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 s uperovulation regimen. They were injected twice daily with FSH-P and e ither 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 PGF(2 alpha) (d 3), and ultrasound (d 1 to 4). A second blood collection was made 6 min after treatment. Sampling con tinued daily until d 13. Embryos (age 6 to 7 d) were collected and eva luated. Concentrations of cortisol (posttreatment minus pretreatment) were greatest (P < .05) in NMP- and ACTH-treated heifers. Treatment di d 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 follicle s (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 PGF(2 alpha), time t o 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 gr eater frequency (P < .05) of reproductive anomalies (no estrus; no ovu lation [i.e., progesterone < 1 ng/mL]; luteal failure [i.e., progester one < 1 ng/mL but embryos recovered]) occurred in NMP (5/11) than in C ontrol (0/10) or ACTH (2/10) heifers. No differences were detected in mean number or quality of embryos recovered from heifers that were ins eminated. In summary, both ACTH and NMP stimulated cortisol release. H eifers 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 heifer s consuming large quantities of plants containing NMP.