| Summary: | The rationale of this thesis was to examine and extend knowledge of boar semen quality, its evaluation and factors which influence quality; with the objective of improving the effectiveness of pig AI. The literature review led to the conclusion that the development of a semen evaluation technique which describes the overall quality of the sperm, correlates well with most semen quality parameters, and most important, applicable at farm level would be a valuable advance. In addition knowledge is needed of the factors affecting semen quality and in particular better semen dilution techniques. Studies on the effect of various factors on semen quality showed: i. With two boar lines (purebred, PB) and (crossbred, CB), CB gave higher total sperm counts (P<0.05), but PB gave better farrowing rates (87% V 78%, P<0.05), ii. Semen collected in Autumn/Winter had higher total sperm counts than semen collected in Spring/Summer (66.4 V 47.8 x 10<sup>9</sup>, P<0.001), iii. General semen quality did not change significantly over 48 hours in the study, iv. Pooling of semen had no effect on semen quality. Semen dilution by a controlled 'Anti-shock' procedure gave a higher proportion of litters with 11 or more piglets born than semen diluted by the standard procedure (78% vs 62%, P<0.05). Sperm motility was affected when, in Kiev diluent, glucose (G) was replaced by fructose (F). Motility was F vs GF vs G: 84.8%; 84.1; 81.0, but by day-3 was 27.7, 60.2 and 62.0 (P<0.01). No significant differences were found between diluents in AI sow fecundity, probably due to the limited numbers of sows. It is concluded that although farrowing rate and litter size are the ultimate indices of semen quality, good correlations with <I>in vitro</I> techniques have yet to be established. The 'swim-up' test is suggested as the most suitable on farm <I>in vitro</I> semen assessment, and that the 'Anti-shock' dilution technique has commercial promise. Fructose should be the usual sugar used in the diluent.
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