5.8. For all examined cows, SAA concentration was greater in winter than summer (P< 0.001), as well as at day 4 than days 11 and 18 after calving (P< 0.05).Also, Hp concentration was greater for winter samples than summer (P< 0.05), and at day 18 than days 4 and 11 after calving (333.33 vs. 299.3 and 300.1 respectively) (P< 0.05). SAA and Hp concentrations were not affected by rumen pH. There was no significant correlation between rumen pH and APPs concentrations in both groups of pH ≤5.8 and pH >5.8. CONCLUSIONS: Results showed that rumen pH ≤5.8 seems not to stimulate the APPs production