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LIBIDO AND EJACULATE TRAITS OF PERFORMANCE TESTED BOARS.

Byline: R. Savic M. Petrovic D. Radojkovic C. Radovic and N. Parunovic

: ABSTRACT

The main objective of this study was to score variability of fertility traits of boars as influenced by breed age at first ejaculation/collection (AFE) the lean meat content (LM) lifetime average daily gain (ADG) and age of boars. The following fertility traits were analysed: libido duration of ejaculation (DE) ejaculate volume (VOL) the density of the ejaculate (DEN) and sperm motility (MO) of boars. Boars' libido was assessed on the basis of duration of preparing to collection (DPC). The study included 7987 ejaculates from 105 boars of three breeds: Swedish Landrace (SL; n=34) Large White (LW; n=39) and Duroc (n=32). Impact assessment was carried out using the GLM procedure of the statistical package SAS 9.1.3 (SAS Inst. Inc. 2002-2003). Of all the traits analysed only the DPC and VOL varied under the influence of all investigated impacts. Boars of SL and LW breeds demonstrated superiority in the trait VOL (+12.53 and +11.25 ml) compared to Duroc.

Ejaculates of boars with AFE from 23 to 27 weeks had the highest VOL but with the lowest qualitative properties. Contrary to the negative trend in the manifestation of libido increase of LM and ADG indicated the trend of increasing DE and VOL. Boars with LM of 61% and higher had the highest VOL and the differences in relation to the first and second class were +6.32 ml (Pless than 0.01) and +5.18 ml (Pless than 0.05) respectively. The ejaculate volume of the boars with the highest ADG compared to the other classes was higher (Pless than 0.001) by 10.88 and 9.81 ml. Boars in different ADG classes produced ejaculate with differing qualitative property DEN. Correlations between production traits and fertility traits were negligible and unlike the ADG only the correlation between LM and DPC was statistically significant (Pless than 0.001).

Key words: boar libido ejaculate traits lean meat content average life daily gain.

INTRODUCTION

High genetic potential of modern breeds of pigs is reflected in the intensive growth high meat content and high fertility. Boars have been bred/selected primarily for properties that have economic importance such as weight gain age at a certain weight and productivity of their daughters (Robinson and Buhr 2005). An important issue in the rearing of pigs is whether the selection in the direction of growth and leanness has a negative impact on the quality of sperm (Wolf 2009). Therefore it is necessary to determine how breeding selection in the direction of increasing weight gain and meat content reflects on the subsequent reproductive performances of boars (libido and ejaculate traits).

Selection in the direction of increasing the muscle depth and reduction of fat can result in reduced fertility of boars (Oh et al. 2006). Much more attention should be paid to the existing breeding practices in selecting of boars for artificial insemination which aims to increase the lean meat content in the carcass and decrease fat thickness which can lead to reduced fertility of boars in the form of reduced sperm production (Wierzbicki et al. 2010). In the study by Wolf (2009) low levels of genetic correlation coefficients (0.00 to 0.13) have been identified between production traits (lean meat content and average daily gain) and the properties of boar sperm.

The aim of this paper is to score variability of boars' libido and ejaculate traits of three breeds during the reproductive exploitation depending on the age at first ejaculation/collection and phenotypic values of production traits at the end of the performance test.

MATERIALS AND METHODS

Data set and analysed traits and measurements: The study included 7987 collections from total of 105 boars of three breeds: Swedish Landrace (SL; n=34) Large White (LW; n=39) and Duroc (n=32). Boars were reared in production (farm) conditions during 2004-2012.

The following boar performance test data were used in the study: lean meat content (LM %) and average life daily gain (ADG kg/day). The performance test was conducted in animals weighing 302 kg to 10010 kg. The group boar test was conducted under the conditions of the testing station on the farm in grouping boxes with 1.5 m2 floor area per animal. Measurement of body weight was performed at the beginning and end of the test. During testing boars were fed two complete mixtures: the first contained 18% of crude proteins (30- 60 kg) and second 15% of crude proteins (60-100 kg). The lean meat content was determined using an ultrasound device PIGLOG 105 at the end of the performance test. The ADG was calculated based on the ratio of the absolute gain (difference in body weight at the end of the test and body weight at birth) and age of boars at the end of the test. Depending on the age at first ejaculation/collection (AFE; age of boars when introduced to reproduction)

LM and ADG boars were grouped into independent classes (Table 1). The study involved the following fertility traits: duration of preparing to collection (DPC) the duration of ejaculation (DE) ejaculate volume (VOL) the density of ejaculate (DEN) and sperm motility (MO). Duration of preparing to collection and duration of ejaculation were measured by a digital clock and are expressed in minutes (min). Duration of preparing to collection is the time from the entry of boars into the room with the mount phantom to early ejaculation. Boars' libido was assessed on the basis of DPC (shorter DPC showed better libido). The ejaculates were collected using a standard manual method (gloved hand method). Ejaculate volume was measured using a graduated cylinder with an accuracy of 10 ml. The density of ejaculate was evaluated using the method of subjective observation that is by observation of sperm sample under a microscope with a standard magnification scores ranging from 1 to 3

Where: 1- rare 2- medium tick and 3- thick sperm. The sperm motility was evaluated based on the intensity of movement/ motility and expressed as numeric value on a scale of 1 to 5 (1- extremely slow movement i.e. flickering with no movement 2- slow movement 3- brisk forward movement 4- rapid progressive movement 5- very active progressive movement). In order to reduce subjectivity in the visual assessment of the sperm motility in case of doubt between two consecutive values of the scale their mean value was considered. Traits that were not clearly measured were without values or had values outside of the biological limit were not used in analysis and therefore the size of the subsamples per traits varied.

Statistical analysis: By applying the GLM procedure of the statistical package SAS 9.1.3 (SAS Inst. Inc. 2002- 2003) the impact assessment was carried out using the following model:Equation

where: yijklm- observed fertility trait - general population average Bi- fixed influence of the breed (i=123) Fj- fixed influence of the class AFE (j=123) Mk- fixed influence of the class LM (k=123) Gl- fixed influence of the class ADG (l=123) b (xijklm - ) linear regression effect of the boar age at the time when ejaculates were taken and eijklm- random error. Least Square Means (LSMeans) values were compared using the t- test with three levels of significance (Pless than 0.05 Pless than 0.01 Pless than 0.001). RESULTS AND DISCUSSION

Variability of the analysed traits: Basic statistical parameters are presented in Table 2. Table 3 shows the significance of the impact of factors included in the model on the variability of boars' libido and ejaculate traits. Of all the traits analysed only DPC and VOL varied under the influence of all investigated impacts.

Linear regression coefficients of influence of boar age on the variability of observed traits had low values indicating linear increase of ejaculate VOL and longer DPC (impaired libido) with increasing age of boars while the qualitative properties of ejaculate (DEN and MO) decreased linearly. A number of studies (Jankeviciute and 1/2ilinskas 2002; Wolf and Smital 2009a; Wolf and Smital 2009b; Banaszewska and Kondracki 2012; Savic et al. 2013) have come to similar conclusions on the increase of VOL with the age of boars. The reason for the VOL increase with the increasing age of the boars is the increase of testicular mass and consequently their ability to produce sperm. According to Ford et al. (2006) and Kanokwan (2011) the primary factor for the daily sperm production is the Sertoli cell count associated with the mass of the testicles. The process of ejaculation in boars is multiphase. The first phase is pre-spermal ejaculate without sperm (prostate secretion).

The second phase is the most important being the seminal fluid of the ejaculate and as most sperm is found in this seminal fluid (according to the various sources 70-80%). The third phase is the post- spermal secretions from accessory sex glands contribute the largest volume to the ejaculate. Contrary to these results in the study by Tomiyama et al. (2008) no regression effect of age on variability of VOL was found. Contarary to our study Wierzbicki et al. (2010) determined that sperm density tended to increase with increasing age of the boars. Wolf and Smital (2009a) determined that dependence of sperm concentration on age started with a short increase until one year of age followed by a long moderate decrease until 3 years and thereafter relative stabilization. Research by Oberlender et al. (2012) has shown that there are no differences in the sperm motility between the boars' age groups. In contrast decreased sperm motility with boar age was found in another study (Wolf and Smital 2009a).

Table 4 shows LSMean values of the analysed fertility traits by factors included in the model.

Effect of breed: Pig breed or genotype significantly affected the variability of the studied traits except for MO. SL boars exhibited the best libido with respect to having the minimum duration of DPC and ejaculates with the highest density. In regard to the VOL fertile breeds (SL and LW) demonstrated superiority compared to Duroc (+12.53 and +11.25 ml).

There is a discrepancy in the results of this study in regard to the evaluation of libido compared to the results obtained by Okere et al. (2005) who found stronger libido in Landrace compared to Yorkshire boars during different seasons but these differences were not significant. This discrepancy in libido may be due to different genetic structure of the studied populations and differences in boar libido assessment methods. There is also a discrepancy in regard to VOL since Okere et al. (2005) established that Yorkshire boars' ejaculate was significantly superior in volume compared to that of Landrace (336.05 and 144.42 ml respectively). The superiority of fertile pig breeds (SL and LW) in relation to the meat-producing breed Duroc with respect to VOL as determined in this study is consistent with the results of research by Savic et al. (2013).

In other research Wolf and Smital (2009a) identified small differences between pig breeds in the properties of sperm as Czech LW boars produced ejaculates with 6 ml less VOL compared to Czech Landrace boars but with a higher concentration of sperm.

Effect of age at first ejaculation: The age of boars when introduced to reproduction i.e. age at first ejaculation/collection had a statistically significant impact on the variation of the studied traits except on the duration of ejaculation. Differences in sperm motility were determined only between AFE groups. Boars who had the first ejaculation/collection at an early age (23-27 weeks) exhibited the weakest libido during their reproductive life. In fact premature introduction of boars to reproduction had a negative impact on subsequent sexual activity regardless of the higher VOL (Pless than 0.05) compared to the boars introduced at a later age. Quantitatively the ejaculates of such boars had the highest VOL but with the lowest qualitative properties (DEN and MO) which indicated that by the end of the performance test for the young boar a preparatory period was required before the introduction in the reproduction.

Effect of production traits: Libido of boars varied (Pless than 0.001 Table 3) influenced by production traits (LM and ADG). Boars with lower carcass meat yield at the end of the performance test (less than 60%) demonstrated the best libido and the preparation time for collection was 0.11 min less (Pless than 0.001) compared to the boars with higher carcass meat yield (60% or more). The increase in ADG indicated the trend of weakening of libido as in boars of the first class (ADG=0.481-0.579 kg/day) preparation time for collection was shorter by 0.14 and 0.22 minutes compared to the second (ADG=0.580-0.619 kg/day) and third class (ADG=0.620-0.701 kg/day) boars. Contrary to the negative trend of the manifestation of libido increase in LM and ADG indicated the trend of increasing DE and VOL. Boars with the highest carcass meatiness (third class LM) had the highest VOL and the differences compared to the first or second class were +6.32 ml (Pless than 0.01) and +5.18 ml (Pless than 0.05) respectively.

The ejaculate volume of the boars with the highest ADG (class 3) in relation to other two classes was greater (Pless than 0.001) by 10.88 and 9.81 ml respectively. In regard to the qualitative properties of ejaculate differences existed only between the ADG classes in the average density manifestation so that boars with the lowest daily gain (first class) had ejaculates with a density score higher by 0.02 compared to the general average. Increase of the preparation time for the collection (impaired libido) should not be a limiting factor in breeding selection directed towards the increase of LM and ADG given the great economic importance of these production traits. On the other hand however it is necessary to appreciate biological limits in the selection and monitor the level of sexual drive with mandatory inclusion of libido in the estimation of breeding values of boars.

There was a positive genetic correlation between the size of the testicles (testicular mass) and production traits (back fat thickness body mass) when the measurements were taken at a constant age (Johnson et al. 1994). There was also a strong correlation between boar body weight and measures of boar testicular size (length and width) with sperm production (correlation coefficient 0.79 to 0.91) according to a study by Ugwu et al. (2009). Research results obtained by Huang and Johnson (1996) suggest that the selection in the direction of increase of the size of the testicles can be a way of improving the reproductive capacity of boars used for artificial insemination. Because of the nature of these correlations it can be concluded that in boars with intensive growth the testicular size will be larger and thus the production of sperm and ejaculate volume will also be greater.

Correlations between analysed traits: The linear correlation between production traits and fertility traits of boars is shown in Table 5. The correlations between the production traits LM and ADG and fertility traits were extremely weak. Correlation coefficients had low values and contrary to ADG only the correlation between the traits LM and DPC was statistically significant (Pless than 0.001). Increased ADG had a positive effect on the VOL but conversely led to decreases in qualitative semen traits and weakening of libido (longer DPC).

According to a rough approximation of the value of correlations in Petz (2004) correlations between fertility traits and production traits found in current study were negligible. Therefore increasing the lean meat content and lifetime daily gain will not have a negative impact on the subsequent reproductive performance of boars i.e. this negative effect is negligible. One reason for the negligible correlations may be the different ages of animals at the time when phenotypic values of these traits were measured. In fact the phenotypic values of production traits were determined when the boars were around 6 months of age while fertility traits were necessarily measured later in the boars' reproductive life. Similar conclusions were highlighted in the study by Wolf (2009) in which the genetic correlation of production traits and properties of sperm were close to zero (i.e. LM and ADG to VOL and concentration -0.05 and -0.03 and 0.08 and 0.08 respectively).

Oh et al. (2006) showed that there was low phenotypic correlation of average daily gain and ejaculate volume (r = -0.02) and concentration (r = 0.11).

Table 1. Classes of the age at first ejaculation lean meat content and average life daily gain of the analysed boars.

###Variable

###Age at first ejaculation###Lean meat content###Average life daily gain

Classes###Value (weeks)###Classes###Value (%)###Classes###Value (kg/day)

###1###23-27###1###57.1-59.9###1###0.481-0.579

###2###28-31###2###60.0-60.9###2###0.580-0.619

###3###32-52###3###61.0-64.1###3###0.620-0.701

Table 2. Basic statistical parameters of the studied boars.

###Trait###N###MeanSD###Interval

Duration of preparing to collection (min)###7543###3.560.63###1.00-7.00

Duration of ejaculation (min)###7535###6.090.70###3.00-8.00

Volume of ejaculate (ml)###7576###235.8177.41###40.00-810.00

Density of ejaculate###7504###2.020.29###1.00-3.00

Sperm motility###7516###3.980.15###1.00-5.00

Lean meat content (%)####-###60.281.38###57.10-64.10

Average life daily gain (kg/day)####-###0.5930.044###0.481-0.701

Table 3. Effect of involved factors in the model on variability of the analysed traits.

###Trait###Factor

###b###Breed###AFE (weeks)###LM (%)###ADG (kg/day)

Duration of preparing to collection (min)###0.0001###

Duration of ejaculation (min)###0.0006###

###NS###

Volume of ejaculate (ml)###0.0643###

Density of ejaculate###-0.0001###

###NS###

Sperm motility###-0.0000###NS###

###NS###NS

Table 4. Least square mean (LSMean) of the analysed traits by factors.

###Traits

###Factors

###DPC (min)###DE (min)###VOL (ml)###DEN###MO

###SL###3.45AA###6.11AA###239.62AA###2.05Aa###3.99

Breed###LW###3.60BB###6.13AA###238.34AA###2.02Bb###3.98

###Duroc###3.63BB###6.04BB###227.09BB###2.03###3.99

###23-27###3.65AAAa###6.12aa###238.68aa###2.00AA###3.97AA

Age at first

###28-31###3.59AABb###6.09###233.52bb###2.04BB###3.99BB

ejaculation/collection (weeks)

###32-52###3.44BB###6.07bb###232.85bb###2.05BB###3.99BB

###57.1-59.9###3.49AA###6.06AA###232.53Aa###2.03###3.98

Lean meat content (%)###60.0-60.9###3.60BB###6.08Aa###233.67aa###2.02###3.99

###61.0-64.1###3.60BB###6.14BBBb###238.85Bbbb###2.04###3.98

###0.481-0.579###3.44AA###6.06AA###231.03AA###2.05AAaa###3.99

Average###life###daily###gain

###0.580-0.619###3.58BB###6.07AA###232.10AA###2.02BB###3.99

(kg/day)

###0.620-0.701###3.66CC###6.16BB###241.91BB###2.03bb###3.98

###3.56###6.09###235.02###2.03###3.99

Table 5. Correlation coefficient (r) between production and fertility traits.

###Duration of preparing###Duration of###Volume of###Density of###Sperm

###Trait

###to collection (min)###ejaculation (min)###ejaculate (ml)###ejaculate###motility

Lean meat content (%)###0.04###0.00NS###-0.01NS###0.01NS###0.01NS

Average life daily gain

###0.15###0.05###0.06###-0.08###-0.04

Conclusions: Overall the demonstration/manifestation and variability of fertility traits of boars during reproductive exploitation is influenced by various genetic and paragenetic factors/effects. In the current study there were differences between pig breeds and Duroc boars by comparison with fertile breeds showed inferiority in use in reproduction. After completion of the performance test a preparatory period is required before the introduction of young boars to reproduction because too early an introduction has negative impact on their later sexual activity. Given the extremely low or negligible correlation between production traits and fertility traits selection aimed to increase the lean meat content and lifetime daily gain will not have a negative impact on the subsequent reproductive performance of boars.

Regardless of the great economic importance of production traits (growth and carcass quality) they should not be the only criterion for selection but rather it is necessary to also evaluate the breeding value of boars based on assessment of their libido and ejaculate traits. This approach to breeding and selection should achieve faster genetic progress and successful expansion of genes of genetically valuable breeding males while also optimising their use in reproduction.

Acknowledgement: This research was financed by the Ministry of Education Science and Technological Development of the Republic of Serbia project TR 31081.

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