ADMINISTRATION OF TESTOSTERONE FROM DAY-13 OF THE ESTROUS-CYCLE TO ESTRUS INCREASED THE NUMBER OF CORPORA-LUTEA AND CONCEPTUS SURVIVAL IN GILTS

The effects of exogenous androgens on the number of corpora lutea (CL) and conceptus survival were examined in crossbred gilts. In Exp. 1, g ilts received 1 mg of testosterone per day from d 13 (d 0 = first day of estrus, n = 21) or d 16 until estrus (n = 23). Gilts in the vehicle group received corn oil (n = 20). Gilts were mated and on d 11.5 thei r concepti and CL were evaluated. In Exp. 2, conceptus survival was ex amined at the 4- to 8-cell, early blastocyst or hatching blastocyst st ages for gilts given vehicle or 1 mg testosterone from d 13 (24 gilts per group). In Exp. 3, gilts received 1 mg of androstenedione (n = 20) or vehicle (n = 18) per day from d 13 to estrus and then were mated a nd evaluated on d 11.5. Results from Exp. 1 indicated that the number of CL was greater (P < .04) in gilts treated with testosterone from d 13 to estrus than in gilts receiving vehicle (16.4 vs 14.8, respective ly). Similarly, the number(P < .01) and recovery rate (P < .04) of bla stocysts were greater in gilts treated with testosterone from d 13 to estrus than in gilts treated with testosterone from d 16 to estrus or in gilts receiving vehicle (number, 15.3 vs 12.8 or 12.8; recovery rat e, 95 vs 87 or 86%, respectively). Gilts treated with testosterone or vehicle did not exhibit differences (P > .05) in number of normal conc epti at the 4- to 8-cell and hatching stages. However, prior treatment with testosterone delayed conceptus death; gilts treated with testost erone had more (P < .01) normal concepti at the intermediate stage (ea rly blastocyst) than those treated with vehicle (treatment x embryo st age interaction, P < .05). In Exp. 3, androstenedione treatment did no t influence (P > .10) the number of CL or the number and recovery rate s of d-11.5 blastocysts. Treating gilts with testosterone from d 13 of the estrous cycle to the following estrus increased the number of CL and blastocyst survival, perhaps by improving some, as yet unknown, as pect(s) of oocyte quality.