Semen and testis characteristics and sexual behaviour of boars
Authors: Hancock J. L. 
Published: March 2009

Two procedures were followed to train boars to mount a dummy sow for semen collections. Of thirty-nine boars which were introduced to the dummy sow with no previous training twelve were trained successfully. Of eight boars which were first allowed daily mating with an oestrous sow in the pen housing the dummy sow, seven were trained successfully.

Measurements of semen characteristics were made on twenty-five fertile boars including nine boars (morphological characteristics only) in use at commercial insemination centres.

The mean ejaculate volume of thirty-four ‘first’ ejaculates was 173·7 ml. (range 85–275 ml.). The mean volume of the fluid fraction was 109·3 ml. (range 15·220 ml.). For second ejaculates these values were 156·9 ml. (range 80·220 ml.) and 93·2 ml. (range 25·165 ml.).

The mean sperm concentration in thirty-five ‘first’ ejaculates was 284·5 x 106/ml. (range 11 × 106/ml. to 925 × 106/ml.). The mean concentration for ten second ejaculates was 224·4 × 106/ml. (range 18 × 106to 295 × 106/ml.).

In samples collected in successive 20 ml. fractions the highest concentration was found in the first 20–40 ml. In some boars the spermatozoa were distributed more uniformly throughout the ejaculate than in others.

The mean number of spermatozoa per first ejaculate was 28·26 × 109(range 0·77 × 109to 80·0 × 109). The mean for second ejaculates was 15·88 × 109(range 0·76 × 109to 44·17 × 109). The mean initial pH of thirty-four first ejaculates was 7·22 (range 6·85–7·9); for second ejaculates it was 7·54 (range 7·22–8·0).

There was a marked increase of pH with time after collection when semen was stored in open vessels; this did not occur when semen was stored in filled stoppered vessels.

The mean pH of the sperm fraction in six ejaculates was 7·06 (range 6·8–7·4); the mean pH for post-sperm fractions of the same ejaculates was 7·36 (range 7·0–7·6).

The freezing points of three ejaculates were –0·54, –0·55 and –0·56° C.

The mean methylene blue reduction time for seven ejaculates was 5·0 min. (range 2·5–6·5 min.). The reducing power of boar semen was virtually unaffected when all the spermatozoa were killed by freezing.

Motility of boar semen was lost rapidly when it was examined under a cover-glass; motility was restored by aeration (removal and replacement of the cover-glass).

The mean percentages of nine morphological classes of spermatozoa in ejaculated semen of fertile boars were as follows: Malformed heads, 3·0; malformed middle-pieces, 2·7; bent tails, 4·5; coiled tails, 0·9; headless, 0·3; tailless, 0·3; broken necks, 0·1; neck beads, 11·8; middle-piece beads, 17·18.

The decline in the concentration of spermatozoa in successive fractions of an ejaculate was associated with a decline in the frequency of middle-piece beads.

The semen of one sterile boar showed a mean frquency of 77% malformed middle-pieces.

The mean percentages of the above classes in samples from the vasa deferentia of nineteen fertile boars were: malformed heads, 5·7; malformed middle-pieces, 5·1; bent tails, 3·6; coiled tails, 0·06; headless, 0·6; tailless, 0·3; broken necks, 0·1; neck beads, 17·4; middle-piece beads, 59·2.

The average percentages in samples from vasa deferentia of four sterile boars were: malformed heads, 11·9; malformed middle-pieces, 30·7; bent tails, 9·1; coiled tails, 0·5; headless, 0·4; tailless, 0·5; fractured necks, 0·9; neck beads, 24·2; middlepiece beads, 30·0.

The mean testis and epididymis weights were 359·2 and 84·7 g. Expressed as percentages of body weight the weights were 0·285 and 0·068. The mean within pair differences in weights were 48·9 g. (between testes) and 8·5 g. (between epididymides).

The macroscopic and microscopic histological features of the testes are described. Tubular atrophy associated with impaction was found to be a common feature of this sample of boar testes. There was no clear relationship of the histological features of the testes either to semen characteristics or to fertility. It is shown that fertile boars may show grossly pathological testes characteristics. The cause of the observed pathological changes was not identified. The findings are discussed.