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Improving The Genetic Impact Of AI Boars

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Improved assessment of the fertility of commercial AI boars and a move to single-boar AI programs would have significant economic benefit for the swine industry, says Dr. George Foxcroft of the Swine Research and Technology Centre at the University of Alberta.

Identification of the most fertile boars would enable lower numbers of sperm per AI dose, allowing the use of techniques such as post-cervical insemination and single, fixed-time insemination, he suggests. Furthermore, Foxcroft believes, using the higher genetic merit of these boars across a greater number of gilts and sows bred would provide substantial benefits to the producer in terms of the performance of terminal line progeny.

Current practice in AI studs is to evaluate semen quality parameters such as concentration, morphology and motility.

“While these evaluations can establish that an animal is either sub-fertile or infertile, they cannot identify the relative fertility of boars that meet accepted industry standards semen quality,” said Foxcroft. “The relatively high sperm numbers used in commercial AI practice and the pooling of semen from boars that may have inherently different fertility, masks the reduced fertility in some of these boars.

Better measurement of relative boar fertility would allow the removal of less fertile boars from commercial studs. “This will optimize the use of proven, high fertility, and genetically high indexed boars at lower sperm numbers per AI dose,” he said. “It would also allow stronger genetic selection pressure by increasing the number of offspring bred per collection from high-ranking boars.”

Producers would benefit from improved performance and higher margins, even if the same genetic royalties were paid for fewer doses of semen, he adds.

The almost universal use of pooled semen doses in commercial boar studs severely limits the collection of data on relative boar fertility at production level, Foxcroft notes. However, evidence suggests that a substantial range of fertility exists.

“Data from 31 Landrace boars in a commercial stud showed that, while their average litter size (total born) was 12.26, taking out the 10 worst boars increased the average to 13.29,” he said. “If the genetic merit of the three boars in this group that averaged over 14 total born was high, the application of more efficient AI technologies would allow their merits to spread across a larger proportion of sows bred.”

Variations between individual boars are masked by the practice of pooling semen from a number of boars from the same breed during semen processing. This has the benefit that the impact of a sub-fertile boar is reduced, but does not allow the more fertile boars to be recognized. Foxcroft believes that the industry should move towards single-sire AI. “Simply from the perspective of optimizing breeding herd productivity, a move to single-sire AI programs seems to be justified,” he said. “The very best boars will express their real potential, and overall herd productivity appears to increase. Furthermore, the small percentage of very inferior boars will quickly be identified and can be removed from commercial production.”

While new methods of evaluating fertility are currently being developed, in the meantime, ranking boars on the basis of normal production criteria such as farrowing rate and litter size would enable this to take place, he adds.

The logical conclusion of Foxcroft’s arguments is to maximize the impact of the most fertile boars with the highest genetic merit by moving towards the use of lower semen doses with single fixed-time AI programs. Commercial trials using hormones to induce ovulation at a fixed time after weaning have shown acceptable results, he notes. The results in Table 1 show that the use of a gel-based product containing GnRH (Gonadotrophin Releasing Hormone) after weaning resulted in slightly higher farrowing rate and litter size than where no treatment was given, while almost doubling the number of piglets born per semen dose.

“These and other results suggest that the implantation of single fixed-time AI programs in a well-managed sow herd can be a reality,” comments Dr. Foxcroft. “Linked to the use of proven superior sires, post-cervical insemination catheters and lower doses of semen, this new technology will allow the pork production industry to apply the genetic value of elite boars to breeding programs that are competitive with other livestock species.”

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