Impact of puberty status and melengestrolacetate supplementation before the breeding period on reproductive efficiency of Bos indicus beef heifers. Two experiments were designed to evaluate the impact of puberty status and the administration of melengestrolacetate (MGA) before onset of the breeding period on ovulatory responses (Exp. 1) and conception rate after AI performed on estrus detection
Response of prepubertal Bos taurus and Bos indicus x Bos taurus heifers to melengestrolacetate with or without gonadotropin-releasing hormone. The effectiveness of treatments to induce estrus in prepubertal beef heifers was evaluated. Angus x Hereford (n = 148) and Brahman x Hereford (n = 148) heifers were sorted after weaning by body weight into light and heavy weight blocks. Heifers were 1 ng/ml (0 or 10 d before treatment), were assigned randomly within breed and nutrition group to either a melengestrolacetate + saline (MGA+S) or MGA + gonadotropin-releasing hormone (MGA+GnRH) treatment. Prepubertal Angus x Hereford heifers (n = 11) and Brahman x Hereford heifers (n = 49) were fed 0.5 mg MGA for 7 d. Forty-eight hours after MGA, heifers were injected with 500 ug s.c. GnRH or 5
Estrus synchronization with melengestrolacetate in cyclic ewes. Insemination with fresh or frozen semen during the first or second estrus post treatment. A total of 540 cyclic ewes were randomly allocated to 1 of 6 groups according to synchronization or not with melengestrolacetate (MGA), insemination with fresh or frozen semen, and insemination during the first or second estrus post treatment
[Effect of anti-androgen and progesterone on development of regrowth antlers in 6 year old sika deer]. To investigate the effects of anti-androgen drugs and melengestrolacetate (MGA) on development of regrowth antlers in 6 year old sika deer, twenty healthysika deerwith similar body weight and antler weightwere randomly divided into five groups by using single factor test design: flutamide (=4 ), bicalutamide (=4), progesterone acetate (CPA, =4), melengestrolacetate (MGA, =4), control(=4). All deer were fed with same diets and were housed outside together in an opened fence of 15 m×30 m with free access to water and feed. Treatment groups were injected subcutaneously sustained-release agents of the four drugs respectively when two-branched antlers were harvested. The control group had no special
not differ (P = 0.68) between CONTROL and HiCON treatments (47 vs. 46 ± 4%, respectively). Additionally, PR/AI were similar (P = 0.65) between CONTROL and HiCON treatments (46 vs. 45 ± 3%). In Exp. 2, 190 Angus-based beef heifers were enrolled at 2 locations. Heifers were exposed to the melengestrolacetate (MGA)-PGF2α protocol where they were offered 0.5 mg MGA per day from days 1 to 14. On day 33
analysis. Particle size distributions were generated from TSP samples only, while steroid analysis was conducted on extracts of PM samples using liquid chromatography mass spectrometry. Of seven targeted steroids, 17α-estradiol and estrone were the most commonly detected, identified in over 94% of samples at median concentrations of 20.6 and 10.8 ng/g, respectively. Melengestrolacetate and 17α
Timed insemination of beef heifers using the 7-11 Synch protocol. Two experiments were conducted over 3 yr to determine pregnancy rates in beef heifers after a timed AI in response to the 7-11 Synch protocol. In Exp. 1, 179 heifers were either fed melengestrolacetate (MGA; 7-11 Synch) or given an intravaginal progesterone (P4)-releasing insert [controlled intravaginal drug releasing device (CIDR
Ovariectomy as a means of abortion and control of estrus in feedlot heifers. Three hundred and six heifers were randomly assigned to treatment groups in a three by six factorial design. Treatments were ovariectomy, melengestrolacetate (MGA), manual abortion, intramuscular estradiol cypionate (ECP) or Prostaglandin F2alpha and untreated controls. The Average Daily Gain (ADG) of the Ovariectomized
Phototransformation rates and mechanisms for synthetic hormone growth promoters used in animal agriculture. Trenbolone acetate, melengestrolacetate, and zeranol are synthetic hormones extensively used as growth promoters in animal agriculture, yet despite occurrence in water and soil little is known about their environmental fate. Here, we establish the time scales and mechanisms by which these synthetic growth promoters and their metabolites (SGPMs) undergo phototransformation in sunlit surface waters. The families of trenbolone acetate (including 17β-trenbolone, 17α-trenbolone, and trendione) and melengestrolacetate (including melengestrol) readily undergo direct photolysis, exhibiting half-lives between ∼0.25 and 1 h in both natural and simulated sunlight that were largely insensitive
Evaluation of melengestrolacetate and equine chorionic gonadotropin for out-of-season breeding in sheep on Prince Edward Island. The purpose of this study was to compare the efficacy of a recommended protocol of oral melengestrolacetate (MGA) to intravaginal medroxyprogesterone acetate (MPA), with or without equine chorionic gonadotropin (eCG), for out-of-season breeding of sheep on Prince
Development of estrous synchronization protocols using melengestrolacetate in Bos indicus cattle. Five experiments were conducted on commercial farms in Brazil designed to develop the basis for an estrus synchronization protocol using melengestrolacetate (MGA) in Bos indicus cattle. These studies resulted in the development of the following protocol: 0.5 mg x d(-1) of MGA between d -14 and -1
replaced all linseed meal and partially replaced corn at 8% of diet DM. All diets provided 0.5 mg of melengestrolacetate, 2,000 IU of vitamin E, and 232 mg of monensin per heifer daily. Cattle were slaughtered by block after 96, 97, and 124 (2 blocks) d on feed. At 24 h postmortem, carcass data were collected, and a portion of the loin was removed, vacuum-packaged, and aged for 14 d. After aging, 2
assigned to 1 of 6 growth promotant treatments: control (no growth promotant), estrogenic implant (E), trenbolone acetate implant (TBA), E + TBA (ET), melengestrolacetate (MGA), and ET + MGA (ETM). Blood samples were collected from 4 heifers per pen per study on d 0, 28, 56, and 84 via jugular puncture. Near the midpoint of both studies, TT were obtained from the heifers. There was a season by sample
Melengestrolacetate as an effective alternative to induce a decline in egg production and reversible regression of the reproductive tract in laying hens. II. Effects on postmolt egg quality. Induced molting increases egg quality and egg production and extends the productive life of hens. Molting is accomplished by feed withdrawal, which has received criticism, and alternatives described thus far result in poor postmolt performance. Melengestrolacetate at a dosage of 4 or 8 mg/d, in a balanced diet, leads to reversible regression of the reproductive tract. However, this alternative must also increase egg quality after rest to be considered an adequate method by the industry. Hy-Line W-36 (n = 497) laying hens were assigned randomly to a diet containing 0 mg of melengestrolacetate (MGA
Melengestrolacetate in experimental diets as an effective alternative to induce a decline in egg production and reversible regression of the reproductive tract in laying hens. I. Determining an effective concentration of melengestrolacetate. Induced molting increases egg quality and egg production and extends the productive life of hens. Molting is accomplished by feed withdrawal, which has been criticized for not addressing hen well-being, and current alternatives have resulted in poor postmolt performance and inadequate well-being. Molting leads to regression of follicles on the ovary and causes loss of steroidogenic support for the oviduct, leading to cessation of lay. Melengestrolacetate (MGA), an orally active progestin, may decrease support for the ovary, resulting in loss
to the melengestrolacetate-PGF(2α) protocol (MGA-PG; n = 50) received MGA (0.5 mg·animal(-1)·d(-1)) in a 1.0-kg carrier from d 0 to 13 and were administered PGF(2α) (25 mg, intramuscularly) 19 d after MGA withdrawal (d 32). Heifers assigned to the Show-Me-Synch protocol (n = 49) received a controlled internal drug release (CIDR) insert (1.38 g of progesterone) from d 2 to 16 followed by PGF(2α) administration 16 d
Reproductive response of ewes synchronized with different lengths of MGA treatments in intrauterine insemination program. A total of 415 fat tailed ewes were randomly assigned to two groups to assess the effect of duration of melengestrolacetate (MGA) (9 versus 12d) administration on reproductive parameters associated with laparoscopic artificial insemination. At the end of MGA treatment, ewes
Prolonging the MGA-prostaglandin F2 alpha interval from 17 to 19 days in an estrus synchronization system for heifers. Our objective was to determine whether extending the interval from 17 to 19 d between removal of melengestrolacetate (MGA) feed and administration of PGF2 alpha would alter conception rates, pregnancy rates and the degree of synchrony in replacement beef heifers. A commercial
Development of a progestin-based estrus synchronization program: II. Reproductive response of cows fed melengestrolacetate for 14 days with injections of progesterone and prostaglandin F2alpha. We tested the efficacy of an estrus control system designed to provide optimal control of follicular development. In Exp. 1, postpartum cows (n = 133) and yearling heifers (n = 57) were fed either .5 mg x female(-1) x d(-1) of melengestrolacetate (MGA) or the carrier for MGA from d -13 to d 0 (d 0 = last day of MGA feeding). All females received 25 mg of PGF2alpha (i.m.) on d -13 and 0. On d -6, cows and heifers fed MGA were administered an i.m. injection of progesterone (200 mg; MGA/P4), and those fed the corn carrier (2XPGF2alpha) received no progesterone. Beginning on d 1, females were bred by AI
Development of a progestin-based estrus synchronization program: I. Reproductive response of cows fed melengestrolacetate for 20 days with an injection of progesterone. We designed two experiments to determine the efficacy of an estrus control system in cows that combined long-term progestin exposure (20 d) with an acute increase in progesterone concentration. In Exp. 1, cows (n = 30) were fed either melengestrolacetate (MGA; .5 mg x cow(-1) x d(-1)) or ground ear corn (MGA carrier) for 20 d. On d -15 (last day of MGA feeding = d 0), cows were administered 25 mg of PGF2alpha to regress the corpus luteum (CL) and establish an environment conducive to the development of persistent follicles. To synchronously regress persistent follicles, cows fed MGA (n = 15) were injected with 200 mg