Sustained testicular atrophy in bulls actively immunized against GnRH: potential to control carcase characteristics

Delivering an Immunocastration Vaccine via a Novel Subcutaneous Implant

Immunocastration relies on the vaccine-mediated stimulation of an immune response to gonadotropin-releasing hormone (GnRH) in order to interrupt spermatogenesis. This approach offers a less painful alternative to traditional castration approaches but the current, commercially available options require multiple doses of vaccine to maintain sterility. Thus, a series of pilot studies were conducted to determine the feasibility of a single-dose immunocastration vaccine implant. These five studies utilized a total of 44 Holstein bulls to determine the optimal vaccine composition and validate the ability of a stainless-steel subcutaneous implant to deliver a vaccine. Outcome measures included the duration of implant retention, scrotal dimensions and temperature, implant site temperature, anti-GnRH antibodies, and serum testosterone concentration. Over the course of several studies, anti-GnRH antibodies were successfully stimulated by vaccine implants. No significant treatment effects on scrotal dimensions or testosterone were detected over time, but changes in spermatogenesis were detected across treatment groups. Results indicate that a single-dose implantable immunocastration vaccine elicits a humoral immune response and could impact spermatogenesis in bulls. These findings provide opportunities for the refinement of this technology to improve implant retention over longer periods of time. Taken together, this approach will offer producers and veterinarians an alternative to physical castration methods, to improve animal welfare during routine livestock management procedures.

Immunization against Gonadotropin-Releasing Hormone in Female Beef Calves to Avoid Pregnancy at Time of Slaughter

Precocious puberty in beef heifers can result in unwanted pregnancies due to accidental breeding by farm bulls. Inbreeding, premature calving followed by dystocia and a high stillbirth rate or slaughtering of pregnant heifers are the consequences of this behaviour. The aim of the study was to postpone puberty by using Improvac^®, an anti-GnRH vaccine. Therefore, n = 25 calves were twice vaccinated, once at the age of 5 and then at 6.5 months. n = 24 calves served as unvaccinated case controls. The onset of puberty was assigned if progesterone analysis in the blood exceeded 1 ng/mL. Progesterone values were excluded if the corresponding serum cortisol levels were ≥60 nmol/L. Our target was met, as in the vaccinated group none of the calves exceeded a progesterone value >1 ng/mL until the scheduled age of slaughter at 11 months and only 12.5% of the animals exceeded a progesterone value of 1 ng/mL over the whole measuring period (>400 days) compared with 56.5% of the calves in the control group. In conclusion, the favourable results from our study using the vaccine Improvac^® represent an animal-friendly, non-invasive and reliable way to avoid early pregnancy in heifers as well as the slaughter of pregnant cattle.

Effectiveness of a New Recombinant antiGnRH Vaccine for Immunocastration in Bulls

Simple Summary

Castration of males is a common procedure in cattle production. Surgical procedures are most commonly used, but there is an increasing interest in non-invasive alternatives to avoid risk of infection, bleeding, pain, stress and to improve animal welfare. Immunization against gonadotropin-releasing hormone is currently being used in livestock, but there is only one commercially available vaccine for cattle and results regarding the number of doses needed to maintain castration are variable. The efficacy, safety, and production parameters of a new antigen for immunocastration in bulls was assessed. Results showed that two doses of the vaccine to 40 10-month-old bulls achieved testosterone suppression below productive performance. Live weight at slaughter and carcass yield was greater in immunized animals than in surgically castrated cattle. Castration effects of the vaccine were maintained until the end of the trial at 24 weeks.

Abstract

Castration by surgical techniques is common in livestock; however, post-surgery complications and concerns for animal wellbeing have created a need for new non-invasive alternatives. The objective of this study was to evaluate immunocastration in bulls using antigen GnRX G/Q; a recombinant peptide proved to be effective in laboratory and companion animals. A nine-month trial with 80 9-month-old Normand x Hereford bulls, kept in a pastured system, was conducted. The herd was divided in half with 40 bulls surgically castrated (SC) and 40 castrated by immunization against GnRH (IC). The antigen was injected on days 0 and 40 of the experiment. After the second dose, the IC group had elevated GnRH antibodies and decreased testosterone levels (below 5 ng/mL) that were maintained for 23 weeks. At slaughter on day 190, the immunocastrated group obtained a higher weight, hot carcass, and dressing percentage than the SC group. There was no difference in pH, color of meat, fat coverage, cooking loss, or tenderness between groups. The bulls showed no inflammatory reaction at the injection site or adverse side effects from the vaccine. Our results demonstrate that immunocastration with GnRX G/Q is an efficient and safe alternative to surgical castration in livestock. Additional work evaluating antigen effects over a longer period is needed to validate commercial viability.

Effect of a single or two doses of an anti-GnRH vaccine on testicle morpho-functional characteristics in Nelore bulls

The aim of this study was to compare testicle morpho-functional characteristics in bulls undergoing a single or two immunizations against GnRH. Nelore (Bos taurus indicus) bulls were randomly allocated into three experimental groups: G1 (n=12), a single 400 μg dose of anti-GnRH vaccine on day 0; G2 (n=11), a first 400 μg dose of anti-GnRH vaccine on day 0 followed by a second (boost) dose 30 days later; and control group (CG, n=12), 1 mL saline 0.9% at day 0. Every 30 days, from day 0 until slaughter at day 90, the bulls were weighed and underwent testicular biometry, semen collection and analysis, and blood sample collection for testosterone measurement. Immediately after slaughter, the testicles were removed and transport at 15°C to the laboratory for histopathological analysis. There was a decrease in testicular height (P=0.0476), width (P=0.0021), and in scrotal circumference (P=0.0001), after either a single (G1) or two (G2) immunizations against GnRH. Both G1 and G2 had lower testosterone concentrations than CG from day 60 on (P<0.01), but in G2, it was also lower than in G1 at day 90 (P=0.0006). All sperm parameters were affected by active immunization against GnRH (P<0.05), and in G2, averages were lesser (P<0.05) than in G1 from day 60 on. No signs of seminiferous tubule degeneration were found in any sample from the CG, contrasting with 75.0% and 100.0% of the samples from G1 and G2, respectively. In summary, immunocastration affected testicle morpho-functional characteristics in bulls in a time- and dose-dependent way.

Effect of Kisspeptin-54 immunization on performance, carcass characteristics, meat quality and safety of Yiling goats

This study aimed to evaluate the effects of kisspeptin-54 immunocastration vaccine on performance, carcass characteristics, meat quality, and safety of Yiling goats. Thirty buck goats were randomly assigned into three groups: PVAX-B2L-Kisspeptin-54-asd immunized (PBK-asd), control, and surgically castrated. PBK-asd immunization significantly stimulated serum anti-kisspeptin antibody production and reduced testosterone hormone compared with the control group (p < .05). Interestingly, PBK-asd plasmid did not integrate into the host genome and had no significant effect on growth hormone, body weight, and average daily gain (ADG). Conversely, surgical castration significantly reduced ADG and carcass weight compared to the control group. Furthermore, PBK-asd immunization did not affect carcass characteristics (dressing percentage, loin area, and fat thickness) and meat quality traits (pH, color, cooking loss, drip loss, and shearing force). These results indicate that the Kisspeptin-54 DNA vaccine is safe and has potential to be used as an alternative to surgical castration for goats without negatively affecting carcass and meat quality.

Effects of immunocastration performed at two live weights on the growth physiology, temperament and testicular development of feral beef bulls

The aim of this study was to examine the effect of administering an anti-gonadotropin-releasing hormone vaccine (Improvac^® , developed for pigs) on the performance, temperament, testicular development, and hormone and metabolite profiles of feral bulls (Bos taurus) vaccinated at two different live weights (LW). In all, 16 Serrana de Teruel animals were involved in this 2 x 2 factorial design using the factors LW (LIGHT vs. HEAVY) and vaccine treatment (control, C vs. vaccinated, VA). All animals received the same diet (ad libitum concentrate plus straw) over a 164-day fattening period. Temperament was assessed using chute and flight speed tests. Testicular diameter and subcutaneous fat thickness were recorded. Testosterone, IGF-1, urea, NEFA, and creatinine profiles were analyzed. Bull weight gain was reduced in VA compared to C animals, regardless of the initial LW. The vaccine did not affect the temperament tests, subcutaneous fat thickness or NEFA and creatinine concentrations and had minor effects on linear body measures. The vaccine inhibited testicular growth, reduced plasma testosterone to residual levels, and increased urea concentrations. LIGHT-C animals exhibited increased mean plasma IGF-1 concentrations compared to LIGHT-VA animals. In conclusion, vaccination reduced bull growth and sexual development irrespective of LW at immunization.

Field-testing a single-dose immunocontraceptive in free-ranging male capybara (Hydrochoerus hydrochaeris): Evaluation of effects on reproductive physiology, secondary sexual characteristics, and agonistic behavior

Controlling wildlife populations to mitigate human-wildlife conflicts and the spread of zoonotic diseases is an ever-growing necessity. The objective of this study was to evaluate a single-dose anti-gonadotropin-releasing hormone vaccine (GonaCon, USDA/NWRC, Fort Collins, CO, USA) as a non-lethal alternative for population control in free-ranging, synanthropic male capybara. In addition to infertility efficacy of this treatment, potential effects on the alpha male's secondary sexual characteristics and agonist behavior need to be assessed because any alterations in these factors could lead to population management failure. The treatment group (n = 3) received 1 mL of the anti-GnRH vaccine, intramuscularly, and the control group (n = 2) a 1 mL sham vaccine. Reproductive behavior and social group dynamics were monitored for 30 days prior to inoculation (June 2017) with continuous observations occurring during the study period. Antifertility effects were assessed by conducting exams of testicular morphology, semen characteristics, and histological analysis (after 270 days via hemi-gonadectomy). Compared to the control group, the testicles of the treated males had severe atrophy (P <  0.05), oligozoospermia and greater numbers of sperm cells in a static developmental phase. Courtship and agonistic alpha male behavior were not altered, and the group's social integrity was maintained. Results indicate there was 100% infertility in capybara males, observed throughout the study period of 18 months, and equally important, the male's alpha characteristics were not affected by the treatment, which is imperative for successful capybara population control efforts.

Effects of an anti-gonadotrophin releasing hormone vaccine on the morphology, structure and function of bull testes

Castration reduces aggressive and sexual behaviour and provides better carcass quality in bull calves. Vaccination against gonadotrophin-releasing hormone (GnRH) is used as an alternative to surgical castration for the purposes of reducing pain and distress in the animals. Currently, no anti-GnRH vaccine has been authorized for use in cattle in the European Union. The aim of the present study was to assess the effect of an anti-GnRH swine-specific vaccine (Improvac®, Zoetis, USA) on the morphology, structure and function of bull testes. Animals were vaccinated at days 1, 21 and 104 of the experimental period and were classified based on their live weight into the following two groups: LIGHT (172.9 ± 30.00 kg) and HEAVY (323.8 ± 37.79 kg). The scrotal circumference was measured on day 1 and prior to slaughter (day 164). At slaughter, the sperm motility and concentration in the caudae epididymis were assessed. Testes were weighed, measured and examined using ultrasound, and then tissue samples were collected and fixed in formalin. Histological and immunohistochemical studies were performed on the testes to measure the diameter of the seminiferous tubules and assess the testicular cell populations. The results revealed that suppression of testicular development was associated with the use of the Improvac® vaccine, which resulted in a smaller size of the testes and impaired spermatid production. However, the effect of Improvac® was more pronounced and consistent in calves vaccinated at a low live weight than at a heavy live weight, which suggested that vaccination is more effective when calves are vaccinated before or early during puberty. However, testes from calves vaccinated at a low live weight were more prone to the development of intraluminal concretions in the seminiferous tubules.

Effects of immunocastration on the performance and meat quality traits of feedlot-finished Bos indicus (Nellore) cattle

This study aimed to evaluate the effects of immunocastration on the performance, testosterone concentration, carcass traits and meat quality of feedlot-finished Nellore cattle. Fifty-eight males (430 ± 36 kg bodyweight; 24 months old) were separated into three groups in a randomised complete design: surgically castration (n = 15), immunocastrated (anti-gonadotropin-releasing hormone (Bopriva®) vaccine, n = 21) and non-castrated (n = 22). The animals were housed in individual pens and fed ad libitum for 90 days with a common diet comprising 70% concentrate and 30% roughage (corn silage). The non-castrated animals had a greater average daily gain, feed efficiency, hot carcass weight and carcass yield than the surgically castrated and immunocastrated animals (P &lt; 0.05). Surgically castrated cattle grew faster and more efficiently than those castrated immunologically (P &lt; 0.05). The surgically castrated and immunocastrated animals had higher colour values L*, a* and b* and cooking loss than non-castrated animals (P &lt; 0.05). In conclusion, immunocastration decreased cattle performance compared with surgically castrated or non-castrated animals. However, immunocastration resulted in better meat quality compared with non-castrated, making it an alternative to surgical castration with no negative effects on animal welfare.

Preliminary study of the effects of an anti-gonadotropin-releasing factor vaccine at two initial liveweights on the carcass traits and meat quality of bulls

The aim of this experiment was to study the effect of the Improvac® anti-gonadotropin-releasing factor vaccine developed for pigs on the carcass quality and shelf life of meat from Serrana de Teruel bulls at two liveweights at the start of immunisation. The anti-gonadotropin-releasing factor vaccine stopped testosterone production regardless of the liveweight. The carcasses of immunised bulls were less heavy and had poorer conformation than those of entire bulls, although the dressing percentages were similar. Immunisation had no influence on the degree of carcass fatness or intramuscular fat content. Immunisation decreased metmyoglobin formation during storage, especially in light bulls. Immunisation reduces the total meat collage, improving tenderness and reducing the ageing time. Minimum toughness was reached 2 weeks earlier than in entire bulls. Quick tenderisation was achieved regardless of the liveweight at immunisation; therefore, the technique studied here could be effective for producing tender meat and avoiding long periods of maturation. In conclusion, immunisation at any of the initial liveweights trialed may be detrimental to animal performance. However, it was effective in delaying metmyoglobin formation and produced more tender meat than that of entire bulls from the first day, thus reducing the ageing time.

Differences between sexes, muscles and aging times on the quality of meat from Wagyu × Angus cattle finished in feedlot

Our objectives were to assess quality parameters and chemical composition, and to evaluate the effects of sex, muscle and aging time on the quality of meats from Wagyu × Angus cross cattle reared under tropical conditions. Analyses were performed on the longissimus thoracis, semitendinosus and triceps brachii muscles obtained from chilled carcasses of a total of 30, 24-month-old, male (immunocastrated) and female animals (15 each sex). An effect of sex (P ≤ 0.05) was observed for subcutaneous fat thickness, marbling score, and ribeye area. The longissimus thoracis muscle from males was less (P < 0.0001) marbled than that from females, but males had greater subcutaneous fat thickness (P = 0.0001) and greater ribeye area (P = 0.0411) compared with females. No effect of sex (P ≥ 0.05) was observed for fat colour measures. An interaction effect of sex and muscle (P < 0.03) was detected for cooking loss, yellow intensity (b*), ash, and fat. Main effect of sex was not observed (P > 0.07) only for the ultimate pH and water-holding capacity. Greater shear force and moisture values were observed (P < 0.01) in meat from males than that from females, but a greater value of luminance (L*), red intensity (a*), chroma (C), hue (Ho), dry matter and protein was observed (P < 0.001) in meat from females than that from males. Main effect of muscle was not observed only for water-holding capacity (P = 0.13). Ultimate pH and shear force values were lesser (P < 0.001) in the longissimus thoracis muscle compared with other muscles. The triceps brachii muscle had the least (P ≤ 0.001) L* and Ho values among muscles, whereas the semitendinosus muscle had the greatest values of a* and C (P < 0.001). The semitendinosus muscle presented the greatest (P < 0.01) protein content compared with other muscles, although not differing in moisture and dry matter content from the triceps brachii muscle. An interaction effect of sex × aging time was observed for ultimate pH (P = 0.0110), meat colour parameters (except for Ho; P ≤ 0.01), and fat L* (P = 0.0025). Greater cooking loss, shear force, and fat a* values were observed (P < 0.01) in meat from males than that from females, but greater values of meat Ho, fat a* and Ho, dry matter, and protein were observed (P ≤ 0.03) in meat from females than that from males. Meat aging of longissimus thoracis reduced shear force. Based on these findings, we recommend that meat from Wagyu × Angus cross cattle should be aged during 7 days because, although differences between 7 and 14 days were observed in either aging times, meat subjected to this process is considered as very tender, based on shear force values. In addition, aging in a shorter period of time can reflect on costs by reducing particularly those related with energy, due to less refrigeration time.

Immunization against GnRF in adult cattle: a prospective field study

BACKGROUND

Suppression of cyclic activity in cattle is often desired in alpine farming and for feedlot cattle, not intended for breeding. A cattle specific anti-GnRF vaccine (Bopriva™) is registered for use in heifers and bulls in different countries. In adult cows vaccinated with Bopriva™, the median period until recurrence of class III follicles was 78 days from the day of the 2nd vaccination and reversibility could be proven, as out of 11 experimental cows 10 cows became pregnant at first, and one cow at second insemination. In the present study, 76 healthy, cyclic Eringer heifers and cows were vaccinated twice with Bopriva™ 3-7 weeks apart, to prevent estrus during alpine pasturing. Blood samples were taken for progesterone and GnRF antibody titer analysis on the day of inclusion (7-9 d before the first vaccination) and at the first vaccination. At the same time, gynaecological examinations were performed. When estrus occurred in the course of the alpine pasturing season, a gynaecological examination was done including analysis of a blood sample (progesterone, anti-GnRF antibody titer). Cows were followed for fertility out to 26 months post second vaccination.

RESULTS

Median duration of estrus suppression was 191 days after the second vaccination (when the 2 vaccinations were given 28-35 days apart). From n = 13 cows showing signs of estrus on the alpine pasture, n = 7 could not be confirmed in estrus (serum progesterone value >2 ng/ml, no class III follicles seen using ultrasonography). Median duration between second vaccination and next calving was 496 days (25%/75% quartiles: 478/532 days).

CONCLUSION

Bopriva™ induced a reliable and reversible suppression of estrus for more than 3 months in over 90% of the cows.

Effect of immunocastration with Bopriva on carcass characteristics and meat quality of feedlot Holstein bulls

To evaluate the effect of immunocastration on carcass and meat characteristics, Holstein bulls aged between 7 and 8months with a live weight of 232±1.19kg were given two separate treatments, placebo (intact bulls) versus Bopriva, and then slaughtered after approximately 239days of fattening. While the testosterone levels in intact bulls remained at 0.42ng/ml throughout the study, by day 181, differences (P<0.05) were observed in immunized bulls, with values of 0.21ng/ml. The carcasses of animals treated with Bopriva recorded both a higher hot carcass weight (HCW) and a cold carcass weight (CCW), as well as higher dorsal fat density, marbling and KPH (P<0.05); however, no differences (P>0.05) were observed in the Longissimus lumborum area. No significant differences (P>0.05) were recorded between the treatments for pH, L*, a*, b* C* and H*. The carcasses of the animals treated with Bopriva were heavier, with higher dorsal fat density and marbling score.

Effect of anti-gonadotropin-releasing factor vaccine and band castration on indicators of welfare in beef cattle

Angus crossbred bulls (n = 60; 257 ± 5.4 d of age; initial BW 358.8 ± 3.78 kg) were used to study the effect of a vaccine against gonadotropin-releasing factor (GnRF) and band castration on behavioral and physiological indicators of pain. Cattle were randomly assigned to 1 of 3 treatments: bulls, band-castrated calves without pain mitigation (castrated), and immune-vaccinated animals administered an anti-GnRF vaccine (vaccinated). All animals were fitted with a radio frequency ear tag so that individual animal feed intake and feeding behavior were recorded daily over the entire trial using an electronic feed bunk monitoring system. Two doses of anti-GnRF vaccine were administrated on d -35 and 0 and band castration was performed on d 0. Animal BW was recorded weekly starting on d -36 until d 56. Visual analog scores (VAS) were measured on d -36 -35, -1, and 0, and salivary cortisol concentration was measured at -30, 0, 30, 60, 120, and 270 min on d -35 and 0 after castration. Saliva and blood were obtained on d 1, 2, 5, and 7 and weekly until d 56 for determination of cortisol and complete blood cell count. Video data were collected for pain, sexual, and aggressive behavior daily the first week and once a week until d 56. Data were analyzed with a mixed-effect model with castration, time, and their interactions as main effects. Vaccinated calves had reduced ADG and intake (P < 0.05 and P < 0.001, respectively) during the first week after vaccination. Band-castrated calves had reduced ADG and intake (P < 0.001) until the end of the study. No differences in salivary cortisol and VAS were observed among groups at d -35 after the first vaccination and before band castration. However, on d 0, castrated cattle had greater cortisol concentrations and VAS (P < 0.05 and P < 0.01, respectively) than bulls and vaccinated animals. Complete blood cell count did not differ (P > 0.05) between treatments on d 0, 1, and 2. At d 56, vaccinated calves had greater (P < 0.05) final BW than band-castrated calves and both had less final BW than bulls. There was no indication that vaccination caused any physiological or behavioral changes indicative of pain. In contrast, band castration resulted in elevated cortisol scores and VAS indicative of a pain response and behavior related to pain (P < 0.001) until d 42 of the study. The present study demonstrates that anti-GnRF vaccine is a viable animal welfare-friendly alternative to traditional band castration in beef cattle under North American feedlot practices.

Design, synthesis and evaluation of a gonadotropin releasing hormone-based subunit vaccine in rams (Ovis aries)

Immunocastration using gonadotropin-releasing hormone (GnRH)-based vaccines has been investigated in rams to reduce aggressive and sexual behaviour and to control meat quality. Despite considerable efforts, a practical GnRH vaccine has yet to be developed for rams. In the present study, a A GnRH-lipopeptide vaccine (GnRH-LP) including two copies of GnRH, 2-amino-d,l-hexadecanoic acid (C16), and a unique T helper epitope, was examined in rams. Rams received a primary and secondary vaccination of GnRH-LP without additional adjuvant (Group 1) or with the adjuvant AdjuVac™ (Group 2). In both Group 1 and 2 anti-GnRH antibody titres increased after secondary vaccination, however, the antibody titres were higher (p<0.01) for rams in Group 2. The latter rams showed a marked decrease in testicular size. The marked and sustained reduction in testicular size in rams treated with GnRH-LP+AdjuVac™ provides the basis for an effective immunocastration vaccine in rams.

Immunization of dogs with recombinant GnRH-1 suppresses the development of reproductive function

This study was designed to evaluate the effect of active immunization using recombinant GnRH-I protein on reproductive function in dogs. Six male and six female dogs were randomly assigned to either a control group or an immunization group (n = 3 males or 3 females/group). Dogs (aged 16 weeks) were immunized against GnRH-I with a maltose-binding protein-gonadotropin-releasing hormone I hexamer generated by recombinant DNA technology. Blood samples were taken at 4-week intervals after immunization. The serum concentrations of testosterone and estradiol and anti-GnRH-I antibodies were determined by RIA and ELISA, respectively. The results showed that active immunization with recombinant GnRH-I increased the serum levels of anti-GnRH antibodies (P < 0.05) and reduced the serum concentrations of testosterone (P < 0.05) and estradiol (P < 0.05) as compared with the controls. At 28 weeks of age, testes and ovaries were taken surgically for morphologic evaluation. Histologic studies performed on testicular and ovarian tissues revealed clear signs of atrophy in the recombinant GnRH-I-immunized dogs and a significant reduction (P < 0.05) in the weights and sizes of paired testes and ovaries in the treated dogs. Microscopically, spermatogonia were visible, but no spermatids and spermatozoa were detected in the seminiferous tubules. Neither early antral nor antral follicles were found in the immunized group. These results demonstrate that recombinant GnRH-I is an effective immunogen in dogs.

Immunization against recombinant GnRH-I alters testicular structure in an experimental boar model

The aim of this study was to evaluate and to compare testicular tissue in immunized and control boars. Eighteen male piglets, aged 12 weeks, were vaccinated twice intramuscularly with a maltose-binding protein-gonadotropin-releasing hormone I hexamer peptide (MBP-GnRH-I6). Blood samples were taken at 12, 18, 21 and 24 weeks of age. Serum concentrations of testosterone and GnRH-I antibodies were determined by radioimmunoassay. The pigs were sacrificed 6 weeks after the second immunization. Testicular weight and size were recorded and tissue samples were collected for histological examination. The results demonstrated that active immunization against MBP-GnRH-I6 increased serum GnRH-I antibody levels (P < 0.05) and reduced serum concentrations of testosterone (P < 0.05) when compared with controls. Histological studies performed on testicular tissue revealed clear signs of atrophy in the MBP-GnRH-I6 immunized pigs, and a significant reduction (P < 0.05) in paired testes weight and size were seen in the treated boars. Microscopically, the mean diameter of the seminiferous tubules was markedly reduced (P < 0.01). Spermatogonia were visible, as well as few spermatocytes, but no spermatozoa were detected in the seminiferous tubules. Ultramicroscopic analysis of testicular tissue revealed an increase in the thickness of the basement membrane and extensive damage in the cell organelles of the treated animals, including small spermatogonial size, decreased number of mitochondria and endoplasmic reticulum in the primary spermatocyte and spermatid, a shallow hollow for nuclear membranes in Sertoli cells and mitochondrial vacuolation in Leydig cells. We conclude that MBP-GnRH-I6 induces severe atrophy in the testes of immunized boars.

Immunization against recombinant GnRH-I alters ultrastructure of gonadotropin cell in an experimental boar model

BACKGROUND

Gonadotropin cell is the main responsible for the secretion of follicle stimulating hormone (FSH) and luteinizing hormone (LH), and immunocastration reduces the concentrations of serum FSH and LH. A few studies have reported the histological structure of gonadotropin cells obtained from immunocastration animals at the light microscopy level. However, the ultrastructure of gonadotropin cells remains largely unexplored. The aim of this study was to evaluate and to compare ultrastructure of gonadotropin cell in gonadally intact boars and immunologically castrated male animals.

FINDINGS

In this study, serum and adenohypophysis tissue were collected from nine gonadally intact boars and nine male pigs treated with recombinant gonadotropin releasing hormone I (GnRH-I). Anti-GnRH-I antibodies in serum and the ultrastructure of gonadotropin cell in adenohypophysis were determined by enzymelinked immunosorbent assay and electron microscopy, respectively. The results demonstrated that active immunization against recombinant GnRH-I increased serum GnRH-I antibody levels (P<0.05). Ultramicroscopic analysis of gonadotropin cell revealed a decrease (P<0.05) in the number and size of the large granules and small granules in the recombinant GnRH-I immunized animals.

CONCLUSIONS

We conclude that immunization against recombinant GnRH-I induces severe atrophy of granules in gonadotropin cell of boars, possibly reflecting GnRH-I regulation of gonadotropin cell.

Early postnatal immunisation against gonadotrophin-releasing hormone induces a high but differential immune response in heifer calves

The aim of this study was to evaluate endocrinological and immunological effects of early postnatal immunisation against gonadotrophin-releasing hormone (GnRH) in heifer calves, as similar treatment in sheep provokes long-term immunocastration. Heifer calves were injected with either a construct of GnRH - bovine herpes virus 1 glycoprotein D (BHV1 gD; n=9) or saline (n=9) at 2, 6 and 13.5 weeks of age. Antibody (GnRH and carrier) and endocrine responses to immunisation were measured twice monthly (FSH and progesterone) or during intensive sampling regimes (LH). Early postnatal immunisation against GnRH induced a high, but variable, antibody response against both GnRH and carrier. Based on antibody responses, animals were divided into high-titre (HT, n=5) and low-titre (LT, n=4). Occurring mainly in HT, a further peak in anti-GnRH antibodies, stimulated independently of the carrier, was observed at 23 weeks of age, with antibody titres ≥ 10% binding for ≈ 9 weeks post-peak. Conversely immunisation had only temporary, reversible effects on reproductive function, not affecting age at puberty. We hypothesise that the newly generated antibody measured 10 weeks after the final immunisation resulted from antigenic stimulation and immunological memory cell activation to an endogenous GnRH release. This outcome offers an opportunity for further manipulation of reproductive function based on modulation of GnRH secretion and activity where long-term immunological memory may contribute to durable endocrine effects.

Vaccination against gonadotropin-releasing factor (GnRF) with Bopriva significantly decreases testicular development, serum testosterone levels and physical activity in pubertal bulls

The aim of this study was to evaluate the effects of vaccination against gonadotropin-releasing factor (GnRF) on testicular development, testosterone secretion, and physical activity in pubertal bulls. The experiment was performed using 44 bulls aged between 6 and 7 mo. Twenty-three animals were vaccinated twice 4 wk apart with 1 mL of Bopriva (Pfizer, Animal Health, Parkville, Australia) and 21 bulls served as matched controls. Serum GnRF antibody titer and testosterone concentration as well as body weight and scrotal circumference were determined in all bulls for 24 wk from the first vaccination. In addition, physical activity was analyzed in 11 vaccinated and in 10 control animals using the ALPRO DeLaval activity meter system (DeLaval AG, Sursee, Switzerland). The results show that vaccination significantly (P < 0.05) influenced all parameters evaluated except body weight. Antibody titers to GnRF began to rise 2 wk after the first vaccination and reached peak values 2 wk after the second injection. Significant group differences in anti-GnRF titer were present for 22 wk following the first vaccination. Testosterone concentrations were significantly lower between weeks 6 to 24 after first vaccination in bulls with Bopriva compared with control animals. In vaccinated bulls testicular development was impaired after the second injection and scrotal circumference was significantly smaller between weeks 8 to 24 after first vaccination. Physical activity of vaccinated bulls was reduced after the booster injection with significant group differences for a continuous period of 106 days. In conclusion, vaccination against GnRF with Bopriva in pubertal bulls decreased testosterone levels in peripheral blood, testicular development, and physical activity but did not affect weight gain.

Neonatal immunisation against a novel gonadotrophin-releasing hormone construct delays the onset of gonadal growth and puberty in bull calves

The aim of the present study was to investigate the effect of the neonatal immunisation of bull calves against a novel gonadotrophin-releasing hormone (GnRH) construct, comprised of GnRH coupled to the glycoprotein D subunit of the bovine herpes virus-1 (GnRH–BHV1 gD), on endocrine status, reproductive organ development and carcass quality. Eighteen bull calves received either GnRH construct (n = 9) or saline (control; n = 9) at 2, 6 and 13.5 weeks of age. Blood samples were taken to determine antibody titres against GnRH, FSH and testosterone (T) concentrations and LH pulse characteristics, with testicular circumference monitored monthly. Immunisation reduced LH pulse amplitude (P < 0.05) and T concentrations (P < 0.05), particularly at the peak in anti-GnRH titres after the second booster at 16 weeks of age (P < 0.001), but not when titres fell. Despite antibody titres decreasing after 16 weeks, immunisation reduced testicular size between 16 to 57 weeks of age (P < 0.05), provoking an 8-week delay in puberty onset, defined as testicular circumference ≥14 cm. In conclusion, neonatal immunisation induced a significant immune response against GnRH, provoking a temporary endocrine disturbance that had a long-term effect on testicular development, delaying the onset of puberty. These results support the hypothesis that a developmental window exists during testicular development, such that disturbance of the endocrine drive to the gonads during this period results in a longer-term impairment of gonadal function.

Phytoestrogen treatment induces testis alterations in dogs. Potential use in population control

Dog overpopulation is considered a human health risk; they are the terrestrial vector of rabies and reservoirs for other human diseases. Surgical neutering and intratesticular injections have been used in male dogs. Physiological and morphological alterations in reproductive organs can be induced by phytoestrogens. Our goal was to evaluate the effect of oral coumestrol on dog ejaculates and testis histology. Two groups of 5 healthy adult dogs were used. One coumestrolcontaining biscuit was given once a week for a 4 week period to the experimental group. Ejaculates were obtained and evaluated. After treatment, testis were obtained and processed for histology. Compared to controls, treated dogs have reduced tubules (462 +/- 1.4 vs 336 +/- 2 micron(2)), spermatogenic epithelium (49.1 +/- 0.01 vs 13.3 +/- 0.01 micron(2)), and lumen opening (891 +/- 1.4 vs 530 +/- 26.9 micron). Ejaculates from treated animals have increased numbers of abnormal spermatozoa and reduced sperm concentration.

Use of recombinant gonadotropin-releasing hormone antigens for immunosterilization of beef heifers1

The objectives of this study were to evaluate the effects of immunization against recombinant GnRH fusion proteins and growth promotants on onset of puberty, feedlot performance, and carcass characteristics of beef heifers. Heifers were immunized against an ovalbumin fusion protein containing 7 GnRH peptides (oGnRH, n = 12), a thioredoxin fusion protein containing 7 GnRH peptides (tGnRH, n = 12), a combination of oGnRH plus tGnRH (otGnRH, n = 12), or a combination of ovalbumin and thioredoxin (control, n = 11). Each heifer received a primary immunization containing 1 mg of protein in 1 mL of adjuvant injected into the mammary gland at wk 0 (mean age = 38 wk) and booster immunizations at wk 6 and 12. Six heifers within each treatment received Synovex H implants at wk -2. Weekly blood samples were collected from wk -2 to 26 for determination of serum progesterone concentrations and GnRH antibody titers. In GnRH-immunized heifers, GnRH antibody titers increased after the first booster injection, peaked after the second booster injection, and remained elevated through the end of the study (P < 0.01). Heifers immunized against oGnRH achieved greater (P < 0.05) GnRH antibody titers than tGnRH heifers but did not differ (P = 0.20) from otGnRH heifers. During the 26-wk study, ovulation was prevented (P < 0.05) in 10 out of 12, 12 out of 12, 11 out of 12, and 0 out of 11 tGnRH, oGnRH, otGnRH, and control heifers, respectively. At slaughter, uterine weights were lighter (P < 0.01) for GnRH-immunized heifers than control heifers. Synovex H-implanted heifers had greater (P < 0.05) ADG from wk -2 to 26, greater LM area, and lesser percentages of KPH, yield grade, and quality grade than nonimplanted heifers, regardless of the immunization treatment. Immunization against GnRH fusion proteins resulted in production of antibodies against GnRH that prevented ovulation in 92% of the heifers without affecting feedlot or carcass performance. Implanting heifers with Synovex H improved ADG, LM area, and yield grade. Improvements in delivery of the oGnRH vaccine may provide a feasible alternative to surgical spaying of heifers.

Reproductive characteristics of grass-fed, luteinizing hormone-releasing hormone-immunocastrated Bos indicus bulls1

Two field trials were conducted in Brazil to evaluate LHRH immunocastration of Bos indicus bulls (d 0 = 2 yr of age). In Study I, 72 bulls were assigned randomly to one of three treatment groups: LHRH0-immunized, castrated, and intact. Immunized animals (n = 25) received a primary and two booster injections of ovalbumin-LHRH-7 and thioredoxin-LHRH-7 fusion proteins on d 0, 141, and 287. Twenty-three bulls were surgically castrated on d 141, and 24 served as intact controls. All animals were slaughtered on d 385, at approximately 3 yr of age. In Study II, 216 bulls were assigned randomly to the same three treatments as in Study I; however, because of a drought in the area, bulls were kept on pasture an additional year, and a fourth treatment was added, in which one-half the LHRH-immunized bulls received an additional booster on d 639 (fourth immunization). All animals in Study II were slaughtered on d 741 (4 yr of age). Luteinizing hormone-releasing hormone antibodies increased following each immunization for immunized bulls, but they were not detectable in castrate or intact animals in either study. Consequently, scrotal circumference was suppressed in immunized bulls compared with intact controls in both studies. By d 287, serum concentrations of testosterone in LHRH-immunized bulls were decreased compared with intact controls (P < 0.01). In both studies, testes and epididymal weights at slaughter were greater (P < 0.01) for intact (500 +/- 17 and 60 +/- 2 g, respectively) than for immunized bulls (173 +/- 22 and 26 +/- 2 g, respectively) and fourth immunization bulls (78 +/- 23 and 20 +/- 2 g, respectively; Study II). At the end of each study, BW was greater (P < 0.01) for intact bulls than for castrated and LHRH-immunized animals. In these two studies, the efficacy of the LHRH fusion proteins to induce an effect similar to that of surgical castration was considered 92 and 93%, respectively. These data support the concept that immunocastration of bulls at 2 yr of age was successful and that it has practical application as a tool for producing grass-fattened bulls in Brazil.

Using gonadotropin-releasing hormone (GnRH) and GnRH analogs to modulate testis function and enhance the productivity of domestic animals

Gonadotropin releasing hormone (GnRH) controls the activity of the gonadotrope cells of the pituitary gland and, as a consequence, is a critical component of the endocrine cascade that determines the growth, development, and functional activity of testicular tissue. The use of GnRH and GnRH analogs is common in domestic animal production systems. Although GnRH and GnRH analogs are most commonly used to control the fertility and reproductive events in female animals, GnRH agonists and antagonists are increasingly used to modulate the fertility, behavior, and productivity of male animals as well. This review will focus on recent advances in this use of GnRH agonists and antagonists.

Sexual development and the effects of active immunization against GnRH in Chinese Tanyang ram lambs

Tanyang is one of the most important sheep breeds in the northwest of China. However, there is no detailed data on sexual development and timing of puberty/sexual maturity of this breed. This experiment was designed to study the relationships between growth rate and sexual development by measuring body weight, testis diameter, and plasma testosterone concentrations, and observing sexual behavior through puberty from 3 to 8 months old of entire Tanyang ram lambs. At same time, to assess the potential efficacy and welfare benefits of non-surgical castration, the effect of active immunization against gonadotrophin-releasing hormone (GnRH) on sexual development and growth rate on ram lambs was evaluated, and compared with surgically castrated and entire lambs. The results showed that body weight increased at a constant rate from 3 to 8 months old of age. Testis diameter increased rapidly between 3 and 5 months, followed by a period of slow growth. Plasma testosterone concentrations increased sharply from 3 to 6 months of age (P<0.05), after which there were no significant changes from 6 to 8 months of age. Sexual behavior started from 5 months of age. After ram lambs were immunized against GnRH at 3 months of age, there was no increase in testis diameter in the first 4 months after immunization. Plasma testosterone concentrations remained at similar levels to surgically castrated lambs until 6 months of age, and the onset of sexual behavior was delayed, compared with entire ram lambs. GnRH immunization and surgical castration had no significant effect on the body weight by the end of this experiment. These results suggest that 4-5 months of age is a critical period for pubertal changes and testosterone plays an important role in the initiation of puberty and sexual maturity of Tanyang ram lambs in China. In addition, a single shot GnRH immunization at 3 months, acting as an alternative to surgical castration, is a practical method for Chinese Tanyang ram lambs, and provides animal welfare benefits.