**7. Factors affecting the success of boar semen cryopreservation**

Boar semen differs in several respects from the semen of other domestic animals. It is pro‐ duced in large volume (200 to 250 ml) and is extremely sensitive to cold shock. The success of freezing boar semen depends on both internal and external factors. Internal factors in‐ clude the inherent characteristics of sperm and the existing differences among boars and ejaculates, while external factors are composed of the composition of the extenders, freezing packages, and the method of freezing and thawing of the semen, for example [48].

### **8. The semen donors**

Variation between individuals in the extent to which their sperm are damaged by freezethawing has been reports in many species including pig [52-55]. For instance, some study assigned individual boars into good, average and poor freezability groups on the basis of their post-thaw sperm viability using a system of multivariate pattern analysis, and suggest‐ ed that cryosurvival of the sperm was not necessarily related to the observed quality of the semen sample. In addition to inter-animal variation, intra-animal variation such as differ‐ ence between ejaculate fractions has also been described as a source of difference in boar sperm freezability [56,57]. Some researcher found that sperm present in the first 10 ml of the sperm-rich fraction (portion I) better sustain cooling and freeze-thawing compared to those present in the rest of the ejaculate (portion II) [56]. These differences were manifested by motility patterns, the maintenance of membrane integrity and capacitation-like changes of sperm after thawing. However, variation between ejaculate fractions is dependent of indi‐ vidual boars, with some boars differing in the ability of the two ejaculate portions to sustain cryopreservation, while in other boars such differences were not detected [57]. The mecha‐ nisms underlying differences in cryosensitivity between different individuals and different ejaculate portions have yet to be elucidated, but there is some evidence for physiological dif‐ ferences between sperm from individual boars. Harrison and co-workers demonstrated that the stimulatory effects of bicarbonate on the process of capacitation differ among individual boars [58]. Also, the existence of differences in seminal plasma composition and sperm mor‐ phology has been hypothesized as a possible explanation for the distinct ability of different boars and different ejaculate portions to sustain cryopreservation [59,60]. In general, boar sperm heads present in portion I were significantly shorter and wider than those present in portion II, detected by using computer-assisted sperm head morphometry analysis (ASMA) [57]. It has been hypothesized that such differences could be genetic in origin. Thurston and co-workers using Amplified fragment length polymorphism (AFLP) technology to analyze genome of 22 Yorkshire (Y) boars indicated that 16 candidate genetic markers linked to genes controlling sperm freezability and these genomes varied among individual boars. Consequently, they may be useful for the prediction of both post-thaw semen quality and fertility of individual boars [55].

Cryoprotective agents (CPAs) have been divided into those that penetrate the cell and those which remain extracellular. Glycerol considered as penetrating agents and other non-pene‐ trating agents such as various sugars have been evaluated for cryoprotective effect in boar sperm [64,65]. Glycerol in low concentrations (3 to 4%) has been utilized in various techni‐ ques of sperm cryopreservation [47,66]. At these concentrations, glycerol gives maximum post-thaw viability and also in vitro fertilizing capacity of sperm [43]. Both post-thaw motili‐ ty and acrosome integrity of boar sperm would be decreased when glycerol concentration reached 5%. Glycerol and other penetrating agents could improve FT sperm survival by penetrating sperm and reduce the shrinkage of the cells developed during cooling [8]. They could also lower the freezing point of extra-cellular fluid via action of non-penetrating CPAs [67]. Therefore, the damage of sperm from the formation of intracellular ice occurred during

Improvement of Semen Quality by Feed Supplement and Semen Cryopreservation in Swine

http://dx.doi.org/10.5772/51737

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The success of the boar sperm cryopreservation was dramatically increased when the deter‐ gent Sodium Dodecyl Sulphate (SDS; later known as Equex STM paste) was included in the cryopreservation protocol [68,69]. The addition of SDS to semen extenders decreases freezethaw damage to sperm in several species, including boar [70-72]. Pursel and co-workers stat‐ ed that the use of 0.5% Orvus Es Paste, a commercial preparation of SDS, in the BF5 extender significantly enhanced the preservation of fertilizing capacity concomitant with an increase in post-thaw percentages of normal acrosome morphology and motility of boar sperm [69]. The beneficial effect of SDS on the sperm membrane is not fully understood, but it has been suggested that its protective effect is mediated through a change in the extending medium, by solubilization of the protective lipids in the egg yolk contained in the extenders.

Boar sperm have been frozen in many forms of packages. Pellet, a form of freezing bull se‐ men on dry ice, was adapted to freeze boar semen and first reported as in [47]. Boar sperm have also been frozen in 5-ml maxi-, 0.5-ml medium- and 0.25-ml mini-straws, as well as dif‐ ferent types of 5-ml flat plastic bags [67,75]. All package forms have their own advantages and drawbacks. The 5-ml maxi-straw contains one insemination dose but has a relatively small surface-to-volume ratio, which constrains optimal freezing and thawing throughout the sample. The plastic bags allow even more homogeneous freezing and thawing and also contain a whole insemination dose, but they are not suited for storage in standard liquid ni‐ trogen containers, and therefore are not in commercial use [71]. Pellets and the small straws (0.25- and 0.5-ml straws) have a cryobiologically suitable shape with a large surface-to-vol‐ ume ratio; thus theoretically, FT sperm in pellets and small straws are less damaged than those in maxi-straws [76,77]. However, with pellets, there are difficulty in the identification of the doses and a risk of cross-contamination during storage, and the thawing procedure is rather complicated as well [71]. Also, the small packages could contain relatively few sperm

tional AI in pigs. Eriksson and Rodriguez- Martinez developed a new flat plastic container

sperm per straw, which are not enough for a single dose of conven‐

This effect enhanced the cold shock resistance of sperm [73,74]

freezing is reduced.

**10. Freezing packages**

such as 250 to 500 x106
