Abstract
We investigated the impact of prostaglandinF2α (PGF2α) on estrous cycle reduction and the reproductive performance of pigs, on either days 8-10 (Experiment 1) or days 11-13 (Experiment 2) of the estrous cycle, when day 0 was defined as the last day of the previous estrus.
Experiment 1 : A mixture of Landrace breed sows and gilts as well as crossbred swine, all with normal estrous cycles, were used. Pigs were divided into two groups : a control group and a PGF2α treated group of 10 animals each, respectively. Setting the last day of the previous estrus at day 0, the pigs in the PGF2α treated group were injected intramuscularly with PGF2α in the neck behind the ear (Dinoprost : 15mg/3ml /time) twice daily, 0900h and 1700h, six administrations in total , for three days 8 to 10.
The animals in the control group received physiological saline by the same method as the treated group. Mean estrous start day in the PGF2α treated group was reduced to 14.2±0.4 days compared with 19.5±0.7 days for the control group (p<0.01). The plasma progesterone (P) level in the PGF2α treated group began to decrease one or two days after the start of treatment and leveled off at a low average of 1ng /ml after day 12. When the pigs in PGF2α induced estrus were inseminated, their conception rate was 90%, as one of the animals failed to become pregnant. On day 5, we performed laparotomies on two of the animals to observe their ovaries and collect embryos. It was found that the number of corpora lutea was 13 and 11 and the number of embryos collected was 12 and 8, respectively. The development stages of the embryos appeared to be within the normal range. The reproductive performance of the other seven farrowing pigs was normal ; the average length of pregnancy, litter size and birth weight were 115.1±1.2 days, 10.6±1.9 and 1.4±0.3kg, respectively.
Experiment 2 : The experimental procedures were the same as in Experiment 1, except that the three days administration of PGF2α was carried out on days 11-13 of the estrous cycle. Ten crossbred pigs with normal estrous cycles were used ; five in the PGF2α treated group and five in the control group. In the PGF2α treated group, estrus commenced at 16.4 ±0.6 days. It was a significant (p<0.01) reduction compared with the control group. The P level in the PGF2α treated group began to decline one day after the start of treatment (day 12) and leveled off at a low average of 1ng/ml after day 13. When the animals in PGF2α induced estrus were inseminated, all of the animals became pregnant. The reproductive performance of the animals was normal ; the average length of pregnancy, litter size and birth weight were 114.6±0.9 days, 9.6±2.5 and 1.2±0.2kg respectively. It was therefore concluded that the repeated administration of PGF2α at intervals of 8 hours for3 successive days during the functional luteal stage between days 8 and 13 induced the early regression of the corpora lutea and that the reproductive performance of pigs whose estrus was induced by PGF2α was normal.
