Effective Oxytocin Treatment on Placental Expulsion After Foaling in Heavy Draft Mares
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FULL PAPER Theriogenology Effective Oxytocin Treatment on Placental Expulsion after Foaling in Heavy Draft Mares Mitsuo ISHII1)*, Syuichi KOBAYASHI1), Tomas J. ACOSTA1), Wataru MIKI2), Motozumi MATSUI1), Takahiro YAMANOI3), Yoh-Ichi MIYAKE1) and Akio MIYAMOTO1) 1)Obihiro University of Agriculture and Veterinary Medicine, Nishi 2-sen, Inada-cho, Obihiro, Hokkaido 080–8555, 2)Hokkaido NOSAI, 612 Motonopporo, Ebetsu-shi, Hokkaido 069–0867 and 3)Hokkai Gakuen University, Faculty of Engineering, Minami 26-jo, Nishi 11- chome, Chuo-ku, Sapporo, Hokkaido 064–0926, Japan (Received 29 October 2007/Accepted 7 November 2008) ABSTRACT. The aim of this study was to establish the effectiveness of administration of oxytocin (OT) on placental expulsion after foaling. Four foaling mares with the placentas retained for up 1 hr after foaling received OT (50 IU) administration at 1 hr intervals before expul- sion of the placenta. The changes in the plasma concentrations of OT and the PGF2alpha metabolite (PGFM) were investigated, and the influence of OT administration was considered. The results were as follows. The placenta was expelled after one to three OT admin- istrations in all four mares that received OT. In two mares, which expelled the placenta within 30 min after OT administration, the OT concentration increased and remained high. Expulsion of the placenta was delayed in two mares, and one of these mares, which received three doses of OT beginning 1 hr after foaling, showed only a small increase in the OT concentration after the first administration; the other mare did not receive OT until 3 hr after foaling. The OT concentration was increased before placental expulsion in all the mares, and the PGFM concentration also increased in the two mares with retained placentas. In conclusion, we suggest that intramuscular administration of 50 IU of OT at 1-hr intervals beginning 1 hr after foaling is effective for inducing placental expulsion. KEY WORDS: mare, oxytocin, PGFM, placental expulsion. J. Vet. Med. Sci. 71(3): 293–297, 2009 In heavy draft mares, retained placenta occurs frequently PG during delivery are mutually and closely related [1, 15]. and can have serious consequences, such as puerperal fever The aim of present study was to establish an effective and laminitis. Extension of the placental retention time method to administer OT after foaling in heavy draft mares. reduce the subsequent conception rate in heavy draft mares For this purpose, we conducted tested several methods of [5]. Although the conception rate of foal heat in mares with administering OT after foaling and monitored the time of a placental retention time of less than 1 hr is 66%, it falls placental expulsion. Changes in the OT and PGF2alpha significantly to 51.7% in mares with a placental retention metabolite (PGFM) concentrations were also analyzed to time that exceeds 4 hr [5]. To promote expulsion of the pla- assist in evaluation of these methods. centa, oxytocin (OT) administration is usually used in mares after foaling. There are some reports that describe effective MATERIALS AND METHODS OT treatments for retained placenta, such as an intravenous drip infusion containing 30–100 IU of OT [3, 14] and Animals: This study was conducted in Kushiro, Hok- repeated subcutaneous or intramuscular administration of kaido, Japan. It involved a total of 4 heavy draft mares from 20–120 IU of OT [4, 7, 16]. Ishii et al. [5] reported that the 4 farms that were mixed breeds belonging to Breton, conception rate at foal heat of heavy draft mares whose pla- Percheron or Belgian Draft hoses with an estimated average centas were expelled after intramuscular administration of body weight of 900 kg after foaling and varying from 6 to 50 IU of OT up to 4 hr after foaling was more than 70%. In 16 years in age. Foaling occurred from March to June, and addition, the conception rate at foal heat of mares that pregnancy ranged from 331 to 340 days in length. All foal- received OT was higher than that of non-OT treated mares ing appeared to be normal, and all foals lived. The owner of among the mares that expelled the placenta 1–4 hr after foal- the mares provided minimal help during delivery of the ing [5]. However, whether this is a more effective method foals. of treatment to not only induce expulsion of the placenta, OT administration: All four mares received OT after but also to improve subsequent reproductive performance foaling. Two mares whose placentas were retained for up to after foaling, has not yet been clarified. Prostaglandin (PG) 1 hr after foaling received 50 IU of OT intramuscularly 1 hr F2α might play a role in the contraction stimulus of the myo- after foaling (Nos. 1 & 2; Figs. 1 & 2), and one mare metrium during delivery. The action and release of OT and received three doses of OT at 1 hr intervals for up to 3 hr after foaling because the placenta had not been expelled *CORRESPONDENCE TO: ISHII, M., Research Center for Animal Hygiene and Food Safety, Obihiro University of Agriculture and (No. 3; Fig. 3). The other mare that had a retained placenta Veterinary Medicine, Nishi 2-sen, Inada-cho, Obihiro, Hokkaido received one dose of OT 3 hr after foaling, and OT was 080–8555, Japan. administered once again at 1-hr intervals (No. 4; Fig. 4). e-mail: [email protected] Data and investigation: The placental retention time of 294 M. ISHII ET AL. each mare and whether the foal stood, sucked or was hand- to three OT administrations in all four mares that received milked were recorded. OT administration and changes in OT before placental expulsion (Nos. 1–4). In two (Nos. 1 & circulating OT and PGFM were investigated by comparing 2) of the three mares that received OT 1 hr after foaling, the these data. placenta was expelled around 30 min after administration Blood sampling: Blood samples were collected from 20 (Figs. 1 & 2). In mare No. 3, which received three doses of min before foaling for one mare (No. 4) and immediately OT (50 IU) at 1-hr intervals, the placenta was expelled about after foaling for the other 3 mares; blood sampling contin- 1 hr after the third OT administration (Fig. 3). In the other ued until 2 hr after expulsion of the placenta in all mares. mare, No. 4, which received the first dose of OT 3 hr after Blood samples were collected every 5 min from immedi- foaling, the placenta was expelled 30 min after the second ately after foaling to 1 hr after foaling in all mares. When OT administration at 1-hr intervals (Fig. 4). the placenta was retained, sampling was continued at 5-min Changes in the plasma OT concentration: The fluctua- intervals until expulsion of the placenta, and blood samples were collected 1 and 2 hr after placental expulsion. A 160 mm long 14-G catheter with a 2-m long tube was kept in the jugular vein during the experiment and filled up 10 ml of physiologic saline including 200 IU of heparin sodium after collection of each sample. The blood samplings were repeated carefully with as little stress as possible to the mare. After collection, the blood was placed in a chilled 10 ml glass tube containing ethylenediaminetetraacetic acid (EDTA). The blood was centrifuged immediately after col- lection. The harvested plasma was frozen at –20°C until assayed. OT extraction: The plasma samples (5 ml) were diluted with 5 ml of distilled water, and the pH was adjusted to 2.5. All samples were then applied to a Sep-Pak C18 Cartridge (Waters, Millford, MA, U.S.A.) as described previously [10]. The residue was evaporated and then dissolved in 200 µl assay buffer (42 mM Na2HPO4, 8 mM KH2PO4, 20 mM NaCl, 4.8 mM EDTA, 0.05% bovine serum albumin [BSA], Fig. 1. Transition of the OT and PGFM concentrations in the blood of mare No. 1, which received OT 1 hr pH 7.5) for a peptide enzyme immunoassay (EIA). Thus, the after foaling and the placenta was expelled. P: parturi- samples were concentrated 25-fold as a result of this pro- tion M: hand-milking E: expulsion of the placenta cess, which enabled us to determine peptide concentrations OT50: intramuscular administration of 50 IU of OT. in EIA within the range of a standard curve. The recovery rate of OT added to the plasma was 70%. OT determination: The EIA for OT, which has been pre- viously described [12], was based on the second antibody method using the biotin-streptavidin-peroxidase technique [11]. The standard curve for OT ranged from 1.9 to 2000 pg/ml, and the ED50 of the assay was 80 pg/ml. The intra- and interassay CVs were 5.8 and 6.4%, respectively. PGFM extraction: The plasma was extracted by diethyl ether after adjusting the pH of each plasma sample (2 ml) to 3.5 using HCl [10]. The residue was evaporated and then dissolved in 200 µl assay buffer (40 mM PBS, 0.1% BSA, pH 7.2). The samples were concentrated 10-fold as a result of this process. The recovery rate of PGFM added to the plasma was 70%. PGFM determination: PGFM concentrations were deter- mined by a second antibody EIA as reported previously [9]. The standard curve for PGFM ranged from 4 to 1,000 pg/ml, and the ED50 of the assay was 48 pg/ml. The intra- and inter-assay CVs were 7.7 and 13.0%, respectively. Fig. 2. Transition of the OT and PGFM concentrations RESULTS in the blood of mare No. 2, which received OT 1 hr after foaling and the placenta was expelled.