MORPHOLOGICAL CHANGES IN WILD BOAR (SUS SCROFA L.) SEMEN IN ANNUAL CYCLE

Roland Kozdrowski, Andrzej Dubiel

ABSTRACT

The objective of the study was to trace morphological changes in the wild boar semen in annual cycle. During 14 months 167 ejaculates were obtained from 3 boars. Smears were made of each ejaculate and evaluated. Classification of morphological changes of spermatozoa was based on Blom's scheme. Most defects of spermatozoa were found to vary seasonally. The proportion of normal spermatozoa in wild boar semen was the lowest in autumn, the main defect being spermatozoa with plasmatic droplets in proximal or distal position. However, in none of the months the proportion of defective spermatozoa exceeded 25%, which suggests that the observed morphological changes did not limit the fertility of the examined boars.

Key words: wild boar, spermatozoa morphology, reproductive season.

INTRODUCTION

The wild boar (Sus scrofa L.) reproduces seasonally. The period of reproductive activity falls on late autumn and early winter [6, 9]. The rutting time is under the effect of shortening light period, food availability and social structure of the herd [4, 6, 9, 12]. According to Fruziński [6] in Poland most wild boar sows rut in November and December. In February and March some sows, which were in poor condition in autumn and some young, take part in reproduction.

There is little information on the reproductive function of wild boars [10]. Data on domestic boars indicate that the season has an effect on the quality of semen, including morphological changes of spermatozoa [2, 5, 7, 8, 11, 14]. Evaluation of spermatozoa morphology is one of the methods of estimating semen quality. It is assumed that in the semen of fertile boars the percentage of defective spermatozoa should not exceed 25 [13], and one of the common defects is spermatozoa with a cytoplasm droplet in proximal or distal position [3, 5, 14].

The aim of our study was to trace morphological changes in wild boar semen in annual cycle.

MATERIAL AND METHODS

The material constituted 167 ejaculates obtained from three wild boars from May 1999 till June 2000. Two of the animals were aged 3 years, one 4 years at the beginning of the experiment. The wild boars were subject to natural photoperiod. The semen was sampled "by hand", once or twice a week, using a phantom or a rutting sow as a stimulant. The number of ejaculates taken in consecutive months was: May, June, July - 5 each month, August 11, September 17, October and November 14 each, December 11, January 15, February and March 16 each, April 14, May 16 and June 8. In summer the boars showed no sexual drive, which reduced the number of ejaculates taken during that period. In order to evaluate the morphological changes, smears were made of fresh semen and stained according to Watson [15]. The smears were examined in light microscope, with immersion, magnification 1000x. In each smear 500 spermatozoa were estimated. Classification of morphological changes followed the scheme proposed by Blom [1 ]. According to this scheme defects of spermatozoa are classified as major defects (affecting fertility) and minor defects (not affecting the male's fertility). The scheme was slightly modified to adjust it to the morphological picture of defects observed on the examined smears.

The following defects of spermatozoa were classified as major:

1. spermatozoa with a cytoplasmic droplet in proximal position
2. spermatozoa with abnormal head shape
3. spermatozoa with neck defects
4. spermatozoa with multiply looped tails
5. spermatozoa with double tails
6. spermatozoa with acrosom anomalies

The acrosom anomalies included the following defects observed on smears: swollen acrosom, acrosom separated or absent.

Minor defects of spermatozoa included:
1. spermatozoa with a cytoplasmic droplet in distal position
2. spermatozoa with a single loop on tail
3. spermatozoa with giant heads

The results for all the samples of each month were presented as mean ± standard deviation. Statistical analysis was based on Student t-test, significance level p<0.05. Correlation coefficients (r) between the duration of light period and the observed morphological changes were also calculated.

RESULTS

The results are presented in Tab. 1. The percentage of normal spermatozoa during the whole experimental period was 86.11 ± 5.47%. Normal spermatozoa were the least numerous in October and December, the most numerous in April and May 2000 (statistically significant difference, p<0.05). The most frequent defect was cytoplasmic droplet in proximal position (mean for the whole experimental period 3.01 ± 2.14%). The highest percentage of spermatozoa with this defect was observed in September, October and November, the lowest - in June 1999 and July (significant at p<0.05). The second most frequent defect was cytoplasmic droplet in distal position (mean for the whole experimental period 2.98 ± 1.86%). The frequency of this defect was the highest in October, December and January, and the lowest in June 1999, April and May 2000 (significant at p<0.05). Spermatozoa with anomalies of acrosom constituted on an average 2.49 ± 1.05% in the whole experimental period. Their percentage was the highest in May 1999, June 1999, July and August, and the lowest in November and December (significant at p<0.05). Spermatozoa with neck defects constituted on an average 1.88 ± 1.37%, ranging from 1.06 ± 0.98% in September to 3.09 ± 1.76% in December. Spermatozoa with a single-loop tail were noted in 1.65 ± 1.41%, being the most frequent in October and December, and the least frequent in May 1999 and from March to June 2000 (significant at p<0.05). Spermatozoa with multiple-loop tails constituted 0.78 ± 0.92%. There was a fairly wide variation between smears with respect to this defect, as testified by high standard deviation. All the defects listed above underwent changes in annual cycle, depending on the duration of light period (Tab. 2). Spermatozoa with defective acrosom were the most frequent in summer, while other defects reached their maximum frequencies in autumn. The remaining defects, i.e. ab normal head shape, double tails or giant heads, were observed rather rarely and no effect of light period duration on their occurrence was found. The mean frequency of major defects for the whole experimental period was 9.24 ± 3.34, such defects being the least frequent in April and May 2000, the most frequent in May 1999 (significant at p<0.05). Minor defects constituted 4.65 ± 2.62%, and were the least frequent in April and May 2000, and the most frequent in October and December (significant at p<0.05).

Morphological changes in the wild boar semen do not depart essentially quantitatively or qualitatively from such changes in domestic boars [3, 5, 7, 8, 11, 14]. Like in domestic boar semen, also in wild boar the most frequent defect is a cytoplasm droplet in proximal or distal position. In our studies the percentage of spermatozoa with this defect increased with shortening of light period, to reach its maximum in autumn. Also Sławeta and Morstin [14] stress that the season significantly affects the percentage of spermatozoa with a cytoplasm droplet in proximal position, with the maximum in autumn. Dörner and Hühn [5] observed the highest proportion of spermatozoa with cytoplasmic droplets from June till September, and they associated it with higher temperature during that period. Borg et al. [2] maintain that the season has no significant effect on the percentage of spermatozoa with a cytoplasmic droplet in proximal position. In our own studies we found also a significant effect of the dura tion of light period on the proportion of spermatozoa with neck defects, multiple and single tail loops and acrosom anomalies. The percentage of normal spermatozoa was as a rule the lowest in autumn. Likewise, Sławeta and Morstin [14] observed the fewest normal spermatozoa in domestic boar in autumn, while Navrátil et al. [11] in most cases noted the fewest normal spermatozoa in winter. Dörner and Hühn [5] and other authors [7, 8] observed the fewest normal spermatozoa in summer. The disparities may result from conditions in which the boars were kept, their breed, individual differences and frequency of semen sampling.

SUMMARY

The results of our studies indicate clearly that the picture of morphological changes of the wild boar semen undergoes changes depending on the duration of light period, and thus depends on the season. It should be stressed however that the percentage of defective spermatozoa did not exceed the standards adopted for the semen of fertile domestic boars in any month. Thus is should be supposed that the observed seasonal changes in the wild boar semen morphology do not limit the fertility of the animals.

ACKNOWLEDGEMENTS

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