We investigated the impact of prostaglandinF_2α (PGF_2α) 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 PGF_2α treated group of 10 animals each, respectively. Setting the last day of the previous estrus at day 0, the pigs in the PGF_2α treated group were injected intramuscularly with PGF_2α 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 PGF_2α 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 PGF_2α 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 PGF_2α 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 PGF_2α was carried out on days 11-13 of the estrous cycle. Ten crossbred pigs with normal estrous cycles were used ; five in the PGF_2α treated group and five in the control group. In the PGF_2α 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 PGF_2α 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 PGF_2α 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 PGF_2α 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 PGF_2α was normal.

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Twenty-eight castrated male Landrace pigs aged six weeks were used in a 4-week trial to investigate the effect of microbial phytase on growth performance and serum parameters. A corn-soybean meal-based diet containing 27.7mg of Zn/kg of diet was fed alone and supplemented with 20 or 40mg of Zn/kg of diet as ZnCO₃ or with 350, 700, 1050, or 1400U of phytase/kg of diet. Blood was collected on d 21 of the trial for serum Zn concentration and alkaline phosphatase activity. BW gain and feed intake of pigs increased both linearly and quadratically with adding Zn and phytase to the low Zn basal diet (P<0.01). Feed conversion ratio improved linearly by adding Zn and phytase (P<0.05). Serum Zn concentration and alkaline phosphatase activity were linearly increased by adding Zn (P<0.05) and phytase (P<0.01). Nonlinear or linear response equations of the effects of Zn and phytase levels were generated and used to calculate the Zn equivalency values. The average function of Zn equivalency values (Zn, milligrams per kilogram) of microbial phytase (Phy, units per kilogram of diet) was developed based on FI, DG, and FCR : Zn=0.0535+0.0337Phy-0.0000129Phy² (r²=0.99), and also based on SZn and ALP : Zn=-0.6259+0.0062Phy+0.0000066Phy² (r²=0.99). The results indicate that 500U of phytase could release 13.7mg of Zn from the equation developed based on growth performance and 4.12mg of Zn from that on serum parameters.

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The present experiment aimed to examine the effects of controlled feeding (which is well known as a method for body fat deposition reduction) with low-CP feed on the growth and carcass quality of fattening pigs. Feed used in this study was prepared by reducing the CP level by 2.2% from the standard level during the fattening period according to the Japanese feeding standard for swine (1998), and by supplementing it with lysine. Eight crossbred pigs were used and they were divided into two groups having the same mean body weight as follows : a control group, ad libitum of low-CP feed and an experimental group, 85% controlled feeding of low-CP feed. The animals were fed in a temperature-controlled room at 25±2°C using a single cage with feed and water every day. Feed intake, water drinking, and feces were determined every day. Body weight and body size were determined every week. Digestion trial was conducted in the last week. After slaughtering, carcass measurements and analysis of the chemical composition of the loin and the chemical character of the back fat were conducted.
The fattening period, from a body weight of 70kg to 106.9±1.9kg, took 41 days in the control, and in the experimental group it took 55 days to reach 106.5±1.5kg. Although the feeding level of the controlled feeding was designed to be 85% of the control group, it resulted in at about 81%. This reduction induced an increase in the fattening periods and total feed intake. The enlarging of body length, depth of chest, and width of chest in the experimental group was significantly (P<0.05) smaller than that of the control group. Digestibility of ether extracts in the experimental group was significantly (P<0.05) higher than that of the control group, but the levels of nitrogen free extracts and ADF were significantly (P<0.05) lower in the experimental group. In the results of carcass measurements, the shoulder part and waist part of back fat thickness in the experimental group were significantly (P<0.05) thinner than those in the control group.
In the results of amino acid analysis, lysine and threonine intake was insufficient even in the control group. Intakes for those amino acids, sulfur-containing amino acids, tryptophan, and branched-chain amino acids were also insufficient in the experimental group. The present results suggest that controlled feeding reduces the body fat deposition, although the amino acid imbalance might induce body fat deposition.

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