Increasing fertilization rate of boars: Influence of number and quality of spermatozoa inseminated

ABSTRACT The influence of the number and quality of spermatozoa inseminated on litter size in swine is examined in this paper. There is evidence to support the following observations. Litter size varies among boars when insemination doses contain the same numbers of spermatozoa. Increasing the number of sperm inseminated generally has a positive effect on the number of pigs born alive, especially between the range of 1 to 3 × 10⁹ cells. The manner in which litter size responds to increasing the number of spermatozoa inseminated varies among boars. These relationships between the number of sperm inseminated and the resulting litter size provide credence to the idea that boars exhibit unique fertility patterns. These divergent fertility patterns probably reflect variability in the ability of spermatozoa from different boars to fertilize ova. A number of semen quality tests have been developed to estimate the fertility of semen. Several of these have documented that increases in estimates in sperm quality are associated with increases in litter size. However, the relative effectiveness of each of these for determining the optimal number of spermatozoa that should be included in insemination doses remains to be elucidated. In summary, increasing the fertilization rate of boars should be possible by improving semen quality, increasing the number of spermatozoa inseminated, and adjusting using estimates of sperm quality to adjust number of sperm inseminated. However, the magnitude of changes in litter size resulting from these strategies is likely to vary considerably among boars.

Implications

The number and quality of spermatozoa inseminated determine the boar's impact on litter size. The relationship between these traits and litter size tends to be unique for boars and is best described as a fertility pattern or curve. Increasing litter size on operations using natural service is most likely to result from improvements in the quality of spermatozoa. This is due to the fact that most boars contain sufficient spermatozoa in their ejaculate to maximize sperm numbers in the oviduct. In contrast, on operations using artificial insemination, increasing litter size probably can occur in several different ways, including improving semen quality, increasing the number of spermatozoa inseminated, and using estimates of sperm quality to adjust number of sperm inseminated. However, the magnitude of changes in litter size resulting from these strategies is likely to vary considerably among boars.

Key Words: Boars, Litter Size, Spermatozoa

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J. Anim. Sci. 80(E. Suppl. 1):E47-E53