Influence of meclofenamic acid on the initiation of parturition and lactation in the sow.

The effect of inhibition of prostaglandin (PG) synthesis on the initiation of parturition was studied in 4 groups of 16 sows each. Oral administration of meclofenamic acid (5.0 mg/kg body weight/day) on Days 112, 113 and 114 of pregnancy significantly delayed parturition compared to controls (P less than 0.001). Exogenous PGF-2 alpha after meclofenamic acid treatment synchronized parturition 20.4 +/- 1 h later. Functional luteolysis as indicated by a decline in maternal progesterone levels began during meclofenamic acid treatment; the fall in progesterone was then arrested in sows treated only with meclofenamic acid. Meclofenamic acid treatment in late pregnancy modified the normal initiation of lactation, as indicated by the high concentration of lactose and low concentrations of protein and Na+ in colostrum in treated sows compared to controls. We suggest that PG synthesis is required for the initiation of parturition in the sow and that luteal regression may involve two stages: the first which may be independent of prostaglandin, and the second, dependent on prostaglandin.