Fungal mediated biotransformation of melengestrol acetate, and T-cell proliferation inhibitory activity of biotransformed compounds.

Glomerella fusaroide, and Rhizopus stolonifer were effectively able to transform the steroidal hormone melengestrol acetate (MGA) (1) into four (4) new metabolites, 17α-acetoxy-11α-hydroxy-6-methyl-16-methylenepregna-4,6-diene-3,20-dione (2), 17α-acetoxy-11α-hydroxy-6-methyl-16-methylenepregna-1,4,6-triene-3,20-dione (3), 17α-acetoxy-6,7α-epoxy-6ß-methyl-16-methylenepregna-4,6-diene-3,20-dione (4), and 17α-acetoxy-11ß,15ß-dihydroxy-6-methyl-16-methylenepregna-4,6-diene-3,20-dione (5). All these compounds were structurally characterized by different spectroscopic techniques. The objective of the current study was to assess the anti-inflammatory potential of melengestrol acetate (1), and its metabolites 2-5. The metabolites and the substrate were assessed for their inhibitory effects on proliferation of T-cells in vitro. The substrate (IC50 = 2.77 ± 0.08 µM) and its metabolites 2 (IC50 = 2.78 ± 0.07 µM), 4 (IC50 = 2.74 ± 0.1 µM), and 5 (IC50 = < 2 µM) exhibited potent T- cell proliferation inhibitory activities, while compound 3 (IC50 = 29.9 ± 0.09 µM) showed a moderate activity in comparison to the standard prednisolone (IC50 = 9.73 ± 0.08 µM). All the metabolites were found to be non-toxic against 3T3 normal cell line. This study thus identifies some potent compounds active against T-cell proliferation. Their anti-inflammatory potential, therefore, deserves to be further investigated.

Comparison of long-term progestin-based protocols to synchronize estrus prior to natural service or fixed-time artificial insemination in Bos indicus-influenced beef heifers.

This experiment was designed to evaluate breeding strategies involving natural service or fixed-time artificial insemination (FTAI) in Bos indicus-influenced beef heifers (n = 1456) when there were field-type management conditions. Body weights and reproductive tract scores (RTS; Scale 1-5) were obtained for heifers before assignment to one of five treatments: 1) Non-synchronized control exposed for natural service (NS), n = 299; 2) melengestrol acetate + natural service (MGA + NS; 0.5 mg/heifer/d), n = 295; 3) 14-d controlled internal drug release insert + natural service (CIDR + NS), n = 289; 4) 14-d MGA-prostaglandin F2α (PG) + FTAI, n = 295; or 5) 14-d CIDR-PG + FTAI, n = 278. Fertile bulls were placed in pastures with heifers of the three NS treatment groups for a 65-day period which began 10 days after progestin treatments (MGA or CIDR) ended. Heifers in FTAI treatment groups were administered PG (25 mg, IM) 16 days after CIDR removal or 19 days following MGA withdrawal, respectively, and FTAI was performed at 66 (CIDR-PG) or 72 h (MGA-PG) after PG. Gonadotropin-releasing hormone (GnRH; 100 µg, i.m.) was administered at FTAI. Pregnancy status was determined at the end of a 65-day breeding period. Pregnancy rates on Days 21 and 65 of the breeding period differed among treatment groups based on pre-treatment pubertal status (P ≤ 0.02) and body weight (P ≤ 0.05) but did not differ by group. These data highlight the need for continued research efforts to improve reproductive management of Bos indicus-influenced females.

Developmental profiles of progesterone receptor transcripts and molecular responses to gestagen exposure during Silurana tropicalis early development.

Environmental gestagens are an emerging class of contaminants that have been recently measured in surface water and can interfere with reproduction in aquatic vertebrates. Gestagens include endogenous progestogens, such as progesterone (P4), which bind P4-receptors and have critically important roles in vertebrate physiology and reproduction. Gestagens also include synthetic progestins, which are components of human and veterinary drugs, such as melengestrol acetate (MGA). Endogenous progestogens are essential in the regulation of reproduction in mammalian species, but the role of P4 in amphibian larval development remains unclear. This project aims to understand the roles and the regulatory mechanisms of P4 in amphibians and to assess the consequences of exposures to environmental gestagens on the P4-receptor signaling pathways in frogs. Here, we established the developmental profiles of the P4 receptors: the intracellular progesterone receptor (ipgr), the membrane progesterone receptor ß (mpgrß), and the progesterone receptor membrane component 1 (pgrmc1) in Western clawed frog (Silurana tropicalis) embryos using real-time qPCR. P4-receptor mRNAs were detected throughout embryogenesis. Transcripts for ipgr and pgrmc1 were detected in embryos at Nieuwkoop and Faber (NF) stage 2 and 7, indicative of maternal transfer of mRNA. We also assessed the effects of P4 and MGA exposure in embryonic and early larval development. Endocrine responses were evaluated through transcript analysis of a suite of gene targets of interest, including: ipgr, mpgrß, pgrmc1, androgen receptor (ar), estrogen receptor α (erα), follicle stimulating hormone ß (fshß), prolactin (prl), and the steroid 5-alpha reductase family (srd5α1, 2, and 3). Acute exposure (NF 12-46) to P4 caused a 2- to 5-fold change increase of ipgr, mpgrß, pgrmc1, and ar mRNA levels at the environmentally relevant concentration of 195 ng/L P4. Acute exposure to MGA induced a 56% decrease of srd5α3 at 1140 ng/L MGA. We conclude that environmental exposure to P4 induced multiple endocrine-related transcript responses in amphibians; however, the differential responses of MGA suggest that the effects of MGA are not mediated through the classical P4 signaling pathway in S. tropicalis.

Impact of puberty status and melengestrol acetate 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 melengestrol acetate (MGA) before onset of the breeding period on ovulatory responses (Exp. 1) and conception rate after AI performed on estrus detection during 10 d and the pregnancy rate through 80 d of breeding period (Exp. 2) of pasture-grazed beef heifers. In Exp. 1, heifers (15 pubertal and 15 prepubertal) received 0.5 mg per heifer/d -1 of MGA over 14 d. No differences in the ovulatory responses were found 10 d after the MGA administration (pubertal = 46.7% vs. prepubertal P = 53.3%; P = 0.72). In Exp. 2, 368 heifers were randomly assigned to groups according to pubertal status and the MGA treatment. All heifers were inseminated on estrus detection for up 10 d after MGA administration and following exposure to bulls between 20 and 80 d. The MGA-treated heifers exhibited a greater AI service rate than control heifers (72.1 vs. 41.6%;P < 0.01); however, heifers receiving MGA had lower conception results following AI (51.6 vs. 71.4%; P = 0.01). In addition, MGA-treated heifers were more likely to have a corpus luteum in the middle of the breeding period (95.3 vs. 87.5%;P < 0.01), although the Cox proportional hazard of pregnancy rate was similar (P = 0.29) at the end of the breeding period. At onset of the breeding period, pubertal heifers presented a greater pregnancy rate following AI (pubertal P = 42.2% vs. prepubertal P = 24.9%; P = 0.01). Therefore, pubertal heifers seem to have greater overall reproductive efficiency than prepubertal heifers, particularly at the beginning of the breeding period. Interestingly, administration of MGA before the onset of the breeding period increased AI service rate but did not alter the rate of pregnancy throughout the breeding period of pasture-grazed beef heifers.

Fungal transformation and T-cell proliferation inhibitory activity of melengestrol acetate and its metabolite.

Biotransformation of melengestrol acetate (MGA, 17α-acetoxy-6-methyl-16-methylenepregna-4,6-diene-3,20-dione) (1) was investigated for the first time by using fungal cultures. Incubation of compound 1 with Cunninghamella blakesleeana yielded a new major metabolite, 17α-acetoxy-11ß-hydroxy-6-methyl-16-methylenepregna-4,6-diene-3,20-dione (2). The metabolite 2 was purified by using HPLC, followed by characterization through (1)H- and (13)C-NMR and other spectroscopic techniques. Single crystal X-ray diffraction analysis was used to deduce the three dimensional structures of melengestrol acetate (1) and metabolite 2 for the first time. T-cell proliferation assay was employed to evaluate the immunosuppressant effect of compounds 1 and 2 with IC50=0.5±0.07 and 0.6±0.08µg/mL, respectively. The results indicated that these compounds possess sixfold potent T-cell proliferation inhibitory activity as compared to the standard prednisolone (IC50<3.1µg/mL). Both compounds were found to be non-toxic in a 3T3 (mouse fibroblast) cell-based cytotoxicity assay. This discovery of potent anti-inflammatory activity of compounds 1 and 2 can lead the way to develop new immunosuppressant compounds for clinical application.

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 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 F2αwas 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.

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 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 (10×10(7) or 20×10(7) sperm per 0.5 ml insemination dose) of fresh diluted semen. Inseminations were carried out 11-18 h 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 (20×10(7) or 40×10(7) or 60×10(7) sperm per 0.5 ml 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 11-16 h; 63% for 17-18 h) when insemination was held at 17-18 h after first detected estrus following MGA treatments. Pregnancy rates were found to be similar in ewes inseminated with 10×10(7) (36%) or 20×10(7) (47%) motile spermatozoa at first AI, and 20×10(7) (44%) or 40×10(7) (59%) or 60×10(7)(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 17-18 h after estrus onset and with 20×10(7) sperm per insemination dose.

Comparison of long-term progestin-based estrus synchronization protocols in beef heifers.

Two experiments evaluated long-term progestin-based estrus-synchronization programs on the basis of potential for use in facilitating fixed-time AI in estrous cycling and prepubertal beef heifers. In Exp. 1, heifers were assigned to 1 of 2 treatments by age, BW, and estrous cyclicity status. Heifers assigned to the melengestrol acetate-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 after CIDR removal (d 32). All heifers were fitted with HeatWatch estrus-detection transmitters at the time of progestin removal for continuous estrus detection through the synchronized period after PGF(2α). In Exp. 2, heifers (n = 396) were assigned to the same 2 treatments described in Exp. 1 by age, BW, and reproductive tract score. Heifers in Exp. 2, however, were fitted with HeatWatch estrus-detection transmitters at PGF(2α) to characterize estrus-distribution patterns during the synchronized period after PGF(2α). Heifers in both experiments were inseminated approximately 12 h after the onset of estrus. In Exp. 1, estrous response after PGF(2α) and mean interval to estrus after PGF(2α) did not differ between MGA-PG and Show-Me-Synch treatments (P = 0.97). The variance for interval to estrus after PGF(2α) tended (P = 0.06) to be reduced among MGA-PG-treated heifers compared with Show-Me-Synch-treated heifers. Conception to AI, AI pregnancy, and final pregnancy rates did not differ (P > 0.1) between treatments. In Exp. 2, estrous response after PGF(2α) was greater (P = 0.01) among Show-Me-Synch-treated heifers (92%) compared with MGA-PG-treated heifers (85%); however, mean interval to estrus after PGF(2α) did not differ (P = 0.74) between MGA-PG (57.4 ± 2.5 h) and Show-Me-Synch (56.2 ± 2.5 h) treatments. The variance for interval to estrus after PGF(2α) was reduced (P < 0.01) among Show-Me-Synch-treated vs. MGA-PG-treated heifers. Conception to AI, AI pregnancy, and final pregnancy rates did not differ (P > 0.1) between treatments. In summary, the Show-Me-Synch protocol compared favorably with the MGA-PG protocol on the basis of estrous response, synchrony of estrus, and resulting fertility after treatment administration.

Melengestrol acetate enhances adipogenic gene expression in cultured muscle-derived cells.

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 O were seen not only in single MDC, but also in fused myotubes. An increase (P < 0.05) in relative PPARgamma messenger RNA (mRNA) levels was measured in MDC incubated with IOC. However, myogenin mRNA levels in MDC incubated with IOC were repressed (P < 0.05) compared with nontreated MDC. Cultures of MDC treated with 10 microM insulin, 10 microM oleic acid, 10 microM ciglitizone, 10 nM estradiol-17beta (E2), and 10 nM MGA resulted in cultures with highly distributed lipid droplets not only in single cells, but also in the multinucleated myotubes. Relative C/EBPbeta and PPARgamma 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/EBPbeta mRNA levels and tended (P = 0.06) to increase the PPARgamma mRNA level. There was no difference (P > 0.10) in relative myogenin mRNA among the control, E(2), and MGA treatments. Relative C/EBPbeta, PPARgamma, 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/EBPbeta levels (P < 0.05) in C2C12 myoblasts and tended (P = 0.08) to increase C/EBPbeta 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.

Development of estrous synchronization protocols using melengestrol acetate in Bos indicus cattle.

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 x 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.

Idiopathic infertility in two captive male gerenuk (Litocranius walleri walleri).

Two adult male gerenuk (Litocranius walleri walleri) were confirmed infertile with distinctly varying clinical presentations. One animal had unilateral testicular degeneration/hypoplasia, and within 8 mo experienced atrophy/degeneration of the remaining testicle. The second animal had been previously treated with melengesterol acetate (MGA) milled in feed for 1 yr during puberty as part of an aggression-control study. The testes in this individual appeared normal both visually and on palpation; however, repeated semen collection consistently produced ejaculates containing high numbers of immotile spermatozoa, all of a single abnormal morphology: shortened tails, with normal total sperm counts for this species. Both gerenuk had cortisol concentrations within normal ranges for adult male gerenuk. Analysis of serum mineral concentration revealed zinc levels that would be considered low in domestic cattle. Testosterone levels were low for the animal discussed in case 1, but were within normal range for the animal in case 2 compared with other gerenuk. Investigations into endocrine causes, such as abnormal thyroid hormone concentrations and adrenal function, were unrewarding. Both animals discussed in this report are maternally related; therefore, a genetic cause of infertility cannot be ruled out. Further investigation into MGA, as well as the dietary zinc requirements for gerenuk, and resulting effects on spermatogenesis and testicular development are warranted.

Effects of melengestrol acetate and P.G. 600 on fertility in Rambouillet ewes outside the natural breeding season.

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.

Melengestrol acetate as a tool for inducing early ovulation in transitional mares.

The efficacy of melengestrol acetate (MGA) to shorten the vernal transition of mares by synchronising and accelerating the first ovulation of the year after 60 days of phototherapy was determined by ultrasonographic monitoring. Sixteen mares in late transition were fed two doses of MGA (150 mg/mare/day and 100 mg/mare/day, respectively) for 10 days. A luteolytic dose of prostaglandin was administered to each mare one day after the end of MGA treatment. The presence and duration of oestrus, follicular growth, uterine oedema and presence of ovulation were monitored by ultrasonography and the cervical tone was evaluated by rectal palpation. Ovulation was detected in 87.5% of the mares treated with 150 mg MGA/mare/day for 10 days, and in 62.5% of the mares receiving 100 mg MGA/mare/day for 10 days. This was statistically different (P = 0.03) from the untreated control mares having an ovulation rate of 20%. Mares that received 150 mg MGA/day for 10 days had a mean treatment to ovulation interval of 13.1 +/- 5.97 days after the end of treatment, while mares that received 100 mg MGA/day for 10 days had a mean of 25.6 +/- 10.50 days (P = 0.01) to ovulation. These results suggest that MGA can be used for synchronising and hastening the first ovulation of the year in mares.

Evaluation of short estrus synchronization methods in dairy cows.

In the present study, two new short estrus synchronization methods have been developed for lactating dairy cows. The study was completed in three consecutive phases. In experiment (Exp) 1, 32 cows, that were not detected in estrus since calving between the 50th and 84th post-partum days, were treated with PGF2alpha (PGF, d-cloprostenol, 0.150 mg), estradiol propionate (EP, 2mg) and GnRH (lecirelina, 50 microg) at 24h intervals, respectively, and timed artificial insemination (TAI) was performed 48 h after PGF. Different from Exp 1, EP and GnRH were given at 48 and 60 h, respectively after PGF in Exp 2 (n=20), instead of 24 and 48 h. Ovulations were investigated by ultrasound for 7 days starting from the day of PGF treatment, and ovulation rates were compared with the ones obtained in Exp 1. In Exp 3, cows were given the same treatments as Exp 2, but treatments started at certain estrus stages. Cows detected in estrus and with a confirmed ovulation (n=27) after the second PGF given 11 days apart were assigned to three treatment groups. Treatment was initiated at Day 3 (group metestrus, n=9), Day 12 (group diestrus, n=9) and Day 18 (group proestrus, n=9) after ovulation. All cows included in Exp 3 were TAI between 16 and 20 h after GnRH treatment. In Exp 2 and 3, blood samples were obtained once every 2 days, starting from Day 0 to the 10th day after GnRH injection, and once every 4 days between the 10th and the 22nd days after GnRH to examine post-treatment luteal development. During the study, animals exhibiting natural estrus were inseminated and served as controls (n=85). The rate of estrus was found to be significantly higher in cows with an active corpus luteum (CL) at the start of Exp 1 (72.7% vs. 30.0%, P<0.05) and the pregnancy rate tended to be higher than cows without an active CL (40.9% vs. 10.0%, P=0.08). Compared to those in Exp 1, cows in Exp 2 had higher rates of synchronized ovulation (94.1% vs. 59.1%, P=0.013). In Exp 3, estrus (P<0.001) and pregnancy rates (P=0.01) were found to be significantly higher in cows in the proestrus group than in those in the metestrus group. Comparable pregnancy rates were obtained from the first and second inseminations in Exp 1 and 3 with results from those inseminated at natural estrus (P>0.05). It was concluded from the study that the treatment in Exp 1 and 3 could result in comparable pregnancy rates after timed AI of lactating dairy cows at random stages of the estrus cycle relating to those inseminated at natural estrus, but the stage of the estrus cycle can have significant effects on pregnancy rates.

Utilization of soybeans or corn milling by-products in beef heifer development diets.

Whole raw soybeans (SB), wet corn gluten feed (WCGF), and corn dried distillers grains (DDG) are sources of protein in heifer development rations. The objectives of this study were to compare puberty status before synchronization of estrus, response to synchronization, and AI and final pregnancy rates in heifers developed on diets containing SB, WCGF, or DDG that were formulated to be similar in energy and CP. These ingredients vary substantially in fat content, which may affect reproductive performance. Rate of gain during the feeding period and post-AI performance were also compared. In a preliminary experiment, 104 crossbred heifers were fed diets containing either 1.25 kg of SB/d or 2.0 kg of WCGF/d for 110 d (DM basis), beginning at 10 mo of age. In Exp. 1, 100 crossbred heifers received either 1.25 kg of SB/d or 2.5 kg of WCGF/d from approximately 7 to 10 mo of age (91 d; 4 pens/diet), and then were fed 1.25 kg of SB/d for an additional 114 d (4 pens/diet). In Exp. 2, 1.25 kg of SB/d or 1.25 kg of DDG/d was fed to 100 crossbred heifers for 226 d, beginning at 6 mo of age (4 pens/diet). At approximately 13 mo of age, heifers were fed melengestrol acetate (0.5 mg/d) for 14 d, followed by an i.m. injection of PGF(2 alpha) (25 mg) 19 d later to synchronize estrus. Heifers (14 mo of age) received AI for 5 d after PGF(2 alpha), at which time the dietary treatments were ended. Heifers were commingled while grazing on native pasture and were exposed to bulls for approximately 60 d beginning 10 d after the last day of AI. Pregnancy to AI was determined by ultrasound 45 d after the last day of AI. Heifers fed SB in the preliminary experiment had a lower (P < 0.05) synchronization rate (81 vs. 96%) and longer interval (P = 0.05) from PGF(2 alpha) to estrus (76.6 vs. 69.2 h) compared with heifers fed WCGF. In Exp. 1, the age at which the heifers were begun on SB diets did not alter (P > 0.10) the synchronization rate (79%) or timing of estrus after PGF(2 alpha) (77.8 h). In Exp. 2, the synchronization rate (86%) and timing of estrus after PGF(2 alpha) (69.3 h) did not differ (P > 0.10) because of diet. No differences (P > 0.10) were due to diet for AI conception rates (overall mean for each experiment: 76.5, 60, and 68.5%), percentage of all heifers becoming pregnant to AI (67, 46, and 59%), or final pregnancy rates (92, 90, and 90%) in the preliminary experiment, Exp. 1, or Exp. 2, respectively. In summary, SB, DDG, and WCGF can be used as sources of protein in heifer development diets at the inclusion rates used in these studies.

Effect of prebreeding body weight or progestin exposure before breeding on beef heifer performance through the second breeding season.

Two experiments evaluated prebreeding target BW or progestin exposure for heifers developed lighter than traditional recommendations. Experiment 1 evaluated the effects of the system on heifer performance through subsequent calving and rebreeding over 3 yr. Heifers (229 kg) were assigned randomly to be developed to 55% of mature BW (299 kg) before a 45-d breeding season (intensive, INT; n = 119) or 50% of mature BW (272 kg) before a 60-d breeding season (relaxed, RLX; n = 142). Prebreeding and pregnancy diagnosis BW were greater (P 0.15) between systems. Cost per pregnant 2-yr-old cow was less for the RLX than the INT heifer development system. Of heifers that failed to become pregnant, a greater proportion (P = 0.07) of heifers in the RLX than in the INT system were prepubertal when the breeding season began. Therefore, a second 2-yr experiment evaluated melengestrol acetate (MGA, 0.5 mg/d) as a means of hastening puberty in heifers developed to 50% of mature BW. Heifers were assigned randomly to the control (n = 103) or MGA (n = 81) treatment for 14 d and were placed with bulls 13 d later for 45 d. Prebreeding and pregnancy diagnosis BW were similar (280 and 380 kg, respectively; P > 0.10) for heifers in the control and MGA treatments. The proportion of heifers pubertal before breeding (74%), pregnancy rate (90%), calving date, calf weaning weight, and second breeding season pregnancy rate (92%) were similar (P > 0.10) between treatments. Developing heifers to 50 or 55% of mature BW resulted in similar overall pregnancy rates, and supplementing the diets of heifers developed to 50% of mature BW with MGA before breeding did not improve reproductive performance.

Comparison of controlled internal drug release device and melengesterol acetate as progestin sources in an estrous synchronization protocol for beef heifers.

The objectives of this experiment were to compare estrous synchronization responses and AI pregnancy rates of beef heifers using protocols that included either CIDR or MGA as the progestin source. The hypotheses tested were that: (1) estrous synchronization responses after (a) progestin removal, and (b) PGF(2alpha); and, (2) AI pregnancy rates, do not differ between heifers synchronized with either progestin source. At the start of the experiment (Day 0) in both years, heifers were assigned randomly to receive, MGA supplement for 14 days (MGA-treated; n=79) or CIDR for 14 days (CIDR-treated; n=77). On Day 14 progestin was removed and heifers were observed for estrus up to and after PGF(2alpha) on Days 31 and 33 for CIDR-treated and MGA-treated heifers, respectively. Heifers that exhibited estrus within 60h after PGF(2alpha) were inseminated by AI 12h later; the remaining heifers were inseminated at 72h after PGF(2alpha) and given GnRH (100mug). More (P<0.05) CIDR-treated heifers exhibited estrus within 120h after progestin removal than MGA-treated heifers. Intervals to estrus after progestin removal were shorter (P<0.05) for CIDR-treated heifers than MGA-treated heifers. More (P<0.05) CIDR-treated heifers exhibited estrus and were inseminated within 60h after PGF(2alpha) than MGA-treated heifers. Pregnancy rates did not differ (P>0.10) between MGA-treated (66%) and CIDR-treated (62%) heifers. In conclusion, the use of CIDR as a progestin source in a 14-day progestin, PGF(2alpha), and timed AI and GnRH estrous synchronization protocol was as effective as the use of MGA to synchronize estrus and generate AI pregnancies in beef heifers.

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

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).

Motivation of hens to obtain feed during a molt induced by feed withdrawal, wheat middlings, or melengestrol acetate.

Traditionally, molting was initiated by withdrawing feed. However, public criticism of feed deprivation, based on the perception that it inhumanely increases hunger, has led the poultry industry to ban the practice. Thus far, alternatives have not been demonstrated to ameliorate the increase in hunger that led to the ban on inducing molting by feed deprivation. Incorporating melengestrol acetate (MGA), an orally active progestin, into a balanced layer diet induces molting and increases postmolt egg quality. Hy-Line W-98 hens (n = 60) were randomly assigned to a balanced layer ration (control), a balanced layer ration containing MGA, or a 94% wheat middlings diet (wheat) for 20 d, or were feed deprived for 8 d. Hens were trained to peck a switch to receive a feed reward based on a progressive ratio reinforcement schedule. Motivation of hens to acquire feed was measured as the total number of pecks recorded in 15 min on d 0, 4, 8, 12, 16, and 20. On d 20, abdominal fat pad and digesta-free gizzards were weighed. The number of pecks in the feed-deprived group was greater than controls by d 4 and remained greater at d 8, when these hens were removed from the experiment. Hens in the wheat group that were rewarded with a layer diet pecked more than controls from d 8 to 20. Hens in the MGA group pecked for a reward at the same rate as control hens throughout the experiment. Hens fed the wheat diet had heavier gizzards compared with control and MGA-fed hens. Hens fed MGA had greater abdominal fat pad compared with wheat and control hens. Hens molted using a diet containing MGA have a similar motivation to obtain feed as control hens; therefore, this alternative does not appear to increase hunger. However, hens molted with a wheat middling diet appear to be as motivated to obtain feed as did the feed-deprived hens.

Resynchronization of estrus in beef cattle: ovarian function, estrus and fertility following progestin treatment and treatments to synchronize ovarian follicular development and estrus.

The objective was to optimize rebreeding of nonpregnant, previously inseminated beef cattle. In Experiment 1, 43 cows received a used intravaginal progesterone-releasing insert (IVPRI; Days 0-7) 12.3 d after ovulation and received concurrently no treatment, 100 microg gonadotropin releasing hormone (GnRH), 1 mg estradiol cypionate (ECP), or 150 mg progesterone. Emergence of a new ovarian follicular wave was most synchronous (P < 0.0001) in the GnRH group. In Experiment 2, 675 heifers were given GnRH or no treatment on Day 0, fed melengestrol acetate (MGA; 0.5 mg/head/d) from Days 0-5 (Day 0 = 13-14 d after timed insemination; TAI), given 0.5 mg ECP or nothing on Day 7, and reinseminated 6-12 h after onset of estrus. Estrus was more synchronous (P < 0.05) in heifers given GnRH versus no treatment on Day 0. In Experiment 3, 317 TAI heifers were resynchronized with either MGA or a used IVPRI with or without ECP on Day 7; estrus was more synchronous (P < 0.05) and pregnancy rates were higher (54.1% versus 39.2%, P < 0.05) in heifers given a used IVPRI than those fed MGA. For resynchronization of heifers, pregnancy rates were not significantly improved with GnRH treatment, but were higher with a used IVPRI than with MGA.