A transvaginal ultrasonic approach to elimination of singleton pregnancy in the mare: application to reduction of twin pregnancy

Abstract

Quarter Horse-type mares (n=36) were used to investigate transvaginal ultrasonographically-guided allantoic aspiration as a method of pregnancy reduction in the mare. Mares were randomly assigned to one of two treatment groups at Day 40-50 of gestation: 1) needle puncture of allantois and treatment with erogenous progestins (Altrenogest, 22 mg, per os, once daily, 30 days) (Group PP; n = 12), or 2) aspiration of allantoic fluid and treatment with erogenous progestins (Group AP; n = 12). Exogenous progestins were administered to simulate elevated progesterone concentrations, as would be detected if a single fetus remained viable following the termination of a twin. For comparative purposes, two treatment groups were added during the second year: 3) puncture or aspiration of the allantois without erogenous progestin treaunent (Group NP; n=8), or 4) ultrasonography without needle entry into allantois or treatment with erogenous progestins (control; Group C; n=4). Pregnancy status was monitored using transrectal ultrasonography for one week following treatment and weekly for three additional weeks. Intrauterine endoscopic examinations were performed on all mares with non-viable fetuses 30 days following treatment to identify and retrieve mummified fetuses. Fetal death occurred as a result of both allantoic puncture and aspiration procedures with a tendency (P=0.06) for fetal death rates to be higher following allantoic aspiration (I O/ 1 2; 83 %) than allantoic puncture (6/12: 50 %). The control procedure did not result in fetal death. Day of treatment affected fetal outcome in the allantoic puncture group. Fetal death rate was increased (P=0.01) when the allantois was punctured between Days 40-44 of gestation as compared with Days 4550 of gestation. Following fetal death, retained mummified fetuses occurred more often (P=0.03) in mares treated with exogenous progestins than in mares not treated with exogenous progestins. Mean plasma concentration of PGFM was higher (P=0.05) for mares in Group PP with non-viable fetuses than in Group PP mares with viable fetuses or Group AP mares with non-viable fetuses. Differences were not detected between treatment groups for mean plasma progesterone concentration.