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The present study verified that it is possible to analyze melengesterol acetate using the existing multi-residue method. Melengestrol acetate was extracted from livestock products using acidic acetonitrile acidified with acetic acid in the presence of n-hexane and anhydrous sodium sulfate. The crude extracts were cleaned up using an octadecylsilanized silica gel cartridge column. Separation by HPLC was performed using an octadecylsilanized silica gel column with linear gradient elution of 0.1 vol％ formic acid and acetonitrile containing 0.1 vol％ formic acid. For the determination of the analyte, tandem mass spectrometry with positive ion electrospray ionization was used. In recovery tests using four livestock products fortified with maximum residue limits levels of melengestrol acetate (0.001–0.02 mg/kg), the truenesses ranged from 82％ to 100％, and the repeatabilities for the entire procedure ranged from 0.5 RSD％ to 5.6 RSD％. In recovery tests using 11 livestock products fortified with 0.0005 mg/kg of melengestrol acetate, the truenesses ranged from 88％ to 99％, and the repeatabilities ranged from 1.3 RSD％ to 5.4 RSD％. The limit of quantification for melengestrol acetate in livestock products was 0.0005 mg/kg. [ABSTRACT FROM AUTHOR]

• ALT, DRO, and MLA experienced abiotic-transformation in mineral suspensions. • The transformation of the progestins were sensitive to environmental variables. • Hydrolysis was the major transformation pathway for DRO and MLA on SiO 2 surface. • Oxidation was the major transformation pathway for ALT in MnO 2 suspension. • Transformation products identification is a priority for risk assessment. Altrenogest (ALT), drospirenone (DRO), and melengestrol acetate (MLA) are three highly potent synthetic progestins that can be released into agricultural soils, while their fate in soil minerals remains unclear. This study explored the transformation of these progestins in MnO 2 , SiO 2 , and ferrihydrite suspensions and identified their transformation products (TPs) via high resolution mass spectrometry and density functional theory calculations. Transformations were only observed for DRO and MLA in SiO 2 suspension and ALT in MnO 2 suspension (half-lives = 0.86 min – 9.90 day). ALT transformation was facilitated at higher MnO 2 loadings, while DRO and MLA transformations were inhibited at higher SiO 2 loadings. These data indicated that hydrophobic partitioning interaction was dominant at higher SiO 2 loadings rather than specific interaction, which limited subsequent surface-catalyzed transformation. ALT transformation rate decreased with increasing pH because MnO 2 reduction requires proton participation. In contrast, relatively high pH facilitated MLA and DRO transformation, indicating that base-catalyzed hydrolysis occurred in SiO 2 suspension. The clustermap demonstrated the formation of abundant TPs. Lactone ring and acetoxy group hydrolysis was the major transformation pathway for DRO and MLA, with estimated yields of 57.7% and 173.2% at 6 day, respectively. ALT experienced C12 hydroxylation and formed the major TP 326g (yield of 15.4% at 8 hr). ALT also experienced allyl group oxidation and subsequent C5 hydroxylation, forming the major TP 344a (yield of 14.1% at 8 hr). This study demonstrates that TPs of metastable progestins are likely the main species in soils and that TP identification is a particular priority for risk assessment. [Display omitted]. [ABSTRACT FROM AUTHOR]

Tigers (Panthera tigris spp.) are endangered in the wild; ensuring sustainable insurance populations requires careful planning within zoological collections. In captive situations, contraceptives are often used to control breeding and ensure genetically viable populations that contain manageable numbers of animals; reversible contraceptives are ideal because they offer flexibility for breeding management. Historically, synthetic progestins, such as melengestrol acetate implants, were used in female tigers, but these are associated with an increased risk of reproductive pathology and subsequent infertility. Recent management advice to ex‐situ collections has been to transition to the use of gonadotropin‐releasing hormone agonists, such as deslorelin acetate implants, which do not appear to have a similar risk of reproductive pathology but are associated with highly variable reversal times in exotic felids. Using data from 917 contraceptive records in female tigers captured by the Association of Zoos and Aquariums Reproductive Management Center and the European Association of Zoos and Aquaria Reproductive Management Group's joint Contraception Database and from supplementary surveys, this study reviews the changing use of contraceptives in captive female tigers. The aim was to describe the historical and current use of contraceptives and provide a comprehensive assessment on the use of deslorelin implants, including data on product protocols, efficacy, pathology, and reversibility. This study determined that current dose, frequency, reversibility, and anatomical placement sites of deslorelin implants are highly variable, indicating that specific, readily available, unified, evidence‐based recommendations on the use of deslorelin would be useful for future contraceptive use in managed tiger populations. Research Highlights: Deslorelin acetate appears to be safe, effective and reversible in female tigers.Deslorelin acetate is associated with little pathology.Time between deslorelin acetate treatment and return to fertility is highly variable in female tigers. [ABSTRACT FROM AUTHOR]

Abstract: The objective of this work was to evaluate the effects of supplementation with melengestrol acetate (MGA), after timed artificial insemination (TAI), on the conception rate of Nellore cows, according to cyclicity during the protocol, estrus expression between intravaginal device withdrawal and insemination, and diameter of the largest follicle at the time of insemination, in order to identify predictors of the use of MGA. Multiparous lactating cows (577) were subjected to a hormonal protocol for ovulation synchronization. On day -2 of the protocol, the animals were painted with a marker on the base of their tail. On day 0, they were evaluated for estrus expression; the preovulatory follicle diameter (POFD) was measured by ultrasonography, and the artificial insemination was performed. The animals were assigned to two experimental groups according to the supplementation or not with 0.50 mg MGA, between 13 and 18 days after TAI. Pregnancy diagnosis was performed using an ultrasound examination 35 days after TAI. A positive effect of the treatment with MGA on the conception rate occurred generally in animals in anestrus, irrespective of the estrus expression. For animals treated with MGA, only those with POFD greater than 14 mm showed better conception rates that the control group.

The present study verified that it is possible to analyze melengesterol acetate using the existing multi-residue method. Melengestrol acetate was extracted from livestock products using acidic acetonitrile acidified with acetic acid in the presence of n-hexane and anhydrous sodium sulfate. The crude extracts were cleaned up using an octadecylsilanized silica gel cartridge column. Separation by HPLC was performed using an octadecylsilanized silica gel column with linear gradient elution of 0.1 vol% formic acid and acetonitrile containing 0.1 vol% formic acid. For the determination of the analyte, tandem mass spectrometry with positive ion electrospray ionization was used. In recovery tests using four livestock products fortified with maximum residue limits levels of melengestrol acetate (0.001-0.02 mg/kg), the truenesses ranged from 82% to 100%, and the repeatabilities for the entire procedure ranged from 0.5 RSD% to 5.6 RSD%. In recovery tests using 11 livestock products fortified with 0.0005 mg/kg of melengestrol acetate, the truenesses ranged from 88% to 99%, and the repeatabilities ranged from 1.3 RSD% to 5.4 RSD%. The limit of quantification for melengestrol acetate in livestock products was 0.0005 mg/kg.

This experiment compared pregnancy rates in Bos indicus cows assigned to temporary calf weaning ( TCW ) or eCG administration during estrus synchronization, with or without melengestrol acetate ( MGA ) supplementation after artificial insemination ( AI ). A total of 3042 lactating, multiparous, non-pregnant Nelore cows were managed in 48 groups, and assigned to an estrus synchronization + fixed-time AI protocol (d −11 to 0, with AI on d 0). On d −11, groups were randomly assigned to receive 1 of 2 gonadotropic stimulus, which were either 48-h TCW from d −2 to AI (n = 9 groups, 604 cows) or 300 IU i.m. injection of eCG on d −2 (n = 39 groups, 2438 cows). On d 1, groups were assigned to receive, in a 2 × 3 factorial arrangement, 1 of 3 MGA treatments: 0.5 mg of MGA/cow from d 5–18 ( M5to18 ; n = 16 groups, 1074 cows) or from d 13–18 ( M13to18 ; n = 16 groups, 971 cows), or no MGA supplementation ( CON ; n = 16 groups, 997 cows). Estrus expression was evaluated by painting the tailhead of each cow on d −2, and evaluating the presence of tailhead paint at AI. Body condition score ( BCS; 1–9 scale) was recorded at AI, and cows were classified as adequate (≥ 4.5) or inadequate (< 4.5) BCS. Pregnancy rates on d 30 and 80 were greater ( P ≤ 0.05) in M5to18 and M13to18 compared with CON cows (62.9%, 62.9%, and 55.3% on d 30, 58.1%, 59.2%, and 50.5% on d 80, respectively; SEM = 3.1), and similar ( P ≥ 0.79) between M5to18 and M13to18 cows. Pregnancy rates on d 30 and 80 were similar ( P ≥ 0.17) between cows assigned to eCG and TCW (58.1% and 62.6% on d 30, 54.3% and 57.6% on d 80, respectively; SEM = 2.7). The MGA supplementation × gonadotropic stimulus interaction was not significant ( P ≥ 0.41) whereas no interactions of main treatment effects with cow BCS and estrus expression were detected ( P ≥ 0.21) for pregnancy outcomes. Hence, supplementing B indicus beef cows with MGA post-AI increased pregnancy rates compared with non-supplemented cows, and this outcome was independent of period and length of MGA supplementation, gonadotropic stimulus, cow BCS status, and estrus expression during the synchronization protocol. [ABSTRACT FROM AUTHOR]

This study aimed to evaluate minimally invasive protocols for estrus synchronization in the brown brocket deer (Subulo gouazoubira). Females were submitted to Latin square design, in different treatments. All females received 0.25 mg of estradiol benzoate on the first day of treatment, concomitant with one of the following sources of progesterone: (1) DIP: an intravaginal progesterone releasing device for eight days, (2) MGA1x: once a day (in the morning) oral dose of 1 mg melengestrol acetate for eight days, (3) MGA2x: twice a day (morning and afternoon) oral doses of 0.5 mg of MGA for eight days, (4) P4LA: a single i.m. administration of 75 mg of long-acting progesterone (P4LA). Eight days after the beginning of each treatment, females received an i.m. administration of 265 µg of prostaglandin (PGF 2α ; cloprostenol). Treatment efficacy was evaluated by manifestation of behavioral estrus after treatment and concentration of fecal progesterone metabolites (FPM). The time to onset of estrus in treatment P4LA was significantly longer (180 ± 38.9 h) compared to DIP (63 ± 6.6 h), MGA1x (53 ± 14.4 h) and MGA2x (41 ± 10.1 h) (P = 0.008). According to individual baseline FPM and FPM concentration during the days after estrus, the corpus luteum formation was suggested in all females which responded to the treatments (93.75 %). Low synchrony, longer interval between PGF 2α administration and onset of estrus suggest that the P4LA dose (75 mg) is too high and not effective for S. gouazoubira. DIP, MGA 1x and MGA 2x, were effective in estrus synchronization. • First report of long-acting progesterone in a deer estrus synchronization protocol. • FPM concentrations suggest ovulation after estrus synchronization in all treatments. • Treatment MGA2x promoted great estrus synchrony similar to treatment DIP. [ABSTRACT FROM AUTHOR]

Gestagens, a class of veterinary drugs also called progestogens, are synthetic hormones used to increase feed efficiency and rate of gain in heifers. The Canadian Food Inspection Agency analyzes progestogens melengestrol acetate (MGA), megestrol acetate, and chlormadinone acetate using liquid chromatography-mass spectrometry (LC-MS). Our conventional gestagen method for kidney fat has many time-consuming steps, including solid-phase extraction. A sample preparation procedure having fewer clean-up steps was developed for routine diagnostic analysis of kidney fat and provided similar results faster, and at lower cost. A confirmatory liver method for gestagens, developed using salt-assisted extraction, employed minimal clean-up steps that resulted in high chemical background at the desired lower limit of quantification (LLOQ). Differential ion mobility spectrometry, specifically high-field asymmetric waveform ion mobility spectrometry (FAIMS), was used to filter chemical background in the gas phase. The effect of the ionization probe position on FAIMS parameters, including sensitivity, is described. With LC-FAIMS-MS, chemical background for each gestagen was virtually eliminated, resulting in a quantitative liver method having the desired 0.6 ng/g LLOQ and estimated limits of detection (LODs) up to 140 times lower than LC-MS. Incurred MGA samples, analyzed using kidney fat and liver methods from the same animal, show levels within the quantitative ranges of both methods.

Highlights: [•] Biotransformation of melengestrol acetate (1) was carried out with C. blakesleeana. [•] The above transformation yielded a new major metabolite 2. [•] Single crystal X-ray structures of 1 and 2 are reported for the first time. [•] Immmunosuppressant effect of 1 and 2 was evaluated by T--cell proliferation assay. [Copyright &y& Elsevier]

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 melengestrol acetate (MGA; 7-11 Synch) or given an intravaginal progesterone (P4)-releasing insert [controlled intravaginal drug releasing device (CIDR); 7-11 CIDR] for 7 d. Prostaglandin F2α was administered on the last day of MGA feeding or at CIDR removal followed by the CO-Synch protocol (GnRH-PGF2α-GnRH) beginning 4 d after MGA withdrawal or 2 d after CIDR removal. Heifers received a timed AI with GnRH beginning 48 h after the second PGF2α. Blood samples were collected at d -10, 0 (start of MGA feeding), and 18 (second PGF2α injection). In Exp. 2, 298 beef heifers were treated with the 7-11 Synch protocol with (7-11 Synch) or without (7 Synch) the first GnRH injection. Fixed time AI and GnRH was given 54 h after PGF2α. Blood samples were collected at d -10 and 0 in yr 1 and d -10, 0, 18 and at AI in yr 2. In Exp. 1, no differences were detected between 7 and 11 Synch and 7-11 CIDR for attainment of puberty in noncyclic heifers (94 vs. 78%; P = 0.21), the proportion of heifers that had luteal tissue on d 18 (87 vs. 83%; P = 0.41), or pregnancy rates after timed AI (47 vs. 46%; P = 0.99). In Exp. 2, administration of GnRH 4 d after the last MGA (7-11 Synch) feeding tended (P = 0.07) to induce more prepubertal heifers to cycle (88 vs. 61%) and increased (P < 0.01) the proportion of heifers with luteal tissue on d 18 (88 vs. 72%) compared with heifers in the 7 Synch treatment. Pregnancy rates after the 54 h timed AI were greater (P < 0.01) in the 7-11 Synch treatment (55%) than in the 7 Synch (38%). We conclude that heifer pregnancy rates did not differ whether feeding MGA for 7 d or applying a CIDR insert for 7 d before a CO-Synch protocol. In contrast, use of GnRH at the beginning of the CO-Synch protocol improved pregnancy rates after a timed AI by inducing more prepubertal heifers to ovulate and increasing the proportion of heifers with luteal tissue at the PGF2α injection. [ABSTRACT FROM AUTHOR]

Abstract: From the analysis of 21 Cebu-Swiss heifers healthy, developing, with 235.55 ± 17.81kg of body weight (BW), 118.62 ± 3.97cm and 2.58 ± 0.35 of body condition (BC) scale of 1-5. They were divided into two groups: MGA (n = 10) and control (n = 11). For 55 days were given a constant diet (including 15 days of adaptation), based on concentrate and sorghum straw. The contribution of daily intake was 599.08g of crude protein and 12.18 Mcal. Blood samples were obtained every 5 days. The concentrations of cholesterol, triglyceride, high-density lipoprotein, low-density lipoprotein, urea, total protein and glucose were measured for spectrophotometric using the enzyme-colorimetric technique in plasma. The daily gain was balanced PV of 603.5 to 232.5 grams and height stopped from day 25. The CC did not show significant changes (P> 0.01). The mean concentration of plasma cholesterol was 107.59 ± 13.38 vs. 109.61 ± 11.72mg/dl (MGA and control, respectively) with a downward trend more pronounced from day 25. The concentration of triglycerides was 12.61 ± 6.91 vs. 16.19 ± 8.86mg/dl (MGA and control), no trend in the first 20 days and from day 25 there was an increase compared to the average of the previous days. The concentrations of HDL 63.73 ± 3.26 vs. 63.79 ± 10.27mg/dl (MGA and control) and 43.56 ± 6.24 vs. LDLc. 46.54 ± 14.89mg/dl (MGA and control) were irregular, but within normal ranges. The values of total protein were 5.70 ± 0.40 vs. 5.22 ± 0.31mg/dl (MGA and control), no trend the first 15 days and from day 20 increased in concentration compared to previous surveys. Urea levels were 14.79 ± 5.22 vs. 14.13 ± 4.8mg/dl (MGA and control) with a tendency to discharge. Glucose levels were 60.06 ± 7.62 vs. 58.24 ± 5.43mg/dl (MGA and control), with an irregular behavior in the normal range. The consumption of 0.5mg/dl of MGA for 40 days increased plasma concentrations of triglycerides and total protein, but did not affect cholesterol levels, HDL and LDL cholesterol, urea and glucose. [Copyright &y& Elsevier]

Abstract: A total of 415 fat tailed ewes were randomly assigned to two groups to assess the effect of duration of melengestrol acetate (MGA) (9 versus 12d) administration on reproductive parameters associated with laparoscopic artificial insemination. At the end of MGA treatment, ewes in each group were subdivided and inseminated with one of two different insemination doses (10×107 or 20×107 sperm per 0.5ml insemination dose) of fresh diluted semen. Inseminations were carried out 11–18h after first detected estrus. Ewes were screened for their return to oestrus from 10 to 21 days post AI and inseminated at their returned oestrus. Pregnancy diagnosis was done from approximately 55 days after insemination in both synchronized and return estrus. For short (9-day) and long (12-day) term MGA treated groups, estrus rates were 62% versus 89% (P <0.0001), respectively. Ewes (n =115) that returned to estrus were inseminated (7–11h after estrus detection) with fresh diluted semen at different doses (20×107 or 40×107 or 60×107 sperm per 0.5ml insemination dose). Pregnancy rates were 41% and 44% for short term and long term MGA treated ewes, respectively. Pregnancy rate of ewes which returned to oestrus was 53.4%. There was a significant (P <0.05) increase in pregnancy rates (38–52% for 11–16h; 63% for 17–18h) when insemination was held at 17–18h after first detected estrus following MGA treatments. Pregnancy rates were found to be similar in ewes inseminated with 10×107 (36%) or 20×107 (47%) motile spermatozoa at first AI, and 20×107 (44%) or 40×107 (59%) or 60×107(48%) at second AI. It was concluded that short term MGA treated ewes were recorded with lower estrus rates but was similar to pregnancy rates with long term MGA treatment. Acceptable pregnancy rates were achieved in MGA induced estrus when insemination is conducted at 17–18h after estrus onset and with 20×107 sperm per insemination dose. [Copyright &y& Elsevier]

Melengestrol acetate (MGA) has been used in the United States for nearly 40 yr to enhance feedlot heifer performance, yet unequivocal studies have not been conducted to discover the mechanism of action. Our hypothesis was that MGA may induce various populations of muscle-derived cells (MDC) to the adipogenic pathway in both a bovine and murine cell culture model. To determine this, MDC were digested from the semimembranosus muscle tissue of six 14-mo-old crossbred steers. The addition of insulin, oleic acid, and ciglitizone (IOC) with cultured bovine MDC resulted in morphological differences compared with control cultures. Multilocular lipid droplets stained with Oil Red 0 were seen not only in single MDC, but also in fused myotubes. An increase (P < 0.05) in relative PPAR-γ messenger RNA (mRNA) levels was measured in MDC incubated with IOC. However, myogenin mRNA levels in MDC incubated with JOC were repressed (P < 0.05) compared with nontreated MDC. Cultures of MDC treated with 10 μM insulin, 10 μM oleic acid, 10 μM ciglitizone, 10 μM estradiol-17β (E2), and 10 nM IVIGA resulted in cultures with highly distributed lipid droplets not only in single cells, but also in the multinucleated myotubes. Relative C/EBPβ and PPARγ mRNA levels in total RNA isolated from MDC treated with MGA increased (P < 0.05) compared with control cultures. Estradiol treatment had no effect (P > 0.05) on these mRNA levels. The addition of both E2 and MGA to MDC increased (P < 0.05) C/EBPβ mRNA levels and tended (P = 0.06) to increase the PPAR1 mRNA level. There was no difference (P > 0.10) in relative myogenin rnRNA among the control, E2, and MGA treatments. Relative C/EBPβ, PPARγ, and myogenin mRNA levels were investigated in murine C2C12, C3H 10T 1/2, and 3T3-L1 cells. Treatment of cultures with 10 nM MGA increased C/EBPβ levels (P < 0.05) in C2C12 myoblasts and tended (P = 0.08) to increase C/EBPβ levels in 3T3-L1 preadipocytes. These data indicate that populations of cells are present in postnatal skeletal muscle that, under the appropriate stimuli in a culture model, express adipogenic genes and accumulate lipids. In addition, the synthetic progestogen MGA appeared to upregulate the genes necessary for conversion to the adipogenic pathway. [ABSTRACT FROM AUTHOR]

Five experiments were conducted on commercial farms in Brazil designed to develop the basis for an estrus synchronization protocol using melengestrol acetate (MGA) in Bos indicus cattle. These studies resulted in the development of the following protocol: 0.5 mg·d-1 of MGA between d -14 and -1; 2.0 mg i.m. injection of estradiol cypionate on d -9; 48 h temporary weaning between d 0 and 2; and natural service beginning on d 0. The basis of this protocol was to induce estrous cyclicity before postpartum loss of body condition, prevent premature luteolysis, eliminate the need for labor required to detect estrus, and consequently increase the likelihood of pregnancy early during the postpartum period. This treatment effectively induced estrous cyclicity among anestrous cows, synchronized estrus activity, and prevented premature luteolysis with no negative effect on pregnancy. [ABSTRACT FROM AUTHOR]

Abstract: The effects of melengestrol acetate (MGA) and P.G. 600 on ewe fertility outside the natural breeding season were evaluated. Rambouillet ewes were assigned to one of four groups: (1) control (C; n =92); (2) PG600 (n =86); (3) MGA (n =99); and (4) MGA+PG600 (n =92). A pellet with or without MGA (0.3mg/ewe/d) was fed at 0.15kg/ewe/d for 7d. On the last day of pellet feeding, ewes were given either saline or 5mL of P.G. 600 i.m. (400IU equine chorionic gonadotropin (eCG) and 200IU human chorionic gonadotropin (hCG)). Ultrasonography was performed between Days 20 and 25 of gestation for ewes that were mated during the first 6 d of the breeding period from the MGA (n =15) and MGA+PG600 (n =8) groups, and the number of luteal structures and embryos were counted. During the first 6d of the breeding period, MGA increased (P <0.05) the percentage of ewes that mated and conceived when compared to C and PG600 (24.2% vs. 3.3% and 10.5%, respectively). Relative to MGA, the mean (±S.E.M.) number of luteal structures per ewe was enhanced (P <0.03) in MGA+PG600 (1.53±0.13 vs. 2.38±0.42, respectively), however as pregnancy progressed, the number of embryos (1.5±0.13 vs. 1.8±0.16, respectively) and lambs born (1.3±0.15 vs. 1.5±0.27, respectively) did not differ. Treatment with MGA reduced (P <0.01) the interval from ram introduction to lambing relative to groups that did not receive MGA (168±0.8d vs. 171±0.6d, respectively). In conclusion, treatment with MGA increased the percentage of ewes conceiving early in the breeding period. Although P.G. 600 increased the number of luteal structures present per ewe, it did not significantly enhance ewe prolificacy. [Copyright &y& Elsevier]

This experiment was designed to compare pregnancy rates in postpartum beef cows resulting from fixed-time Al (FTAI) after treatment with 1 of 2 protocols to synchronize estrus and ovulation. Crossbred, suckled beef cows (n = 650) at 4 locations (n = 210; n = 158; n = 88; and n = 194) were assigned within a location to 1 of 2 protocols within age group by days postpartum and BCS. Cows assigned to the melengestrol acetate (MGA) Select treatment (MGA Select; n = 327) were fed MGA (0.5 mg·head-1·d-1) for 14 d, GnRH (100 μg of Cystorelin i.m.) was injected on d 26, and prostaglandin F2α (PG; 25 mg of Lutalyse i.m.) was injected on d 33. Cows assigned to the CO-Synch + controlled internal drug release (CIDR) protocol (CO-Synch + CIDR; n = 323) were fed a carrier for 14 d, were injected with GnRH and equipped with an EAZI-BREED CIDR insert (1.38 g of progesterone, Pfizer Animal Health, New York, NY) 12 d after carrier removal, and PG (25 mg of Lutalyse i.m.) was injected and the CIDR were removed on d 33. Fixed-time Al was performed at 72 or 66 h after PG for the MGA Select or CO-Synch + CIDR groups, respectively. All cows were injected with GnRH (100 μg of Cystorelin i.m.) at the time of insemination. Blood samples were collected 8 and 1 d before the beginning of MGA or carrier to determine estrous cyclicity status of the cows (estrous cycling vs. anestrus) before treatment [progesterone ≥ 0.5 ng/mL (MGA Select, 185/327, 57%; CO-Synch + CIDR, 177/323, 55%); P = 0.65]. There was no difference (P = 0.20) in pregnancy rate to FTAI between treatments (MGA Select, 201/327, 61%; CO-Synch + CIDR, 2 14/323, 66%). There was also no difference (P = 0.25) between treatments in final pregnancy rate at the end of the breeding period (MGA Select, 305/327, 93%; CO-Synch + CIDR, 308/323, 95%). These data indicate that pregnancy rates to FTAI were comparable after administration of the MGA Select or CO-Synch + CIDR protocols. Both protocols provide opportunities for beef producers to utilize Al and potentially eliminate the need to detect estrus. [ABSTRACT FROM AUTHOR]

Previous research from our laboratory has indicated that melengestrol acetate (MGA) added to the diet during the first 35 d after arrival in the feedlot improves growth rates and tends to reduce chronic respiratory disease in heifers naturally challenged with bovine respiratory disease. The current study was conducted to provide further insight into the possible immunomodulatory effects of MGA. Crossbred heifers (n = 48; 232 ± 5.5 kg of BW) were used in a randomized complete block design to determine the effects of MGA on lung pathology and markers of inflammation after Mannheimia haemolytica challenge. On d 0, cattle were blocked by BW and randomly assigned, within block, to diets (54% concentrate) that provided 0 or 0.5 mg of MGA per heifer daily for the duration of the experiment. Inoculum containing from 1.3 × 109 to 1.7 × 109 cfu of M. haemolytica (20 mL) was instilled at the bifurcation of the trachea on d 14. Blood samples were collected, clinical observations were made, and rectal temperatures were recorded for each animal at 0, 12, 24, 48, 72, 96, 120, and 138 h after inoculation. Heifers fed MGA had greater circulating concentrations of eosinophils and postchallenge concentrations of segmented neutrophils and white blood cells (P < 0.01) than controls, as well as elevated plasma protein, serum haptoglobin, and fibrinogen after M. haemolytica challenge (P < 0.01). Heifers fed MGA had lower plasma glucose (P < 0.01), greater plasma urea N (P = 0.02), and elevated respiratory indices (P < 0.01) compared with controls. Necropsies performed on d 6 after inoculation suggested that M. haemolytica challenge was relatively mild, because lesions were confined to a small portion of the lungs. On a 0 to 100 scale, average lung lesion scores were 3 and 1 for MGA-fed and control groups, respectively (P < 0.06). Heifers fed MGA before mild M. haemolytica challenge were more susceptible to infection, as evidenced by a greater number of heifers fed MGA exhibiting pulmonary lesions 138 h after inoculation than controls (14 out of 23 vs. 6 out of 24 for MGA and controls, respectively; P < 0.02). [ABSTRACT FROM AUTHOR]

In vitro experiments were performed to investigate the effects of melengestrol acetate (MGA) or progesterone (P4) on bovine muscle satellite cells and C2C12 myoblasts. Addition of MGA at physiological and supraphysiological concentrations resulted in a dose-dependent decrease (P < 0.05) in DNA synthesis as measured by ³H] -thymidine incorporation (TI). Similarly, P4 addition (0.01 nM) reduced (P < 0.05) TI. Addition of MGA (10 nM) increased (P < 0.05) IGF-I mRNA abundance but did not affect myogenin mRNA. Progesterone addition (10 nM) increased myogenin mRNA abundance (P < 0.05). In C2C12 cultures, P4 addition resulted in a dose-dependent decrease in TI. The anti- progestin RU486, in combination with MGA or P4, also resulted in reduced (P < 0.05) TI. Treatment with RU486 alone had a negative effect (P < 0.05) on TI that was similar to the progestins. Treatment of C2C12 myoblasts with MGA (100 nM) resulted in an increase (P < 0.05) in myogenin mRNA. These studies suggest that progestins may reduce satellite cell proliferation, ultimately affecting carcass composition. [ABSTRACT FROM AUTHOR]

In vitro experiments were performed to investigate the effects of melengestrol acetate (MGA) or progesterone (P4) on bovine muscle satellite cells and C2C12 myoblasts. Addition of MGA at physiological and supraphysiological concentrations resulted in a dose-dependent decrease (P < 0.05) in DNA synthesis as measured by ³H] -thymidine incorporation (TI). Similarly, P4 addition (0.01 nM) reduced (P < 0.05) TI. Addition of MGA (10 nM) increased (P < 0.05) IGF-I mRNA abundance but did not affect myogenin mRNA. Progesterone addition (10 nM) increased myogenin mRNA abundance (P < 0.05). In C2C12 cultures, P4 addition resulted in a dose-dependent decrease in TI. The anti- progestin RU486, in combination with MGA or P4, also resulted in reduced (P < 0.05) TI. Treatment with RU486 alone had a negative effect (P < 0.05) on TI that was similar to the progestins. Treatment of C2C12 myoblasts with MGA (100 nM) resulted in an increase (P < 0.05) in myogenin mRNA. These studies suggest that progestins may reduce satellite cell proliferation, ultimately affecting carcass composition. [ABSTRACT FROM AUTHOR]

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. Melengestrol acetate (MGA), an orally active progestin, may decrease support for the ovary, resulting in loss of support for the oviduct, while hens are fed a balanced diet. hi this experiment, a dose response study, fly-Line W-36 hens were fed 0, 0.1, 1,4, or 8 mg of MGA per hen/d in a balanced diet for 28 d and then returned to a normal diet. Four birds on d 0 and 4 birds per treatment on d 1, 2, 4, 8, 12, 16, 20, 24, 28, 32, 36, 40, and 44 were euthanized. The weight of the ovary with follicles, magnum, shell gland, and oviduct were determined. A decrease in egg production was observed in those groups receiving 4 and 8 mg of MGA, until removal of MGA from the diet. After d 28, egg production increased to the production level of hens fed 0, 0.1, or 1 mg of MGA. The weight of the ovary with follicles, oviduct, magnum, and shell gland were unchanged throughout in groups fed 0, 0.1, or 1 mg of MGA. However, groups fed 4 or 8 mg of MGA exhibited a decrease (P < 0.05) in the weight of the ovary with follicles, oviduct, magnum, and shell gland until d 28. Recrudescence of the large yellow follicles as well as rejuvenation of the oviduct and its components, the magnum and shell gland, in the 4 and 8 mg MGA groups occurred by d 44. Melengestrol acetate, fed to hens on a balanced layer diet, caused reversible regression of follicles and, therefore, removal and return of support for the oviduct. [ABSTRACT FROM AUTHOR]

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. Melengestrol acetate 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 melengestrol acetate (MG A; control) throughout the experiment or 4 or 8 mg of MGA/d for 2, 4, or 6 wk. Upon reaching 50 and 70% lay, after MGA removal, eggs were collected for measurements of egg quality, including Haugh units (i.e., internal egg quality), shell thickness, and breaking strength (i.e., external egg quality). Haugh units were greater (P < 0.05) for eggs laid by hens molted with a diet containing 8 mg of MGA for all durations compared with controls. Shell thickness was greater (P < 0.05) when hens were treated with 4 mg of MGA for 6 wk and 8 mg of MGA for 4 and 6 wk compared with control. Egg breaking strength was greater (P < 0.05) than controls for all hens fed MGA, regardless of dosage or duration of feeding. A subset of hens was fed 8 mg of MGA per hen/d for 2 wk, and eggs were collected for 3 wk. Seven days after MGA was removed from the diet, the amount of MGA in the yolk was below the level of detection of the assay, and the concentration found in the eggs at all time points was 3 orders of magnitude below the Food and Drug Administration's tolerance for MGA in edible tissue. When used as an alterative method to induce a rest, MGA leads to an increase in the internal and external egg quality of hens compared with nonmolted hens. [ABSTRACT FROM AUTHOR]

Abstract: To provide insight into potential mechanisms contributing to the various biological responses of cattle to treatment with progesterone, norgestomet, and melengestrol acetate (MGA), MCF-7 cells were utilized to determine the relative binding affinity of the progesterone receptor for MGA, norgestomet, progesterone, and a progesterone agonist (R5020), and to determine if progesterone, MGA, or norgestomet have estrogenic and/or anti-estrogenic activities. The progesterone receptor had greater affinity (P < 0.05) for MGA, R5020, and norgestomet than for progesterone; and the affinity for norgestomet exceeded (P < 0.05) that of MGA and R5020. Estrogen stimulates proliferation of MCF-7 cells; therefore these cells have been utilized as a bioassay to detect estrogenic and anti-estrogenic activity. Progesterone (10-11 to 10-5M) did not promote cellular proliferation. However, MGA (10-8, 10-7, and 10-6M) increased (P < 0.05) cell proliferation compared to the control group (10-11 to 10-9 and 10-5M MGA did not stimulate cell proliferation), and MGA-induced cell proliferation (10-8M) was reduced (P = 0.095) by an estradiol antagonist (ICI 182,780; ICI). Cellular proliferation increased (P < 0.05) with norgestomet (10-5M) compared to the control group (10-11 to 10-6M norgestomet did not stimulate cell proliferation) and the increased proliferation was decreased (P < 0.05) by ICI. Neither progesterone nor MGA demonstrated anti-estrogenic activity. Norgestomet (10-10 to 10-6M) did reduce (P < 0.05) maximal estrogen-stimulated cell proliferation, but not to basal levels. In summary, the affinities of the progesterone receptor for norgestomet, MGA, and progesterone are consistent with their effective dose to inhibit ovulation in vivo, but their progestin and their estrogenic/anti-estrogenic activities cannot fully explain why progesterone and norgestomet are more capable of reprogramming the reproductive axis in anestrous postpartum cows compared to MGA. [Copyright &y& Elsevier]

Presents abstracts of several studies about poultry reproductive physiology. "Effect of Heat Stress on Production, Reproduction Hormone Levels, Acid-Base Statis, and Liver Expression of Heat Shock Protein-70 Observed in Three Varieties of Laying Hens," by D. J. Franco, L. Robeson, and M. M. Beck; "Melengestrol Acetate (MGA) as an Alternative Method to Induce Molting in Hens," by J. M. Koch, J. S. Moritz, D. C. Lay, Jr., and M. E. Wilson; "Chicken Sperm Motility and Metabolism are Altered Immediately by Semen Dilution," by H. M. Parker, and C. D. McDaniel; "Progesterone Injections Induce a Polycystic Ovarian Follicle Syndrome (PCOF) in Young Turkey Hens," by W. L. Bacon and H.- K. Liu.

Presents abstracts of several studies about poultry reproductive physiology. "Effect of Heat Stress on Production, Reproduction Hormone Levels, Acid-Base Statis, and Liver Expression of Heat Shock Protein-70 Observed in Three Varieties of Laying Hens," by D. J. Franco, L. Robeson, and M. M. Beck; "Melengestrol Acetate (MGA) as an Alternative Method to Induce Molting in Hens," by J. M. Koch, J. S. Moritz, D. C. Lay, Jr., and M. E. Wilson; "Chicken Sperm Motility and Metabolism are Altered Immediately by Semen Dilution," by H. M. Parker, and C. D. McDaniel; "Progesterone Injections Induce a Polycystic Ovarian Follicle Syndrome (PCOF) in Young Turkey Hens," by W. L. Bacon and H.- K. Liu.

Three experiments were conducted to evaluate methods to decrease or eliminate the detection of estrus inherent to a melengestrol acetate (MGA)-PGF2&alpha (PGF) protocol for synchronization of estrus in heifers. In each experiment, all heifers received 0.5 mg of MGA-animal-1·d-1 for 14 d (d −32 to −19) and PGF (25 mg, i.m.; d 0, 0 h) 19 d after the last feeding of MGA (MGA-PGF protocol). In Exp. 1, heifers (n = 709) were assigned to each of the following protocols: 1) the MGA-PGF protocol with AI 6 to 12 h after detection of estrus (estrus AI; MGA-PGF); 2) MGA-PGF plus 100 μg, i.m. of GnRH on d −7 (1x GnRH) and estrus AI; or 3) MGA-PGF, GnRH on d −7, and GnRH (100 μg, i.m.) at 48 h after PGF, coincident with insemination (2x GnRH-TB48). In Exp. 2, heifers (n = 559) received the MGA-PGF protocol and were inseminated by either estrus AI or fixed-time AI (TAI) at 60 h, coincident with an injection of GnRH (GnRH-TB60). In Exp. 3, all heifers (n = 460) received the MGA-PGF protocol and were inseminated by estrus AI when detected up to 73 h. Heifers not observed in estrus by 73 h received TAI between 76 and 80 h. Half the heifers inseminated by TAI received no further treatment (TB80), and the remaining half was injected with GnRH at insemination (GnRH-TB80). Variance associated with the interval to estrus and the proportion in estrus from d 0 to 5 was similar for 1x GnRH and MGA-PGF treatments in Exp. 1. Pregnancy rate (d 0 to 5) did not differ for the MGA-PGF and 1x GnRH treatments (62.5 and 60.4%, respectively), and both were greater (P < 0.05) than TAI pregnancy rate in the 2x GnRH-TB48 treatment (42.3%). In Exp. 2, the peak estrous response occurred 60 h after PGF. Pregnancy rate during the synchrony period was greater (P < 0.05) for the MGA-PGF (255/401; 63.6%) than the GnRH-TB60 (74/158; 46.6%) treatment. In Exp. 3, 75.7% of heifers (348/460) were detected in estrus by 73 h and were inseminated, with a conception rate of 74.4%. Pregnancy rates after TAI did not differ between TB80 and GnRH-TB80 (14/56 = 25% and 19/ 56 = 33.9%, respectively). Total pregnancy rate was 63.5% for heifers inseminated after detected estrus and by TAI. Collectively, these data indicate that the exclusive use of TAI for heifers treated with the MGA-PGF protocol resulted in lower pregnancy rates than when AI was performed after detection of estrus. However, estrus AI for 3 d and TAI at the end of d 3 could result in pregnancy rates similar to those achieved after a 5-d period of detecting estrus. [ABSTRACT FROM AUTHOR]

There is growing concern about environmentally released man-made chemicals suspected to be responsible for a number of adverse effects on endocrine function in wildlife species and possibly also in humans. Sex hormones are of particular interest due to their regulatory role in developmental processes such as sexual differentiation. Endogenous hormones of human or animal origin as well as exogenous sex steroids used for contraception or as anabolics for farm animals are excreted and reach the environment. We investigated the transport of the synthetic growth promoters trenbolone (TbOH) and melengestrol acetate (MGA) in agricultural soil by means of column experiments with aggregated soil materials (Ap and Bt horizons of a Luvisol). Column effluent concentrations and depth profiles of TbOH and MGA were determined with sensitive enzyme immunoassay systems and HPLC (RP-18), respectively. All procedures were confirmed by liquid chromatography-mass spectrometry. Small amounts of TbOH and MGA passed the columns very quickly. However, both hormones exhibited a high affinity to the organic matter of both horizons leading to a high retardation within the upper layers of the soil columns. Although we cannot deduce whether hormones of animal origin reach the ground water under field conditions, our model experiments show that their transition can be presumed. [Copyright &y& Elsevier]

For eight weeks, two heifers each had been orally administered daily doses of 0, 1.5, or 5 mg melengestrol acetate (MGA) in a feed premix. Four heifers received the labeled dose of 0.5 mg/day. Regular feces samples were taken throughout the experiment. A rapid screening method for the determination of MGA in feces was developed, consisting of liquid extraction, clean-up on solid-phase extraction cartridges and quantification by enzyme immunoassay (ELISA). Residues in feces were dose-dependent with mean values of < 0.25, 2.0, 4.4, or 15.4 ng/g for 0, 0.5, 1.5, and 5 mg/day doses, respectively. In contrast to urine analysis, feces analysis appeared to be a suitable means of non-invasive screening before slaughter for surveillance of MGA treatment and verification of its compliance with labeled dosage. [ABSTRACT FROM AUTHOR]

This study compared the efficacy of two sources of PGF2α on the reproductive performance of virgin beef heifers, after synchronization of estrus using melengestrol acetate (MGA) and PGF2α. Angus-based heifers (n=1002) in five herds were fed 0.5 mg per head per day of MGA for 14 days. Nineteen days after the last day of MGA feeding, heifers were randomly assigned to receive (i.m.) either 0.5 mg cloprostenol (n=504; Estrumate®, E) or 25 mg dinoprost tromethamine (n=498; Lutalyse®, L) as a source of exogenous PGF2α. Heifers were observed twice daily for 5 days for signs of estrus and artificially inseminated 8–12 h later, except in herd A, wherein animals not detected in estrus by 80 h after PGF2α were mass-mated and no longer monitored for signs of estrus. Estrumate and Lutalyse were equally (P>0.1) effective among all response variables evaluated, including estrus response (E, 89% and L, 86%), conception rate (E, 67% and L, 67%), and synchronized pregnancy rate (E, 61% and L, 57%). Synchrony of estrus was not affected (P>0.1) by PGF2α source, and peak estrus response occurred 60 h post-PGF for both treatments. Conception rate to timed insemination was not different (P>0.1) among Estrumate- and Lutalyse-treated heifers within herd A (14%, 4/28 and 7%, 2/29, respectively). Herd had a significant (P<0.05) effect on all indicators of reproductive performance. Conception rates within herds A and D were influenced by technician (P<0.05), however, this effect was balanced across treatments and no treatment by technician interaction was detected. In conclusion, when administered 19 days after a 14-day MGA feeding period, cloprostenol and dinoprost tromethamine are equally efficacious for synchronous induction of a fertile estrus in virgin beef heifers. [Copyright &y& Elsevier]

The development of a sensitive screening method of MGA residues in bovine perirenal fat and muscle based on a competitive microtitration plate enzyme immunoassay is described. The samples were extracted with petroleum ether and purified with octadecyl-silica-cartridges. The detection limit for fat was 0.4ng/g and for muscle tissue 0.05ng/g, much lower than required for reliable detection of positive samples. The mean recovery rates of fortified samples amount to 75%, the mean intraassay variations to 7% and the interassay variation to 13%. Determination limits were validated for fat at 2ng/g and for muscle at 0.1ng/g. The efficiency of the new screening method was successfully demonstrated by the direct comparison to GC-MS and LCMS methods performed at natural positive samples originating from an animal experiment in which the labelled dose (0.5mg per animal and day) with and without a 48h withdrawal period or 3-fold or 10-fold the amount of MGA, respectively, was fed to Holstein Frisian heifers. In conclusion, this new screening method can be used for sensitive determination of MGA residues in adipose tissues even after low treatment doses or longer withdrawal periods. [ABSTRACT FROM AUTHOR]