Dose‐dependent effects of melengestrol acetate (MGA) on plasma levels of estradiol, progesterone and luteinizing hormone in cycling heifers and influences on oestrogen residues in edible tissues

Abstract

Melengestrol acetat (MGA) is widely used as a growth promoting feed additive in cattle breeding in the USA and several other non-European countries. To explore the physiological effects of MGA four heifers were fed during 8 weeks with 0.5 mg MGA daily as registered in the USA and two heifers each received 0, 1.5 or 5 mg/day, respectively. Plasma samples were collected twice a week and concentrations of MGA, progesterone (P4) and estradiol-17beta (E2-17beta) were quantified. The pulsatile secretion of luteinizing hormone (LH) was investigated in 6-hour profiles before and during treatment. After slaughter the reproductive organs were examined and oestrogen residues in edible tissues were measured. Four days after the beginning of MGA feeding MGA concentrations in plasma reached levels of 30 and 100-400 pg/mL depending on the dose received. Three weeks after the beginning of MGA feeding P4 plasma concentrations had dropped to base levels below 0.3 ng/mL in all three treatment groups. Mean plasma E2-17beta levels increased in physiological range from 1 to 5 pg/mL during 0.5 mg MGA/day feeding with many acyclic peaks. Overdosed MGA decreased E2 levels and suppressed cyclic peaks. Number and size of ovarian follicles were not altered by any treatment. Mean LH levels and pulse frequencies increased significantly during labelled treatment (0.5 mg/day), while higher doses had reducing effects. The development of corpus luteum was suppressed. E2-17beta residues in fat increased about 300% following labelled MGA treatment.

Food Safety

“…The magnitude of this increase strongly depends on the compound or metabolite and the tissue examined, for example ranging from 3.7 in muscle to 6.4 in fat for estradiol-17β and from 1.2 in muscle to 1.9 in fat for estrone in animals with estradiol-containing implants [70]. Similar results have been reported for animals treated with other growth promoters [71,72]. Note that zeranol, i.e., α-zearalenol, is a minor metabolite in the tissue of untreated pigs if their feed is contaminated with the mycotoxin ZEA, whereas it was found to be undetectable in muscle or liver tissue of cattle that had received ZEA-contaminated feed.…”

Impact of preimplantational oral low‐dose estradiol‐17β exposure on the endometrium: The role of miRNA

“…Analyses of estradiol-17β (E2) and total estrogen (estrone, E2, estradiol-17α) concentrations in endometrial tissue were performed using an in-house competitive enzyme immuno assays (EIA) (Hageleit, Daxenberger, Kraetzl, Kettler, & Meyer, 2000;Meyer, Sauerwein, & Mutayoba, 1990). Endometrial tissue was homogenized in liquid nitrogen using a mortar and pestle.…”

Biochemistry and physiology of anabolic hormones used for improvement of meat production

“…Due to continuous follicle development, endogenous oestradiol becomes elevated to about 5 pg/ml blood plasma which is obviously sufficient for steady growth promotion in heifers. Threefold or 10-fold dosages result in blood levels of 100-300 pg MGA/ml and a negative feed back on the gonadotrophins (29). As a consequence oestradiol also remains low at around 1-2 pg/ml.…”