Use of altrenogest alone or in combination with PMSG to control the preovulatory LH surge in gilts

Abstract

Sixty-four cycling gilts were used to study the effects of altrenogest (AT) alone or in combination with pregnant mare's serum gonadotropin (PMSG). PMSG was administered at different times before and after AT removal and the variations in onset of the preovulatory LH surge, estrus and the interval to peak LH concentrations were studied. Each gilt was individually administered 15 mg AT daily in the ration for 14 consecutive days, with the day of AT removal designated as day 0. PMSG (750 I.U.) was injected SC at day −1, 0 and 1 ( N= 16 treatment ). Sixteen control gilts (C) received a saline (1 ml) injection on the last day of AT feeding. Percentages of gilts failing to exhibit estrus were: PMSG−1 (0%), PMSG−0 (0%), PMSG+1 (6.2%) and controls (31.2%). Mean intervals( ± SEM) from last feeding of AT to onset of the preovulatory LH surge were 104±5, 99±3, 106±3 and 103±5 h for the PMSG−1, PMSG−0, PMSG+1 and C groups, respectively. Time from last feeding of AT to onset of standing estrus was 116±6, 107±4, 112±3 and 112±4 h, respectively, for the four groups. The respective mean LH peak values were 5.5±0.7 ( P<0.01), 8.9±0.8, 8.2±0.9 and 9.2±0.7 ng/ml for the PMSG−1, PMSG−0, PMSG+1 and C groups. Injection of PMSG on the day after last AT feeding caused a greater ( P<0.05) synchrony of occurrence of the onset of estrus and the preovulatory LH peak. These results indicate that when a combination treatment of AT and PMSG is given, greatest synchrony of estrus and ovulation most likely occurs when the PMSG treatments are administered 24 h after termination of the progesterone agonist.