Follicular dynamics, embryo production, and hormonal responses in Brahman heifers following sympathetic stimulation

The purpose of this experiment was to characterize adrenal and ovarian responses to N-methyl-beta-phenethylamine (NMP) or ACTH. Thirty-three heifers with functional midcycle corpora lutea were placed on a 4-d superovulation regimen. They were injected twice daily with FSH-P and either saline (Control), ACTH (80 IU), or NMP (1 mg/kg BW). An initial blood collection preceded jugular delivery of saline, NMP, or ACTH, i.m. delivery of FSH and PGF2-alpha (d 3), and ultrasound (d 1 to 4). A second blood collection was made 6 min after treatment. Sampling continued daily until d 13. Embryos (age 6 to 7 d) were collected and evaluated. Concentrations of cortisol (posttreatment minus pretreatment) were greatest (P .05) in NMP- and ACTH-treated heifers. Treatment did not affect mean numbers of small ( 4mm), large ( 8mm), or total follicles on d 2 to 4. Heifers receiving NMP had fewer medium follicles (4 to 8 mm) on d 2 and 3, and ACTH-treated heifers had fewer medium follicles on d 4 (P .07). Mean estradiol concentrations on d 2 to 4 were unaffected by treatment (P .32). Following PGF2-alpha, time to onset of standing estrus was less (P .05) in Control than in ACTH- and NMP-treated heifers (41.4 vs 47.9 and 58.9 h, respectively). A greater frequency (P .05) of reproductive anomalies (no estrus; no ovulation [i.e., progesterone 1 ng/mL]; luteal failure [i.e., progesterone 1 ng/mL but embryos recovered]) occurred in NMP (5/11) than in Control (0/10) or ACTH (2/10) heifers. No differences were detected in mean number or quality of embryos recovered from heifers that were inseminated. In summary, both ACTH and NMP stimulated cortisol release. Heifers given NMP or ACTH had an increased interval to onset of estrus and, in NMP-treated heifers, overall abnormalities of the reproductive cycle were increased. Reproductive function may be impaired in heifers consuming large quantities of plants containing NMP