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.

Chronic treatment with an agonist of gonadotropin-releasing hormone enhances luteal function in cattle.

Our hypothesis was that luteal function, as determined by plasma progesterone concentrations, and corpus luteum (CL) size is enhanced in cattle administered an agonist of GnRH when the CL is developing as compared with administration of an agonist when the CL is fully functional. Cattle were chronically administered a GnRH agonist, azagly-nafarelin, from Day 3 to Day 21 (D3) or Day 12 to Day 21 (D12) or served as untreated control females (Day 0 = behavioral estrus). Blood samples were serially collected on Days 7 and 14 to evaluate LH secretory patterns and twice daily to measure plasma progesterone. Ultrasonographic examinations were conducted daily to record the area of the CL. CL size and plasma progesterone concentrations were both enhanced in the D3 group as compared with the control group. Progesterone was increased in the D12 group on Days 16 and 17 as compared with the control females. Treatment with GnRH agonist increased basal and mean LH concentrations in both D3 and D12 groups as compared with the controls. We rejected our hypothesis because chronic administration of a GnRH agonist increased plasma progesterone when administered both when the CL was developing and when it was fully functional. The enhanced luteal function was likely due to increased basal LH.

Effect of chronic treatment with the gonadotrophin-releasing hormone agonist azagly-nafarelin on basal concentrations of LH in prepubertal bulls.

Administration of GnRH agonist for an extended period inhibits pulsatile LH release but enhances testicular function of bulls. The mechanism whereby long-term administration of GnRH agonist enhances testosterone concentration in the blood of bulls has not been determined. The aim of this study was to determine whether chronic treatment with the GnRH agonist, azagly-nafarelin, increases blood concentrations of LH and FSH in prepubertal bulls. Two different doses of the GnRH agonist were administered via Alzet mini-osmotic pumps for 28 days. Blood samples were collected at 20 min intervals for 24 h at days 2, 13 and 25 of treatment. Agonist-treated groups had reduced testosterone pulse frequency (P < 0.05) and increased mean and basal concentrations of testosterone (P < 0.05) compared with untreated control bulls. Basal LH concentrations were higher in agonist-treated bulls during all three periods (P < 0.05) and overall (1 ng ml(-1) higher, compared with control bulls; P < 0.001). Frequency of LH pulses in the agonist-treated groups was reduced to less than one pulse in 24 h. Agonist-treated bulls tended to have (P < 0.10) or had (P < 0.05) a slight but significant increase in blood FSH concentration. In conclusion, the higher blood testosterone concentration in bulls after prolonged treatment with GnRH agonist may result, at least in part, from changes in the testes induced by enhanced basal concentration of LH.

Energy level in winter diets of Fallow deer: effect on plasma levels of insulin-like growth factor-I and sex ratio of their offspring.

To determine the effect of dietary energy level in the first winter on subsequent puberty onset, pregnancy, growth, and secretion of progesterone and insulin-like growth factor-I (IGF-I) in Fallow deer, prepubertal deer were fed either a high (H) or a low (L) energy diet in a randomised complete block design. June-born female Fallow deer were fed ad libitum either 12.5MJ/kg DM (H, n=29) or 10MJ/kg DM (L, n=29) in pelleted rations once per day during the winter (approximately 4-10 months of age) preceding puberty. Blood samples were collected twice weekly during the peripubertal period. During the winter feeding period, DM intake was similar for both groups but average daily gain was greater (P<0.05) for deer fed the H versus L diet. Onset of puberty was not affected (P>0.10) by dietary treatment. Concentrations of progesterone in plasma did not differ (P>0.10) between dietary treatments before or after puberty, increasing after puberty in both groups, and reaching maximal levels 8-12 days after the onset of puberty. Concentrations of plasma IGF-I increased (P<0.05) before puberty in both groups reaching maximal levels 3-4 days before the onset of puberty but did not differ (P>0.10) between H and L diets before or after puberty. Of the 28 does fed the H diet that calved, 75% of the calves born were male versus 46% in the L diet (P<0.05). In conclusion, increased plasma IGF-I concentrations were associated with the onset of puberty in Fallow deer regardless of the level of dietary energy intake during the preceding winter. Increased dietary energy during winter does not alter pregnancy rates but does alter sex ratio of calves born.

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.

Testosterone, LH and FSH episodic secretory patterns in GnRH-immunized bulls.

The objective was to determine: (i) the secretory patterns of LH, FSH and testosterone in bulls, and the temporal relationships between the pulses of these hormones; and (ii) the effect of GnRH immunization on these parameters. Friesian bulls (n = 72) were given a primary immunization on day 0 (10-week-old) and a booster immunization on either day 28 (n = 36) or day 56 (n = 36) against either a GnRH-human serum albumin (HSA) conjugate (n = 48) or HSA (n = 24; control). On the basis of GnRH antibody titres at a plasma dilution of 1:160, 1 week after booster immunization, 12 GnRH-immunized and six control bulls from each booster-immunized group were selected and allocated to one of three groups: control bulls and bulls with medium and high antibody titres (0.3, 32 and 51% binding, respectively; pooled SED 4.3%). Blood samples were taken from these animals (n = 36) every 15 min for 8 h on three occasions: (i) 2 weeks after booster immunization when bulls were 4-5 months of age (prepubertal); (ii) at 7 months of age (peripubertal); and (iii) at 11 months of age (post-pubertal). Data were analysed by PULSAR, ANOVA and chi-squared test. The mean antibody titre of the high antibody titre group was greater (P < 0.05) than that of the medium antibody titre group in prepubertal bulls only, but the mean antibody titres of both antibody titre groups were greater (P < 0.05) than that of the control bulls at all times. The frequency and amplitude of LH and FSH pulses in the control bulls were greater (P < 0.05) during prepuberty than after puberty. The frequency, amplitude and duration of LH pulses were greater (P < 0.05) in control bulls than those in medium and high antibody titre bulls at prepuberty. The mean and basal concentrations of FSH and the amplitude and duration of FSH pulses were greater (P < 0.05) in the control bulls than in the high antibody titre bulls at prepuberty. The frequency of testosterone pulses was greater (P < 0.05) in the control bulls than in the medium and high antibody titre bulls at peripuberty. The mean and basal concentrations and pulse amplitude of testosterone were greater (P < 0.05) in high antibody titre bulls than in control bulls after puberty. There was a close temporal relationship between LH and FSH (62.5% of LH pulses were followed by FSH pulses within 75 min) at prepuberty in the control bulls but there was no relationship after puberty. The opposite trend occurred in the high antibody titre bulls, that is, there was no relationship between LH and FSH at prepuberty but there was a close temporal relationship after puberty. The temporal relationship between LH and testosterone was closest at peripuberty (86.7%) in the control bulls, but increased in the high antibody titre bulls from 0% at prepuberty to 57.1% after puberty. In summary, there was an age-related decrease in LH and FSH pulse frequency and amplitude and also in the temporal relationships between these hormones in control bulls. Prepubertal GnRH immunization had a suppressing effect on the pulsatile release of LH, FSH and testosterone before but not after puberty. The presence of high amplitude testosterone pulses in the GnRH-immunized bulls after puberty indicates that the long-term tonic release of LH may be sufficient to initiate a late pubertal-type increase in testosterone concentrations.

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.

Effects of suppressing cortisol following castration of bull calves on adrenocorticotropic hormone, in vitro interferon-gamma production, leukocytes, acute-phase proteins, growth, and feed intake.

The objective was to determine the effects of reducing the plasma cortisol rise in calves following castration on plasma ACTH concentrations, keyhole limpet hemocyanin (KLH)- and concanavalin A (Con A)-induced in vitro interferon (IFN)-gamma production, white blood cell (WBC) numbers, neutrophil:lymphocyte (N:L) ratio, plasma haptoglobin and fibrinogen concentrations, ADG, and ADFI. Forty 5-mo-old Friesian bull calves (169 +/- 1.7 kg) were assigned to four treatments: 1) control (CON); 2) oral metyrapone administration (MET); 3) surgical castration at 0 h on d 0 (SURG); and 4) oral metyrapone administration and surgical castration (MET+SURG). Cortisol, ACTH, IFN-gamma production, haptoglobin, fibrinogen, ADFI, and ADG were not different between CON and MET animals. The MET+SURG calves had lower (P < .001) peak and mean cortisol during .25 to 1.5 h than SURG animals, but area under the cortisol vs time curve from 0 to 12 h did not differ (P > .39) between SURG and MET+SURG calves. Peak ACTH concentrations and area under the ACTH vs time curve from 0 to 6 h were greater (P < .05) for MET+SURG than for SURG calves. There were no differences between MET+SURG and SURG animals in IFN-gamma production, WBC numbers, and ADFI. On d 1, MET+SURG and SURG animals had lower (P < .01) KLH- and Con A-induced IFN-gamma production and higher (P < .05) neutrophil numbers and N:L ratio compared with CON animals. Plasma haptoglobin on d 1 and 3 and fibrinogen concentrations on d 3 and 7 were elevated (P < .05) for MET+SURG and SURG compared with CON animals, whereas SURG animals had greater (P < .05) haptoglobin and fibrinogen concentrations than MET+SURG animals on d 7. The ADG of SURG calves was lower (P < .05) than that of MET+SURG calves during d 0 to 7. Metyrapone treatment partially suppressed cortisol and increased ACTH in castrated calves but did not alter the castration-induced suppression of IFN-gamma and increases in neutrophil numbers and the N:L ratio.

Effects of cortisol on in vitro interferon-gamma production, acute-phase proteins, growth, and feed intake in a calf castration model.

The objective of this study was to determine the effects of castration, with its presumed pain and inflammatory effects, including increased cortisol, and elevated cortisol per se on in vitro interferon-gamma (IFN-gamma) production, ADG, ADFI, and plasma haptoglobin and fibrinogen. Thirty Friesian bull calves (174 +/- 3.8 kg) were assigned to three treatments (given on d 0): 1) control (CON); 2) i.v. cortisol administration to mimic castration-induced increases in cortisol (CORT); and 3) surgical castration (SURG). Blood samples were collected for 12 h on d 0 and at 24 and 72 h after treatment for cortisol determination. Keyhole limpet hemocyanin (KLH)- and concanavalin A (Con A)-induced in vitro IFN-gamma production in blood, and plasma haptoglobin and fibrinogen were measured in blood samples taken before treatment on d 0 and on d 1 and 3. On d 0, CORT and SURG animals had higher peak cortisol (P < .001) and area under the cortisol curve (P < .001) than CON animals. There were no differences (P > .05) between CON, CORT, and SURG animals in cortisol at 24 and 72 h. There were no differences (P > .05) between CON and CORT animals in IFN-gamma production, haptoglobin, fibrinogen, ADG, and ADFI. Compared with CON animals, SURG animals had lower (P < .05) KLH-induced IFN-gamma on d 1 and CON A-induced IFN-gamma on d 1 and 3. Haptoglobin concentrations were greater (P < .05) for SURG than for CON animals on d 1 and 3. Fibrinogen concentrations were greater (P < .001) for SURG than for CON animals on d 3. The SURG animals had lower (P < .01) ADG and ADFI during d 0 to 7 than CON animals. In conclusion, castration decreased IFN-gamma production, ADG, and ADFI and increased haptoglobin and fibrinogen, and these effects seemed to be independent of plasma cortisol concentrations.

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.

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.

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.

Immunization of prepubertal beef heifers against gonadotropin-releasing hormone: immune, estrus, ovarian, and growth responses.

To develop an effective immunization protocol against human serum albumin-Cys-Gly-GnRH (HSA-GnRH) conjugate to delay the onset of puberty in heifers, 58 heifers (8 mo of age; mean +/- SE BW = 203 +/- 1 kg) were randomly assigned to each of six treatments: 1) controls, .1 mg of HSA, with diethylaminoethyl (DEAE)-dextran as adjuvant, on d 0 and 28; 2) .1 mg of HSA-GnRH, with DEAE-dextran, on d 0; 3) as 2) and booster on d 28; 4) as 3) but boosters also on d 84, 140, 196, and 252; 5) as 2) but half the conjugate given with DEAE-dextran adjuvant and half with non-ulcerative Freund's adjuvant (NUFA), injected in two separate sites; and 6) as 2) but the conjugate given with DEAE-dextran and NUFA, emulsified and injected in two sites. The duration of the experiment was 342 d. Mean plasma GnRH antibody titers (samples every 2 wk) for heifers in Treatments 2 to 6 were 9.4 +/- 1.16, 20.6 +/- 2.21, 43.9 +/- 2.86, 27.9 +/- 2.67, and 44.5 +/- 3.75% binding at a plasma dilution of 1:640. The mean number of times estrus was observed in heifers was less (P < .05; pooled SEM = .53) in Treatments 4 (.2) and 6 (2.4) than in Treatments 1, 2, 3, and 5 (7.8, 7.0, 7.0, and 6.6, respectively). The mean interval to the onset of puberty (the first increase in plasma progesterone > or = .5 ng/mL for > or = 10 d with samples at 3- to 4-d intervals) was greater (P < .05; pooled SEM = 11.6) for heifers in treatments 4 (339 d) and 6 (276 d) than for heifers in Treatments 1, 2, 3, and 5 (164, 159, 165, and 170 d, respectively). Mean ADG of heifers was reduced (P < .05) in treatments 2, 3, 4, and 6 (.71, .72, .68, and .69 kg, respectively) compared with controls (.77). In summary, the multiple booster immunization treatment induced and maintained sufficient anti-GnRH titer to delay puberty for 175 d; a single immunization against GnRH with DEAE and NUFA increased antibody titers enough to delay puberty for 112 d. However, GnRH immunization treatments reduced ADG of heifers in Treatments 2, 3, 4, and 6.

Immunization of heifers against gonadotropin-releasing hormone: antibody titers, ovarian function, body growth, and carcass characteristics.

To investigate the effects of active immunization of cyclic beef heifers with different doses of a human serum albumin-Cys-Gly-GnRH (HSA-GnRH) conjugate on antibody titers, ovarian function, body growth, and carcass characteristics, 32 heifers (BW = 477 +/- 7.1 kg; mean +/- SE) were assigned to one of four immunization treatments: .1 mg of HSA or .01, .1, or 1.0 mg of HSA-GnRH, respectively. All heifers received a primary (d 0) and booster (d 28) immunization using DEAE-dextran as adjuvant. The duration of the experiment was 158 d. Overall antibody titers against GnRH were greater (P < .05) for heifers immunized against GnRH (13 +/- 3.3, 22 +/- 3.8, and 19 +/- 2.8% binding at a plasma dilution of 1: 640 for Treatments 2 to 4, respectively) than for controls (1 +/- .1%). The numbers of heifers that became anestrous (plasma progesterone < .5 ng/mL for > 21 d) were 1/8, 8/8, 7/8, and 8/8, respectively. The interval from primary immunization to anestrus (40.7 +/- 6 d) and the duration of anestrus (78 +/- 7 d) were not affected by dose of HSA-GnRH conjugate. The number of ovulations detected was reduced (P < .05) in GnRH-immunized (4.6 +/- .64, 4.0 +/- .70, and 3.6 +/- .60 for Treatments 2 to 4, respectively) compared with control heifers (9.4 +/- .20). During induced anestrus, follicular growth was generally arrested (< 5 mm in diameter) and plasma estradiol decreased.(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.

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)

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.

Active immunization against prostaglandin F2 alpha: effect of conjugate dose and booster interval on antibody titers and estrous behavior in postpubertal beef heifers.

To optimize the prostaglandin F2 alpha (PGF) immunization protocol (conjugate [PGF-human serum albumin; PGF-HSA] dose and immunization regimen) to achieve prolonged suppression of estrous behavior (EB) in beef heifers, 56, 14-mo-old cyclic heifers were assigned (n = 7 per treatment) to eight treatments: 1) 3.3 mg of PGF-HSA on d 0 (single); 2) 3.3 mg of PGF-HSA on d 0 and 28 (booster; B); 3) as (2) except on d 0 and 55; 4) as (2) except on d 0 and 83; and 5 to 8) as in Treatments 1 to 4 except using 10 mg of PGF-HSA. The adjuvant was diethylaminoethyl-dextran, and duration of the experiment was 170 d. Heifers were checked twice daily for EB. A persistent corpus luteum (CL) was considered present when progesterone (P4) was > or = .5 ng/mL for > or = six consecutive samples (every 3 to 4 d). Data were analyzed using ANOVA for a factorial plan. All heifers produced plasma antibody titers (samples every 2 wk) against PGF (peak range: 7 to 84% binding at 1: 1,250). There were no effects (P > .10) of conjugate dose and no interactions between dose and immunization regimen for any variable; therefore, data were combined across dose. Mean and peak titers were greater (P < .05) in heifers in 55- and 83-d B treatments than those in single immunization and 28-d B treatments. Overall, 48/55 heifers formed a persistent CL (41/41 for B heifers). In the single, and 55- and 83-d B treatments, 23/42 heifers formed persistent CL in response to single/primary immunization. There was no difference between immunization regimens in duration (133 +/- 4.4 d) of persistent CL.(ABSTRACT TRUNCATED AT 250 WORDS)

Immunization of bull calves with a GnRH analogue-human serum albumin conjugate: effect of conjugate dose, type of adjuvant and booster interval on immune, endocrine, testicular and growth responses.

Bull calves were immunized with GnRH analogue-human serum albumin (HSA-Cys-Gly-GnRH) conjugate to determine the effects of dose, adjuvant type and interval between primary and booster injections on plasma testosterone and LH concentrations, and testes and body growth. Friesian bull calves aged between 8 and 10 weeks (n = 72) were blocked according to age and weight and, within block, randomly assigned to 12 treatment combinations (n = 6 per treatment combination) in a 3 x 2 x 2 factorial plan. Main effects were (i) conjugate dose (0.0, 0.1 or 1.0 mg HSA-Cys-Gly-GnRH), (ii) adjuvant (diethylaminoethyl-dextran or non-ulcerative Freund's adjuvant), and (iii) interval between primary (day 0) injection and booster injection (day 28 or 56). Plasma testosterone and LH concentrations and antibody titres were determined in blood samples collected at 14 day intervals during the experiment (140 days). Testicular measurements were taken in situ every 28 days. Antibody titres (% binding at 1:160 dilution) were > or = 10% 28 days after booster injection and remained high for 140 days in 47 of 48 GnRH-immunized bulls. The mean titre was higher (P < 0.05) in response to the 1.0 mg dose compared with the 0.1 mg dose (37.7% versus 29.6% binding, respectively; pooled SED 2.55%). Mean LH and testosterone concentrations were reduced (P < 0.05) in immunized animals compared with controls. However, the 1.0 mg dose decreased mean testosterone concentrations by a greater extent (P < 0.001) than either the 0.1 mg or 0.0 mg doses. Testes length and depth, and scrotal circumference were decreased (P < 0.001) in immunized animals compared with controls; however, the 1.0 mg dose decreased (P < 0.001) testes parameters to the greatest extent. There was no effect of conjugate dose on average daily gain in body mass. It is concluded that (i) dose of conjugate, type of adjuvant and interval between primary and booster injections affected antibody titres, (ii) the use of 0.1 or 1.0 mg of HSA-Cys-Gly-GnRH decreased LH and testosterone concentrations, and testicular development throughout the experiment, without adversely affecting body growth, and (iii) an effective protocol is 1.0 mg GnRH-HSA conjugate, given in the adjuvant diethylaminoethyl dextran, with a primary-booster interval of 56 days.

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.