to examine the relationships among stress, behavioral characteristics and meat quality of commercial turkeys. The first objective of this study was to determine if the heat stressed or immune challenged turkeys experienced greater negative effects on overall meat quality compared to a control group. The second objective of the study was to determine if the frequency of nonaggressive pecking behaviors among the birds was related to final meat quality. A total of 92 commercial male, beak-trimmed turkeys were used in two trials (in time replicates) with a total of 15 rooms and 4-7 birds per room. There were two to three rooms experiencing each treatment at a time. The heat stressed (HS) treatment subjected the birds to an ambient temperature of approximately 29 °C, depending on the room’s humidity, and lasted 120 minutes before returning to the normal temperature range. The immune challenge (IC) treatment consisted of inoculating the birds with a live vaccine for hemorrhagic enteritis virus. The control (CON) group was not subjected to heat stress or an immune challenge. The birds were rotated every two weeks starting at 10 weeks of age so that each group experienced each of the three treatments in a balanced Latin square design. The last treatment period was at 14 weeks of age. Birds were harvested at the Purdue Boiler Maker Butcher Block where several meat quality measures (feather retention force, pH, color, fatty acid composition and drip loss, among others) were recorded. There were no significant differences in fatty acid composition (P > 0.05) across treatment groups for any of the 38 fatty acids tested. There were also no significant differences in percent protein (P < 0.05) among treatment groups. Initial pH values were significantly different between treatment groups (P < 0.01), which corresponded with the significant differences in other meat quality attributes such as lightness (L*) and shear force (tenderness) values. Results indicate that even a short heat stress period lasting for 120 min can affect certain aspects of meat quality. Similarly, vaccination with hemorrhagic enteritis vaccine one week prior to slaughter also affects some meat quality measures.
To examine the relationship between non-aggressive pecking behavior and meat quality, turkey behavior was video-recorded at 14 weeks of age prior to any of the treatments that week. Video footage was analyzed to determine the number of aggressive and non-aggressive pecks given and received by each bird in the room. Aggression occurred too infrequently to be able to examine the relationship between aggression and meat quality. Therefore, analyses were only performed using non-aggressive pecking behavior. From these data, turkeys were given a rank that was calculated by dividing the number of non-aggressive pecks given by the number of non-aggressive pecks received. Ranks were standardized for the number of turkeys in each room. A cluster analysis was performed to categorize the birds into low, medium, and high groups based on their frequency of pecking. Clusters were tested to verify that they were significantly different from one another. Once each turkey had been assigned to a cluster, meat quality measures were compared among clusters to determine the relationship between non-aggressive pecking and meat quality. There was a trend (P < 0.10) for L* (lightness) and drip loss to differ among clusters; however, post hoc analysis did not reveal any significant differences. There were no significant differences (P > 0.05) among clusters for any other meat quality attributes. Therefore, turkeys’ tendency to perform and receive non-aggressive pecks does not seem to have an effect on the meat quality attributes tested in this study. Research with other species has indicated a relationship between other behavioral characteristics such as aggressive interactions, fear responses, social rank, body weight, and meat quality; therefore, future research examining other behavioral traits will be valuable in examining factors that can influence turkey meat quality.