Effect of the uterine environment during fescue toxicosis on embryonic survival

An experiment was performed to determine if the administration of ergotamine tartrate to simulate fescue toxicosis alters the ability of the uterus to establish and maintain pregnancy following transfer of frozen-thawed embryos. Forty five heifers (x = 317.4 kg) that had exhibited two normal estrous cycles received corn silage top dressed with a 2:1 supplement of ground corn:soybean meal mixed with either 0 (CON, n=25) or 40 ug/kg body weight (BW) of ergotamine tartrate (ET) daily (TRT, n=20). All animals were fed their respective treatment diets for a 30-d adjustment period and continued until determination of pregnancy status. Heifers were monitored weekly for changes in BW and content of ET was adjusted accordingly. After the 30-d adjustment period, estrus (d=0) was synchronized with SyncroMate-B and followed by the placement of two embryos with an average quality score of 2.4 (range 1, excellent to 4, poor) into the uterine horn ipsilateral to the CL on d 7. Quality scores of CL (range 1, excellent to 3, poor) and embryos were determined by two experienced technicians. Heifers were bled weekly by jugular venipuncture for determination of progesterone (P₄) and prolactin (PRL). Pregnancy (presence of an embryo with heartbeat) was determined 28 d after embryo transfer by transrectal ultrasonography utilizing a 7.5 MHz transducer. Concentrations of PRL were lower in TRT (173.6 ± 21 ng/mL) than in CON heifers (274.1 ±21 ng/mL;P< .005). Average daily gain was not affected by treatment (pooled ADG = 1.3 kg/d; P > .10). Pregnancy rates did not differ (P >. 10) between CON (8/25; 32%) and TRT (10/20; 50%) animals. Rectal temperatures at the time of embryo transfer tended to be higher (P= .06) in TRT (39.6°C ± .1) than in CON (39.2°C ± .1). Furthermore, neither concentrations of P4 on the day of embryo transfer (3.9 ± .3 ng/mL) nor CL quality score (1.6 ± .2) had any effect on pregnancy rates (P > .10). In conclusion, the uterine environment of heifers during simulated fescue toxicosis is suitable for maintenance of embryonic development and establishment of pregnancy.