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 (< 4 mm), large (> 8 mm), 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.(ABSTRACT TRUNCATED AT 250 WORDS)