Mg Of Melengestrol Acetate Research Articles

Effects of Ractopamine (Optaflexx) Fed in Combination with Melengestrol Acetate on Feedlot Heifer Performance

Two commercial feedlot experiments were conducted to determine the effects of feeding melengestrol acetate (MGA) or MGA plus ractopamine (MGA+OPT) on the performance and carcass characteristics of finishing heifers. In Nebraska (Exp. 1), 1,807 heifers (337.3 ± 20.0 kg) and in Texas (Exp. 2), 1,964 heifers (331.5 ± 6.1 kg) were fed 0.4 mg of MGA daily. For heifers fed MGA+OPT, 200 mg of ractopamine was fed daily the last 29 (Exp. 2) or 36 d (Exp. 1). Live and carcass-adjusted performance data were collected. On a carcass-adjusted basis, G:F for the entire feeding period was improved (P 0.47) between treatments in Exp. 1. Carcasses from heifers fed MGA+OPT had decreased marbling scores (P = 0.01) and greater LM area (P = 0.01) than carcasses from heifers fed MGA in Exp. 2. In Exp. 1, in which G:F was improved by 8.1%, no effect on QG was observed. In Exp. 2, in which G:F was improved by 27.2%, QG decreased. Based on these results, feeding MGA+OPT increased ADG and improved G:F, with variable effects on carcass characteristics.

Performance and carcass traits of finishing heifers fed crude glycerin1,2

Crossbred heifers (n = 373; 421.6 kg +/- 28.9) were fed finishing diets containing 0, 2, 4, 8, 12, or 16% crude glycerin (DM basis). Diets consisted of steam-flaked corn with 6% alfalfa hay and 1.2% urea and provided 300 mg of monensin, 90 mg of tylosin, and 0.5 mg of melengestrol acetate per animal daily. Cattle were stratified by BW and allocated randomly, within strata, to concrete-surfaced feedlot pens each containing 6 to 7 heifers, with 9 pens per dietary treatment. Cattle were transitioned from the control diet to diets containing increasing proportions of glycerin over a period of 10 d. Cattle had ad libitum access to feed, and diets were delivered once daily throughout the 85-d trial period. As the concentration of glycerin increased, DMI decreased linearly (P < 0.001). Heifers fed 0, 2, 4, 8, 12, and 16% glycerin had ADG of 1.19, 1.34, 1.29, 1.25, 1.17, and 1.03 kg, respectively (linear, P = 0.013; quadratic, P = 0.010). Feeding glycerin had a quadratic effect on G:F, and G:F was optimal when glycerin was fed at 2% of the diet (quadratic, P = 0.046). Glycerin increased the final BW by 12.7, 8.1, and 5.3 kg when fed at 2, 4, and 8% of the diet, respectively, but reduced the final BW by 1.9 and 14.3 kg when included at 12 and 16% of the diet (linear, P = 0.009; quadratic, P = 0.006). Similarly, HCW increased by 8.1, 5.1, and 3.3 kg when glycerin was fed at 2, 4, and 8% of the diet, respectively, but were 1.2 and 9.1 kg less than controls when glycerin was fed at 12 and 16%, respectively (linear, P = 0.009; quadratic, P = 0.006). Longissimus muscle area decreased linearly as glycerin concentrations increased (P < 0.013). Feeding glycerin resulted in linear decreases in subcutaneous fat over the 12th rib and marbling scores (P = 0.045). Glycerin tended to decrease the percentage of cattle grading USDA Choice (P = 0.084) and increase the percentage of cattle grading USDA Select. Adding glycerin to cattle-finishing diets improved BW gain and feed efficiency, particularly when added at concentrations of 8% or less on a DM basis.

Effects of melengestrol acetate on the inflammatory response in heifers challenged with Mannheimia haemolytica1

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 x 10(9) to 1.7 x 10(9) 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).

Effect of processing flax in beef feedlot diets on performance, carcass characteristics, and trained sensory panel ratings1

To assess the effects of flax addition and flax processing on feedlot performance and carcass characteristics, 128 yearling beef heifers (360 +/- 14 kg of initial BW) were blocked by weight and assigned randomly to feedlot diets that included no flax (control), whole flax (WHL), rolled flax (RLD; 1,300 microm), or ground flax (GRD; 700 microm). Heifers were fed a growth diet (31% corn, 30% corn silage, 18% barley malt pellets, 14% alfalfa, 4% linseed meal, and 3% supplement; DM basis) for 56 d, after which they were adapted to a finishing diet (79% corn, 7% corn silage, 7% alfalfa, 4.75% linseed meal, and 2.25% supplement; DM basis). In WHL, RLD, and GRD, flax replaced all linseed meal and partially replaced corn at 8% of diet DM. All diets provided 0.5 mg of melengestrol acetate, 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 steaks were removed from each loin for Warner-Bratzler shear force measurement, sensory panel evaluation, and fatty acid analysis (approximately 100 g of muscle was collected). Flax inclusion (WHL, RLD, and GRD vs. control) did not affect DMI (P = 0.79), fat thickness over the 12th rib (P = 0.32), or LM area (P = 0.23). Flax inclusion increased ADG (P = 0.006), G:F (P = 0.006), and USDA yield grade (P = 0.01). Flax processing (RLD and GRD vs. WHL) increased ADG (P = 0.05), G:F (P = 0.08), and apparent dietary NEm and NEg (P = 0.003). Muscle from heifers fed flax had greater phospholipid 18:3n-3 (P < 0.001), 20:5n-3 (P < 0.001), 22:5n-3 (P < 0.001), and 22:6n-3 (P = 0.02) fractions, and greater neutral lipid 18:3n-3 (P < 0.001). Feeding 8% flax to feedlot heifers increased gain and efficiency, and processing flax increased available energy and resulted in increased efficiency of gain. Feeding 8% flax also increased levels of n-3 fatty acids in fresh beef.

Melengestrol acetate 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 melengestrol acetate

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. In this experiment, a dose response study, Hy-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.

Melengestrol acetate 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. 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 (MGA; 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.

Methods to reduce or eliminate detection of estrus in a melengestrol acetate-PGF2alpha protocol for synchronization of estrus in beef heifers.

Three experiments were conducted to evaluate methods to decrease or eliminate the detection of estrus inherent to a melengestrol acetate (MGA)-PGF2alpha (PGF) protocol for synchronization of estrus in heifers. In each experiment, all heifers received 0.5 mg of MGA x animal(-1) x 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 microg, i.m. of GnRH on d -7 (1x GnRH) and estrus AI; or 3) MGA-PGF, GnRH on d -7, and GnRH (100 microg, 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.

Resynchronization of estrus in cattle of unknown pregnancy status using estrogen, progesterone, or both.

Our objective was to develop treatments applied to cattle of unknown pregnancy status that would resynchronize the repeat estrus of nonpregnant females. In Exp. 1, previously inseminated dairy and beef heifers were assigned randomly to each of three treatments 13 d after AI: 1) no treatment (controls; n = 44); 2) 0.5 mg of estradiol cypionate (ECP) i.m. on d 13 and 20 at the time of insertion and removal of a used intravaginal progesterone (P4)-releasing insert (CIDR; P4 + ECP; n = 44); and 3) same as P4 + ECP without injections of ECP (P4; n = 42). The P4 + ECP (>90%) and P4 (>75%) protocols effectively synchronized repeat periods of estrus to 2 d and did not harm established pregnancies. In Exp. 2, treatments similar to those in Exp. 1 were applied to previously inseminated beef heifers (n = 439). Feeding 0.5 mg of melengestrol acetate (MGA) from d 13 to 19 after AI replaced the CIDR as a source of progestin. Of those heifers not pregnant (n = 65) after the initial AI, more than 86% were reinseminated, but conception was decreased (P < 0.05) by 28 to 39% compared with controls. In Exp. 3, previously inseminated lactating beef cows at four locations were assigned within herd to each of three treatments: 1) no treatment (control; n = 307); 2) same as in Exp. 1, but with P4 + 1 mg of estradiol benzoate on d 13 and 20 (P4 + EB; n = 153); and 3) same as in Exp. 1, P4 + ECP (n = 149). Treatments with P4 plus estrogen did not decrease conception rates in pregnant cows at any location, but increased (P < 0.05) the percentage of nonpregnant cows returning to estrus between 19 and 23 d after timed AI from 29% in controls to 86% in P4 + EB and 65% in P4 + ECP cows. Conception rates at the return estrus were not decreased when treatments occurred between d 13 and 20. In Exp. 4, lactating beef cows were assigned as in Exp. 3 to each of three treatments: 1) no treatment (controls; n = 51); 2) P4 + ECP (n = 47), as in Exp. 1; and 3) a single injection of ECP on d 13 (n = 48). Previously established pregnancies were not harmed (P = 0.70), and return rates of nonpregnant cows did not differ (P = 0.78) among treatments. In summary, in both heifers and lactating beef cows, the P4-based resynchronization treatments increased synchronized return rates when estrus detection rates were low, had no negative effects on established pregnancies, and decreased or tended to decrease conception rates at the resynchronized estrus.

Supplemental norgestomet, progesterone, or melengestrol acetate increases pregnancy rates in suckled beef cows after timed inseminations1

In Exp. 1, 187 lactating beef cows were treated with injections of GnRH 7 d before and 48 h after prostaglandin F2alpha (PGF2alpha; Cosynch) or with Cosynch plus a 7-d treatment with an intravaginal progesterone (P4)-releasing insert (CIDR-B; Cosynch + CIDR). In Exp. 2, 183 lactating beef cows were treated with the Cosynch protocol or with Cosynch plus a 7-d treatment with norgestomet (Cosynch + NORG). In Exp. 1 and 2, blood samples for later P4 analyses were collected on d -17, -7 (first GnRH injection), 0 (PGF2alpha injection), and at timed artificial insemination (TAI; 48 h after PGF2alpha). In Exp. 3, 609 lactating beef cows were treated with the Cosynch + CIDR protocol or were fed 0.5 mg of melengestrol acetate (MGA) per day for 14 d before initiating the Cosynch protocol 12 d after the 14th d of MGA feeding (MGA + Cosynch). Blood samples were collected as in Exp. 1 and 2, plus additional samples on d -33 and -19 before PGF2alpha. In Exp. 4, 360 lactating beef cows were treated with a Cosynch + CIDR protocol, with TAI occurring at either 48 or 60 h after PGF2alpha, while receiving either GnRH or saline to form four treatments. Blood samples were collected as in Exp. 1 and 2. In Exp. 1, addition of P4 reduced the ability of the first GnRH injection to induce ovulation in anestrous cows with low P4 before PGF2alpha but improved (P = 0.06) pregnancy rates (61 vs 66%). In Exp. 2, the addition of NORG mimicked P4 by likewise increasing (P < 0.01) pregnancy rates (31 vs 51%) beyond those after Cosynch. In Exp. 3, the Cosynch + CIDR protocol increased (P < 0.001) pregnancy rates from 46 to 55% compared to the MGA + Cosynch protocol. In Exp. 4, administration of GnRH at TAI improved (P < 0.05) pregnancy outcomes (50 vs 42%), whereas timing of TAI had limited effects. We conclude that a progestin treatment concurrent with the Cosynch protocol improved pregnancy outcomes in all experiments, but pretreatment of cows with MGA was not as effective as the CIDR insert or NORG implants in this Cosynch-TAI model. Most of the improvement in pregnancy rates was associated with the increase in pregnancy rates of anestrous cows, regardless of whether ovulation was successfully induced in response to GnRH 7 d before PGF2alpha. Injection of GnRH at TAI following the Cosynch + CIDR protocol increased pregnancy rates in cycling cows with high P4 before the PGF2alpha injection and in anestrous cows with low P4 before PGF2alpha injection.

Breeding ewes out-of-season using melengestrol acetate, one injection of progesterone, or a controlled internal drug releasing device

A series of studies was designed to identify methods of improving out-of-season breeding success in ewes. In Experiment 1, 190 mature ewes were assigned to receive in April, either: (A) a control ration of 0.3 kg corn twice daily for 8 d before ram introduction (control ewes n=49), (B) the control ration containing 0.125 mg of melengestrol acetate (MGA) in 0.3 kg corn (MGA8a ewes n=46), (C) the control ration for 7.5 d followed by 1 feeding of 0.5 mg MGA in 0.3 kg corn (MGA 1 ewes n=48), or (D) the control ration plus a 20 mg im injection of progesterone on D 8 (P ewes n=47). Ewes were exposed to rams for 21 d. A greater percentage of MGA8a and P ewes lambed than did control ewes (P < 0.04). The lambing rate was greatest among MGA8a (P < 0.02 vs. control), intermediate among P ewes (P < 0.19 vs. control) and least among MGA1 and control ewes (P > 0.79). In Experiment 2, 70 mature ewes were assigned to receive in June, either: (A) a control ration of 0.3 kg of corn twice daily for 8 d before to ram introduction (control ewes n=25, (B) the control ration containing 0.125 mg of MGA per 0.3 kg corn (MGA8b ewes n=21), or (C) the control ration and simultaneous treatment of ewes with a progesterone-containing controlled internal-drug releasing device (CIDR ewes n=24). Ewes were exposed to rams for 21 d. Both CIDR and MGA8b ewes exhibited estrus earlier than did control ewes (P < 0.01). The CIDR ewes exhibited estrus earlier than did the MGA8b ewes (P < 0.05). A greater percentage of ewes treated with CIDR or MGA8b lambed than did control ewes (P < 0.01), with more CIDR ewes lambing than MGA8b ewes (P < 0.01). The lambing rate was greater in CIDR ewes than in control ewes (P < 0.04). These data provide evidence that several options exist to improve pregnancy success in ewes bred out of season and that success varies with method of treatment.

Sincronização de estro e dinâmica folicular de éguas Crioulas submetidas a tratamentos com norgestomet, acetato de melengestrol e altrenogest

21 Crioulo mares on reproductive age were grouped into 3 groups (I, II e III) with 7 animals each; group I was treated with unique 3 mg norgestomet + 5 mg estradiol valerate intramuscular injection and a subcutaneous implant of norgestomet during 9 days; group II received unique 5 mg of 17-b estradiol intramuscular injection and 0,5 mg of melengestrol acetate given orally during 9 days; group III consisted on mares given 0,045 mg/kg altrenogest orally during 9 days. At progestogen treatment removal (9th. day), all mares from the 3 groups received luteolytic dose of luprosteol and 3.000 UI of hCG when dominant follicle was ultrasonographically detected in ovulatory conditions . All mares were daily evaluated by rectal palpation and ultrasound examination for retrospectively measurement of the largest and second largest follicles, and mated by tested stallions closed to ovulation. Follicular development was not observed on group II (MGA). Considering 5 days post PGF2a-analogue administration, synchronization rates for groups I and III were, respectively, 85.71% and 66.70% (p > 0.05). Porcentage of oestrus supression for these groups were, respectively, 85.71% and 100.00% (p > 0.05). Pregnancy rate was not significantly different between the two groups (I, 100% and II, 85.71%; p > 0.05). Results were based on mares showing response to the synchronization regimen. PGF2a-oestrus, PGF2a-hCG, hCG-ovulation and PGF2a-ovulation intervals for groups I and III were 4.5 ± 0.80 and 4.2 ± 0.8 (p > 0.05), 8.0 ± 1.41 and 6.17 ± 0.6 (p > 0.05), 1.5 ± 0.22 and 2.28 ± 0.28 (p > 0.05) and 9,8 ± 1,02 and 8,6 ± 1,32 (p > 0.05) days respectively. The results prove the eficiency of oestrus synchronization regimens by norgestomet implant and oral administration of altrenogest, with tendency to higher synchronization rate to norgestomet system, although no significantly diferences were observed concerning to reproductive parameters and follicular dynamics data, with exception to the minor largest diameter of dominant follicles and ocurrence of only one major wave for supressed cycles by progestogen-estradiol regimen.

Change in morphology of corpora lutea, central luteal cavities and steroid secretion patterns of postpartum suckled beef cows after melengestrol acetate with or without prostaglandin F 2α

Change in morphology of the corpus luteum (CL) and patterns of progesterone and estradiol secretion after treatment with melengestrol acetate (MGA) were monitored in postpartum beef cows. Twenty Angus cows were randomly assigned to MGA or MGA + prostaglandin F 2α (PGF) treatments. All cows were fed 0.5 mg of MGA per cow per day for 14 d. The MGA-treated cows (n = 10) were allowed to return to estrus spontaneously at the second estrus after withdrawal of MGA from the feed. The MGA + PGF-treated cows (n = 10) received an injection containing 25 mg of PGF 2α 17 d after the last feeding of MGA. Cycle 1 was defined as the first luteal phase after MGA feeding and Cycle 2 represented the subsequent cycle or luteal phase after PGF. Blood sampling and transrectal ultrasonography of the ovaries was done daily through the completion of 2 estrous cycles upon removal of MGA from the feed. Blood samples were analyzed for plasma progesterone and estradiol concentrations. Area of CL and fluid-filled cavities within each CL were determined by ultrasonography. Concentrations of progesterone and area of CL were similar between cycles and treatments. Estradiol concentrations were higher (P < 0.05) in Cycle 2 than in Cycle 1. Fluid-filled cavities were larger (P < 0.001) in Cycle 1 than in Cycle 2 for both mid-luteal (Days 5 to 9) and late-luteal (Days 10 to 14) phases. Multiple CL (2 or more during 1 cycle) were observed in 5 cows. Progesterone concentrations and total area of luteal tissue did not change with respect to treatment or cycle, but CL morphology was altered in the first cycle after MGA treatment. Of the 19 cows that ovulated after withdrawal of MGA, 3 experienced a short luteal phase. These data characterize changes that occur among cows that are fed melengestrol acetate during the postpartum period and enhance observations from prior studies regarding MGA use.

Use of melengestrol acetate and gonadotropins to induce fertile estrus in seasonally anestrous ewes.

Ewes of three genotypes (Hampshire, n = 59; Rambouillet, n = 36; crossbred, n = 57) were used to determine the efficiency of melengestrol acetate (MGA) and(or) PG-600 (a combination of pregnant mare's serum gonadotropin and human chorionic gonadotropin) in inducing fertile estrus in seasonally anestrus ewes. Ewes were assigned randomly, within genotype, to treatments in a 2 x 2 factorial arrangement. Treatments were control, .125 mg of MGA given twice per day for 9 d (MGA), a single 5-mL injection of PG-600 (PG-600), and the combination of treatments MGA and PG-600 (MGA/PG-600). Feeding of MGA began on May 14, 1990, and ended on May 23. Injections of PG-600 were given immediately after the last feeding of MGA or vehicle on May 23. All ewes were exposed to fertile, brisket-painted rams on May 24 (d 0) for 40 d. Ewes were checked for estrus twice daily for 9 d. Laparoscopy was performed, to assess ovulation rate (OR), on d 6 for ewes that were not detected in estrus and on d 12 for ewes that exhibited estrus. Percentage of ewes mated was increased by MGA (P less than .001). Ovulation rate of ewes exposed to rams was increased by PG-600 (P less than .01) and this effect was enhanced by MGA (P less than .05), whereas MGA alone tended to decrease OR (P less than .10). Melengestrol acetate decreased the interval to lambing by 6.5 d (P less than .05).(ABSTRACT TRUNCATED AT 250 WORDS)

Estrous Synchronization in Beef Cows: Partitioning of Melengestrol Acetate and 48-H Calf Removal

Spring calving, Shorthorn x Angus x Hereford beef cows (N = 287) nursing Simmental-sired calves were allotted to four treatments: 1) .5mg of Melengestrol Acetate (MGA) ·hd-1 ·d-1 in 2.27kg of ground ear corn for 7 d, followed by a 25-mg injection of prostaglandin F2X on d 8 (PGF), and 48-h calf removal (CR) d 8 and 9 (MGA/PGF/CR); 2) MGA/PGF; 3) PGF/CR; and 4) PGF. Treatment was followed by a 72-d breeding season (42 d artificial insemination (Al) and 30 d natural service). Blood was collected on d -10, 0, 7, 14, 28, 35, 42, and 49 (d 1 = 1st d of MGA feeding) for progesterone analysis. A majority of cows (89%) were anestrus before initiation of treatments. Treatments did not differ in postpartum interval (PPI, 76 ± 4 d) or percentage of anestrus cows induced to ovulate (30%). PGF cows showed a greater percentage of standing heat in the first 21 d of the breeding season than MGA/PGF cows (65 vs. 47%). In addition, MGA/PGF cows had a 30% reduction in first service conception rate if they were induced to ovulate. Treatment groups did not differ in conception rate (81%) when bred Al. However, on a whole herd basis, a greater percentage of MGA/PGF/CR cows conceived to Al (77, 65, 63, and 68% for MGA/ PGF/CR, MGA/PGF, PGF/CR, and PGF, respectively). Treatment groups did not differ in overall pregnancy rate (84%) or average calving date the following year. In cows induced to ovulate, greater fertility resulted from CR than MGA. However, MGA must be combined with CR to exceed the reproductive advantages resulting from a single prostaglandin injection alone.

Estrous Synchronization in Beef Cows Using a Melengestrol Acetate, Prostaglandin F2x, 48-H Calf Removal System

One hundred mature, spring calving, Angus beef cows nursing Angus sired calves were allotted to two groups: 1) treated cows which received .5 mg of melengestrol acetate (MGA) in 1.36 kg corn/hd/d for 7 d (d 1 = 1st d of MGA feeding), 25 mg prostaglandin F2X (PGF) on d 8, and 48 h calf removal (48 h CR) on d 8 and 9; and 2) control cows which received 1.36 kg corn/hd/d from d 1 to d 7. Cows were bred during a 60 d period, beginning the day after the PGF administration (34 d artificial insemination (Al) and 26 d natural service). Blood was collected on d –10, 0, 14, 21, 28, 35, 42, and 49 for progesterone analysis. Ovulation was induced in 85% of anestrous treated cows. Ovulation was synchronized during the first 7 d as 90% of treated cows formed corpora lutea. More (P<.05) treated than control cows were bred from d 7 to 21. First service conception rates in the first 7 and 21 d of Al and overall conception rates were similar between treated and control cows (55, 57, and 65%, respectively). Within cows receiving MGA, first service conception rate during the first seven days was greater (P<.05) for pretreatment cows that were estrual than those induced (67% vs 40%). More treated cows (50% vs 32%) conceived to Al. Treated cows had a greater overall pregnancy rate (98% vs 80%) and tended to calve earlier the following year.

Conception rate in Bos taurus and Bos indicus crossbred heifers after postweaning energy manipulation and synchronization of estrus with melengestrol acetate and fenprostalene.

Conception rate in heifers after synchronization of estrus with melengestrol acetate (MGA) and fenprostalene (a prostaglandin F2 alpha analogue; PGF) was determined in pubertal Bos taurus and Bos indicus crossbred yearling heifers. Angus x Hereford (AH, n = 137) and Brahman x Hereford (BH, n = 97) heifers were sorted by body weight after weaning into light (LW) and heavy (HW) weight blocks. Heifers were assigned by age to diets to reach a target weight of 55% (LE) or 65% (HE) of their projected mature weight by the start of breeding. Heifers that exhibited estrus and had serum progesterone greater than or equal to 1 ng/ml (0 or 10 d before estrous synchronization treatment) were assigned randomly within breed and nutritional groups to either an estrous synchronization (S) or control (C) group. Heifers in the S group were fed .5 mg of MGA for 7 d and injected s.c. with 2 mg PGF on d 7 of MGA. All heifers were inseminated 12 h after first detected estrus. A greater proportion of AH (P less than .01) than of BH heifers were in estrus within 6 d after PGF, and more S heifers than C heifers (P less than .01) were in estrus. Conception rate at first service was proportionately higher (P less than .001) in AH than in BH heifers and lower (P less than .02) in S than in C heifers. There was a breed x energy level interaction (P less than .01) for conception rate at first service. Stage of the estrous cycle at the time treatment with MGA was initiated influenced (P less than .05) conception rate at first service in the S, AH heifers, with lower conception rates among heifers beginning treatment late in their estrous cycles (greater than or equal to d 12). Pregnancy rates after 21 d were higher (P less than .01) in AH than in BH heifers and higher (P less than .01) in HW than in LW heifers. More HE than LE heifers (P less than .02), and more AH than BH heifers were pregnant after 45 d. Pregnancy rates at the end of 21 d were higher among HE, BH heifers than among LE contemporaries. A higher (P less than .02) percentage of HE, HW, BH heifers were pregnant at the end of 45 d compared with other BH groups. Results indicated that a 7-d MGA-PGF treatment reduced conception rates at first service in pubertal yearling heifers. Pregnancy rate was affected by prebreeding nutrition in BH yearling heifers at the end of 45 d.

Characteristics of Cervical Mucus from Progestagen-Treated Cattle

SUMMARY Five characteristics of cervical mucus were investigated to determine if abnormalities might be responsible for the lowered fertility observed in cattle following progestagen administration. Mucus from animals fed 1 mg of melengestrol acetate (MGA) daily for 3 and 14 days did not differ significantly from that of controls in quantity, crystallization patterns or alkaline phosphatase content. However, on the last day of MGA feeding (day 14) treated animals had thicker mucus (P Based on quantity, consistency and alkaline phosphatase content of mucus from treated animals on day 4 after MGA withdrawal and from control animals on the day of oestrus, there appears to be no reason to indict cervical mucus as the cause of lowered fertility in MGA-treated animals. However, the altered crystallization patterns and sperm migration might indicate changes of significance in relation to feritlity.

Synchronization of Estrus, Reproductive Performance, and Lactational Response of Holstein Heifers Treated with Melengestrol Acetate®,1

Effects of oral administration of melengestrol acetate on estrus synchronization and conception were investigated in 24 Holstein heifers. In addition, effects of feeding melengestrol acetate starting at 90 days postconception through 30 days postpartum on growth, gestation length, birth weight, and lactation were studied.Daily feeding of 1mg of melengestrol acetate to heifers for 14 consecutive days irrespective of stage of estrous cycle inhibited estrus during treatment and synchronized estrus following withdrawal. Treatment lowered (P<.05) conception at first post-treatment estrus. No difference in conception was observed between single and double inseminations. Services per conception for the treated animals were higher (P<.05) than controls (2.64 versus 1.54). Postconception feeding of melengestrol acetate resulted in no differences (P>.05) in weight gain, gestation length, or calf birth weight. There were no differences (P>.05) in lactation length, milk and fat production during post-treatment lactation.

Control of sexual activity in ranch cows by intramuscular and intravaginal administration of progestagens.

The results of 2 trials examining the effects of 3 progestagens chlormadinone acetate (CAP) melengestrol acetate (MGA) and megestrol acetate (MA) on the sexual activities of ranch cows are reported. Cows of indigenous breeds had sexual and ovarian activities recorded for 30 months preceding the trials. Ovaries were palpated per rectum at weekly intervals. In the first trail injection of CAP 6 mg a day inhibited manifestation of estrus in 10 of 10 cows while 6 of these cows showed full heat 4-6 days after cessation of treatment. When CAP was administed by intravaginal tampon 200 mg per tampon 8 of 10 cows showed full heat during the 18 days of treatment and 2 showed full heat in the 7 days after cessation of treatment. Trial 2 had 6 groups of 10. CAP was injected 6 mg a day for 16 days and at 12 mg a day on alternated days for 16 days. MGA was injected .5 mg a day for 16 days or administered 60 mg per tampon for 16 days. MA was injected 4 mg each day or administered 100 mg per tampon again for 16 days. With the exception of 1 cow receiving MA injection all progestagens completely inhibited manifestations when injected. In the tampon trials 2 of 10 cows receiving MGA and 2 of 10 receiving MA showed estrus during treatment. During Days 5-10 following treatment heat was shown by 100% of cows receiving CAP injections 80% of those receiving CAP on alternate days and 70% of those receiving MGA or MA. The high incidence of anovulatory heats 20-80% indicated that the first heat after cessation of progestagen treatment would be associated with low fertility. In these studies between 10% and 50% of tampons were ejected prematurely. 60 mg of MGA applied intravaginally resulted in a small amount of vaginal discharge. 200 mg CAP resulted in a copious amount of foul-smelling mucus in the vagina.

Control of ovulation in cattle with melengestrol acetate. V. Effect of ovulation induction on corpus luteum development during MGA treatment.

Summary. Sixty-four normally cycling Holstein heifers were randomly assigned into four equal groups (three treatment and one control). Each of the three treatment groups received 0·5 mg of melengestrol acetate (MGA®) daily and a single injection of either oestradiol cypionate (ECP®), human chorionic gonadotrophin (hcg) or pituitary luteinizing hormone (plh) between Days 22 and 26 following oestrus or Days 8 to 12 of MGA feeding. The control animals received neither MGA nor an injection. Heifers from each treatment group were spayed (overiectomized) on Days 2, 5, 8 and 11 from the injection and control heifers were spayed on Days 1, 4, 7 and 10 from oestrus. The corpora lutea (cl) and the largest follicles on the ovaries of each heifer were observed for size and colour. Oestrus was observed in only the ECP-treated group within 24 hr following the injections (nine of sixteen animals). Ovulation occurred following the injection in all of the sixteen animals in the hcg group and in fifteen of the sixteen animals in each of the ECP and plh groups. All the control heifers ovulated following oestrus. Normal cl were present in all the treated heifers spayed by Day 5. On subsequent days, increasing numbers of heifers had cl which were regressing. The percentages of heifers spayed on Day 8 and Day 11 after injection with regressing cl were: 0% and 50% for the ECP group; 25% and 100% for the hcg group; and 75% and 50% for the plh group. All the heifers in the control group had normally developing cl regardless of the day of spaying. The follicles from those animals which had regressing cl were generally larger than those from control heifers.