Screening Techniques in Pigs That Allows Us to Look for Reduced Fertility - 30/03/2021

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The domestic pig is the leading source of meat protein globally and provides 43% of meat consumed worldwide. Generally speaking, the breeding of pigs for commercial reasons occurs in a pyramidal structure. The top tier, which is the nucleus level, consists of purebred boars that are selected based on their genetic merit (i.e. meat quality). The fertility of the boar however is sometimes overlooked.

If fertility problems are detected in these top tier boars, they can have profound effects on fecundity rates and litter sizes. As a result, this leads to a reduction in food production and higher environmental costs, as unproductive males produce unnecessary greenhouse gases.

Chromosome rearrangements (such as translocations) are often the driver between fertility issues. In males, such rearrangements result in a high proportion of genetically unbalanced sperm. In the case of boars, higher proportions of unbalanced sperm will lead to significantly smaller litter sizes (25% - 50% smaller than expected).

Artificial Insemination (AI)

Artificial insemination (AI) further perpetuates these problems. The male to female ratio when using AI for breeding is 1:1000. And so, in the case of using an infertile boar in the breeding pyramid, the potential environmental and financial costs are enormous. There is a clear need to identify those animals that carry a translocation and prevent their use in the breeding population.

Routine semen analysis is inefficient in detecting the presence of chromosome translocations, as affected boars look perfectly normal.

Karyotyping is the industry-standard approach to screening for these abnormalities, and many breeding companies karyotype to proactively screen their boars before entry into the AI stud. Through the method of karyotyping, around 170 different chromosome translocations have been identified (across all breeds) over the last 40 years. An incidence rate of 1/200 (0.5%) of boars used for AI has also been reported. In France there is a legal requirement that all boars used for AI are certified as translocation free.

CytoScreen Solutions

However, karyotyping does not present without its drawbacks; it is labour-intensive, it requires pig-specific expertise and does not allow identification of cryptic translocations. To overcome these limitations, the University of Kent have established a new service called ‘CytoScreen Solutions’. This was achieved through the innovative adaptation of a technique known as ‘FISH’ (fluorescence in situ hybridisation). This new method allows for the identification of even the smallest of translocations, as well as operating in a rapid, accurate and cost-effective manner.

Of the 1,600+ boars that have been screened via the CytoScreen Solutions service; translocations have been detected in over 70 (5%). The results indicate that translocations in the breeding population are significantly higher than previously thought. In addition to the in-house screening service for pigs, the service is actively expanding to North America, Australia and South East Asia. One of the most recent projects has been in Thailand, using the technology to make pig production more cost-effective and environmentally sustainable.

The CytoScreen Solutions method offers support to initiatives in South East Asia to improve the genetic quality of their breeding stock. This helps to ensure long-term market growth and reduces the financial and environmental risks associated with excess waste. Improving the margins for the pig breeding industry will enable the re-investments of profits in local businesses, leading to long-term growth and sustainability of this market. Importantly, this improved investment puts emphasis on generating high-quality meat products, bred under first-class welfare and environmental conditions.

Sustainable economic growth for both industry leaders and workers in local communities, as well as support for local jobs, can be achieved through the expansion of the breeding industry as a result of the investment. Improved nutrition of the end-consumer and a decreased reliance on cheaper imports ensures that local suppliers benefit from gains in genetic progress developed in the UK and Europe

In the broader sense, a more efficient food production chain can be achieved by screening for translocations using the highly accurate CytoScreen Solutions method, with the benefits not just limited to well-established breeding industries but can be adopted by communities worldwide.