Each of ten female pigs was administered prostaglandin F_2α (PGF_2α) : 15mg for Group I, 10mg for Group II, 5mg for Group III, or saline for the control twice daily for 3 days from Day 8 to Day 10, defining Day 0 as the last day of the previous estrus, to examine its effects on inter-estrous interval and reproductive performance. The inter-estrous intervals in Groups I, II, and III were 15.7±0.6 days, 17.9±3.8 days, and 17.5±2.5 days, respectively, and were significantly shorter than that in the control group (21.2±1.2 days). In Groups II and III, the inter-estrous intervals of each 3 animals did not shorten, ranging from 21 to 26 days. In the control group, the blood progesterone concentration decreased gradually from Day 14, reaching 1ng/ml on Day 18, and leveled off until the return of estrus. In the PGF_2α treated groups, except for the pigs whose estrous cycles were not shortened, the progesterone level was significantly lower than in the control group between Day 10 to 14, sharply decreased from Day 10 and leveled off in the 1ng/ml range from Day 12 until the onset of estrus. Of the pigs whose estrous cycles were not shortened, the progesterone levels showed some fluctuation during the administration of PGF_2α, increased after the administration, and remained at high levels until Day 15-21. Indicators of reproductive performance such as gestation period, litter size, and birth weight induced by PGF_2α were found to be standard. These results indicate that 15mg of PGF_2α for one dose is necessary to ensure success in shortening the inter-estrous interval because the inter-estrous intervals of some pigs under reduced doses did not shorten.

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To establish technology for phosphorus removal and recovery from swine wastewater using the struvite (magnesium ammonium phosphate) crystallization method with ceramics, we designed a renewal struvite reactor and investigated its performance on crystallization, using thickener effluent from swine wastewater treated with coagulant and machine separation.
The struvite reactor was made of 250-liter capacity stainless steel with three diffusers to supply micro air bubbles to improve aeration efficiency, and aerated continuously at 45m³ per hour with a blower. Star-shaped ceramics submerged in 30% MgCl2·6H₂O solution were used as struvite recovery materials. Thickener effluent was introduced into the struvite reactor continuously at 4.8m³ (HRT of 1.25hrs) per day, with the addition of 30% MgCl₂·6H₂O solution (10 liters per day). The examination was carried out for 65 days.
The results showed that the pH of raw swine wastewater rose for the period from winter to autumn, and the soluble PO₄-P concentration decreased along with the rise of its pH. The pH of thickener effluent was higher than raw swine wastewater, and average soluble PO₄-P concentration decreased from 79.0mg/l to 39.9mg/l during coagulant and machine separation. Because of the improvement in struvite crystallization efficiency by using the new aeration conditions for struvite recovery, 33-46% of phosphorus in thickener effluent was recovered as struvite while its PO₄-P concentration was low at 22.9mg/l.
To increase struvite recovery efficiency, it is necessary to confirm the pH control techniques for keeping highly soluble PO₄-P concentration in the thickener effluent.

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[in Japanese]

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