vtechworks.lib.vt.edu · Web viewImmunological castration temporarily reduces testis size and function without permanent effects on libido and sperm quality in boars D.W. Lugar1,

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Immunological castration temporarily reduces testis size and function without

permanent effects on libido and sperm quality in boars

D.W. Lugar1, M.L. Rhoads1, S.G. Clark-Deener2, S.R. Callahan1, K.J. Prusa3 and M.J.

Estienne4

1Department of Animal and Poultry Sciences, Virginia Tech, Blacksburg, VA 24061,

USA

2Virginia-Maryland Regional College of Veterinary Medicine, Blacksburg, VA 24061,

USA

3Department of Animal Science, Iowa State University, Ames, IA 50011, USA

4Virginia Tech- Tidewater Agricultural Research and Extension Center, Suffolk, VA

23437, USA

Corresponding author: Mark Estienne. E-mail: [email protected]

Short title: Immunological castration in boars

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Abstract

The objective was to determine the effects of immunization against gonadotropin

releasing hormone on reproductive characteristics in boars. Seventy-two boars were

used in a randomized design with three treatments: single immunization (SI) or double

immunization (DI) with Improvest® (Zoetis Animal Health, Florham Park, NJ, USA) and

intact controls (no Improvest® ; CNT) (n = 24/group). At 10, 15, 20, 25, and 40 wk of age,

blood was collected and serum harvested to evaluate testosterone concentrations.

Testosterone concentrations were less for DI boars compared to CNT boars and SI

boars at 20 and 25 wk (P < 0.001), but not 40 wk of age. At wk 25, 18 pigs (n = 6/

group) were sacrifickilled and testes were removed, weighed, and measured and

seminiferous tubules were examined and scored using histologyical slides of testes

parenchyma. A sample of backfat was assessed for boar taint aroma. All testicular

measurements and weights and seminiferous tubule scores were less for DI boars

compared to SI and CNT boars (P < 0.001). More (P < 0.05) SI and CNT boars had

detectable boar taint aroma than DI boars. Libido was assessed at 32, 36, 47, 60, and

63 wk of age and semen collected at 60 wk of age was analyzed for indicators of quality.

There was no treatment effect (P = 0.41) on libido. Semen volume, gel weight and total

number of sperm cells were not different among treatments. Sperm concentration was

greater for DI than SI (P = 0.01), and tended to be greater for DI compared to CNT (P =

0.10). Sperm motility tended to be greater for DI boars compared to CNT boars (P =

0.066). The results show that there are no permanent effects of immunocastration on

reproductive characteristics in boars.

Key Words: Boar, immunocastration, libido, semen

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Implications

The present study confirms that a single immunization against GnRH at 10 wk of

age does not affect growth or reproductive performance in boars. However,

immunization at 10 and 15 wk of age has transient effects on testicular growth and

function. The results of the present study indicate that it is possible to give boars an

immunization against GnRH and then make selection decisions after growth

performance has been assessed. Boars selected for further consideration as breeders

would not receive a second immunization, and our data suggest that there are no

negative effects on reproduction occasioned induced by the first injection. Boars to be

culled would receive the second immunization and could be marketed approximately

four weeks later. The use of immunological castration in boar studs could increase

profitability by eliminating the discounted prices seen when marketing cull boars.

Though it may be possible to retain for breeding boars that previously received two

immunizations, more research is needed to determine the length of time necessary for

reproductive performance to return to normal after the second immunization.

Introduction

On commercial farms in the USA, male piglets destined for traditional markets are

surgically castrated to prevent pork quality issues (Rydhmer et al., 2010). Boar taint is

the off odor and flavor produced when meat from intact males is heated (Squires et al.,

1991; Xue and Dial, 1997). Approximately 35 percent of consumers are hypersensitive

to boar taint, describing it as offensive (Xue and Dial, 1997). Compounds responsible for

boar taint are androstenone, a steroid produced by the Leydig cells of the testes, and

skatole, a product of microbial breakdown of tryptophan in the gut (Squires and

Schenkel, 2010; Grindflek et al., 2011). The breakdown of skatole is inhibited by

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testosterone and estradiol (Zamaratskia and Squires, 2008).

Surgical castration is an emerging animal welfare issue because as thise

procedure causes pain and stress, and is typically performed without anesthesia or

analgesics (McGlone et al., 1993; Prunier et al., 2005; Moya et al., 2008). Alternatives

to surgical castration are therefore being researched. For example, boars may be

functionally castrated by treatment with a substance that elicits an immune response

and antibody production against hypothalamic gonadotropin releasing hormone (GnRH)

(Fabrega et al., 2010; Bilskis et al., 2012). Subsequent secretion of LH and FSH from

the anterior pituitary gland is suppressed and without gonadotropic support, the testes

are rendered nonfunctional, alleviating the need for surgical removal (Fabrega et al.,

2010; Bilskis et al., 2012). An immunological castration product consisting of a modified

version of GnRH conjugated to diphtheria toxoid is commercially available (Improvest®

or Improvac® ; Zoetis Animal Health, Florham Park, NJ, USA). Boars receive a primary

immunization at 9 to 12 wk of age and a booster is administered a minimum of 4 wk

later. The boars can be marketed 3 to 10 wk after the second immunization and are

functionally considered barrows.

Although potential benefits of immunological castration are greatest for producers

raising slaughter hogs, this technology could also be advantageous for farmers

producing breeder boars. On typical breeding stock operations, growth during the grow-

finish phase of production is assessed and boars displaying unacceptable performance

are culled. These animals are sold at severely discounted prices because of the

potential for boar taint. We hypothesize that immunological castration could be used in

the following strategy: All boars receive a primary vaccination and growth is assessed. If

a boar is classified as a cull based on growth performance, then a second immunization

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is administered and the boar is marketed 3-4 wk later for non-discounted prices and

without concern over boar taint. If boar growth performance is acceptable, however,

then there is no second immunization and the animal would be further evaluated for

breeding. This system is contingent on there being no detrimental effects of the primary

vaccination on future semen quality and libido. Thus, the objective of our study was to

investigate the effects of a single or double immunization against GnRH on growth,

semen quality, reproductive hormone concentrations, and libido in boars.

Materials and Methods

Animals and Protocol

The experiment was conducted at the Virginia Tech-Tidewater Agricultural

Research and Extension Center in Suffolk, VA, USA, and all procedures were reviewed

and approved by the Virginia Tech Institutional Animal Care and Use Committee. A total

of 72 Landrace x Yorkshire boars in two blocks were used (n = 45 in block 1 and n = 27

in block 2). Within each block, boars were randomly placed into one of three treatment

groups: single immunization (SI), double immunization (DI), and a control group that

received no immunization (CNT). A trained representative from the product

manufacturer (Zoetis Animal Health, Florham Park, NJ, USA) administered all

immunizations using a proprietary safety injector. Immunizations were given

administered subcutaneously immediately caudal to the ear at 10 (SI and DI) and 15 (DI

only) wk of age. During the grow-finish period, boars were housed in pens of nine boars

each (n = 3 boars/treatment group/pen) and were fed on an ad libitum basis, fortified

corn and soybean meal diets that met the recommendations for the various nutrients

(NRC, 2012). All boars were weighed at birth and at 10, 15, 20 and 25 wk of age.

Average daily gain (ADG) was calculated for the period prior to first treatment (birth to

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10 wk of age) and for each five wk interval (i.e., 10 to 15, 15 to 20, and 20 to 25 wk of

age) during the grow-finish period.

Blood collection and hormone analyses

Blood was sampled from all boars at 10, 15, 20, and 25 wk of age via jugular

venipuncture using a 20 ga, 25.4 mm vacutainer needle (Kendall Monoject, Covidien,

Mansfield, MA, USA). Samples were also collected from a subset of boars (n = 10

boars/treatment group) at 40 wk of age. Collected blood was allowed to clot for 24 hr at

4ºC and was then centrifuged at 4ºC and 1,800 x g for 30 min. Sera were removed using

transfer pipettes, placed into polypropylene tubes, and stored at -20 ºC until hormone

assays were performed. Testosterone and estradiol concentrations in serum were

determined using commercially available radioimmunoassay kits (Siemens Medical

Solutions, Inc., Malvern, PA, USA) validated for porcine serum (Estienne et al., 2004).

The intra-assay CV was 5.5% for the testosterone assay and 8.2% for the estradiol

assay. Assay sensitivity was 0.04 ng/mL for the testosterone assay and 0.01 ng/mL for

the estradiol assay.

Testicular measurements

Testicular measurements were performed after 18 boars (n = 6 boars/treatment

group) were sacrifickilled at 25 wk of age (penetrating captive bolt followed by

exsanguination). The testes were dissected out of the scrotum and the epididymides

were removed. Each testicle was weighed (Acculab; Minitube of America, Inc., Verona,

WI, USA). Circumference was measured latitudinal around the midpoint of the testes

using a cloth measuring tape. Testicular length and width were measured using a

caliper.

Tissue sampling

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Tissue samples were also collected from the 18 boars killed sacrificed at 25 wk of

age. After gross testicular measurements were obtained as described above, a sample

of the testis parenchyma was dissected away and fixed in 10% neutral buffered formalin

for histological preparation. The fixed parenchyma samples were embedded in paraffin,

cut into thicknesses of 5 µm, mounted onto slides and stained with hematoxylin and

eosin at a commercial laboratory (Histo-Scientific Research Laboratories, Woodstock,

VA, USA). Cross sections of 20 seminiferous tubules from each boar were examined

under 400x magnification using an Olympus phase contrast trinocular microscope

(Oympus America, Inc., Melville, NY, USA) and scored using a previously reported

system (Yoshida et al., 1997): 1- a total absence of cells within the seminiferous tubule,

2- Sertoli cells only, 3- a few spermatogonia, 4- many spermatogonia, 5- a few primary

spermatocytes, 6- many primary spermatocytes, 7-a few secondary spermatocytes, 8-

many secondary spermatocytes, 9- a few round spermatids, 10- many round

spermatids, 11 a few late spermatids, and 12- many late spermatids and/or

spermatozoa.

Backfat samples (5 x 5 x 2 cm sections) were collected at the base of the neck

from each animal. The backfat samples were placed in whirl pak bags (Nasco,

Modesto, CA, USA) and flash frozen in liquid nitrogen. The samples were then shipped

to Iowa State University for boar taint aroma evaluation performed by two trained

sensory panel members. Fat samples were thawed, cut in half, placed in Styrofoam

cups, and then heated for 20 sec in a conventional microwave oven on high power.

Samples were then distributed to the panelists and boar taint aroma was scored on a

scale of 0 to 15, with a score of 0 representing no boar taint aroma detected and 15

representing strong boar taint aroma detected. Panel members were blind to animal

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identification and treatment group. 163

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Semen collection and evaluation

At approximately 30 wk of age, boars (n = 30; 10 boars/treatment group) were

placed in individual pens and began receiving daily 2.3 kg of a fortified corn and

soybean meal diet (NRC, 2012). Beginning at 32 wk of age, boars were individually

moved twice weekly to a semen collection pen containing an artificial sow. Semen

collection training sessions for each boar lasted a maximum of 15 min. At 32, 36, 47, 60

and 63 wk of age, boars were evaluated and scored for libido on a five point scale: 1 =

boars showed no interest in artificial sow; 2 = slight interest in artificial sow but did not

attempt to mount; 3 = mounted the artificial sow but did not display an erection; 4 =

mounted artificial sow and displayed an erection, but did not allow semen collection; and

5 = mounted the artificial sow and allowed semen collection (Kozink et al., 2002).

Beginning at 60 wk of age, collected semen from 9 boars (n = 3 boars/treatment group)

was evaluated over the course of two wk (2 collections/wk/boar).

Semen was collected using the gloved hand technique. During collection, semen

was filtered (US BAG; Minitube of America, Inc.) to remove the gel. Gel-free volume and

gel weight were determined gravimetrically using a top-loading balance (Acculab;

Minitube of America, Inc.). Sperm concentration was determined using a photometer

calibrated for boar semen (Spermacue; Minitube of America, Inc.). The percentage of

sperm displaying motility was subjectively determined by examining spermatozoa using

an Olympus phase contrast trinocular microscope (100x) with a heated stage (37ºC)

(Olympus America, Inc.).

Statistical analyses

Statistical analyses were performed using the PROC MIXED function of SAS 9.3

(SAS Institute, Inc., Cary, NC, USA). Repeated measures ANOVA were performed on

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body weights, ADG, testosterone, estradiol, libido, and semen characteristics.

Compound symmetry, unstructured, autoregressive, and heterogeneous autoregressive

covariant structure were tested to minimize akaike information criterion. For body

weights, ADG, and hormone concentrations in serum, the models included week (time),

pen, treatment and the week (time) by treatment interaction as possible sources of

variation. Body weight at 10 wk of age was used as a covariate for ADG from 10 to 15,

15 to 20, and 20 to 25 wk of age. For testosterone and estradiol concentrations, log

transformations of data were performed for normal distribution and data reported herein

represent the actual mean and standard error. For libido and semen data, the models

included treatment, time and the treatment by time interaction as possible sources of

variation. Testicle measurements were analyzed using ANOVA with models that

included pen and treatment as possible sources of variation. Boar taint aroma scores

were analyzed by one-way ANOVA with a model including treatment as the main source

of variation. When appropriate, Tukey-Kramer mean separation test was used to

compare least square mean differences. Boar taint (present or not present) was also

analyzed using Chi Square analysis. Differences were considered significant with a P

value less than or equal to 0.05 and were considered tendencies if the P value was

between 0.12 and 0.05.

Results

Body Weight and ADG

Body weight at 10 wk of age did not differ among treatment groups (P = 0.88).

Body weights were affected by week (P < 0.01), tended to be affected by treatment (P =

0.08), and were not affected by a treatment by week interaction (P = 0.52). Across

weeks (i.e., 15, 20, and 25 weeks of age) body weight tended (P = 0.08) to be greater

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for DI boars (87.5 ± 1.4 kg) compared to CNT boars (83.4 ± 1.4 kg), and SI boars had an

intermediate value (85.3 ± 1.4 kg) not different from the other two groups.

From birth to 10 wk of age, ADG did not differ among treatment groups (P =

0.92). Across time periods (i.e., 10 to 15, 15 to 20, and 20 to 25 wk of age), ADG was

affected by treatment (P = 0.03) and was greater (P < 0.05) in DI boars (0.58 ± 0.05 kg)

compared to controls (0.52 ± 0.05 kg); The SI boars had an intermediate ADG (0.56 ±

0.05 kg) not different (P > 0.05) from the other two groups. Average daily gain was also

affected by time period (P < 0.01), but not by a treatment by time period interaction (P =

0.94).

Estradiol and testosterone concentrations in serum

There was an interaction of treatment and week (P < 0.01) for estradiol

concentrations (Figure 1a). At 10 and 15 wk of age, estradiol concentrations did not

differ (P > 0.05) among treatments. At 20 and 25 wk of age, DI boars had a reduced (P <

0.05) concentration of estradiol compared to the SI and CNT boars. Estradiol

concentrations did not differ (P < 0.05) between SI and CNT boars at any week.

For testosterone concentrations determined at 10, 15, 20, and 25 wk of age,

there was an interaction of treatment and week (P < 0.01) (Figure 1b). At 10 and 15 wk

of age, testosterone concentrations did not differ (P > 0.05) among treatments. At 20

and 25 wk of age, DI boars had a lesser (P < 0.05) concentration of testosterone

compared to CNT and SI boars and testosterone concentrations were not different (P >

0.05) between SI and CNT boars. A subset of boars (n = 10 boars/treatment group) was

also sampled at 40 wk of age and at that time, there was no difference (P = 0.47) in

testosterone concentrations among treatment groups. Testosterone concentrations at

40 wk of age were 1.9 ± 0.5, 2.79 ± 0.5, and 2.0 ± 0.5 for CNT, SI, and DI boars,

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respectively.

Testicular measurements and seminiferous tubule scores

At 25 wk of age, 18 boars (n = 6/treatment group) were sacrifickilled and the

testes of each boar were removed, weighed, and measured (Table 1). Left and right

testicle weights, lengths, widths, and circumferences did not differ (P > 0.12) between SI

and CNT boars, but values in both groups were greater (P < 0.01) compared to DI

boars. Seminiferous tubule scores were similar (P > 0.05) for SI (8.9 ± 0.9) and CNT

boars (10.1 ± 1.0) and both were greater (P = 0.05) than DI boars (6.0 ± 1.0).

Boar taint aroma

Backfat tissue samples collected from boars at 25 wk of age were tested

evaluated for boar taint by a trained sensory panel. Boar taint was detected in 6 of the

18 samples evaluated, with 3 CNT and 3 SI boars having backfat samples with taint

aroma scores greater than 0. Chi square analysis of the data showed that CNT (50%)

and SI (50%) boars had greater (P < 0.05) proportions of animals with detectable boar

taint aroma compared to DI boars (0%). Boar taint aroma values were 1.1 ± 0.5, 0.7 ±

0.5, and 0 ± 0.5, for control, SI, and DI boars, respectively (P = 0.27).

Libido and Semen Characteristics

Libido was evaluated at 32, 36, 47, 60 and 63 wk of age and data are

summarized in Table 2. At 32 wk of age, libido score was not different among

treatments, although it was numerically greater for SI and CNT boars compared to DI

boars (1.5, 1.5 and 1.0, respectively; P = 0.15). For the period from 32 to 63 wk of age,

there was an effect of week (P = 0.03) and libido scores increased with time across all

treatment groups. There were no effects of treatment (P = 0.41) or an interaction of

treatment and week (P = 0.71).

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Semen characteristics are summarized in Table 2. Semen volume, gel weight

and total sperm cells did not differ among treatment groups (P = 0.56, P = 0.84, and P =

0.41, respectively). Sperm concentration was greater for DI boars compared to SI boars

(P = 0.01), and tended to be greater higher for DI boars compared to CNT boars (P =

0.12). Sperm concentration did not differ between SI and CNT boars (P = 0.58). The

percentage of sperm displaying motility tended to be greater increased for DI boars

compared to CNT boars (P = 0.07), and was not different for DI and SI boars or SI and

CNT boars (P = 0.54 and P = 0.23, respectively).

Discussion

Across weeks of the study, the DI boars tended to have greater larger body

weights than the intact controls. Other researchers have reported that DI boars have a

significantly greater body weight than control boars at market age (25 wk of age;

Dunshea et al., 2001; Rikard-Bell et al., 2009; and Fabrega et al., 2010). Other studies,

however, showed no difference in body weight at harvest between intact boars and

immunological castrates (Bonneau et al., 1994; Wicks et al., 2013). The study by Wicks

et al. (2013) employed only 6 intact control boars compared to 20 immunologically

castrated boars and is perhaps the reason no difference was detected in body weight.

In the Bonneau et al. (1994) study, boars were immunized based on body weight and

not on age. Aside from the present report, Lealiifano et al. (2011) are the only

researchers to compare body weight at slaughter and ADG in boars after single or

double injections of Improvest® and they found no differences between SI and DI

treatments.

In the present study, DI boars grew faster than CNT boars and this finding is

consistent with previous research (Zeng et al., 2002; Oliver et al., 2003; Fabrega et al.,

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2010). Turkstra et al. (2002), however, reported that intact boars had a greater ADG

than immunological castrates. In that study boars were not fed on an ad libitum basis,

which is likely the reason for a greater ADG for intact boars than DI boars. Turkstra et al.

(2002) also reported that intact boars had greater feed conversion efficiency than

immunological castrates. Therefore, by restricting feed, boars grew faster and more

efficient than immunocastrates.

Circulating estradiol and testosterone concentrations have been used as

indicators of testicular function in boars (Zamaratskaia and Squires, 2009). In the

current study, secretion of both hormones was suppressed in DI boars. The results of

the current investigation are in concurrence with other studies investigating the effects of

immunological castration on estradiol production (Zamaratskaia et al., 2008; Kubale et

al., 2013). For example, Kubale et al. (2013) showed that estradiol concentrations in

intact boars began increasing around 19 wk of age and a second immunization against

GnRH at that time blocked the increase with concentrations decreasing thereafter.

Herein, we report that boars given two immunizations had significantly reduced

concentrations of testosterone at five wk post second injection compared to control

boars, which agrees with results from previous studies (Falvo et al., 1986; Bonneau et

al., 1994; Dunshea et al., 2001; Turkstra et al., 2002; Zeng et al., 2002; Zamaratskaia et

al., 2008; Kubale et al., 2013; Wicks et al., 2013). In general, testosterone

concentrations are significantly reduced around 2 to 3 wk after the second immunization

(Falvo et al., 1986; Dunshea et al., 2001; Zeng et al., 2002; Wicks et al., 2013).

Lealiifano et al. (2011) reported that boars receiving only one immunization had

significantly greaterhigher concentrations of testosterone than boars receiving two

immunizations. Moreover, that study showed that in blood collected at slaughter, boars

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given the second immunization 6 wk prior had significantly greater concentrations of

testosterone than boars given the second immunization 2 wk before slaughter. These

results indicate that the effects of immunization on testosterone secretion decrease with

time post second immunization. The present study also showed greater elevated

concentrations of testosterone at 25 wk of age compared to 20 wk of age in DI boars

(1.18 ng/mL and 0.06 ng/mL, respectively).

The present study is the first to show that testosterone concentrations at 40 wk of

age in DI boars are not different from intact or SI boars. The study by Lealiifano et al.

(2011) indicated that the effects of immunization decline with time, which is clearly

shown in the results of the present study. Serum testosterone concentrations at 40 wk of

age (25 wk post second immunization) indicate that testicular steroid production

resumed to levels seen in intact boars.

In the present study, single immunizations had no effect on gross testicular

characteristics and values were similar to intact controls. Double injections, however,

caused significant reductions in testicular weights and measurements, in accordance

with results from other studies (Falvo et al., 1986; Bonneau et al., 1994; Dunshea et al.,

2001; Turkstra et al., 2002; Zeng et al., 2002; Oliver et al., 2003; Jaros et al., 2005;

Zamaratskaia et al., 2008; Einarsson et al., 2009; Lealiifano et al., 2011; Kubale et al.,

2013; Wicks et al., 2013). Lealiifano et al. (2011) showed that testicular length, width,

and weight were significantly greater in SI boars than in boars given the second

immunization at least 3 wk before slaughter. In that study, an intact control group

receiving no immunizations was not included. The data from the present study confirms

data found in previous studies demonstrating a reduction in growth of the testes in DI

boars and also confirms that single immunizations have no effects on testicular growth.

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Moreover, double, but not single immunization negatively impacted spermatogenesis as

evidenced by lower seminiferous tubule scores in DI compared with SI and CNT boars.

The results of the present study agree with previous studies that have

investigated boar taint levels in DI boars compared to intact boars (Bonneau et al., 1994;

Dunshea et al., 2001; Turkstra et al., 2002; Zeng et al., 2002; Jaros et al., 2005;

Zamaratskaia et al., 2008; Kubale et al., 2013). Moreover, Lealiifano et al. (2011)

reported that SI boars had concentrations of androstenone seven times greater than DI

boars.

The results of the present study showed no significant difference in libido for DI,

SI and CNT boars at 17 wk post second injection (32 wk of age), though DI boars had a

numerically lower libido score. Nevertheless, the present study shows immunological

castration does not have a permanent effect on libido. Zamaratskaia et al. (2008)

compared sexual behavior of intact boars and boars treated with two injections of

Improvest® in a 7 min mating test with sows or gilts in estrus. The majority of intact boars

mounted a female in estrus quickly after initiation of the mating test, however, none of

the immunologically castrated boars mounted. In that study, three of the immunological

castrates had to be pulled from the test due to fighting with the sow or gilt (in two cases

the sow or gilt attacked the male at initiation of the test). The study also showed that at

15 wk post second immunization, two immunological castrates attempted to mount the

female, but were unsuccessful.

Bilskis et al. (2012) investigated the effects of immunological castration on

mature, AI boars. Although that study did not contain true controls and the results were

confounded with time, it did show a decrease in libido in boars after three

immunizations. The researchers did not report how long the reduction lasted.

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The results of the present study indicate that immunization against GnRH does

not have permanent effects on indicators of semen quality. Indeed, there were no

effects of SI or DI on semen volume, gel weight, or total sperm cells in the ejaculate.

Moreover, sperm concentration and the percentage of sperm displaying motility were

actually greatest in DI boars. Other studies have shown effects on sperm production

and morphology for up to 22 wk after the second immunization. Wicks et al. (2013)

reported that DI boars had decreased amounts of daily sperm production compared to

CNT boars 10 wk post second immunization, as determined from homogenized

testicular samples. Einarsson et al. (2009) investigated the short- and long-term effects

of immunocastration at 4, 16, and 22 wk post second immunization. In that study, DI

boars had a greater incidence of proximal droplets and head abnormalities, but fewer

distal droplets than CNT boars at 4 wk post second injection. At 16 and 22 wk post

second injection, DI boars also had greater numbers of acrosomal abnormalities and

defects compared to CNT boars. Bilskis et al. (2012) investigated the effects of

immunological castration on mature, AI boars and reported that DI boars had decreased

semen volume, and increased abnormal spermatozoa (proximal droplets, bent tails, and

head abnormalities) compared to pre-immunization evaluations. No differences in sperm

motility or concentration after immunization were reported. This study did not utilize

control boars and thus was confounded with time. Although the current results show

promise for potential use of immunological castration on farms raising breeder boars,

semen characteristics were determined for a limited number of animals. Future studies

should investigate the long-term effects of immunological castration on SI and DI boars

in a commercial setting utilizing a large number of animals. Further research is also

needed to investigate the length of time from second immunization until the negative

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effects of the immunization are no longer evident.

Acknowledgements

Funding for this work was provided in part, by the Virginia Agricultural Experiment

Station and the Hatch Program of the National Institute of Food and Agriculture, U.S.

Department of Agriculture, and a grant from the Virginia Agricultural Council (Richmond,

VA) . Expert technical assistance provided by Lee Johnson, Terry Lee and Kim Williams

is gratefully acknowledged. The authors thank Zoetis Animal Health, Florham Park, NJ,

USA for donation and administration of the Improvest® used for this study.

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Table 1. Testicular characteristics in control boars (CNT) and boars given single (SI) or double

(DI) immunizations against GnRH (Improvest® ; Zoetis Animal Health, Florham Park, NJ).

  Treatment  

Item CNT DI SI SEM P values

Left Testicle

Length, cm 28.7a 18.1b 28.1a 1.2 < 0.01

Width, cm 18.5a 10.8b 18.6a 0.7 < 0.01

Circumference, cm 20.5a 12.3b 20.4a 0.7 < 0.01

Weight, g/kg body weight 275.7a 68.4b 280.6a 20.3 < 0.01

Right Testicle

Length, cm 27.9a 17.4b 27.6a 1.1 < 0.01

Width, cm 17.6a 10.8b 18.0a 0.6 < 0.01

Circumference, cm 20.1a 11.8b 20.1a 0.7 < 0.01

Weight, g/kg body weight 255.1a 63.1b 254.2a 18.6 < 0.01

a,b Within a row, means without common superscripts differ (P < 0.05).480

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Table 2. Libido and semen characteristics in control boars (CNT) and boars given single (SI) or

double (DI) immunizations against GnRH (Improvest® ; Zoetis Animal Health, Florham Park, NJ).

Treatment P values

Item CNT DI SI SEM TRT Week

Treatment

x Week

Libido

32 wk 1.5 1.0 1.5 0.2 0.10 - -

32-63 wk 2.0 2.5 2.6 0.4 0.41 0.03 0.71

Semen Characteristics

Volume, mL 277.5 316.6 372.7 66.7 0.56 0.28 0.64

Gel weight, g 49.2 60.6 52.0 17.4 0.84 0.30 0.81

Concentration,

x106/mL 272.1y 344.1a, x 239.1b 24.9 0.01 0.64 0.64

Total sperm,

x109 75.8 109.3 88.2 20.1 0.41 0.33 0.69

Motile sperm,

% 77.5y 86.9x 83.8 2.6 0.07 0.52 0.12

a,b Within a row, means without common superscript differ (P < 0.05)x,y Within a row, means without common superscript tend to differ (P = 0.12)

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Figure Legend

Figure 1. Estradiol (panel a) and testosterone (panel b) concentrations in serum for

boars receiving no (CNT), one (SI) or two (DI) vaccinations against GnRH. The SI boars

received a single immunization at 10 wk of age and DI boars received the first

immunization at 10 wk of age and the second immunization at 15 wk of age. Intact CNT

boars did not receive an immunization. Vertical arrows indicate when immunizations

were administered. Values are actual means and the SEM was 83.0 pg/ml for estradiol

and 1.6 for testosterone. For both estradiol and testosterone concentrations there were

interactions between treatment and time (P < 0.01). Within specific times, concentrations

for DI boars are less (P < 0.05) than CNT or SI boars, and are indicated with an asterisk.

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