Proton Compton Scattering from Linearly Polarized Gamma Rays.

Differential cross sections for Compton scattering from the proton have been measured at scattering angles of 55°, 90°, and 125° in the laboratory frame using quasimonoenergetic linearly (circularly) polarized photon beams with a weighted mean energy value of 83.4 MeV (81.3 MeV). These measurements were performed at the High Intensity Gamma-Ray Source facility at the Triangle Universities Nuclear Laboratory. The results are compared to previous measurements and are interpreted in the chiral effective field theory framework to extract the electromagnetic dipole polarizabilities of the proton, which gives α_{E1}^{p}=13.8±1.2_{stat}±0.1_{BSR}±0.3_{theo},ß_{M1}^{p}=0.2∓1.2_{stat}±0.1_{BSR}∓0.3_{theo} in units of 10^{-4} fm^{3}.

Assessment of ovulation synchronization protocols in goats and use of pregnancy specific protein B (PSPB) enzyme linked immunsorbent assay (ELISA) to determine kid number at birth.

The efficacy of several protocols for ovulation synchronization and timed artificial insemination (TAI) in goats was examined. In addition, the relationship between levels of pregnancy specific protein B (PSPB) during gestation assessed with a commercially available ELISA and the number of offspring at birth was determined. In Experiment 1, 70 does were randomized into four treatments: (1) breed by estrus [BBE], (2) 6-d treatment with a new [C6N], (3) once-used [C61], or (4) twice-used Controled Internal Drug Release (CIDR) device [C62)]. BBE does received two 15 mg doses of prostaglandin-F2α (PGF) at a 10-d interval and were bred 12 h after estrus onset. CIDR groups received a CIDR for 6 d with 15 mg PGF given at CIDR removal. TAI was performed 48 h after CIDR removal and does were given 50 µg GnRH. All does were inseminated with a single dose of frozen semen using a non-surgical, transcervical technique. Pregnancy rates for the BBE, C6N, C61 and C62 treatment groups were 39% ± 12%, 64% ± 12%, 77% ± 12% and 57% ± 12%, respectively, and did not differ. Reuse of CIDRs, even with reuse extending for a total of 21 d, was as effective as new CIDRs for synchronization of ovulation. In Experiment 2, 68 does were randomized into four treatments: (1) BBE, (2) C6N, (3) NC.Synch [NCS], (4) modified NCS [NCSM]. The BBE and C6N groups were as described for Experiment 1. The NCS and NCSM groups received 15 mg PGF on Day 1, 50 µg GnRH on Day 8 and 15 mg PGF on Day 15 (NCS) or Day 15.5 (NCSM). Does were bred by TAI at 72 h (NCS) or 60 h (NCSM) after the second PGF injection. All does in the NCS and NCSM groups received 50 µg GnRH at TAI. Pregnancy rates were 53% ± 12%, 30% ± 11%, 50% ± 11% and 41% ± 12% for does in the BBE, C6N, NCS and NCSM group, respectively, and did not differ. In Experiment 3, 62 does pregnant to TAI were bled at Days 48 and 85 post-insemination for PSPB. Data on kid numbers and birth weights were subsequently recorded. At Day 48 of gestation, PSPB levels for does birthing singletons were lower than for does birthing twins or triplets (25.0 ± 0.1a, 28.8 ± 0.1b and 30.7 ± 0b ng/mL, respectively, abP<0.05). At Day 85 of gestation, PSPB levels were progressively greater for does birthing singletons versus twins versus triplets (27.0 ± 0.1a, 28.5 ± 0.1b and 31.6 ± 0c ng/mL, abcP<0.05). In conclusion, PSPB concentrations detected using a commercially available ELISA at Day 48 or 85 of gestation could distinguish does carrying single versus multiple fetuses.

Beam-Target Helicity Asymmetry for γ[over →]n[over →]→π

We report the first beam-target double-polarization asymmetries in the γ+n(p)→π^{-}+p(p) reaction spanning the nucleon resonance region from invariant mass W=1500 to 2300 MeV. Circularly polarized photons and longitudinally polarized deuterons in solid hydrogen deuteride (HD) have been used with the CEBAF Large Acceptance Spectrometer (CLAS) at Jefferson Lab. The exclusive final state has been extracted using three very different analyses that show excellent agreement, and these have been used to deduce the E polarization observable for an effective neutron target. These results have been incorporated into new partial wave analyses and have led to significant revisions for several γnN^{*} resonance photocouplings.

Site of PGF2α injection does not alter effectiveness of the Select Synch + controlled internal drug release and timed artificial insemination protocol.

Beef Quality Assurance programs have contributed to significant improvements in the wholesomeness of beef available for consumption. Injection site blemishes in the round have declined since the promotion of administering intramuscular injections in the neck. Unfortunately, many producers continue to administer estrus synchronization (ES) drugs in the rump. The objective of this study was to compare the effectiveness of injection site of PGF2α, in ES protocols, on steroid hormone concentrations and pregnancy rates. A Select Synch + 7-day controlled internal drug release ES protocol was conducted with the site of PGF2α injection alternated between neck and rump in beef cattle (n = 312) at the Ohio State University Agricultural Technical Institute and North Carolina State University. Blood samples (n = 75) were collected at controlled internal drug release insertion and at the time of artificial insemination (AI) to determine if progesterone (P4) and estrogen (E2) concentrations varied due to PGF2α injection site. All cattle were confirmed pregnant by ultrasonography at approximately 30 and 90 days after insemination in North Carolina and approximately 70 days after insemination in Ohio. Data were analyzed as randomized complete block designs in PROC GLIMMIX with animal as the experimental unit. Differences were declared significant at P < 0.05. Site of PGF2α injection, in either the neck or rump, did not affect (P > 0.05) overall conception rates in response to AI (58.4% and 55.6%, respectively). Altering PGF2α injection site did not impact P4, E2 concentrations, or the P4:E2 ratio at AI (P > 0.05). However, cattle inseminated after displaying estrus had greater (P < 0.05) pregnancy rates than timed AI (67.8 vs. 47.5%, respectively). First service conception rates and pregnancy rates were consistent with previous reports. Overall, altering the location of the PGF2α injection during ES did not change circulating hormone concentrations at AI or pregnancy rates; therefore, cattle producers should follow Beef Quality Assurance guidelines when administering ES protocols.

Comparison of pregnancy rates in beef cattle after a fixed-time AI with once- or twice-used controlled internal drug release devices.

The use of fixed-time artificial insemination (FTAI) provides producers with numerous benefits including the use of superior genetics, shorter breeding and calving seasons, and a more uniform calf crop. However, the cost of implementing FTAI protocols is one of the several drawbacks hindering their use in the beef industry. Potential injection-site lesions from intramuscular injections of the hormones necessary for estrus synchronization are also a cause of concern for carcass quality. The objectives of this experiment were to (1) determine whether or not a twice-used controlled internal drug release (CIDR) device would be effective in an FTAI protocol without adversely affecting pregnancy rate and (2) whether or not the subcutaneous administration of PGF2α affects pregnancy rate. Nulliparous females (n = 99) between 13 and 27 months of age and multiparous cows (n = 43) between 48 and 74 months of age were synchronized for estrus using the 7-day CO-Synch + CIDR protocol. The females were randomly assigned to one of the two treatments: (1) a once-used CIDR (control) or (2) a twice-used CIDR device (treatment) incorporated into their synchronization protocol. The females were also randomly assigned to have their injection of PGF2α administered either intramuscularly or subcutaneously. Blood was taken in a random subset of nulliparous females (n = 52) just before device removal and assayed for concentration of progesterone. The concentration of progesterone was higher (P = 0.01) in the animals that received once-used CIDR devices than that in those received twice-used CIDR devices (3.4 ± 0.5 and 1.4 ± 0.5 ng/mL, respectively). There was no significant effect of parity (P = 0.82), artificial insemination technician (P = 0.60), PGF2α administration (P = 0.83), or treatment (P = 0.67) on pregnancy rates to artificial insemination which were 75.4 ± 6.0% and 71.7 ± 6.4%, for animals that received once- and twice-used CIDR devices, respectively. This study provides evidence that although concentration of progesterone is decreased in animals treated with a twice-used CIDR device, there is still a sufficient release of progesterone from the device to effectively synchronize estrus without adversely affecting the fertility of a herd.

Maternal serum progesterone concentration and early conceptus development of bovine embryos produced in vivo or in vitro.

The hormone progesterone is essential for proper embryonic development. The objective of this study was to examine the relationship between recipient serum concentrations of progesterone, at the time of embryo transfer and at conceptus recovery, on conceptus development from in vivo- or in vitro-produced embryos. Embryos were produced in vivo by superovulation of Holstein cows (IVO; n = 17) or in vitro with either serum-containing (IVPS; n = 27) or serum-restricted medium (IVPSR; n = 34). Single grade I blastocysts from each embryo production system were transferred into heifers on day 7 of development. Conceptuses were recovered on day 17 of gestation and classified as complete, degenerated, or no conceptus. Compared with the IVO group, in vitro-produced embryos had more (P = 0.055) degenerated conceptuses (IVO, 0%; IVPS, 18.5%; and IVPSR, 20.6%). There were no differences in progesterone concentrations at the time of transfer when recipients received either male or female embryos (P > 0.05). Progesterone concentrations in recipients receiving in vivo-produced embryos were higher (P < 0.05; 3.74 ± 0.4 ng/mL; least-squares mean ± standard error of the mean) on day 7 compared with those receiving in vitro-produced embryos (IVPS, 2.4 ± 0.2; IVPSR, 2.58 ± 0.3 ng/mL). However, there was no difference in progesterone concentration on day 7 between treatment groups for heifers from which short conceptuses (≤194 mm) were recovered on day 17. In contrast, when longer (>194 mm) conceptuses were recovered on day 17, heifers receiving in vitro-produced embryos had lower (P = 0.05) serum concentrations of progesterone on day 7 compared with those receiving in vivo-produced embryos (IVPS, 2.2 ± 0.5; IVPSR, 2.3 ± 0.5; IVO, 3.9 ± 0.5 ng/mL). In conclusion, differences in autonomy may exist between in vitro- and in vivo-produced embryos during the period of conceptus elongation with in vitro-produced embryos relying more on intrinsic factors to influence elongation.

Antiluteogenic effects of serial prostaglandin F2α administration in cycling mares.

A single dose of PGF2α does not consistently induce luteolysis in the equine CL until at least 5 days after ovulation, leading to the erroneous assumption that the early CL is refractory to the luteolytic effects of PGF2α. We hypothesized that serial administration of PGF2α in early diestrus would induce a return to estrus similar to mares treated with a single injection in mid-diestrus, and fertility of the induced estrus would not differ. The objectives of the study were to evaluate the effects of the 2 approaches as reflected by: (1) concentrations of plasma progesterone; (2) interovulatory and treatment-to-ovulation intervals; (3) the proportion of mares pregnant after artificial insemination. The study consisted of a balanced crossover design in which 10 reproductively normal Quarter Horse Mares were exposed to 2 treatments on 2 consecutive reproductive cycles. At detected ovulation (Day 0), mares were randomly allotted to 1 of 2 treatment groups: I, mid-diestrus treatment, administration of a single 10-mg dose of dinoprost tromethamine (PGF2α) im on Day 10; II, early diestrus treatment, administration of 10-mg PGF2α im twice daily on Days 0, 1, and 2 and once daily on Days 3 and 4. Mares in estrus and with a follicle 35 mm or greater in diameter were artificially inseminated with at least 2 billion motile sperm from a fertile stallion. Pregnancy was defined as detection of a growing embryonic vesicle on 2 consecutive examinations approximately 14 days after ovulation. Serial plasma samples were collected throughout the study period, and concentration of plasma progesterone was determined by RIA. A mixed-model ANOVA for repeated measures was used to analyze hormonal data. Interovulatory and treatment-to-ovulation intervals were compared by a paired t test and fertility by a McNemar chi-square analysis. All mares in group I underwent luteolysis after PGF2α administration denoted by mean (±SD) concentration of plasma progesterone of 0.25 ± 0.21 ng/mL detected 2 days after treatment. In group II, mean concentration of plasma progesterone remained below 1.0 ng/mL during treatment and until the onset of the next estrus. The mean interovulatory interval in group I was 18.5 ± 2.0 days compared with 13.1 ± 3.7 days in group II (P < 0.01). Treatment-to-ovulation intervals were 8.5 ± 2.0 days and 13.1 ± 3.7 days for groups I and II, respectively (P < 0.05). In both groups, 9 of 10 mares were pregnant (P = 1.0). Serial PGF2α administration beginning at ovulation consistently prevented luteal function in 10 of 10 mares in the present study without adversely affecting pregnancy rate of post-treatment cycles.

Chromium propionate enhances insulin sensitivity in growing cattle.

Thirty-six Angus and Angus×Simmental heifers, averaging 291 kg, were used to determine the effects of dietary Cr, in the form of Cr propionate (Cr Prop), on glucose metabolism and serum insulin concentrations following glucose administration. Heifers were stratified by body weight (BW) within a breed and randomly assigned to treatments. Treatments consisted of 0, 3, 6, or 9 mg of supplemental Cr/d from Cr Prop. Based on dry matter (DM) intakes, the daily doses of Cr were equivalent to 0.47, 0.94, and 1.42 mg of supplemental Cr/kg of DM. Heifers were individually fed a corn silage-based diet at a level of 2% of BW. Each heifer was also fed 0.45 kg of a ground corn supplement daily that served as a carrier for supplemental Cr. Glucose tolerance tests were performed on d 44 of the study. Glucose was infused via jugular catheters at a level of 0.45 g/kg of BW(0.75) over a course of 1 to 2 min. Blood samples were collected at -10, 0, 5, 10, 15, 30, 45, 60, 90, 120, 150, and 180 min relative to glucose dosing for glucose and insulin determination. Area under the glucose response curve was lower (1,603 vs. 1,964 mg/dL per minute) in heifers supplemented with Cr from 0 to 45 min following glucose challenge. Serum insulin concentrations were lower in Cr-supplemented heifers than in controls following glucose infusion. The molar ratio of insulin to glucose was also lower in Cr-supplemented heifers relative to controls. Serum insulin and serum insulin to glucose ratios did not differ among heifers supplemented with 3, 6, or 9 mg of Cr/d. Results indicate that Cr Prop supplementation increased tissue sensitivity to insulin in growing heifers. Based on insulin sensitivity, Cr requirements (as Cr Prop) of growing heifers can be met by supplementing with 3 mg of Cr/d or 0.47 mg of Cr/kg of DM.

Effects of stress associated with weaning on the adaptive immune system in pigs.

This study was designed to investigate the effects of weaning age on specific components of the adaptive immune system in pigs. Twenty-three crossbred pigs were randomly assigned to 1 of 3 treatments: weaning at 14 (14D, n = 8), 21 (21D, n = 7), or 28 (28D, n = 8) d of age. Peripheral blood samples, obtained when pigs were 13, 15, 20, 22, 27, 29, and 35 d of age, were analyzed for peripheral blood cell percentages and concentrations of neutrophils, lymphocytes, T cell subsets, mature B cells, and plasma cortisol concentrations. For each of the 3 groups, weaning increased plasma cortisol concentrations (P < 0.001) and reduced BW percentage change (P < 0.017). Lymphocyte concentrations displayed a treatment effect for the 14D (P = 0.074) and 28D (P = 0.014) groups. Albeit inconsistent, lymphocyte concentrations were less in weaned pigs on the day after weaning than in pigs remaining on the sow or weaned at a younger age. Specifically, mature B cells (CD21(+)) and CD4(+)CD8(+) cells decreased (P < 0.05) after weaning at 28 d of age. Other differences occurred among treatments; however, the differences apparently were not associated with weaning. Based upon the immunological measures used in the present study, there was not an explicit benefit to the adaptive immune system for any weaning age. Early weaning did not negatively affect the adaptive immunological competence of pigs as determined by changes in populations of immune cells.

Measuring the relative concentration of H2 and D2 in HD gas with gas chromatography.

Frozen-spin polarized hydrogen deuteride (HD) targets are being prepared for photonuclear experiments at Jefferson Lab. The targets are frozen HD gas. To polarize and achieve the required spin-lattice relaxation times, the targets are made from high purity HD gas in which the residual H(2) and D(2) concentrations are known. To determine these residual concentrations, a gas chromatograph is used. The separation of the gas components is done in a column cooled to ≈120 K by immersing it in a mixture of liquid nitrogen and isopentane and using neon as the carrier gas. The different hydrogen isotopes have different transit times through the column and their arrival is registered by a thermal conductivity detector. The peaks in the chromatograms are fit using an exponentially modified Gaussian line shape to extract the areas of these peaks. The ratios of areas are corrected for differences in thermal conductivity to give the relative concentrations. Here, H(2) and D(2) concentrations on the order of a few percent have been measured with uncertainties of less than ± 5%. The linear response of the system is confirmed to within about ± 6.3%.

Effects of feeding pattern on ghrelin and insulin secretion in pigs.

Ghrelin is a peptide hormone that has been implicated in the regulation of feed intake, but little is known about its secretion in pigs. Hence, the effect of feeding pattern on the regulation of ghrelin secretion was tested. In experiment 1, barrows were allotted randomly into 1 of 2 groups, (1) ad libitum fed (CONT) and (2) limited access to feed (once per day, MEAL). Blood samples were taken through jugular catheters every 15 min for 6 h after 7 d on the experimental feeding regimen. Plasma concentrations of ghrelin and insulin were determined by radioimmunoassay. Ghrelin concentrations in the MEAL pigs were elevated before feeding and declined after feeding (P < 0.01). No pattern in plasma ghrelin concentrations was observed in the CONT pigs, but ghrelin concentrations were lower than in the MEAL group. Insulin concentrations were greater in CONT pigs (P < 0.01) during most of the sampling and increased after feeding in the MEAL pigs (P < 0.01). In experiment 2, the treatments were the same as in experiment 1; however, the amount of feed was increased in the MEAL group so that their daily intake was similar to the CONT pigs. Ghrelin concentrations in the MEAL group were again elevated before the meal and declined afterward (P < 0.01). Insulin but not glucose concentrations were negatively correlated with ghrelin. Once-per-day feeding resulted in increased plasma concentrations of ghrelin, which decreased after feeding. Ghrelin may be involved in the regulation of feed intake in pigs.

Measurements of H-->D-->(gamma-->,pi) and implications for the convergence of the Gerasimov-Drell-Hern integral.

We report new measurements of inclusive pi production from frozen-spin HD for polarized photon beams covering the Delta(1232) resonance. These provide data simultaneously on both H and D with nearly complete angular distributions of the spin-difference cross sections entering the Gerasimov-Drell-Hearn (GDH) sum rule. Recent results from Mainz and Bonn exceed the GDH prediction for the proton by 22 microb, suggesting as yet unmeasured high-energy components. Our pi0 data reveal a different angular dependence than assumed in Mainz analyses and integrate to a value that is 18 microb lower, suggesting a more rapid convergence. Our results for deuterium are somewhat lower than published data, considerably more precise, and generally lower than available calculations.

Pharmacokinetics of carbetocin, a long-acting oxytocin analogue, following intravenous administration in horses.

REASON FOR PERFORMING STUDY: Current therapy protocols to treat persistent post mating endometritis and retained fetal membranes in mares typically include the administration of ecbolic drugs. Evaluation of the pharmacokinetics and tolerability of carbetocin, a long-acting oxytocin analogue, after i.v. administration is required. OBJECTIVES: To determine the pharmacokinetic parameters (principally half-life) of carbetocin in horses. METHODS: Five mature mares and one gelding received 0.175 mg carbetocin i.v. All animals were monitored periodically throughout the study for elevation in rectal temperature, heart rate, respiratory rate and signs of pain or discomfort. Plasma samples were collected for determination of carbetocin concentrations by radioimmunoassay. RESULTS: Administration of carbetocin was well tolerated by all horses and its half-life was 17.2 min. CONCLUSIONS: The half-life of carbetocin is greater than that previously reported for oxytocin (6.8 min). POTENTIAL RELEVANCE: Carbetocin is an attractive alternative to oxytocin therapy in broodmare management.

Growth, reproductive performance, and manganese status of heifers fed varying concentrations of manganese.

An experiment was conducted to examine the effects of dietary Mn on growth, reproductive performance, and Mn status of beef heifers. Eighty Angus (n = 40) and Simmental (n = 40) heifers, averaging 249 kg, were stratified by BW within a breed and randomly assigned to 1 of 4 treatments providing 0 (control), 10, 30, or 50 mg of supplemental Mn/kg of DM from MnSO(4). Heifers were individually fed a diet containing cottonseed hulls, corn gluten feed, citrus pulp, and ground corn, and the control diet contained 15.8 mg of Mn/kg of DM by analysis. Average daily gain, DMI, and G:F for the 196-d period were not affected by Mn supplementation. Control heifers had reduced (P = 0.04) liver Mn when contrasted with the 3 levels of supplemental Mn. Serum cholesterol was greater (P = 0.001) in Angus compared with Simmental heifers over the course of the 196-d experiment but was not affected by treatment. Dietary Mn did not significantly affect measures of reproductive performance. Results of this study indicate that 15.8 mg of Mn/kg of diet DM should be adequate for growth, onset of estrus, and conception of beef heifers.

Feeding a low manganese diet to heifers during gestation impairs fetal growth and development.

A study was conducted to examine the effects of low dietary Mn on growth performance of pregnant heifers and fetal development of their offspring. Twenty pregnant Angus (n = 9) and Simmental (n = 11) heifers averaging 17 mo of age and 447.6 kg of initial body weight were used in the 267-d study. Heifers were selected from a previous study examining the effects of supplemental Mn on growth and reproductive performance of heifers. Ten pregnant heifers per treatment from the control (analyzed at 15.8 mg of Mn/kg of DM) and supplemental Mn (50 mg/kg of DM) treatments were randomly selected at the conclusion of the previous study to continue on their respective dietary treatments through gestation and early lactation. Serum cholesterol for the 267-d period was not affected by treatment. Whole-blood Mn concentration of heifers on d 267 was not affected by treatment. Whole-blood Mn concentration at birth was lower in calves born to control heifers than in those born to supplemented heifers. Calves born to control heifers weighed less at birth than those born to heifers receiving supplemental Mn. Calves born to control heifers suffered from varying signs of Mn deficiency, including superior brachygnathism, unsteadiness, disproportionate dwarfism, and swollen joints. Results suggest that feeding gestating heifers a diet containing 16.6 mg of Mn/kg of DM is not adequate for proper fetal development. Supplementation of 50 mg of Mn/kg of DM to the control diet was sufficient to overcome any signs of Mn deficiency in calves.

Pigs weaned from the sow at 10 days of age respond to dietary energy source of manufactured liquid diets and exogenous porcine somatotropin.

Previous research indicates that the neonatal pig does not alter feed intake in response to changes in the energy density of manufactured liquid diets. Also, the limited response of IGF-I to exogenous porcine ST (pST) previously observed in young pigs may be influenced by the source of dietary energy. Our objectives were to 1) determine the effect of a high-fat (HF; 25% fat and 4,639 kcal/kg ME; DM basis) or low-fat (LF; 2% fat and 3,481 kcal/kg ME; DM basis) manufactured liquid diet on pig performance; and 2) determine whether the limited response to exogenous pST in young pigs depends on the source of dietary energy. Two replicates of 60 pigs (n = 120; barrows and gilts distributed evenly), with an initial BW of 4,207 +/- 51 g, were weaned from the sow at 10 d of age and used in a randomized complete block design. Pigs were assigned by BW to one of six pens. Diets were formulated to provide a constant lysine:ME ratio and were fed on a pen basis for a duration of 9 d. On d 5, barrows and gilts within a pen were assigned randomly to receive either 0 or 120 microg of pST.kg BW(-1).d(-1) for 4 d. Pigs gained 336 +/- 9 g/d, which resulted in an ending BW of 7,228 +/- 120 g, regardless of dietary treatment (P > 0.15). Pigs fed the LF diet consumed 17% more DM per pen daily than pigs fed the HF diet (2,777 +/- 67 vs. 2,376 +/- 67 g/d, P < 0.01), but calculated ME intake did not differ between dietary treatments (P > 0.20). The G:F was 24% greater in HF- than in LF-fed pigs (P < 0.01). Plasma urea N concentrations were higher in the HF-fed pigs (11.0 +/- 0.6 mg/dL) than in pigs fed the LF diet (6.2 +/- 0.6 mg/dL; P < 0.05). Treatment with pST increased circulating IGF-I (P < 0.01) and decreased PUN (P < 0.01) concentration 32 and 25%, respectively, regardless of dietary treatment (P > 0.30). Circulating leptin averaged 1.8 +/- 0.1 ng/mL and was not affected by dietary treatment (P > 0.35) or pST (P > 0.40). These results suggest that the ST/IGF axis is responsive in the young pig and the increase in circulating IGF-I and growth is independent of the source of dietary energy. Also, young pigs respond to a lower energy density liquid diet with increased feed intake, without altering growth performance, apparently utilizing a mechanism other than circulating leptin.

Effect of divergent selection for testosterone production on testicular morphology and daily sperm production in boars.

The objective of this study was to characterize correlated responses in testicular morphology and daily sperm production to divergent selection for testosterone production. Duroc boars from high and low lines (HTL and LTL, respectively) divergently selected over 10 generations for testosterone production in response to a GnRH challenge followed by random selection were used. Testicular tissues were sampled from all available males of generation 20 (HTL, n = 46; and LTL, n = 13). Volume densities for Leydig cells, seminiferous tubules, and Sertoli cells were estimated along with sperm production. The HTL boars had greater volume densities of Leydig cells than did LTL (P < 0.01). Volume density of seminiferous tubules tended to differ between lines (P < 0.07), but Sertoli cell volume densities did not differ (P < 0.27). Sperm production traits, adjusted for age, did not differ significantly between lines. Body, testicular, and epididymal weights were recorded for boars from HTL (n = 82) and LTL (n = 44) from generations 20 and 21. After adjustment for BW, average paired testicular weights for HTL and LTL were 417 and 457 g (P < 0.01), respectively. Epididymal weights, adjusted for BW, were heavier for HTL (P < 0.01) than for LTL. To demonstrate that the selection lines still differed for testosterone production, lines were evaluated in generation 21. Endogenous testosterone production of the HTL (n = 54) and LTL (n = 44) testosterone production line averaged 49.0 ng/mL and 27.8 ng/mL (P < 0.01), respectively. Plasma FSH concentrations did not differ between lines (P < 0.30). Selection for testosterone production in response to a GnRH challenge was an effective method of changing testosterone concentrations, testicular size, epididymal weight, and volume density of Leydig cells. However, daily sperm production per gram of testes was unchanged. Based on the results of this study, selection for testosterone production is not recommended as a method of increasing sperm production in pigs.

The effects of GnRH administration postinsemination on serum concentrations of progesterone and pregnancy rates in dairy cattle exposed to mild summer heat stress.

The objective of this study was to evaluate whether administration of GnRH postinsemination would improve reproductive performance in heat-stressed dairy cattle. Estrous cycles of Holstein cows were synchronized using the OvSynch protocol and cows were artificially inseminated. Cows were then administered the following treatments: control (no GnRH; n=37), GnRH (100 microg) on Day 5 (GnRH-D5; n=34), or GnRH (100 microg) on Day 11 (GnRH-D11; n=34) postinsemination. Cows were provided access to both fans and sprinklers, and environmental data was collected hourly. Rectal temperatures and blood samples were obtained from cows on Days -9, -2, 0 (AI) and on alternate days from Day 5 to Day 19 postinsemination. Blood serum was collected for the analysis of progesterone (P(4)) by RIA. In a subset of cows (n=6/treatment) ultrasonography was performed on alternate days from Day 5 to Day 19 postinsemination to assess numbers of corpora lutea (CL) and CL cross-sectional areas. Pregnancy status of cows was confirmed at Day 30 postinsemination. Environmental data indicated that cows experienced mild heat stress during the trials (mean daily THI=73-77). Serum P(4) was greater (P<0.05) after Day 9 for GnRH-D5 cows and after Day 15 for GnRH-D11 cows through Day 19 postinsemination. The number of CLs present for GnRH-D5 cows was greater (P<0.05) on Day 17 than in either the control or GnRH-D11 treatment groups. On Day 17 postinsemination, both the GnRH-D5 and GnRH-D11 cows were observed to have greater (P<0.05) total CL tissue area than control cows. The interval from insemination to when serum P(4) returned to <1 ng/ml (i.e. luteolysis and return to estrus) did not differ (P>0.10) among treatment groups. Control cows (19%) tended to exhibit lower pregnancy rates (P<0.08) compared to the GnRH-D5 and GnRH-D11 treatment groups combined (35%). In summary, the treatment of heat-stressed dairy cows with GnRH postinsemination (Day 5 or 11) results in the appearance of more CL tissue, increased serum concentrations of P(4) and a tendency toward greater pregnancy rates.

Evaluation of steroid microspheres for control of estrus in cows and induction of puberty in heifers.

Two trials were designed to test whether a single treatment with a microsphere formulation of progesterone (P) could simulate the luteal phase of the estrous cycle and lead to estrus and subsequent luteal development. The first experiment was to characterize the pattern of serum P concentrations and estrus in cows treated with a microsphere formulation (P + E) that contained 625 mg P and 50 mg estradiol (E). Four cows with palpable corpora lutea were treated with 25 mg prostaglandin F2 m. Each cow was given P + E (i.m.) 12 h later. Tail vein blood samples were taken on Days 1 and 2 following P + E treatment and then three times weekly for 24 days. Serum P increased from 0.8 +/- 0.1 ng/ml at P + E treatment to 4.7 +/- 0.6 ng/ml on Day 1, declined gradually to 4.1 +/- 0.3 ng/ml on Day 7 and then declined more rapidly to 0.6 +/- 0.1 ng/ml on Day 13. Treated cows showed estrus 16.25 +/- 0.7 days after P + E treatment. Thereafter, serum P increased beginning on Day 20 after P + E treatment, as expected following estrus. In Experiment 2, Angus and Simmental heifers (10.5-11.5 months of age) were administered i.m. either the vehicle (controls), E (50 mg), P (625 mg) or P + E (n = 13 per group). While treatment with E resulted in behavioral estrus (1-2 days after treatment) in each treated heifer, it did not (P > 0.5) initiate estrous cycles as indicated by subsequent increased serum P. In contrast, the P and P + E treatments increased (P < 0.05) the proportion (11/13) of heifers that showed estrus by 21 days after treatment followed by elevated serum P. We conclude that the microsphere formulation of P simulated the pattern of serum P concentrations during the luteal phase of the estrous cycle and initiated estrous cycles in peripubertal heifers with or without E.

Effect of short-term feed restriction and refeeding on serum concentrations of leptin, luteinizing hormone and insulin in ovariectomized gilts.

Ovariectomized gilts were either placed on full feed (FF) or restricted to one-third of the full feed amount (RST) for 7 days. Blood samples were taken through jugular catheters every 15 min for 4 h at the end of the 7-day period. Then dietary treatments were reversed and 7 days later samples were taken as before. Serum concentrations of leptin, insulin and luteinizing hormone (LH) were determined by radioimmunoassay. LH pulse frequency and mean serum leptin and insulin concentrations were lower (P < 0.01) in RST than FF gilts. Reversal of treatment reversed the patterns of hormone secretion. These results confirm previous observations that feed restriction can inhibit pulsatile LH secretion and also decrease leptin and insulin secretion.