Increasing feed intake in late gestation does not affect plasma progesterone concentration in the sow.

Rate of decline in plasma progesterone concentration may influence the success of lactogenesis in the sow. The aim of this experiment was to investigate whether progesterone concentration and rate of decline of progesterone in the periparturient sow could be manipulated by changing her feeding level. Forty-two sows received either 1.15 or 2 times maintenance energy daily from day 100 of gestation up until and including the day of farrowing. Blood samples were taken on days 98 (pre-treatment baseline) and 109 of gestation, during farrowing, 6h after farrowing and at 09:00 h for the 3 days following farrowing. Plasma progesterone concentration was determined and progesterone half-life was calculated for each sow. High intake feeding had no effect on plasma progesterone concentration at any time of sampling. Progesterone half-life averaged 41.2 +/- 3.81 h and did not differ between treatments. There was no relationship between progesterone concentration, or half-life, and litter weight gain, although there was a weak correlation between decline in progesterone in the first 6h after birth and piglet growth rate from birth to 6 days of age (R(2) = 0.109, P < 0.05). It was concluded that increasing feed intake in late gestation cannot be used to increase progesterone clearance rate and hasten the onset of lactogenesis in sows.