Office of the President Scholarship Copyright (c) 2013 California Polytechnic State University All rights reserved. http://digitalcommons.calpoly.edu/pres_schol Recent documents in Office of the President Scholarship en-us Fri, 25 Jan 2013 20:17:58 PST 3600 Developing Course Materials Using The World Wide Web http://digitalcommons.calpoly.edu/pres_schol/17 http://digitalcommons.calpoly.edu/pres_schol/17 Tue, 29 Nov 2011 08:14:22 PST The World Wide Web provides a powerful new resource for education in agriculture and the life sciences. This article describes some development tools and strategies employed by the College of Agriculture & Life Sciences at North Carolina State University to help teaching faculty to develop and explore new educational methodologies that take advantage of the Web and other emerging technologies.

]]> Mike O'Kane et al. The Teaching and Advising Portfolio: A Guide for NACTA Members http://digitalcommons.calpoly.edu/pres_schol/16 http://digitalcommons.calpoly.edu/pres_schol/16 Tue, 29 Nov 2011 08:14:18 PST Bryce H. Lane et al. Insulin-like Growth Factor-I (IGF-I) and IGF Binding Proteins: Potential Mediators of the Influence of Nutrition on Ovarian Function in the Heifer and Gilt http://digitalcommons.calpoly.edu/pres_schol/15 http://digitalcommons.calpoly.edu/pres_schol/15 Thu, 25 Aug 2011 14:34:00 PDT Nutrition influences age at puberty, duration of postpartum anestrus, and ovulation rate. Mechanisms mediating these effects, however, have not as yet been fully elucidated. Shifts in feed intake are accompanied by changes in circulating levels of insulin-like growth factor-I (lGF-I), and somatotropin (ST). Feed restriction increases ST, decreases IGF-l, and shifts the proportions of IGF binding proteins (IGFBP). Active immunization against growth hormone releasing factor (GRFi) has been used to examine the effects of alterations in the somatotropic axis, independent of feed intake, on reproduction in prepubertal gilts and heifers. GRFi decreased the number of large follicles present on the ovaries prior to puberty, delayed onset of puberty in heifers, and decreased ovulation rate in gilts. GRFi altered follicular turnover in prepubertal heifers. Replacement therapy with somatotropin restored follicle numbers. GRFi decreased serum and follicular fluid IGF-I and IGFBP-3 and increased IGFBP2. Feed restriction also reduced IGF-I in follicular fluid. We speculate that the population of follicles affected by GRFi or feed restriction is related to their sensitivity to IGF-I. Possibly, alterations of ovarian or peripheral IGF-I at critical times during prepubertal follicular growth result in decreased follicle numbers, culminating in delayed onset of puberty in heifers and decreased ovulation rate in gilts.

]]> A.M. Benoit et al. Endocrine Events Prior to Puberty in Heifers: Role of Somatotropin, Insulin-Like Growth Factor-I and Insulin-Like Growth Factor Binding Proteins http://digitalcommons.calpoly.edu/pres_schol/14 http://digitalcommons.calpoly.edu/pres_schol/14 Thu, 25 Aug 2011 14:33:53 PDT We have utilized active immunization against growth hormone releasing factor (GRF) to investigate relationships among somatotropin (ST), insulin-like growth factor-I (IGF-I), IGF binding proteins (IGFBP) and ovarian function in heifers. Active immunization against GRF (GRFi) has been demonstrated to abolish episodic release of ST and decrease serum concentrations of IGF-I. In initial experiments investigating onset of puberty, breeds of heifers differing in growth rate and reproductive traits (Angus, Charolais and Simmental) were immunized against GRF or served as controls (immunized against carrier protein, human serum albumin, HSAi). GRFi decreased rate of muscle and skeletal growth, but increased deposition of adipose tissue. In Angus and Charolais, but not Simmental heifers, GRFi at 6 mo of age significantly delayed onset of puberty beyond 18 mo of age. Retrospective analyses of serum IGF-I revealed that GRFi heifers reaching puberty at a normal age had greater pre-treatment (6 mo of age) IGF-I than GRFi heifers in which puberty was delayed. Collectively, these results strongly indicate that the bovine hypothalamic-hypophyseal-ovarian axis is particularly sensitive to changes in metabolism at or near 6 mo of age.

Another series of experiments tested the hypothesis that lowering serum IGF-I via GRFi initially at 3 mo of age would increase the percentage of Angus and Simmental heifers not reaching puberty. Three mo old Angus and Simmental heifers were assigned to GRFi (n = 18), HSAi (n = 14) or received no treatment (controls, n = 16). HSAi and GRFi heifers were unilaterally ovariectomized (ULO) at 6 mo of age. As anticipated, GRFi at a younger age increased percentage of heifers not reaching puberty; over 75% of control and HSAi heifers reached puberty by 14 mo.of age compared to 22% of GRFi heifers. Serum and follicular fluid (FFL; follicles ≤ 4 mm) concentrations of IGF-I were suppressed by GRFi. Serum, but not FFL concentrations of IGF binding protein-2 (IGFBP-2) were greater in GRFi than in HSAi heifers. GRFi delayed puberty apparently by suppressing follicular growth because number of follicles ≤7 mm was significantly lower in GRFi than in HSAi heifers. In conclusion, active immunization against GRF at 3 or 6 months of age delays puberty in beef heifers. Delayed puberty was preceded by suppression of follicular growth, and decreased concentrations of IGF-I in serum and follicular fluid. Collectively, these studies demonstrate that ovarian function between 3 and 8 mo of age and subsequent onset of puberty are particularly sensitive to changes in the ST-IGF-I axis.

]]> Jeffrey D. Armstrong et al. Pulsatile Administration of Gonadotropin-releasing Hormone to Anestrous Sows: Endocrine Changes Associated with GnRH-induced and Spontaneous Estrus http://digitalcommons.calpoly.edu/pres_schol/13 http://digitalcommons.calpoly.edu/pres_schol/13 Tue, 09 Aug 2011 16:02:18 PDT This experiment determined whether pulsatile administration of gonadotropin-releasing hormone (GnRH) would induce estrus and ovulation in seasonally anestrous primiparous sows and compared endocrine responses of GnRH-induced sows with those of primiparous sows that exhibited spontaneous estrus after weaning. Seventeen primiparous Landrace X Large White sows farroed in August 1982, lactated 23.8 ± 0.4 days (mean ± SEM), and weaned 9.0 ± 0.3 pigs per litter. Blood for determination of progesterone, luteinizing hormone (LH), and estradiol-17β (E) was collected every 6 h from 1 day before to 12 days after weaning. Twelve sows exhibited spontaneous estrus 135 ± 9 h after weaning, and these sows were considered to be normal. Five sows were anestrous for at least 23 days postweaning and failed to ovulate, as indicated by concentrations of progesterone that were less than 1.0 ng/ml in blood samples collected daily during this period. From Day 0 to Day 30 postweaning, levels of estradiol in anestrous sows varied between 3 and 30 pg/ml, concentrations of LH were low, and preovulatory-like LH surges did not occur. Beginning on Day 30 postweaning, four anestrous sows were given 1.5 µg GnRH (i.v.) hourly until onset of estrus and blood was collected every 6 h during GnRH treatment. The average interval from beginning of GnRH treatment to onset of estrus was 84 ± 5 h (range 72 to 96 h). Patterns of estradiol and LH secretion around estrus were similar in normal sows and those treated with GnRH. Estradiol remained elevated above basal concentrations (25 pg/ml) for 49.6 ± 4.0 h in normal sows compared to 48.0 ± 0 h in GnRH-treated sows. Average interval (h) from peak estradiol to the preovulatory LH surge was similar in normal (23.5 ± 4.2) and GnRH-induced sows (18.0 ± 4.2). We conclude the administration of hourly pulses of GnRH to weaned anestrous primiparous sows imposed a proper stimulation to the anterior pituitary that in turn led to an increased gonadotropin secretion that induced estrus and ovulation.

]]> Jeffrey D. Armstrong et al. Seasonal Differences in Function of the Hypothalamic-Hypophysial-Ovarian Axis in Weaned Primiparous Sows http://digitalcommons.calpoly.edu/pres_schol/12 http://digitalcommons.calpoly.edu/pres_schol/12 Tue, 09 Aug 2011 16:02:16 PDT Primiparous sows were fed to appetite during lactations that occurred during winter or summer, and 11.4 ± 0.4 pigs per litter were weaned at 23.5 ± 0.1 days of age. Sows were slaughtered at 0 or 72 h after weaning or blood samples were collected until 24 h after onset of oestrus. Sows that lactated during summer consumed less food and lost more (P < 0.05) weight, heartgirth and backfat than those that lactated during winter. Weaning-to-oestrus interval was greater (P < 0.05) in summer (224 ± 25 h) than in winter (93 ± 13 h). Content of GnRH in the hypothalamus and concentrations of LH in the anterior pituitary and serum were lower (P < 0.05)after weaning in summer than winter. The numbers of visible ovarian follicles < 5 mm in diameter at weaning were lower (P < 0.05) in summer than in winter. In contrast to LH, FSH concentration in serum was higher (P < 0.10) in summer than winter, but FSH values in the anterior pituitary were lower (P < 0.05) in summer than in winter. Post-weaning patterns of secretion of oestradiol and follicular development differed between winter and summer. For example, in some sows weaned during the summer, transient surges of oestradiol occurred repeatedly during 0 to 280 h after weaning without provoking surges of LH. These results indicate that the period of post-weaning anoestrus in summer is prolonged because of altered activity of the hypothalamic-pituitary axis, possibly because of changes in sensitivity to the feedback of oestradiol. Lower feed intake during lactations that occur during summer may predispose the endocrine system to the aberrations.

]]> Jeffrey D. Armstrong et al. Effects of Naloxone or Transient Weaning on Secretion of LH and Prolactin in Lactating Sows http://digitalcommons.calpoly.edu/pres_schol/11 http://digitalcommons.calpoly.edu/pres_schol/11 Tue, 09 Aug 2011 16:02:13 PDT Sows (N = 16) were infused intravenously for 8 h with saline or naloxone (200 mg/h) or their litters were transiently weaned for 8 h. Before infusion, 200 mg naloxone were administered to elevate quickly concentrations of naloxone. Blood samples were collected from sows at 15 min intervals for 24 h, beginning 8 h before and continuing until 8 h after imposition of treatments during the middle 8-h segment. Frequency of episodic release of LH and concentrations of prolactin were similar before, during and after infusion of saline. Average concentration of LH was greater during the last than during the middle 8-h segment when sows were given saline. Frequency of episodic release of LH increased and concentrations of prolactin decreased during infusion of naloxone or transient weaning; however, average concentration of LH increased during transient weaning, but not during infusion of naloxone. After transient weaning or infusion of naloxone, frequency of release of LH decreased, returning to pretreatment values in sows infused with naloxone but remaining above pretreatment values in sows subjected to transient weaning. At the resumption of suckling by litters in sows subjected to transient weaning, prolactin increased to levels not different from those observed during the 8-h pretreatment segment. Prolactin did not increase until 4-5 h after cessation of naloxone infusion. We conclude that continuous infusion of naloxone altered secretory patterns of LH and prolactin. Collectively these results provide evidence that the immediate effects of weaning on LH and prolactin in sows are mediated in part through a mechanism involving endogenous opioid peptides.

]]> Jeffrey D. Armstrong et al. Effect of Somatotropin and/or Equine Chorionic Gonadotropin on Serum and Follicular Insulin-Like Growth Factor I and Insulin-Like Growth Factor Binding Proteins in Cattle http://digitalcommons.calpoly.edu/pres_schol/10 http://digitalcommons.calpoly.edu/pres_schol/10 Tue, 09 Aug 2011 16:02:10 PDT We investigated the effect of administration of somatotropin (ST) and/or eCG on insulin-like growth factor I (IGF-I) and IGF-binding proteins (IGFBP) in serum and follicular fluid (FFL) of cattle actively immunized against growth hormone-releasing factor (GRF). Cyclic beef cattle, previously immunized against GRF-( 1-29)-Gly-Gly-Cys-NH2 conjugated to human serum albumin (synthesized and provided by Hoffmann-LaRoche, Inc., Nutley, NJ; GRFi, n = 31) or to human serum albumin alone (HSAi, n = 26), received (i.m.): 1) 25 mg recombinantly derived methionyl somatotropin (rbST, n = 14; sometribove provided by Monsanto Co., St. Louis, MO); 2) 1100 IU eCG (n = 10); 3) rbST and eCG (rbST-eCG, n = 15); or 4) vehicle (VEH, n = 17) at 0 and 24 h after receiving prostaglandin F2 (PGF2). Serum samples were collected at 0 and 40 h after PGF2, and the ovary bearing the largest follicle (DOM) was removed 44.0 0.5 h after PGF2; FFL was harvested from DOM and the subordinate follicle (SUB). Before treatment (0 h), GRFi cows had lower serum ST (0.6 ± 0.2 vs. 2.2 ± 0.2 ng/ml;p < 0.01) and IGF-I (26 ± 4 vs. 72 ± 4 ng/ml;p < 0.01), but greater IGFBP-2 (594 48 vs. 384 52 ng/ml; p < 0.01) than HSAi cows. Serum and FFL concentrations of IGF-I or IGFBP-2 were not different between rbST- and rbST-eCG-treated cows or between VEH- and eCG-treated cows at Hour 40 after the initial treatment injection; therefore, data were combined and designated as rbST and VEH, respectively. Serum IGF-I was increased to a greater extent (percentage increase above 0 h) by rbST treatment in GRFi (362 ± 24) than in HSAi (176 ± 16) cows (immunization by treatment, p < 0.01). Across GRFi and HSAi, rbST lowered serum IGFBP-2 (342 ± 31 vs. 541 ± 27 ng/ml, rbST vs. VEH; p < 0.01). Diameters of DOM or SUB were not affected by immunization or treatment. Concentrations of IGF-I and IGFBP-3 (determined by ligand blot analysis) in FFL from both DOM and SUB were lower (p < 0.05) in GRFi than in HSAi cows. In contrast, IGFBP-2 in FFL was elevated in SUB, but not DOM, in GRFi compared to HSAi cows. Ligand blot analyses indicated that IGFBP-4 and IGFBP-5 were markedly higher in FFL from SUB in GRFi than in HSAi cows, but not different for DOM. Administration of rbST increased IGF-I and decreased IGFBP-2 in DOM and SUB. In conclusion, GRFi decreased serum and FFL concentrations of IGF-I, while it increased concentrations of IGFBP-2 in serum and in FFL from SUB, but not DOM. Treatment with rbST increased serum and FFL IGF-I, but decreased both serum and FFL IGFBP-2 (in both DOM and SUB). The specific roles that IGF-I and IGFBP play in folliculogenesis are yet to be determined; of particular interest is the divergent effect of GRFi on IGFBP in dominant vs. subordinate follicles.

]]> R. L. Stanko et al. Aspartate and Glutamate Modulation of Growth Hormone Secretion in the Pig: Possible Site of Action http://digitalcommons.calpoly.edu/pres_schol/9 http://digitalcommons.calpoly.edu/pres_schol/9 Tue, 09 Aug 2011 16:02:07 PDT The influence of excitatory amino acids (EAA) on growth hormone (GH) secretion and the possible site of action was investigated in the pig. In Experiment (Exp) I three replicates were conducted with 30 prepuberal gilts, 130 d of age and averaging 70.6 ± 1.3 kg body weight (BW). Six gilts each received intravenously (iv) 0, 50, 100, or 150 mg/kg BW of aspartate (ASP) or glutamate (GLU) in saline. Blood samples were collected every 15 min for 2 hr before and 3 hr after treatment. In Exp II, mature ovariectomized gilts (163 ± 10 kg BW) that had been immunized against growth hormone releasing factor (GRF) conjugated to human serum albumin (GRFi; n = 4) or against human serum albumin alone (HSAi; n = 5) received 150 mg/kg BW ASP or GLU iv in a 2 × 2 factorial arrangement of treatments, which was then repeated in a crossover design. One week later, all animals received 10 mg/kg (NMA; EAA agonist) in saline iv. Blood samples were collected as described above. In Exp III, cultures of anterior pituitary cells from market-weight (averaging 105 kg BW) gilts were studied. On Day 4 of culture, cells (105 seeded/well) were challenged with 10−8, 10−6, or 10−4 M ASP or GLU, 10−6 M [Ala15]-human GRF (1–29)-NH2, or the EAA antagonist, 2-amino-5-phosphonopentonoic acid (10−4 M; AP5), alone or in combination with ASP or GLU. In Exp I, all doses of ASP and the 100- and 150-mg doses of GLU increased (P < 0.05) GH secretion when compared with Time 0. However, serum GH concentrations were higher (P < 0.01) after 150 mg/kg of ASP when compared with those after 150 mg/kg of GLU. In Exp II, serum GH concentrations increased (P < 0.05) in HSAi but not in GRFi pigs (averaging 1.2 ± 0.2 ng/ml before and 8.2 ± 0.7, 6.3 ± 0.5, and 9.2 ± 0.5 ng/ml by 15 min after ASP, GLU, and NMA, respectively). In Exp III, relative to controls (40 ± 6 ng/ml) , GH increased (P < 0.05) 1.6-, 1.9-, and 1.9-fold and 1.7-, 1.8-, and 2.0-fold after 10−8, 10−6, and 10−4 M ASP and GLU, respectively. The EAA receptor antagonist AP5 failed to prevent the GH response to ASP or GLU, except for 10−8 M ASP. In summary, ASP is a more potent secretagogue of GH secretion than is GLU in vivo, whereas each is equipotent in vitro. Because no stimulation of GH by EAA was observed in GRFi pigs and no specific dose-response effect of EAA was found in vitro, it may be concluded that modulation by EAA is mediated primarily at the level of the hypothalamus or higher brain centers.

]]> C. R. Barb et al. Changes in the Hypothalamic-Hypophyseal-Ovarian Axis of Primiparous Sows Following Weaning or Pulsatile Gonadotropin Releasing Hormone Administration and Weaning http://digitalcommons.calpoly.edu/pres_schol/8 http://digitalcommons.calpoly.edu/pres_schol/8 Tue, 09 Aug 2011 16:02:03 PDT Lactating primiparous sows were used to examine relationships among hypothalamic gonadotropin releasing hormone (GnRH), serum, and anterior pituitary gonadotropins and follicular development after weaning or after administering GnRH pulses (1.5 ug) once hourly for 72 h before weaning. Control sows were either slaughtered at 0 or 72 h after weaning or were cannulated for collection of blood samples until 24 h after estrus. Sows pulsed with GnRH were either slaughtered 72 h after beginning of GnRH treatment or were cannulated for collection of blood samples until 24 h after estrus. Exogenous GnRH pulsed hourly during 72 h prior to weaning stimulated follicular growth as demonstrated by an increase in number of surface follicles >5 mm in diameter and a decrease in number of follicles <5 mm in diameter. Interval (h) from weaning to an increase in estradiol (>16 pg/ml) was less in GnRH-pulsed than in control sows (P < 0.05), but hours from weaning to estrus were similar between groups. Amounts of GnRH in the medial basal hypothalamus (MBH), stalk median eminence (SME), and hypophyseal portal area (HPA) were similar among control sows killed at 0 or 72 h and sows pulsed with GnRH. Serum concentrations of luteinizing hormone (LH) and frequency of release of LH were similar between GnRH-pulsed and control sows, but concentrations of LH and follicle stimulating hormone (FSH) in anterior pituitary were lower in GnRH-pulsed sows than control sows. Administration of GnRH for 72 h prior to weaning in primiparous sows stimulated follicular growth as manifested by increased secretion of estrogen; however, the amount of follicular growth was apparently inadequate to hasten the onset of estrus after weaning.

]]> Jeffrey D. Armstrong et al. Influence of follicular ablation during lactation on postweaning interval to estrus, ovulation rate, and endocrine function in sows http://digitalcommons.calpoly.edu/pres_schol/7 http://digitalcommons.calpoly.edu/pres_schol/7 Tue, 09 Aug 2011 16:02:00 PDT Duroc sows farrowed second litters in March and lactated 35 ± 2 days. At 36 hr before weaning, electrocautery of follicles ≥3 mm in diameter (n=8) or sham surgery (n=5) was performed to test the hypothesis that ablation of medium-sized follicles would prolong the duration of postweaning anestrus. Number of follicles and diameters at surgery were: 1.3 ± .6 (> 5 mm diameter), 26 ± 1 (3 to 5 mm) and > 20 (< 3 mm). Blood samples were collected at 15 min intervals for 3 hr beginning at −12, 0, 12, 60 and 96 hr from weaning. Interval to estrus was 3.4 ± .2 days in seven of eight cauterized sows and 3.6 ± .6 days for sham-surgery sows. The remaining cauterized sow was anestrus at slaughter, 40 days after weaning. Number of corpora lutea and pregnancy rate were 15.8 ± .6 and 92%, respectively, and were similar between sham-surgery and cauterized sows. Concentration of follicle stimulating hormone (FSH) at 12 hr before weaning was greater in sows subjected to electrocautery than for sham-surgery sows, but FSH values were similar at other sampling times. Concentrations of estradiol were similar at all times for both treatment groups. Luteinizing hormone (LH) was higher (P<.05) at 60 hr in cauterized sows because of the onset of the preovulatory LH surge in one sow. We conclude that destruction of medium-sized ovarian follicles before weaning did not influence postweaning reproductive performance.

]]> N. M. Cox et al. Absence of a nocturnal rise in either norepinephrine, N-acetyltransferase, hydroxyindole-O-methyltransferase or melatonin in the pineal gland of the domestic pig kept under natural environment photoperiods http://digitalcommons.calpoly.edu/pres_schol/6 http://digitalcommons.calpoly.edu/pres_schol/6 Tue, 09 Aug 2011 16:01:58 PDT Castrated male and intact female pigs were kept under natural photoperiodic and temperature conditions and were killed over a 24 h period in either May (under long days) or in December (under short days). Neither the pineal norepinephrine (NE) concentration nor the melatonin content rose at night; likewise, neither the activities of N-acetyltransferase (NAT) nor hydroxyindole-O-methyltransferase (HIOMT) increased during darkness. In May pineal melatonin content actually decreased (P < 0.05) at night while in December NAT activity fell (P < 0.05) at night. Daytime levels of each of these variables were equivalent to those measured in other species. The absence of a nocturnal increase in pineal melatonin production in either May or December raises the possibility that pineal melatonin may be involved in regulating seasonal breeding in the pig in a manner different from other mammals. Alternatively, pineal melatonin production may be unrelated to seasonal reproduction in the pig.

]]> Russel J. Reiter et al. Opioid control of growth hormone in the suckled sow is primarily mediated through growth hormone releasing factor http://digitalcommons.calpoly.edu/pres_schol/5 http://digitalcommons.calpoly.edu/pres_schol/5 Tue, 09 Aug 2011 16:01:55 PDT Endogenous opioid peptides mediate the effect of suckling on LH and PRL in the domestic pig. However, the role of opioids in modulating GH during lactation in swine is not known. Primiparous sows that had been immunized against GRF(1–29) conjugated to human serum albumin (GRF-HSA, n = 5) or HSA (n = 4) were used to determine changes in GH after naloxone. Treatments were imposed in all sows on day 21 of lactation when antibody titers were 9100 ± 1629. All sows received (i.v.) naloxone (0.25 mg/kg) or saline (0.0125 ml/kg) at 15 min intervals for 165 min. Active immunization against GRF-HSA during lactation decreased (P < 0.05) mean concentration (4.8 ± 0.2 vs 2.6 ± 0.1 ng/ml) and frequency (1.5 ± 0.3 vs 0.4 ± 0.2 peaks/4 hr). Concentrations of LH and PRL were similar in GRF-HSA and HSA immunized sows. Naloxone suppressed (P < 0.05) GH in all sows. In HSA sows, naloxone abolished episodic release of GH and decreased average, but not basal, concentrations of GH. In sows immunized against GRF-HSA, naloxone decreased (P < 0.05) average and basal GH but failed to decrease frequency of GH release. Naloxone failed to alter frequency of LH release. Concentrations of PRL decreased (P < 0.05) after naloxone in all sows. In conclusion, immunization against GRF-HSA blocked most of the effect of lactation on GH. Blocking opioid receptors with naloxone decreased GH and PRL in all sows. In contrast to previous findings naloxone had no effect on LH. Opioids alter concentrations of GH through a GRF dependent and GRF independent pathway.

]]> Jeffrey D. Armstrong et al. Effect of active immunization against growth hormone releasing factor on concentrations of somatotropin and insulin-like growth factor I in lactating beef cows http://digitalcommons.calpoly.edu/pres_schol/4 http://digitalcommons.calpoly.edu/pres_schol/4 Tue, 09 Aug 2011 16:01:53 PDT Two experiments were conducted to determine the effects of immunoneutralization of growth hormone-releasing factor [GRF(1–29)-NH2] on concentrations of somatotropin (ST) and insulin-like growth factor I (IGF-I) in lactating beef cows. In Experiment 1, multiparous Hereford cows were immunized against 2 mg GRF(1–29)-(Gly)4-Cys-NH2 conjugated to human serum albumin (GRFi, n=3) or 2 mg human serum albumin (HSAi, n=3) at 52 ± 1 d prior to parturition. Boosters (1 mg) were administered on days 12, 40 and 114 postpartum (pp). Serum samples were collected at 15-min intervals for 5 hr on days 18, 46 and 120 pp, followed by administration (IV) of an opioid agonist (FK33-824; 10 μg/kg) and an antagonist (naloxone; .5 mg/kg) at hours 5 and 7, respectively. A GRF-analog ([desamino-Tyr1, D-Ala2, Ala15] GRF (1–29)-NH2; 3.5 μg/kg) and arginine (.5 g/kg) were administered at hour 10 on days 47 and 121, respectively. Percentage binding of [125I]GRF (1:100 dilution of serum) 28 d after primary immunization was greater in GRFi (14.3 ± 4.9) than in HSAi (.7 ± .3) cows. Binding increased to 29.3 ± 6.5% after first booster in GRFi cows. Episodic release of ST was abolished by immunization against GRF; concentration and frequency of release of ST were lower (P<.05) in GRFi than in HSAi cows on all days pp. Concentrations of IGF-I were lower in GRFi than in HSAi cows throughout lactation. Serum ST failed to increase following FK33-824 or arginine in GRFi; however, ST increased after both compounds in HSAi cows. Concentrations of ST following GRF-analog were greater (P<.05) in HSAi than in GRFi cows. Experiment 2 was conducted to determine if a lower dose of antigen and a single booster would be sufficient to lower ST and IGF-I in lactating cows. Multiparous Hereford and Angus cows were assigned to GRFi (n=6) or HSAi (n=6). Primary (1.2 mg) and booster (.5 mg) immunizations were administered −14 and 8 d from calving, respectively. Cows were restricted to 60% of recommended intake of energy during lactation in order to elevate concentrations of ST. Serum samples were collected at 15-min intervals for 6 hr on days 26, 50, 73, 90 and 109 pp. Two of six GRFi cows had binding less than 10% (1:1,000 dilution of serum) and were omitted from further analyses. Percentage binding at a 1:1,000 dilution was greater in GRFi (17.0 ± 4.7) than in HSAi (1.4 ± .4) cows at 89 d pp. Consequently, frequency of release, and concentration of ST and IGF-I were lower (P < .05) in GRFi than in HSAi cows. Concentrations of ST increased following FK33-824 in HSAi, but not GRFi cows. Across experiments, interval from calving to ovulation (estimated from weekly progesterone concentrations) was greater in HSAi than in GRFi cows. In conclusion, gestating-lactating beef cows were effectively immunized against GRF as evidenced by antibody binding of [125I]GRF, absence of pulsatile release of ST, low concentrations of ST and IGF-I and failure of ST to increase after IV opioid agonist or arginine.

]]> K. L. Moore et al. Effect of feed restriction on serum somatotropin, insulin-like growth factor-I-(IGF-I) and IGF binding proteins in cyclic heifers actively immunized against growth hormone releasing factor http://digitalcommons.calpoly.edu/pres_schol/3 http://digitalcommons.calpoly.edu/pres_schol/3 Tue, 09 Aug 2011 16:01:49 PDT Feed restriction often increases serum somatotropin (ST) and decreases insulin-like growth factor-I (IGF-I) in ruminants; however, the mechanisms responsible for this change in ST and IGF-I are not well defined. We investigated the effects of feed restriction on serum ST, IGF-I, IGF binding proteins (IGFBP), insulin and nonesterified fatty acids (NEFA) in cyclic Angus and Charolais heifers (n=15) previously immunized against growth hormone releasing factor (GRFi) or human serum albumin (HSAi). Cows were fed a concentrate diet ad libitum (AL) or were restricted to 2 kg cotton seed hulls (R) for 4 d. Each heifer received each dietary treatment in a single reversal design. As anticipated, GRFi decreased ST, IGF-I and insulin (P<.05). In addition, GRFi decreased serum IGFBP-3 (P<.01), but increased IGFBP-2 (P<.01). Feed restriction resulted in an increase in serum ST in HSAi, but not in GRFi heifers. Regardless of immunization treatment, feed restriction decreased serum IGF-I and insulin, and increased NEFA (P<.01). In conclusion, the increase in serum ST levels observed during feed restriction was blocked by active immunization against GRF. However, feed restriction resulted in decreased serum IGF-I in GRFi heifers in spite of initial low levels of IGF-I (due to GRFi). Although GRFi decreased levels of IGFBP-3 and increased levels of IGFBP-2, feed restriction for 4 d did not alter serum IGFBP.

]]> Jeffrey D. Armstrong et al. Ovarian expression of insulin-like growth factor-I (IGF-I), IGF binding proteins, and growth hormone (GH) receptor in heifers actively immunized against GH-releasing factors http://digitalcommons.calpoly.edu/pres_schol/2 http://digitalcommons.calpoly.edu/pres_schol/2 Tue, 09 Aug 2011 16:01:47 PDT Active immunization against GRF at 6 months of age delays puberty in beef heifers. The objectives of the present study were to determine whether active immunization against GRF at an earlier age would affect normal onset of puberty and follicular growth and to determine whether these changes were related to alterations in ovarian insulin-like growth factor I (IGF-I) or IGF binding protein (IG-FBP) messenger RNA (mRNA) levels. Heifers were immunized against human serum albumin (HSAi; n = 15) or against GRF conjugated to HSA (GRFi; n = 18) at 3 months of age. A third group of heifers was not immunized (CON; n = 16). Immunization against GRF delayed puberty beyond 13 months of age in 75% of treated heifers. Unilateral ovariectomy at 191 days of age revealed that the delay in puberty was associated with a reduction in the number of large ( > or = 7 mm in diameter) follicles. Large follicles were present in only 22% of GRFi heifers compared to 77% of HSAi heifers. The number of small ( < or = 3 mm in diameter) and medium (4 to 6 mm in diameter) follicles was not affected by GRFi. The percentage of 1- to 3-mm follicles that were atretic was not different between HSAi (65%) and GRFi (62%) heifers. Unilateral ovariectomy had no effect on age at puberty. Immunization against GRF decreased (P < 0.01) concentrations of IGF-I in serum (23 +/- 2 ng/ml) compared to HSAi heifers (109 +/- 11 ng/ml). IGF-I levels in follicular fluid (FFL) of medium and small follicles were also decreased by GRFi from 82 +/- 3 ng/ml in HSAi heifers to 48 +/- 6 ng/ml (P < 0.01). Levels of IGFBP-3 (determined by ligand blot analysis) in serum and FFL of small follicles were decreased by GRFi (P < 0.01). In contrast, IGFBP-2 serum levels were increased from 422 +/- 32 ng/ml in HSAi heifers to 657 +/- 6 ng/ml in GRFi heifers (P < 0.05). Likewise, IGFBP-2 levels in FFL from small and medium follicles were increased from 785 +/- 44 ng/ml to 926 +/- 44 ng/ml (P < 0.05). Ligand blot analysis indicated that IGFBP levels were lower in FFL from large vs. small follicles. The band intensities of IGFBP-4 and -5 were drastically reduced ( > 80%) while the decreases in IGFBP-2 and -3 were less marked ( < 50%). The decreased levels of IGFBP-5 in FFL from large follicles was not associated with an increase in proteolytic fragments detectable by immunoblot analysis. While mRNA transcripts for IGF-I, GH receptor, and IGFBP-2, -3, -4, and -5 were readily detectable in ovarian tissue, GRFi had no effect on ovarian levels of mRNA for each of these proteins. This suggests that the decrease in follicular development associated with GRFi may be related to changes in circulating IGF-I and/or IGFBPs.

]]> W. S. Cohick et al. Immunization against growth hormone releasing factor or chronic feed restriction initiated at 3.5 months of age reduces ovarian response to pulsatile administration of gonadotropin-releasing hormone at 6 months of age and delays onset of puberty in heifers http://digitalcommons.calpoly.edu/pres_schol/1 http://digitalcommons.calpoly.edu/pres_schol/1 Tue, 09 Aug 2011 16:01:44 PDT A severe or moderate suppression of serum insulin-like growth factor I (IGF-I) was induced in heifers, beginning at 104 days of age, by active immunization against growth hormone-releasing factor (GRFi) or by chronic feed restriction (RES), respectively. We hypothesized that reduced serum IGF-I results in decreased serum estradiol-17 beta (E2), which in turn delays onset of puberty. The objectives of this experiment were to determine 1) whether GRFi and RES would alter follicular development and delay onset of puberty through similar mechanisms, and 2) whether GnRH would enhance follicular growth in control, GRFi, and RES heifers at 6 mo of age. Changes in IGF-I, somatotropin, LH, FSH, and E2 were evaluated. Serum IGF-I was greater in control than in RES heifers, and was greater in both these groups than in GRFi heifers by 169 days of age. Basal LH decreased in control and RES but not in GRFi heifers from 136 to 157 days of age. During the same period, a decrease in mean FSH was detected in control but not in GRFi and RES heifers. RES decreased mean serum E2 from 148 to 183 days of age. At 6 mo of age, pulsatile administration of GnRH (5 micrograms every 2 h for 42-46 h) increased serum LH and FSH similarly across treatments but had no effect on the number of follicles > or = 8 mm in GRFi and RES heifers relative to saline treatment. Serum E2 and IGF-I in follicular fluid from follicles > or = 8 mm were increased in all GnRH-treated heifers; however, concentrations of both hormones were lower in GRFi than in control or RES heifers. The main effect of treatments on serum IGF-I was reflected in follicles < or = 7 mm; follicular fluid IGF-I was greater in control than in RES heifers and was greater in both these groups than in GRFi heifers. Serum E2 was lower in RES than in control and GRFi heifers from 253 to 281 days of age. Because of an interaction, E2 was lower in GRFi-GnRH than in control-GnRH heifers but similar in GRFi-saline and control-saline heifers. By 393 days of age, 0% of RES and 32% of GRFi heifers had reached puberty compared to 71% of control heifers. These data support our hypothesis that decreased serum IGF-I results in decreased serum E2. GRFi appears to delay puberty in heifers because decreased serum IGF-I impairs the ovary's ability to synthesize preovulatory concentrations of E2, thereby delaying stimulation of an LH surge. In contrast, RES may delay puberty by delaying follicular development at two stages: a) decreased IGF-I in follicles < or = 7 mm may delay predominant follicular growth, and b) decreased LH may delay maturation of the preovulatory follicle.

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