Effects influencing boar semen
The aim of this study was to analyze the main influences on the quality and quantity of boar semen. A total of 230,705 records of semen collections were utilised to estimate semen parameters of 2,712 boars belonging to the following breeds: Czech Meat Pig, Duroc, Hampshire, Landrace, Large White, Czech Large White and Pietrain, and various crosses of these breeds. The evaluation was based on volume of semen (VO), concentration of spermatozoa (CO), progressive motion of spermatozoa (MO), abnormal spermatozoa (AB), number of total spermatozoa (NOT) and corrected number of spermatozoa (NOC). A linear model was used for statistical analysis included fixed effects of breed or crossbred combinations, boar within breed or crossbred combinations, month-season, interval between collections and linear and quadratic regression on age of boars at collection. Breeds differed significantly for all examined parameters. The differences between the breeds were for VO 95 ml, for CO 109×103/mm3, for MO 9%, for AB 1.6%, for NOT 24×109 and for NOC19×109. The maximal heterosis effect reached for VO was 12%, for CO 17%, for MO 4%, for AB –14%, for NOT 8% and for NOC 8%. Results demonstrate that the year-seasons have an obvious effect on the quality of semen. The minimal values of semen parameters were observed in summer while the maximal values were in autumn and winter. Direct relationship was found exist between semen output and age of boar. Semen output tended to increase along with the boars' age up to 3.5 years. The acceptable level of semen volume occurred after 3 days of the sexual pause and the pool of spermatozoa was restoring after 5-7 days and fully after 10-11 days.
Keywords: Pig-male reproduction; Semen; Effect of breed; Heterosis; Effect of season; Effect of age; Effect of collection interval
1. Introduction
Monitoring and analyzing the quality and quantity of boar semen has great economic importance for pig breeders. The boar’s impact on the herd reproductive performance is high (Tardif et al., 1999), particularly if the male is mated to many females (Rothschild, 1996; Gadea, 2005). According to Robinson and Buhr (2005) the economic return of an AI centre primarily depends on the boar’s ability to produce spermatozoa during the period. This ability is limited by testicular capacity, libido and physical soundness (feet, legs, back). The production of spermatozoa is affected by collection (frequency and animal handling), health, season, age, feeding and other factors. Commercially important semen quality measures (morphology, motility, longevity in extender, fertilizing ability) are affected by maturation in the male tract, collection and processing, and the dam herself. All of these factors make it difficult to determine if there is a genetic basis for poor semen and complicate the genetic improving of boars for semen traits.
Furthermore, evaluating of semen is important for the development of new reproductive techniques such as artificial insemination (A.I.), multiple ovulation and embryo transfer (MOET), in vitro embryo production (IVEP) and cloning (Visscher et al., 2000; Gerrits et al., 2005; Lin et al., 2006). It also has importance for the development of the sexing technology of sex of offspring in pigs (Johnson et al., 2005). The research of relationships between the semen quality and the fertility in boars (estimated in vivo or in vitro) is also actual (Popwell and Flowers, 2004; Quintero-Moreno et al., 2004). A lot of researches studies indicate that the reproductive fitness of boars depends on the following factors: heritability (Pavlík, 1988; Oh et al., 2003, 2006), testicular size (Clark et al., 2003), nutrition (Khan et al., 2005), age of the boar (Jankeviciute and Zilinskas, 2002), intensity of sexual exploitation (Frangez et al., 2005), photoperiod (Sancho et al., 2004, 2006), outdoor temperature and social environment (Hemsworth, 1996; Kunavongkrit et al., 2005). The aim of the present study was to analyze the influence some of the important effects on the quality and quantity of boar semen.
2. Materials and methods
Data from insemination stations for boars in the Czech Republic
The four basic semen parameters were examined: volume of semen in ml (VO, i.e. volume of sperm rich fraction) measured by graduated cylinder, concentration of spermatozoa (CO) measured by photocolorimetry (×103/mm3), progressive motion of spermatozoa in per cent (MO, i.e. proportion of sperm cells moving straightforward) evaluated microscopically and proportion of abnormal spermatozoa in per cent (AB, i.e. sperm cells deformed or otherwise changed) also evaluated microscopically. The collection and processing of semen was standardized using the methods described in the respective standard (ČSN, 1996). The number of total spermatozoa (NOT, in 109) and the corrected number of spermatozoa (NOC, in 109) were calculated as follows (Smital et al.,2004):
NOT = (VO*CO)/1000
NOC = NOT*(MO/100)*(1-AB/100)
where VO is the volume of semen (ml), COthe concentration of spermatozoa (×103/mm3), MO is the progressive motion of spermatozoa (%), AB the proportion of abnormal spermatozoa (%).
The procedure GLM of SAS®was used (SAS Institute Inc., 1989). The data were analyzed using the following linear model:
PSijklmn =μ+Bi+Mj+Y(j)k+Il+Bo(i)m+[βA+γA2ijklmn]+εijklmn
where PSijklmn is value of the given semen parameters for the nth collection in the mth boar, lth interval of collections, kth year within jth month, jth month and ith breed, μ the overall mean, Bi the effect of ithbreed or crossbred combination (i=1,…,13), Mj the effect of jth month (j=1,…,12), Y(j)k the effect of kthyear within jth month (k=1,…,6), Il the effect of lthinterval of collections (l=1,…,16), Bo(i)m the effect of mth boar within jith breed, Aijklmn the age of boar at collection (days), Β and γ the linear and quadratic regression coefficients, εijklmnis the residual effect.
The effect of heterosis was estimated in the usual way:
HE = (F1-P)/P * 100
where: HE is the estimated effect of heterosis in %, F1 the average value of semen characteristics of hybrid progeny, P is the mid parent value of semen characteristics (P1+P2)/2. For testing the statistical significance of the heterosis effects, the heterosis was considered as linear contrast of the effects of the parental breeds and of the appropriate crossbred combination and the procedure GLM of SAS® was used (SAS Institute Inc., 1989).
3. Results
The values of basic statistics of boar semen parameters are given in Table 1. The traits showed a considerable variability. The highest coefficient of variation (61%) was found for the proportion of abnormal spermatozoa, age of boar and interval between collections (both 55%). The coefficients of variation of other traits were intermediate (ranged from 37 to 46%) and the lowest CV value from semen characteristics (9%) was found only for the motion of spermatozoa.
Table 1 Basic statistics of boar semen parameters
Parameters (unit) | Symbol | Mean | S.D. | CV (%) |
Volume of semen (ml) | VO | 274.20 | 101.297 | 36.9 |
Concentration of spermatozoa (×103/mm3) | CO | 418.76 | 168.980 | 40.4 |
Progressive motion of spermatozoa (%) | MO | 76.07 | 6.978 | 9.2 |
Abnormal spermatozoa (%) | AB | 10.51 | 6.398 | 60.9 |
Number of total spermatozoa (×109) | NOT | 108.11 | 44.952 | 41.6 |
Corrected number of spermatozoa (×109) | NOC | 71.27 | 32.975 | 46.3 |
Age of boar (day) | A | 762.92 | 420.529 | 55.1 |
Interval between two collections (day) | I | 6.96 | 3.831 | 55.0 |
S.D.: standard deviation; CV: coefficient of variation.
N: not significant; LSM: least squares means; S.E.: standard error.
* Significant on the level P<0.05.
** Significant on the level P<0.01.
*** Significant on the level P<0.001.
3.1. Effect of breed and crossing
The effect of breed and hybrid combination were statistically significant (P<0.001) for all the traits. The LSM (Least Square Means) values demonstrate the differences between individual breeds in the observed semen parameters. Other effects included into the linear model (the effect of the month; the effect of the year within the month; the effect of the collection interval; the effect of the boar within the breed and the age of the boar at collection) were also statistically significant (P<0.001). The LSM, standard errors and estimated heterotic effects of the observed semen parameters are summarized in Table 2 for seven of the breeds and six of the crossbred combinations. The differences among the breeds and crossbred combinations for the corrected number of spermatozoa are shown in Fig. 1.
Table 2 Breed differences and heterosis effects in boar semen parameters
Breed – Crossbred (symbol) | No. of collections | LSM | S.E. | Heterosis effect % | Statistical significance of breed differences | ||||||
D | H | L | LW | CLW | P | ||||||
Volume of semen | |||||||||||
Czech Meat (CM) | 6102 | 249.79 | 9.457 | *** | *** | N | N | * | N | ||
Duroc (D) | 7740 | 185.11 | 7.464 | *** | *** | *** | *** | *** | |||
Hampshire (H) | 1208 | 272.16 | 6.767 | N | N | N | N | ||||
Landrace (L) | 38137 | 264.70 | 2.933 | N | *** | N | |||||
Large White (LW) | 44619 | 267.34 | 0.933 | *** | N | ||||||
Czech Large White (CLW) | 25723 | 280.33 | 2.862 | *** | |||||||
Pietrain (P) | 7856 | 260.34 | 8.869 | ||||||||
(CMxP) | 1740 | 214.95 | 2.670 | -15,73 | *** | ||||||
(DxH) | 8838 | 256.58 | 7.104 | 12,22 | *** | ||||||
(DxLW) | 13649 | 232.39 | 5.748 | 2,73 | *** | ||||||
(DxP) | 18598 | 224.04 | 7.709 | 0,59 | N | ||||||
(HxP) | 28142 | 297.73 | 2.294 | 11,82 | *** | ||||||
(LWxP) | 28353 | 273.59 | 6.197 | 3,70 | *** | ||||||
Concentration of spermatozoa | |||||||||||
Czech Meat (CM) | 6102 | 456.33 | 16.521 | N | *** | N | ** | N | N | ||
Duroc (D) | 7740 | 502.56 | 13.040 | *** | *** | *** | *** | *** | |||
Hampshire (H) | 1208 | 394.29 | 11.822 | * | N | * | * | ||||
Landrace (L) | 38137 | 430.84 | 5.125 | *** | *** | ** | |||||
Large White (LW) | 44619 | 405.65 | 1.631 | *** | *** | ||||||
Czech Large White (CLW) | 25723 | 426.93 | 4.999 | * | |||||||
Pietrain (P) | 7856 | 454.31 | 15.493 | ||||||||
(CMxP) | 1740 | 532.46 | 4.666 | 16,94 | *** | ||||||
(DxH) | 8838 | 409.40 | 12.410 | -8,70 | *** | ||||||
(DxLW) | 13649 | 469.79 | 10.041 | 3,45 | *** | ||||||
(DxP) | 18598 | 472.50 | 13.468 | -1,24 | *** | ||||||
(HxP) | 28142 | 393.13 | 4.008 | -7,35 | *** | ||||||
(LWxP) | 28353 | 418.72 | 10.826 | -2,62 | *** | ||||||
Progressive motion of spermatozoa | |||||||||||
Czech Meat (CM) | 6102 | 80.40 | 0.659 | *** | *** | *** | *** | *** | *** | ||
Duroc (D) | 7740 | 71.29 | 0.520 | *** | *** | *** | *** | *** | |||
Hampshire (H) | 1208 | 78.61 | 0.471 | *** | *** | *** | *** | ||||
Landrace (L) | 38137 | 74.69 | 0.204 | *** | * | N | |||||
Large White (LW) | 44619 | 75.96 | 0.065 | *** | *** | ||||||
Czech Large White (CLW) | 25723 | 74.81 | 0.199 | N | |||||||
Pietrain (P) | 7856 | 74.46 | 0.618 | ||||||||
(CMxP) | 1740 | 76.39 | 0.186 | -1,34 | *** | ||||||
(DxH) | 8838 | 78.00 | 0.495 | 4,07 | *** | ||||||
(DxLW) | 13649 | 69.48 | 0.400 | -5,63 | *** | ||||||
(DxP) | 18598 | 71.74 | 0.537 | -1,56 | *** | ||||||
(HxP) | 28142 | 78.29 | 0.160 | 2,29 | *** | ||||||
(LWxP) | 28353 | 75.06 | 0.432 | -0,20 | N | ||||||
Table 2 Breed differences and heterosis effects in boar semen parameters (continued)
Breed – Crossbred (symbol) | No. of collections | LSM | S.E. | Heterosis effect % | Statistical significance of breed differences | ||||||
D | H | L | LW | CLW | P | ||||||
Abnormal spermatozoa | |||||||||||
Czech Meat (CM) | 6102 | 10.64 | 0.629 | N | N | N | N | N | N | ||
Duroc (D) | 7740 | 10.66 | 0.497 | N | N | *** | ** | *** | |||
Hampshire (H) | 1208 | 10.67 | 0.450 | N | * | N | N | ||||
Landrace (L) | 38137 | 10.96 | 0.195 | *** | *** | * | |||||
Large White (LW) | 44619 | 11.82 | 0.062 | * | *** | ||||||
Czech Large White (CLW) | 25723 | 11.46 | 0.190 | *** | |||||||
Pietrain (P) | 7856 | 10.15 | 0.590 | ||||||||
(CMxP) | 1740 | 9.29 | 0.178 | -10,63 | *** | ||||||
(DxH) | 8838 | 10.23 | 0.473 | -4,08 | N | ||||||
(DxLW) | 13649 | 11.79 | 0.382 | 4,89 | *** | ||||||
(DxP) | 18598 | 9.10 | 0.513 | -12,54 | *** | ||||||
(HxP) | 28142 | 9.48 | 0.153 | -8,93 | *** | ||||||
(LWxP) | 28353 | 9.50 | 0.412 | -13,52 | *** | ||||||
Number of total spermatozoa | |||||||||||
Czech Meat (CM) | 6102 | 109.78 | 4.452 | * | *** | N | N | N | N | ||
Duroc (D) | 7740 | 92.07 | 3.514 | N | *** | *** | *** | *** | |||
Hampshire (H) | 1208 | 102.21 | 3.186 | N | N | ** | N | ||||
Landrace (L) | 38137 | 108.53 | 1.381 | *** | *** | *** | |||||
Large White (LW) | 44619 | 103.07 | 0.439 | *** | *** | ||||||
Czech Large White (CLW) | 25723 | 115.46 | 1.347 | N | |||||||
Pietrain (P) | 7856 | 115.86 | 4.175 | ||||||||
(CMxP) | 1740 | 110.58 | 1.257 | -1,99 | N | ||||||
(DxH) | 8838 | 99.63 | 3.344 | 2,56 | N | ||||||
(DxLW) | 13649 | 105.20 | 2.706 | 7,82 | *** | ||||||
(DxP) | 18598 | 104.64 | 3.629 | 0,65 | N | ||||||
(HxP) | 28142 | 112.14 | 1.080 | 2,85 | N | ||||||
(LWxP) | 28353 | 109.37 | 2.917 | -0,09 | N | ||||||
Corrected number of spermatozoa | |||||||||||
Czech Meat (CM) | 6102 | 75.63 | 3.170 | *** | *** | N | *** | N | N | ||
Duroc (D) | 7740 | 56.56 | 2.502 | ** | *** | *** | *** | *** | |||
Hampshire (H) | 1208 | 68.93 | 2.268 | N | N | N | N | ||||
Landrace (L) | 38137 | 70.22 | 0.983 | *** | *** | ** | |||||
Large White (LW) | 44619 | 66.72 | 0.313 | *** | *** | ||||||
Czech Large White (CLW) | 25723 | 74.05 | 0.959 | N | |||||||
Pietrain (P) | 7856 | 76.05 | 2.972 | ||||||||
(CMxP) | 1740 | 73.79 | 0.895 | -2,70 | * | ||||||
(DxH) | 8838 | 67.49 | 2.381 | 7,56 | * | ||||||
(DxLW) | 13649 | 62.13 | 1.927 | 0,79 | N | ||||||
(DxP) | 18598 | 66.86 | 2.584 | 0,84 | N | ||||||
(HxP) | 28142 | 77.15 | 0.769 | 6,43 | *** | ||||||
(LWxP) | 28353 | 73.26 | 2.077 | 2,63 | *** | ||||||
Fig. 1. Breed and crossbred differences in corrected number of spermatozoa (in 109).
The lowest volume of semen (185 ml) was observed in D boars and the highest volume for purebred populations of about 280 ml was recorded for CLW boars. The statistically significant difference between the breeds was 95 ml. The statistically significant heterosis in semen volume was between 3 and 12% for 4 investigated crossbred combinations. No effect of heterosis (i.e. –16%) was obtained only in the combination CM×P. The best of thin semen was in H boars (394×103/mm3) and the best of dense semen was in D boars (503×103/mm3). The statistically significant difference between them was 109×103/mm3. The favourable heterotic effects for the concentration of spermatozoa were manifested only in two from six of crossbred combinations (i.e. D×LW 4% and CM×P 17%). The difference between breeds for the progressive motion of spermatozoa was 9% (interval: from D boars 71% to CM boars 80%) and the low statistically significant heterosis was observed only for two crossbred combinations H×P and D×H (2% and 4%, respectively). The difference between breeds for abnormal spermatozoa was low 1.6% (interval: from P boars 10.2% to LW boars 11.8%) and the statistically significant heterosis was observed in four crossbred combinations between –9 and –14%. The boars of D breed had the lowest number of total spermatozoa (92×109). In contrast, the boars of P breed had the highest number of total spermatozoa (116×109) and the statistically significant difference between them was 24×109 of spermatozoa per ejaculate. The statistically significant heterosis was observed only in the combination D×LW 8%. The results for the complex trait (NOC) were similar to the previous parameter. The minimum was for the D boars 57×109, the maximum for the P boars 76×109 and the difference was 19×109of spermatozoa. The statistically significant effects of heterosis were observed in the combinations LW×P, H×P and D×H (3%, 6% and 8%, respectively).
3.2. Effect of season
The values LSM given in Table 3 demonstrate the changes in the semen parameters during the annual period. The changes of the corrected number of spermatozoa are showed in Fig. 2. The volume of semen had a downward trend until April when it reached a minimum (231 ml). The volume then increased until November when it reached a maximum (280 ml). In contrast, the concentration of spermatozoa was the lowest in September (414×103 in mm3) and the highest during March and April (468×103 in mm3). The progressive motion of spermatozoa and abnormal spermatozoa did not vary extremely during the year. They slight tended to increase in autumn and winter months. Similar seasonal changes for the number of total spermatozoa and corrected number of spermatozoa were observed. The minimal values were recorded in August while the maximal values were in December and January.
Table 3 Effect of season on boar semen parameters
Month | No. of collections | VO | CO | MO | AB | NOT | NOC | |||||||||||
LSM | S.E. | LSM | S.E. | LSM | S.E. | LSM | S.E. | LSM | S.E. | LSM | S.E. | |||||||
1 | 17445 | 252.69 | 3.963 | 461.16 | 6.922 | 74.91 | 0.276 | 9.85 | 0.264 | 112.54 | 1.865 | 74.58 | 1.328 | |||||
2 | 16553 | 240.99 | 3.493 | 461.00 | 6.101 | 74.95 | 0.243 | 9.97 | 0.232 | 107.63 | 1.644 | 71.05 | 1.171 | |||||
3 | 19156 | 233.57 | 3.011 | 467.81 | 5.260 | 75.23 | 0.210 | 10.00 | 0.200 | 105.83 | 1.417 | 69.92 | 1.009 | |||||
4 | 18903 | 231.37 | 2.518 | 467.13 | 4.399 | 75.43 | 0.175 | 9.99 | 0.168 | 104.73 | 1.186 | 69.40 | 0.844 | |||||
5 | 19946 | 238.61 | 2.031 | 453.30 | 3.548 | 75.40 | 0.141 | 9.98 | 0.135 | 104.04 | 0.956 | 68.78 | 0.681 | |||||
6 | 18517 | 243.71 | 1.561 | 440.26 | 2.727 | 75.30 | 0.109 | 10.37 | 0.104 | 102.67 | 0.735 | 67.16 | 0.523 | |||||
7 | 20423 | 245.18 | 1.105 | 436.78 | 1.931 | 75.20 | 0.077 | 10.46 | 0.074 | 102.37 | 0.520 | 66.85 | 0.370 | |||||
8 | 21591 | 249.21 | 0.720 | 425.24 | 1.257 | 75.22 | 0.050 | 10.50 | 0.048 | 101.18 | 0.339 | 66.02 | 0.241 | |||||
9 | 21227 | 260.96 | 0.591 | 413.85 | 1.033 | 75.28 | 0.041 | 10.86 | 0.039 | 102.41 | 0.278 | 66.34 | 0.198 | |||||
10 | 21067 | 274.37 | 0.823 | 423.03 | 1.437 | 75.52 | 0.057 | 10.94 | 0.055 | 109.53 | 0.387 | 71.04 | 0.276 | |||||
11 | 18469 | 280.41 | 1.244 | 429.79 | 2.174 | 75.64 | 0.087 | 11.15 | 0.083 | 113.27 | 0.586 | 73.21 | 0.417 | |||||
12 | 17408 | 275.76 | 1.702 | 443.97 | 2.974 | 75.78 | 0.119 | 11.23 | 0.113 | 115.50 | 0.801 | 74.57 | 0.571 | |||||
Fig. 2. Seasonal variability of corrected number of spermatozoa (in 109).
3.3. Effect of boar age
The dependency of the semen parameters on the age of the boar (A) expressed by quadratic regressions were as follows:
For the volume of semen VO=189.28+0.1655×A−0.000055×A2;
the concentration of spermatozoa CO=473.48−0.0968×A+0.000025×A2;
the progressive motion of spermatozoa MO=75.29+0.0013×A−0.0000003×A2;
the proportion of abnormal spermatozoa AB=9.07+0.0031×A−0.000001×A2;
the number of total spermatozoa NOT=88.30+0.0419×A−0.000016×A2 and for
the corrected number of spermatozoa NOC=58.16+0.0270×A−0.000010×A2.
The Fig. 3 shows the changes of the NOC during the boar’s life cycle. Semen output increased rapidly with the boar’s age during the first three years. It culminated at the age of 3.5 years and then a decline occurred.
Fig. 3. The dependency of corrected number of spermatozoa (in 109) on the age (in day) of boar (NOC=58.16+0.0270×A−0.000010×A2).
3.4. Effect of collection interval
The effect of the interval between collections on the semen parameters is described in Table 4 and the effect on the NOC shows Fig. 4. The results demonstrate that the changes in semen parameters are relevant to the sexual intensity of boars. The volume of semen was initially increased in parallel with the increasing interval between collections until the interval reached 5 days when the plateau occurred. The CO culminated after 11 days of the sexual pause. The MO achieved the plateau after 3 days. The variation of AB has been slight without any evidence of culmination. The NOT and NOC culminated after 10 days of the sexual pause.
Table 4 Effect of collection interval on boar semen parameters
Day | No. of collections | VO | CO | MO | AB | NOT | NOC | ||||||||||
LSM | S.E. | LSM | S.E. | LSM | S.E. | LSM | S.E. | LSM | S.E. | LSM | S.E. | ||||||
1 | 2130 | 200.27 | 1.974 | 316.36 | 3.448 | 74.55 | 0.137 | 10.25 | 0.131 | 65.50 | 0.929 | 41.59 | 0.662 | ||||
2 | 7200 | 231.49 | 1.466 | 342.00 | 2.561 | 75.49 | 0.102 | 10.22 | 0.098 | 75.95 | 0.690 | 50.74 | 0.491 | ||||
3 | 8567 | 247.00 | 1.426 | 370.67 | 2.491 | 75.71 | 0.099 | 10.20 | 0.095 | 87.13 | 0.671 | 58.04 | 0.478 | ||||
4 | 22378 | 248.81 | 1.293 | 399.22 | 2.259 | 75.75 | 0.090 | 10.21 | 0.086 | 93.58 | 0.609 | 62.17 | 0.433 | ||||
5 | 32750 | 258.77 | 1.268 | 422.59 | 2.215 | 75.77 | 0.088 | 10.26 | 0.084 | 102.48 | 0.597 | 67.68 | 0.425 | ||||
6 | 6953 | 260.14 | 1.482 | 447.02 | 2.589 | 75.78 | 0.103 | 10.31 | 0.099 | 108.71 | 0.698 | 71.60 | 0.497 | ||||
7 | 104582 | 264.85 | 1.218 | 460.96 | 2.128 | 75.72 | 0.085 | 10.20 | 0.081 | 114.47 | 0.573 | 75.57 | 0.408 | ||||
8 | 5207 | 260.97 | 1.548 | 474.27 | 2.704 | 75.76 | 0.108 | 10.25 | 0.103 | 116.55 | 0.729 | 77.01 | 0.519 | ||||
9 | 13133 | 261.43 | 1.348 | 480.42 | 2.355 | 75.49 | 0.094 | 10.29 | 0.090 | 118.42 | 0.635 | 77.90 | 0.452 | ||||
10 | 8786 | 267.99 | 1.413 | 488.15 | 2.468 | 75.67 | 0.098 | 10.16 | 0.094 | 123.25 | 0.665 | 81.41 | 0.474 | ||||
11 | 3248 | 261.93 | 1.727 | 494.76 | 3.017 | 75.62 | 0.120 | 10.20 | 0.115 | 122.42 | 0.813 | 80.76 | 0.579 | ||||
12 | 3326 | 260.44 | 1.710 | 493.44 | 2.986 | 75.35 | 0.119 | 10.38 | 0.114 | 121.93 | 0.805 | 79.90 | 0.573 | ||||
15 | 5026 | 262.56 | 1.560 | 491.87 | 2.725 | 74.95 | 0.109 | 10.66 | 0.104 | 122.64 | 0.734 | 79.63 | 0.523 | ||||
21 | 2702 | 261.01 | 1.811 | 493.63 | 3.163 | 74.51 | 0.126 | 11.15 | 0.120 | 122.21 | 0.852 | 78.56 | 0.607 | ||||
30 | 2705 | 256.79 | 1.863 | 479.22 | 3.255 | 73.91 | 0.130 | 12.52 | 0.124 | 116.86 | 0.877 | 72.70 | 0.624 | ||||
>30 | 2012 | 231.31 | 1.987 | 443.20 | 3.470 | 75.13 | 0.138 | 9.81 | 0.132 | 96.85 | 0.935 | 63.30 | 0.666 | ||||
Note
>30: The interval between two collections was higher then the month.
Fig. 4. Effect collection interval on corrected number of spermatozoa (in 109).
4. Discussion
Overall, the comparison with our previous work (Smital et al., 2004) shows that examined boars had higher values of parameters of the quantity (VO, CO, NOT, NOC), but less values of parameters of the semen quality (MO, AB) than boars who were kept to breed in AI centers during 1990 to 1997. Moreover, it was noticeable that the manifestation of heterosis in the present combinations of crossing was less expressive than in the combinations which occurred 10 years ago.
4.1. Effect of breed and heterosis
A lot of research acknowledges that differences in boar fertility are mainly due to genetics and not due only to environmental effects (Rothschild, 1996; Robinson and Buhr, 2005; Oh et al., 2006). This development has been reflected by a large amount of scientific papers on population genetic analyzes (e.g. Grandjot et al., 1997; Oh et al., 2003; Smital et al., 2005). The differences among breeds in the semen parameters given in this study correspond with it. In addition, it is evident that it is rather complicated to determine which breed is the best as far as semen quality and quantity. There are simply too many partial indicators. No breed proved superior in all the observed traits. However, it can be summarized that, in the count on the NOC, there were above-average boars (P, CM and CLW) and average boars (L, H and LW). Boars of the D breed were traditionally bellowing the average. Most authors agree that no breed excels in all semen characteristics. Differences among breeds are often manifested by extremely low volume of ejaculate in Duroc boars (Kennedy and Wilkins, 1984).
The manifestation of favourable heterosis in the parameters of semen conform to a general theory, that the heterosis is displayed in faster development of crossbred animals, lower age at puberty, greater weight at a constant age and greater testicular weight and total number of spermatozoa (Neely and Robison, 1983).
4.2. Effect of season
The season appears to be another comparatively important factor affecting the fertility of boars. A number of authors come to the conclusion that decreasing daylight in the autumn generally causes physiological changes stimulating reproduction functions in boars and it results in variability of a several semen characteristics (Claus and Weiler, 1985; Trudeau and Sanford, 1990; Ciereszko et al., 2000; Sancho et al., 2004). According Marchev et al., (2003) the semen collected in the autumn and winter had significantly better semen volume (P<0.001), sperm concentration (P<0.01) and dose number (P<0.05).
4.3. Effect of age
Fertility of boars is time-limited and during the development of an animal it changes a great deal. Summarizing reports of various authors have the following conclusions: 1) the onset of sexual reflexes in boars is between 2.5 and 3.5 months; 2) the erection appears about 3 months of age; 3) the first ejaculate may be collected at 3 to 5 months of age; 4) the normal spermatogenesis and the normal semen which can be used in AI can be expected at the age of 7 to 8 months. However, it is necessary to take into account that an early onset of reproduction activity in young boars will result in reduced fertility not only during full sexual life but at the end of reproduction activity as well. Falkenberger et al. (1992) reported that boars reach the optimum sperm production with the termination of growth. That is at 2.5 to 3 years of age. According Marchev et al., (2003) the boar’s age has a positive and significant effect (P<0.05) on semen volume, dose number and survival rate at storage of up to 72 h. By Jankeviciute and Zilinskas (2002) all three parameters (ejaculate volume, spermatozoa concentration and sperm morphology) except sperm motility were also significantly affected by age (P<0.05). The volume of ejaculate increased with advancing age, while the concentration of spermatozoa decreased. The highest incidence of spermatozoa with pear-shaped heads occurred in boars <12 months of age and the highest incidence of spermatozoa with simple bent tails occurred in boars >30 months.
4.4. Effect of collection interval
In the current system of insemination in pigs, the sexual intensity may be considered as one of the most important factors influencing fertility of boars. Most authors agree that the increasing the intensity of boar collections deteriorates semen parameters. Johnson et al.(2000) suggest that frequent and periodical ejaculation causes rapid decrease of sperm output. There was observed, that the secondary ejaculation after 24 hours contained about 47% less of sperm cells than the first ejaculation. On the basis of relationships among the collection frequency, the number of sperm cells per the ejaculate and the total sperm output over a period of time, Falkenberg et al. (1992) recommended the optimum collection interval from 2 to 5 days and indicated that higher frequency of ejaculation tended to reduce the number of sperm cells and libido. According to Frangez et al., (2005) the sperm quality decreases with increasing collection frequency and is most pronounced if the collection frequency is 7× per week. Taking into account the fertility rate and litter size, with the number of semen doses obtained per week, the most suitable ejaculate collection frequency in mature boars is two or three times per week. Our results are in agreement with before mentioned findings where the standard level of the semen volume found to be occurred after 3 days of the sexual pause and the pool of sperm cells was restoring acceptably after 5-7 days and fully after 10-11 days.
Comparatively low or zero correlation coefficients concerning the relationships between semen characteristics (VO, CO, MO and AB) indicate, that none of them can be used alone for assessment of the semen quality without considering the remaining characteristics (Pavlík, 1988). Accordingly, a precise method is needed for determination of the semen quality in order to improve the utilization of the most fertile ejaculates (Christensen et al., 2001). According to Robinson and Buhr (2005) it is necessary to develop a complex system for evaluation the ability of boars to provide spermatozoa with a high quality for insemination. It appears that information coming from routine semen analysis carried out at insemination stations might be suitable for this purpose. A good designed analyzing study for the extensive data available in large boar studs regarding to heritability and correlations of boar sperm characteristics and fertility could be of immense value to the swine AI industry. A precise estimation of the fertilizing ability of a boar’s ejaculates would be very useful to improve pig assisted reproduction results. For this purpose, Quintero-Moreno et al., (2004) tested the mathematical combination of several parameters of the boar semen quality analysis, including the computer-assisted semen motility analysis (CASA), as a predictive fertility tool. Their results support the belief that the predictive use of the results obtained in a standard boar semen quality analysis can reasonably be achieved by applying logistic correlation analysis among several function parameters of boar semen quality analysis and in vivo conception rates obtained after artificial insemination. In our study the composite trait of semen quality and quantity were used. This trait was the number of corrected spermatozoa (NOC) in which VO, CO, MO and AB are included. The application of this trait in a selection is assumed to be very convenient as it includes all of the four basic traits of the semen quality and quantity.
5. Conclusion
It can be summarized that the effects referred to in this study (breed, season, sexual intensity and age of boar) have statistically significant influence on the variability of the boars semen parameters. In respect to the number of corrected spermatozoa, the difference between the worst and the best of breeds was 19×109 of spermatozoa, the difference between the months was 9×109 of spermatozoa, the difference between the collections was 39×109 of spermatozoa and the difference between the ages of the boar was 13×109of spermatozoa. In addition, the maximal favourable effect of heterosis for NOCwas 8%. Semen parameters vary seasonally. The seasonal variability implicates the improvement of the parameters in the autumn and winter and the impairment of parameters in the summer. With increased sexual activity of the boar, the semen output and quality decreases. The semen parameters during lifeof the boar improve until body adult age is reached. The better knowledge of these interrelationships could be a beneficial aid for the AI industry in their selection of boars and semen collection strategies and for researches on boar’s fertility in vivo and in vitro as well.
Acknowledgements
Financial support for this study was provided through the project MZE 0002701401of the Czech Republic Department of Agriculture. The author thanks to the Association of Pig Breeders in the Czech Republic for making available the data and Miss. Pavlína Chadrabová for excellent technical assistance.
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