THE EFFECT OF DIETARY-PROTEIN SOURCE ON BIOCHEMICAL INDEXES OF STRESSIN STRESS-SUSCEPTIBLE PIGS

The porcine stress syndrome (PSS) is responsible for major economic lo sses to the swine industry. The present study was performed to determi ne if 8-wk-old pigs representing each of three genotypes (NN = homozyg ous noncarrier, Nn = heterozygous carrier, nn = homozygous carrier) wi th respect to the PSS, differ in selected biochemical indices related to stress (exp. 1), and to examine if these indices are affected durin g 5 wk of dietary adaptation to a cereal-based swine diet (control die t) or to a feed containing casein, a higher quality protein (exp. 2). The first experiment demonstrated that nn and Nn 8-wk-old female pigs have a significantly greater glycemic response to a blood sampling str essor than do NN female pigs. In contrast, no genotype differences in glycemic response were observed within young male pigs. Pigs of nn gen otype also demonstrated a significantly greater plasma dopamine-beta-h ydroxylase (DBH) activity than did the NN pigs. Results of the second experiment revealed that pigs of the nn and Nn genotypes experienced a greater glycemic response to the initial blood sampling stressor than did the NN pigs. Compared with initial levels, upon the sixth weekly blood sampling stressor the nn and Nn pigs experienced reduced plasma glucose concentration irrespective of diet, while no change in glycemi c response was observed in the pigs of the NN genotype. Finally, the D BH activity of the Nn pigs adapted for 2 wk to the casein diet was fou nd to be reduced when compared to control-adapted Nn pigs. This study suggests that in addition to genotype differences, regular exposure to stress combined with dietary adaptation to feed containing a higher q uality protein (casein) may confer increased resistance to stress in p igs of the Nn genotype.