Comparative response of rams and bulls to long-term treatment with gonadotropin-releasing hormone analogs.

The objective was to compare the relative response between rams and bulls in characteristics of LH, FSH and testosterone (T) secretion, during and after long-term treatment with GnRH analogs. Animals were treated with GnRH agonist, GnRH antagonist, or vehicle (Control) for 28 days. Serial blood samples were collected on day 21 of treatment, and at several intervals after treatment. Injections of natural sequence GnRH were used to evaluate the capacity of the pituitary to release gonadotropins during and after treatment. Treatment with GnRH agonist increased basal LH and T concentrations in both rams and bulls, with a greater relative increase in bulls. Endogenous LH pulses and LH release after administration of GnRH were suppressed during treatment with GnRH agonist. Treatment with GnRH antagonist decreased mean hormone concentrations, LH and T pulse frequency, and the release of LH and T after exogenous GnRH, with greater relative effects in bulls. Rams previously treated with antagonist had a greater release of LH after administration of GnRH compared with control rams, while rams previously treated with agonist showed a reduced LH response. Bulls previously treated with agonist had reduced FSH concentrations and LH pulse amplitudes compared with control bulls while bulls previously treated with antagonist had greater T concentrations and pulse frequency. The present study was the first direct comparison between domestic species of the response in males to treatment with GnRH analogs. The findings demonstrated that differences do occur between rams and bulls in LH, FSH and testosterone secretion during and after treatment. Also, the consequences of treatment with either GnRH analog can persist for a considerable time after discontinuation of treatment.

Effects of infusions of various doses of bovine growth hormone-releasing factor on blood hormones and metabolites in lactating Holstein cows.

In two experiments, the effects of i.v. infusions of various doses of bovine GH-releasing factor (GRF) on blood hormones and metabolites in lactating Holstein cows were determined. In experiment 1, cows were infused with GRF (0, 3.125, 6.25, 12.5, 25.0 or 50.0 mg/cow per 24 h) for 24 h. Blood was sampled at -1, 5, 11, 15 and 23 h relative to the start of the infusion. The serum concentration of somatomedin C (SM-C) before infusion was 303 +/- 8 (S.E.M.) micrograms/l. Doses of GRF of between 3.125 and 50.0 mg were equipotent in stimulating (P less than 0.05) SM-C by 1.5- to 2.5-fold. GRF-induced increases in SM-C occurred by 11 h from the start of the infusion. In experiment 2, primiparous cows were infused with GRF (0, 1 or 3 mg/24 h) for 20 days. Blood was sampled for 12 h on days 1, 10 and 19. The 1 mg dose of GRF increased (P less than 0.05) blood concentrations of SM-C (on days 10 and 19) and glucose (on day 19), but did not affect blood concentrations of prolactin, insulin, cortisol, tri-iodothyronine (T3), thyroxine (T4), non-esterified fatty acids (NEFA) or glucose. The 3 mg dose of GRF increased (P less than 0.05) blood concentrations of SM-C (on days 10 and 19), T3 (on days 10 and 19), insulin (on day 19), NEFA (on days 1, 10 and 19) and glucose (on day 19), but did not affect blood concentrations of prolactin, cortisol or T4. We conclude that these data are consistent with the hypothesis that the galactopoietic effect of exogenous GRF in dairy cattle is mediated by increased secretion of GH.

Effects of growth hormone-releasing factor and vasoactive intestinal peptide on proliferation and steroidogenesis of bovine granulosa cells.

Recent studies have suggested that growth hormone-releasing factor (GRF), like vasoactive intestinal peptide (VIP), may enhance follicle-stimulating hormone (FSH)-stimulated steroidogenesis in cultured rat granulosa cells (GC). Because effects of GRF or VIP on GC proliferation have not been reported, we evaluated and compared the effect of GRF to that of VIP using cultured bovine GC. Undifferentiated GC from 1-5 mm bovine follicles were established for 2 days in medium containing 10% fetal calf serum, washed and then cultured in chemically defined medium for an additional 2 days. Two-day treatment with 2.5-1000 ng/ml of VIP had no effect (P greater than 0.05) on proliferation or progesterone production of bovine GC in the presence or absence of 200 ng/ml FSH. In comparison, 100, 250, 500, 1000 or 2000 pg/ml of human [desNH2Tyr1,D-Ala2,Ala15]-GRF(1-29)-NH2 analog caused a dose-dependent stimulation (P less than 0.05) of GC proliferation in the absence and presence of 5 micrograms/ml insulin. However, the GRF analog had no effect (P greater than 0.05) on GC progesterone production (expressed as ng/10(5) cells/24 h) in the absence or presence of 5 micrograms/ml insulin. The effects of GRF analog on progesterone production and cell proliferation were not influenced by co-culture with 200 ng/ml FSH. GRF(1-44)-NH2 also stimulated cell proliferation but had no effect on basal or FSH-induced progesterone production. These results suggest that GRF may play a role in GC proliferation during follicular development in the bovine.

Prostaglandin F2 alpha immunization of prepubertal beef heifers: effects of conjugate dose and timing of immunization relative to puberty on the onset of puberty and subsequent ovarian function.

Fifty-six prepubertal Hereford cross Friesian heifers were assigned to seven treatment groups: (1) primary (day 0) and booster (day 41) using 10 mg human serum albumin (HSA) (control); (2) primary and booster (day 41) immunizations using 3.3 mg prostaglandin F2 alpha PGF-HSA conjugate; (3) primary and booster (day 83) using 3.3 mg PGF-HSA; (4) primary and booster (day 210) using 3.3 mg PGF-HSA; (5-7) as in treatments 2-4 except 10 mg PGF-HSA were used. Plasma progesterone concentrations were used to determine the onset of puberty and the presence of a corpus luteum (CL); plasma PGF antibody titres were determined at 28-day intervals. There was no effect (P > 0.05) of conjugate dose or booster interval on mean antibody titres and there was no interaction between them. However, heifers in the 83- and 210-day booster treatments had higher (P < 0.05) peak antibody titres than heifers in the 42-day booster treatments. Puberty was delayed in 40% (16/40) of PGF-immunized heifers and 40% (16/40) of heifers formed persistent CL after puberty. Overall, eight of the heifers with delayed puberty also formed a persistent CL. There was a positive correlation between mean titre and onset of puberty but not with duration of persistent CL.

Estrogen and androgen elicit growth hormone release via dissimilar patterns of hypothalamic neuropeptide secretion.

The dimorphic pattern of growth hormone (GH) secretion and somatic growth in male and female mammals is attributable to the gonadal steroids. Whether these hormones mediate their effects solely on hypothalamic neurons, on somatotropes or on both to evoke the gender-specific GH secretory patterns has not been fully elucidated. The purpose of this study was to determine the effects of 17beta-estradiol, testosterone and its metabolites on release of GH, GH-releasing hormone (GHRH) and somatostatin (SRIF) from bovine anterior pituitary cells and hypothalamic slices in an in vitro perifusion system. Physiological concentrations of testosterone and estradiol perifused directly to anterior pituitary cells did not affect GH releases; whereas, dihydrotestosterone and 5alpha-androstane-3alpha, 17beta-diol increased GH. Perifusion of testosterone at a pulsatile rate, and its metabolites and estradiol at a constant rate to hypothalamic slices in series with anterior pituitary cells increased GH release. The androgenic hormones increased GHRH and SRIF release from hypothalamus; whereas, estradiol increased GHRH but decreased SRIF release. Our data show that estradiol and the androgens generated distinctly different patterns of GHRH and SRIF release, which in turn established gender-specific GH patterns.

Effects of continuous administration of gonadotropin-releasing hormone (GnRH) or a potent GnRH analogue on blood luteinizing hormone and testosterone concentrations in prepubertal bulls.

The objective was to determine if continuous administration of gonadotropin-releasing hormone (GnRH) or a potent analogue (GnRH-A) for 28 or 56 d would decrease blood concentrations of luteinizing hormone (LH) and testosterone (T) in 5-month old bull calves. Treatments (5 calves/treatment), using a completely randomized design, were: control (vehicle), 3.3, 10 and 30 micrograms GnRH, and 3.3 and 10 micrograms GnRH-A (Leuprolide) per kg bodyweight/d for 28 d, administered via subcutaneously implanted mini-osmotic pumps. A second pump was implanted on day 28 in controls and bulls receiving 10 micrograms GnRH-A until day 56. Blood samples were taken every second day for plasma LH and T concentrations, and every 15 min for 6 hr on days 1, 14 and 27 (and days 40 and 55 where applicable) for plasma LH concentrations. There was an increase (P < 0.05) in basal plasma LH in response to GnRH and GnRH-A on day 1 (1.6, 2.1, 2.1, 2.5, 2.1 and 1.9 ng/ml for control, 3.3, 10 and 30 micrograms GnRH, and 3.3 and 10 micrograms GnRH-A, respectively; pooled s.e.d. = 0.2), but not on days 14 or 27. The number of LH pulses/6 hr was similar on day 1 for GnRH-treated and control calves, but there was a linear decrease (P < 0.05) in pulse frequency in response to GnRH doses on days 14 (1.8, 1.2, 0.6 and 0.0 for control, 3.3, 10 and 30 micrograms GnRH; s.e.d. = 0.5) and 27 (1.8, 1.0, 0.0 and 0.0; s.e.d. = 0.3). On days 1, 14 and 27, both GnRH-A doses suppressed (P < 0.05) LH pulsatility. GnRH (days 1-14) and GnRH-A (days 1-27) increased (P < 0.05) plasma T in a dose-dependent manner. Mean T was greater (P < 0.05) in 10 micrograms GnRH-A-treated than in control calves during days 29-41 (4.6 and 1.8 ng/ml; s.e.d. = 0.6) and days 43-55 (4.1 and 1.8 ng/ml; s.e.d. = 0.4). In conclusion, continuous administration of GnRH or GnRH-A to 5-month old bulls for 28 or 56 d chronically decreased LH pulse frequency, had no effect on basal LH, but increased testosterone concentrations.

Androgens modulate growth hormone-releasing factor-induced GH release from bovine anterior pituitary cells in static culture.

Static primary cultures of bovine anterior pituitary (AP) cells were utilized to study the effect of sex steroids on basal growth hormone (GH) and GH-releasing hormone (GRF)-stimulated release of GH. The AP cells (5 x 10(5) cells/well) were allowed to attach for 72 hr and become confluent before treatments were imposed. Cells were incubated for an additional 24, 48 or 72 hr with either estradiol-17 beta (E2, 10(-11) to 10(-8) M), testosterone (T, 10(-8) to 10(-5) M), dihydrotestosterone (DHT, 10(-9) to 10(-6) M) or 5 alpha-androstane-3 alpha, 17 beta-diol (3 alpha-diol, 10(-11) to 10(-8) M). Media were collected every 24 hr and GH concentrations determined by RIA. Incubation of calf AP cells with gonadal steroids did not affect (P > 0.05) basal GH released at 24, 48, or 72 hr. In another experiment, calf AP cells were incubated with the same concentrations of the steroids for 24 hr, media harvested, cells washed and challenged in serum-free media for 1 hr with bovine GRF 1-44-NH2 (10(-8) M). In non-steroid treated wells, GRF increased (P < 0.05) GH from 58 to 134 ng/ml. Incubation with E2 or 3 alpha-diol did not affect (P > 0.05) GRF-induced GH release; however, preincubation with T (10(-5) M) and DHT (10(-9), 10(-8) and 10(-7) M) increased (P < 0.05) GRF-induced GH release above control concentrations (195, 235, 190 and 185 ng/ml, respectively). At the doses tested, sex steroids did not affect basal release of GH, but androgens increased responsiveness of somatotropes to GRF.

Effects of cimaterol administration on plasma concentrations of various hormones and metabolites in Friesian steers.

The aim of the experiment was to determine the acute and chronic effects of the beta-agonist, cimaterol, on plasma hormone and metabolite concentrations in steers. Twelve Friesian steers (liveweight = 488 +/- 3 kg) were randomly assigned to receive either 0 (control; n = 6) or .09 mg cimaterol/kg body weight/day (treated; n = 6). Steers were fed grass silage ad libitum. Cimaterol, dissolved in 140 ml of acidified distilled water (pH 4.2), was administered orally at 1400 hr each d. After 13 d of treatment with cimaterol or vehicle (days 1 to 13), all animals were treated with vehicle for a further 7 d (days 14 to 20). On days 1, 13 and 20, blood samples were collected at 20 min-intervals for 4 hr before and 8 hr after cimaterol or vehicle dosing. All samples were assayed for growth hormone (GH) and insulin, while samples taken at -4, -2, 0, +2, +4, +6 and +8 hr relative to dosing were assayed for thyroxine (T4), triiodothyronine (T3), cortisol, urea, glucose and non-esterified fatty acids (NEFA). Samples taken at -3 and +3 hr relative to dosing were assayed for IGF-I only. On day 1, cimaterol acutely reduced (P less than .05) GH and urea concentrations (7.6 vs 2.9 +/- 1.4 ng/ml; and 6.0 vs 4.9 +/- 0.45 mmol/l, respectively; mean control vs mean treated +/- pooled standard error of difference), and increased (P less than .05) NEFA, glucose and insulin concentrations (160 vs 276 +/- 22 mumol/l, 4.1 vs 6.2 +/- 0.15 mmol/l and 29.9 vs 179.7 +/- 13.9 microU/ml, respectively). Plasma IGF-I, T3, T4 and cortisol concentrations were not altered by treatment. On day 13, cimaterol increased (P less than .05) GH and NEFA concentrations (7.7 vs 14.5 +/- 1.4 ng/ml and 202 vs 310 +/- 22 mEq/l, respectively) and reduced (P less than .05) plasma IGF-I concentrations (1296 vs 776 +/- 227 ng/ml). Seven-d withdrawal of cimaterol (day 20) returned hormone and metabolite concentrations to control values. It is concluded that: 1) cimaterol acutely increased insulin, glucose and NEFA and decreased GH and urea concentrations, 2) cimaterol chronically increased GH and NEFA and decreased IGF-I concentrations, and 3) there was no residual effect of cimaterol following a 7-d withdrawal period.

Effect of dietary intake on concentrations of insulin-like growth factor-I in plasma and follicular fluid, and ovarian function in heifers.

The objective of this study was to determine if alterations in dietary intake of heifers can influence IGF-I concentrations in plasma and(or) follicular fluid (FFL), size of follicles, and steroid concentrations in FFL (as an indicator of steroidogenic capacity). Cyclic heifers [n = 23; mean +/- SE body weight (BW) = 373 +/- 7 kg] were individually fed for 10 weeks either: a) 1.8% of BW in dry matter (DM) per d (GAIN; n = 7), b) 1.1% of BW in DM per d (MAINT; n = 8) or c) 0.7% of BW in DM per d (LOSE; n = 8). After 10 wk of treatment, heifers were ovariectomized 36-40 hr after the second injection of prostaglandin F2 alpha analog (2 injections 11 d apart), and plasma and ovaries were collected. Heifers weighed 444 +/- 13,387 +/- 8 and 349 +/- 9 kg in the GAIN, MAINT and LOSE groups, respectively, at time of ovariectomy. Mean diameter of follicles greater than or equal to 10 mm was greater (P less than .05) for GAIN (15.6 mm) than for MAINT (11.0 mm) or LOSE (12.5 mm) heifers. Numbers of follicles and concentrations of IGF-I in plasma and FFL did not differ (P greater than .20) between LOSE, MAINT and GAIN heifers. Progesterone concentrations were greater (P less than .05) in small and medium follicles of GAIN than MAINT or LOSE heifers, but were unaffected by diet in large follicles. Estradiol concentrations in FFL in small, medium and large follicles were unaffected (P greater than .20) by dietary treatment.(ABSTRACT TRUNCATED AT 250 WORDS)

Modulation of growth hormone-releasing factor-induced release of growth hormone from bovine pituitary cells.

Growth hormone (GH)-releasing factor (GRF) at concentrations of 10(-12) through 10(-7) M for 6 hr linearly increased GH release (b1 = 10.4 +/- .3) from bovine anterior pituitary cells in culture. Maximum release of GH (262% above controls) occurred at 10(-7) M GRF. In contrast, GH release-inhibiting factor (SRIF) at 10(-12) through 10(-5) M had no effect on basal concentrations of GH. In a second experiment, as the proportion of SRIF relative to GRF increased, SRIF suppression of GRF-induced GH release from anterior pituitary cells increased. In a third experiment, anterior pituitary cells cultured in media containing fetal calf serum (FCS) were treated with cortisol (0 or 10 ng/ml media) for 24 hr before exposure to 10(-13) through 10(-7) M GRF. GRF linearly increased GH secretion (b1 = 7.4 +/- .3) and cortisol augmented this response (b1 = 10.5 +/- .6). However, when cells were cultured in media containing dextran-charcoal treated FCS, cortisol did not alter GRF-induced GH release. Our results demonstrate that GH response of bovine anterior pituitary cells to GRF was modulated negatively by SRIF. However, augmentation of GRF-induced GH release by cortisol was evident only when cells were cultured in media supplemented with untreated FCS.

Energy balance and body condition influence luteal function in Holstein heifers.

A factorial experiment was conducted to determine influence of energy balance (EB) and body condition (BC) on luteal function in heifers. Heifers with moderate (MBC) or fat (FBC) BC were fed individually to sustain positive EB (PEB) or to cause negative EB (NEB). Intake of feed was measured daily and body weight weekly. Progesterone was quantified daily in serum for 3.5 estrous cycles. On days 9, 10, or 11 after fourth estrus, blood was sampled every 15 min for 12 hr to quantify luteinizing hormone (LH), growth hormone (GH), insulin and non-esterified fatty acids (NEFA). The next day, luteal cells were incubated and proportions of small to large cells were determined. After fourth estrus, area of progesterone profiles in serum for 10 days postestrus was reduced in all heifers relative to MBC-PEB heifers. But, luteal weight from FBC-PEB and MBC-NEB heifers was less than MBC-PEB heifers and FBC-NEB heifers were intermediate. Secretion of progesterone in vitro was increased by LH for PEB but not NEB heifers. MBC-NEB heifers had increased ratios of small to large luteal cells. Independent of BC, NEB decreased concentrations of insulin and increased GH and NEFA. Secretion of progesterone was not associated with LH, GH or insulin, but was correlated negatively with NEFA. We conclude that reduced concentrations of progesterone in serum of FBC-PEB and MBC-NEB heifers is due to impaired luteal development. But, reduced concentrations of progesterone in serum of NEB heifers is due also to reduced basal (MBC) and LH-induced (MBC and FBC) secretion of progesterone by luteal cells. Body condition at onset of NEB may determine when effects of NEB on progesterone are detected.

Normal or induced secretory patterns of luteinising hormone and follicle-stimulating hormone in anoestrous gonadotrophin-releasing hormone-immunised and cyclic control heifers.

The objective was to determine the effect of gonadotrophin-releasing hormone (GnRH), GnRH analogue (GnRH-A) or oestradiol administration on luteinising hormone (LH) and follicle-stimulating hormone (FSH) release in GnRH-immunised anoestrous and control cyclic heifers. Thirty-two heifers (477 +/- 7.1 kg) were immunised against either human serum albumin (HSA; controls; n = 8), or a HSA-GnRH conjugate. On day 70 after primary immunisation, control heifers (n = 4 per treatment; day 3 of cycle) received either (a) 2.5 micrograms GnRH or (b) 2.5 micrograms of GnRH-A (Buserelin) and GnRH-immunised heifers (blocked by GnRH antibody titre; n = 6 per treatment) received either (c) saline, (d) 2.5 micrograms GnRH, (e) 25 micrograms GnRH or (f) 2.5 micrograms GnRH-A, intravenously. On day 105, 1 mg oestradiol was injected (intramuscularly) into control (n = 6) and GnRH-immunised anoestrous heifers with either low (13.4 +/- 1.9% binding at 1:640; n = 6) or high GnRH antibody titres (33.4 +/- 4.8% binding; n = 6). Data were analysed by ANOVA. Mean plasma LH and FSH concentrations on day 69 were higher (P < 0.05) in control than in GnRH-immunised heifers (3.1 +/- 0.16 vs. 2.5 +/- 0.12 ng LH ml-1 and 22.5 +/- 0.73 vs. 17.1 +/- 0.64 ng FSH ml-1, respectively). The number of LH pulses was higher (P < 0.05) in control than in GnRH-immunised heifers on day 69 (3.4 +/- 0.45 and 1.0 +/- 0.26 pulses per 6 h, respectively). On day 70, 2.5 micrograms GnRH increased (P < 0.05) LH concentrations in control but not in GnRH-immunised heifers, while both 25 micrograms GnRH and 2.5 micrograms GnRH-A increased (P < 0.05) LH concentrations in GnRH-immunised heifers, and 2.5 micrograms GnRH-A increased LH in controls. FSH was increased (P < 0.05) in GnRH-immunised heifers following 25 micrograms GnRH and 2.5 micrograms GnRH-A. Oestradiol challenge increased (P < 0.05) LH concentrations during the 13-24 h period after challenge with a greater (P < 0.05) increase in control than in GnRH-immunised heifers. FSH concentrations were decreased (P < 0.05) for at least 30 h after oestradiol challenge. In conclusion, GnRH immunisation decreased LH pulsatility and mean LH and FSH concentrations. GnRH antibodies neutralised low doses of GnRH (2.5 micrograms), but not high doses of GnRH (25 micrograms) and GnRH-A (2.5 micrograms). GnRH immunisation decreased the rise in LH concentrations following oestradiol challenge.

Validation of a sensitive radioimmunoassay to measure serum follicle-stimulating hormone in cattle: correlation with biological activity.

Meaningful biological interpretation of the role of follicle-stimulating hormone (FSH) requires use of a validated radioimmunoassay (RIA) that closely estimates biologically active FSH, which was the objective of this work. Three FSH antibodies [NIDDK anti ovine FSH (oFSH); JAD anti oFSH; USDA anti bFSH] were screened against three tracer preparations [USDA oFSH-19-SIAFP-I2(USDA oFSH I2); LER1976a oFSH; USDA bFSH I2] in a RIA using USDA bFSH B1 or I2 as the assay standard. Sera obtained from three heifers at 4- to 8-h intervals for 5 days after injection of PGF2 alpha during the luteal phase were assayed for both FSH immunoactivity using each of the three optimized assay formats (NIDDK anti oFSH and JAD anti oFSH with USDA oFSH I2 as tracer; USDA anti bFSH with USDA bFSH I2 as tracer), and FSH bioactivity, using a rat Sertoli cell bioassay. Cross reactivity of bLH (NIH bLH B9) in all three assay formats was minimal (0.7, 0.9 and < 0.4% at 50% binding for the NIDDK, JAD and USDA antibodies, respectively). There was parallel displacement of tracer between bovine serum dilutions of 10 to 500 microliters and the two FSH standards. Correlations between JAD and USDA RIA data and bioassay results were not significant (P > or = 0.10), but were significant (r = 0.78; P = 0.0001) for the NIDDK RIA FSH and the bioactive FSH measurements. The assay sensitivity of the NIDDK RIA was 0.55 ng USDA bFSH B1 (0.013 ng USDA bFSH I2)/ml. The inter- and intra-assay CV were between 5.8 and 7.9 %. This RIA detected a pre-ovulatory FSH surge coincident with the LH surge, in all heifers studied. Furthermore, the emergence of each wave of follicle growth (up to day 12 of the cycle), was preceded by a transient increase (P < 0.02; days 0.5 to 1.5 and 8 to 10.5 of the cycle) in serum FSH, while LH concentrations remained unchanged. In conclusion, the RIA utilising NIDDK anti oFSH and USDA oFSH I2 as tracer provides a good estimate of bioactive FSH in cattle, and detects physiologically relevant increases in serum FSH related to emergency of each new wave of follicle growth.

The effect of immunization of heifers against alpha 1-26 inhibin conjugate on the superovulatory response to pFSH.

A total of 121 heifers was blocked by time and diet and then randomly assigned, within block, to an inhibin-immunized (I) or a control (C) group. Immunized heifers (n = 61) received a primary immunization (Day 0) with 0.33 mg of an alpha 1-26 bovine inhibin fragment-human serum albumin (HSA) conjugate injected with non-ulcerative Freund's and DEAE-dextran adjuvants. Booster injections were given on Days 28 and 56. Control heifers (n = 60) received HSA and adjuvants. On Days 56 and 83 the ovaries of heifers were examined by ultrasound to determine the ovulation rate, and blood samples were collected for antibody titer determination. On Day 84, 61 heifers (C, n = 30; I, n = 31) received a total of 24 mg of porcine follicle stimulating hormone (pFSH), while 60 heifers (C, n = 30; I, n = 30) received 12 mg im pFSH, which was administered twice daily for 4 d in decreasing doses during the mid-luteal phase of the estrous cycle. Luteolysis was induced with prostaglandin F(2alpha) analog. The heifers were artificially inseminated and were slaughtered 7 d after estrus. Embryos were recovered and morphologically graded on a scale of 1 to 5 (1 = excellent; 5 = degenerated). Antibody titers (percentage binding at 1:125 serum dilution) differed (P < 0.01) between Group C and I heifers at Days 56 (0.1 vs 30%) and 83 (0.2 vs 37%), and 26% of Group I and 1% of Group C heifers (P < 0.01) had twin ovulations on Day 83. The mean number of embryos recovered was reduced (P = 0.02) in Group I heifers (8.9 +/- 1.2) compared with C heifers (12.1 +/- 1.1); however, the mean number of freezable embryos (Grades 1 and 2) was not affected (P = 0.61) by immunization, and there was no interaction with pFSH (P = 0.36). Ovulation rate as well as embryo yield and quality were not different (P > 0.10) between Group C and I heifers when 12 mg pFSH were administered; however, immunization decreased the superovulatory response to 24 mg of pFSH.

Interaction between dietary intake and ovariectomy on concentrations of insulin-like growth factor-I, GH and LH in plasma of heifers.

The objective of this study was to determine if alterations in dietary intake and(or) ovariectomy influence plasma concentrations of IGF-I, GH and LH in heifers. Cyclic heifers (n = 23) were individually fed for 10 wk either 1) 1.8% of body weight in dry matter per day (GAIN; n = 7) 2) 1.1% of body weight in dry matter per day (MAINT; n = 8); or 3) 0.7% of body weight in dry matter per day (LOSE; n = 8). After 10 wk of dietary treatment, heifers were ovariectomized 36 to 40 h following the second injection of prostaglandin F2alpha analog (2 injections 11 d apart). Heifers weighed 444 +/- 13, 387 +/- 8, and 349 +/- 9 kg in the GAIN, MAINT and LOSE groups, respectively, at the time of ovariectomy; the average daily weight gains during the 10-wk period were 0.96, 0.17 and -0.31 kg, respectively (P < 0.001), for the 3 groups. Blood plasma was collected for 6 h at 15-min intervals 1 d before and 2 wk after ovariectomy. The MAINT group of heifers had greater IGF-I concentrations than either the LOSE or GAIN groups; IGF-I decreased (P < 0.05) by 23 and 35% after ovariectomy in the MAINT and GAIN groups, respectively, but did not change (P > 0.10) in the LOSE groups. Dietary restriction tended to increase (P < 0.10) GH pulse frequency and mean GH. Ovariectomy had no effect (P > 0.10) on mean GH or GH pulse frequency but increased (P < 0.05) GH pulse amplitude in the GAIN groups. Dietary treatment had no effect (P > 0.10) on mean LH, or LH pulse amplitude and frequency. However, across dietary treatments, ovariectomy increased mean LH and LH pulse frequency but did not affect (P > 0.10) LH pulse amplitude. In summary, dietary restriction increased GH secretion while ovariectomy increased LH secretion. There appears to be a dichotomy of response between GH and IGF-I in the way heifers respond to dietary treatment and(or) ovariectomy.

The effects of once or twice daily injections of pFSH on superovulatory response in heifers.

Follicle stimulating hormone (FSH) is a glycoprotein hormone with a short half-life and has to be given twice daily for 3-4 days to induce superovulation in heifers. Since such a regimen is time consuming we compared the ovulatory response and yield of embryos in heifers following superovulation with either once or twice daily injections of pFSH for 4 days during the mid-luteal phase of a synchronized estrous cycle or during a prolonged luteal phase in heifers which had been immunized against prostaglandin F2alpha (PG). In Experiment 1, crossbred heifers (n = 42) previously actively immunized against a PG immunogen were superovulated in a 2 (cyclic or persistent corpus luteum) x 2 (once or twice daily injection) factorial plan. The heifers were superovulated with 75 units pFSH, which was injected subcutaneously once (22.5, 22.5, 15 and 15 units per day) or twice daily (9.3 units per injection) for 4 days. In Experiment 2, cyclic crossbred beef heifers (n = 80) were superovulated using pFSH which was given randomly to heifers once daily subcutaneously (T1) or twice daily intramuscularly (T2) using the same daily dose of 9, 7, 5, and 3 mg per day. Estrus was induced in all heifers in both experiments using 500 mug and 250 mug Cloprostenol 12 hours apart on the third day of pFSH injections. All heifers were inseminated twice with frozen-thawed semen at 12 and 24 hours after the onset of standing estrus or at 56 and 72 hours after the first PG if estrus was not observed. Embryos were recovered at slaughter and graded on a scale of 1 to 5 (1 = excellent, 5 = degenerated). Data were recorded for the number of corpora lutea (CL), large (>/=10 mm) and medium (5-9 mm) follicles, number of embryos recovered and embryo morphology. Data were analyzed by least squares analysis of variance procedures. In Experiment 1, there was no difference in ovulation rate between main effects. Fewer embryos were recovered from heifers with a persistent corpus luteum (pCL) and injected once daily (1.71+/-.75 vs 5.75+/-1.27) than from any other group. Heifers with pCL yielded lower (P < 0.05) numbers of freezable embryos than cyclic animals, regardless of injection regimen. In Experiment 2, T2 heifers had a significantly higher number of CL (16.4+/-1.7 vs 7.7+/-1.7; P = 0.0003), large follicles (4.1+/-0.5 vs 2.8+/-0.5; P = 0.04), medium follicles (6.4+/-0.7 vs 4.4+/-0.7; P = 0.04), embryos recovered (9.6+/-1.1 vs 4.9+/-1.1; P = 0.0025) and freezable embryos (4.7+/-0.7 vs 2.1+/-0.7; P = 0.014) than T1 heifers. It is concluded that a single daily subcutaneous injection of pFSH results in a lower superovulatory response than the twice daily regimen in heifers.

Concentrations of insulin-like growth factor I and steroids in follicular fluid of preovulatory bovine ovarian follicles: effect of daily injections of a growth hormone-releasing factor analog and(or) thyrotropin-releasing hormone.

To determine whether long-term administration of growth hormone (GH)-releasing factor (GRF) and(or) thyrotropin-releasing hormone (TRH) alters ovarian follicular fluid (FFL) concentrations of insulin-like growth factor-I (IGF-I), progesterone, and estradiol (E2), and follicular growth, Friesian x Hereford heifers (n = 47; 346 +/- 3 kg) were divided into the following four groups: control (vehicle; n = 11); 1 micrograms GRF (human [Des NH2 Tyr1, D-Ala2, Ala15] GRF [1-29]-NH2).kg-1 BW.d-1 (n = 12); 1 microgram TRH.kg-1 BW.d-1 (n = 12); or GRF + TRH (n = 12). Daily injections (s.c.) continued for 86 d. On d 89, heifers that had been synchronized were slaughtered and ovaries were removed. Follicles were grouped by magnitude of diameter into the three following sizes: 1 to 3.9 mm (small, n = 55), 4.0 to 7.9 mm (medium, n = 63), and greater than or equal to 8 mm (large, n = 71). Growth hormone-releasing factor and(or) TRH did not affect (P greater than .10) IGF-I concentrations in FFL of any follicle size group. Growth hormone-releasing factor increased (P less than .06) size (means +/- pooled SE) of large follicles (14.7 vs 13.0 +/- .6 mm). Growth hormone-releasing factor also increased (P less than .05) progesterone concentrations 4.4-fold above controls in FFL of medium-sized follicles but had no effect on progesterone in FFL of the small or large follicles. Thyrotropin-releasing hormone did not alter FFL progesterone or E2 concentrations in any follicle size group. We conclude that the GRF and(or) TRH treatments we employed did not affect intra-ovarian IGF-I concentrations, but GRF may alter steroidogenesis of medium-sized follicles and growth of large follicles.

Growth and estrous behavior of heifers actively immunized against prostaglandin F2 alpha.

To determine the effects of active immunization against prostaglandin F2 alpha (PGF) on estrous activity and performance traits of beef heifers, 50 14-mo-old cyclic heifers (358 +/- 3.3 kg) were assigned to two treatments (n = 25 per treatment): 1) heifers (controls) given 3.3 mg of human serum albumin (HSA) on d 0 (primary) and 27 (booster), and 2) heifers (PGF-immunized) given 3.3 mg of PGF-HSA on d 0 and 27. The adjuvant was DEAE-dextran, and the duration of the experiment was 167 d. Plasma progesterone concentrations (every 3 to 4 d) were used to monitor corpus luteum (CL) presence; PGF antibody titers were determined every 2 wk. Heifers were checked twice daily for estrous behavior and were weighed every 2 wk. Data were analyzed using ANOVA. Antibody titers for PGF-immunized heifers increased to a peak (43 +/- 2.9% binding at a plasma dilution of 1:1,250) on d 55 +/- 4.6. Antibody titers were greater (P = .02) in PGF-immunized than in control heifers by d 15 and remained elevated (P < or = .001) throughout the experiment. Twenty-four of 25 PGF-immunized heifers formed persistent CL with a mean duration of 129 +/- 6.4 d. The mean number of estrous period per heifer were less for PGF-immunized (1.5 +/- .27) than for control heifers (7.0 +/- .32). Mean daily live weight gain of the PGF-immunized heifers was decreased (P < .05; .75 +/- .024 kg) compared with that of controls (.83 +/- .014 kg), largely due to a 31.5% decrease during the 28-d period after booster.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of single or primary plus booster prostaglandin F2 alpha immunization regimens on immune, ovarian, and growth responses of heifers.

Growth rate of heifers is reduced by prostaglandin F2 alpha (PGF) immunization following a primary and booster regimen. The objective was to attenuate the immune response with or without a booster immunization; specifically, the effects of booster interval, dose of PGF-human serum albumin (HSA) conjugate at booster, adjuvant type, or single immunization with one or two adjuvants were examined. Three experiments were conducted using 175 cyclic heifers. Plasma PGF antibody titers were measured every 2 wk and progesterone concentrations every 3 to 4 d. In Exp. 1, single immunization with one adjuvant (3.3 mg of PGF-HSA in either DEAE-dextran [DEAE] or non-ulcerative Freund's adjuvant [NUFA]; or 10.0 mg of PGF-HSA in NUFA) did not induce sufficient antibody titers to consistently induce persistent corpora lutea (CL). Booster intervals of either 14, 21, or 28 d increased titers sufficiently to induce persistent CL (34/35 heifers), but ADG of heifers was less (P < .05) than for those given a single immunization. In Exp. 2, 1.0 mg of conjugate for booster immunization induced a greater (P < .05) immune response than 3.3 mg, and both doses decreased (P < .05) ADG. Single immunization, with half the conjugate dose in DEAE and half in NUFA injected separately, induced persistent CL in 7/8 heifers without decreasing ADG compared with controls. In Exp. 3, single immunization, with half the conjugate dose in DEAE and half in NUFA injected separately, prolonged (P < .05) the intervals to peak titer compared with the booster treatment, but the incidence (13/15 vs 8/8) and duration (120 +/- 4.8 vs 111 +/- 7.9 d) of persistent CL were similar, and ADG was greater (P < .05). In conclusion, attempts to attenuate the immune response following booster immunization were unsuccessful. Single immunization, using two adjuvants separately, induced persistent CL for at least 120 d without decreasing ADG compared with the primary and booster regimen.

Effect of castration method and the provision of local anesthesia on plasma cortisol, scrotal circumference, growth, and feed intake of bull calves.

To determine the effects of castration of calves, with or without local anesthesia, on plasma cortisol, scrotal circumference, ADG, and ADFI, 56 Friesian bulls (5.5 mo of age; mean +/- SE BW = 173 +/- 2 kg) were randomly assigned to each of seven treatments: 1) control (CON); 2) s.c. injection of .1 mg of a human serum albumin-GnRH conjugate with DEAE-dextran adjuvant (HSA-GnRH); 3) burdizzo castration without local anesthetic (BURD); 4) burdizzo castration following local anesthetic administration (BURD + LA); 5) surgical castration without local anesthetic (SURG); 6) surgical castration following local anesthetic administration (SURG + LA); and 7) local anesthetic administration alone (LAA). Blood samples for cortisol analyses were taken via jugular catheter from -2 to 10 h and at 24, 48, and 72 h relative to treatment. Average daily feed intakes were recorded for 5-d periods and calves weighed at 7-d intervals before and after treatment. Local anesthetic alone had no effect (P > .10) on any variable. The HSA-GnRH calves had elevated (P < .05) plasma cortisol from 2 to 6 h compared with CON calves. Peak plasma cortisol was elevated (P < .01) in BURD, BURD + LA, SURG, and SURG + LA compared with CON calves. The SURG calves (46.0 ng/mL) had higher (P < .03) peak cortisol than BURD (31.4 ng/mL) and SURG + LA (35.4 ng/mL) calves. There was no difference in peak cortisol between BURD and BURD + LA (26.5 ng/mL) calves. The ADG from d 0 to 7 was reduced (P < .05) in calves in BURD + LA, SURG, and SURG + LA treatments (-.01, -.83 and -.24 kg, respectively) compared with CON calves (.54 kg). The ADFI were reduced (P < .05) in BURD and BURD + LA calves during d 1 to 5 and in BURD + LA, SURG, and SURG + LA calves during d 6 to 10 compared with CON calves. The scrotal circumferences of BURD and BURD + LA calves were greater (P < .05) than those of CON calves for 7- and 35-d periods post-castration, respectively. Castration induced increases in cortisol and decreases in ADG and ADFI. Surgical castration induced a greater plasma cortisol response than burdizzo castration, and the administration of local anesthetic reduced the cortisol response of surgical castrates but was less effective for burdizzo castrates.