| Abstrakt: |
Breed and sex effects on muscle properties and physiological parameters of stress-susceptibility were studied on purebred Pietrain (P× P), purebred Minnesota No. 1 (M× M) and F1(P× M) cross-bred pigs. Four gilts and four barrows were used in each breed group. Blood samples were taken 10 min after heat stress (40.5 C) at approximately 60 kg live weight and analyzed for blood creatine kinase (CK) by the Rosalki method. Animals were sacrificed at 100 ± 4 kg live weight following a 10 min, 40.5 C heat stress. Lactate, glucose, cholesterol, lactate dehydrogenase (LDH) and CK (Rosalki, Sigma, Biodynamics) were determined on blood obtained from the carotid artery at exsanguination. Backfat thickness, longissimusmuscle area, carcass length, percentage ham plus loin, longissimusmuscle quality properties, adrenal weight and histology and heart weight were determined. P× P and M× M breeds displayed sharply contrasting traits: P× P pigs displayed the fastest longissimusmuscle pH decline, the greatest longissimusmuscle area and percentage ham plus loin of the three groups. M× M pigs exhibited the highest values for color, structure, marbling, adrenal weight, backfat thickness and carcass length. The P× M group exhibited means intermediate between the two purebred groups for the following: longissimuspH 45 min postmortem, structure, marbling, longissimusarea, percentage ham plus loin and backfat thickness. The means for carcass length and adrenal weight in the P× M group were close to the means for M× M pigs. No significant differences were noted for heart weight unless it was expressed as grams per kilogram ham plus loin (an index of muscularity) in which case P× P pigs exhibited lower ratios than P× M and M× M pigs. No significant breed differences were noted for blood glucose or cholesterol. Lactate was significantly (P<.05) higher in P× P than M× M pigs. However, if expressed as milligrams lactate per kilogram ham plus loin, the statistical significance of the breed differences for lactate vanished. Serum levels of CK were higher (P<.05) in P× P pigs than in M× M and P× M pigs prior to and following heat stress at 60 kg live weight. Following heat stress, levels of CK and LDH were generally high in P× P, intermediate in P× M and low in M× M pigs at 100 kg live weight as determined by the Rosalki, Sigma and Biodynamic procedures. Significant sex differences were noted for blood CK (Sigma), backfat thickness, longissimusmuscle area, carcass length and percentage ham plus loin which characterized gilts as more muscular than barrows (P<.01) and also exhibiting higher blood CK (P<.05). The same serum sample analyzed for CK (Rosalki) demonstrated that a significant (P<.05) breed × sex interaction existed in which for P× M pigs, barrows exhibited higher blood CK than gilts; for P× P pigs, gilts exhibited higher CK than barrows; and for M× M pigs, gilts and barrows were very similar in blood CK value. |
