Effect of propionic acid on ketogenesis in lactating sheep fed restricted rations or deprived of food

Propionic acid was used as a possible preventive agent against ketogenesis. A total of 12 Suffolk lactating sheep were allocated to groups of 4 and fed isocaloric isonitrogenous rations containing 0, 5 and 10% propionic acid for 2 wk at 1.25 kg twice daily, followed by 4 days of food restriction to .5 kg/day and 2 days of food deprivation to induce ketogenesis. During the restricted feeding, concentrations of glucose in blood plasma were higher (50 to 57 versus 41 to 53 mg/dl) and concentrations of D (--)-3-hydroxybutyrate and acetoacetate lower (3.0 to 5.9 versus 3.9 to 7.6 mg/dl; .39 to .83 versus .43 to .92 mg/dl) in animals fed propionic acid. Propionic acid did not change free fatty acid concentrations of blood plasma or milk and subcutaneous fatty acid composition. Restricted feeding and fasting markedly lowered glucose and elevated concentrations of ketone bodies and free fatty acids in plasma. Furthermore, during these periods proportions of milk fatty acids containing 4 to 14 carbon atoms were decreased and those of stearic and oleic acid (18:0 and 18:1) were increased (16.6 versus 6.5%; and 41.0 versus 17.4%).