Ask an expert: Genetics and reproduction

Dr Craig Lewis, chair of the European Forum of Farm Animal Breeders and PIC Genetic Services manager answers your questions.
calendar icon 31 August 2018
clock icon 5 minute read

How many litters per year can a sow have and how soon after giving birth can a sow get pregnant?

I think litters per sow per year can depend on individual system and local legislation. As a general rule, gestation length is fixed to about 116 days today, and with increasing litter size we see this extending slightly into the future. To then increase litters per sow per year, the only things an individual farmer can influence is lactation length (there are some legal limits to this in Europe) and keeping non-productive days down. Of course, this number can also be manipulated in some herd recording systems considering when you ‘enter’ gilts into your herd.

In terms of how soon after giving birth can a sow get pregnant, the major driver of this would be wean age: once the sow is weaned we would aim to get her bred back 3-4 days post wean.

How is line breeding and inbreeding different?

How are you defining line breeding? I could define it by ‘within-line breeding’, which, in the context of pig production, is keeping a line ‘alive’. We see this commonly in terms of breeding companies having lines of Landrace or Pietrain, for example, which are kept pure and improving into the future. The other way to define line breeding is using closely related animals in a breeding scheme so that a really outstanding ancestor is represented a great deal in the following generations.
In terms of the second definition, this can be utilised, however breeders do need to control for inbreeding and maintain genetic diversity in base populations. Inbreeding is traditionally thought of as breeding close relatives together and can happen when improving lines of pigs. Inbreeding today however is rapidly moving away from being measured using traditional pedigree methods and is now calculated using degrees of relationship at the level of the genome. Certainly, we embrace this approach as it allows for much more accurate and detailed management of inbreeding while having increased rates of genetic improvement.

My sow will only breed with her son! Will the health and welfare of their progeny be affected by their genetic relation?

I have personally not encountered a situation where a sow will only breed with her son. Also, we would not recommend this considering there is an increased change of potentially deleterious alleles coming together that could compromise the health or welfare of the next generation.

How can I select for lower feed conversion rates when breeding my pigs?

Feed conversion is basically derived from growth and feed intake. In order to maximise true conversion, you want to maximise a balanced selection of multiple traits (lean gain, robustness, carcass value) while limiting associated costs. We use a balanced selection using multiple traits to maximise the profit equation for customers. Within a breeding programme however you can only improve what you measure so detailed data collection on scale is vitally important for improving any metric.

How can gene editing affect the welfare and productivity of my herd as well as the sustainability of my production?

I think there are many ways gene editing can increase welfare and production and today only a few are explored. With just the example of using gene editing to eliminate PRRS from commercial populations, while the economic benefits are obvious, in terms of increased production there are welfare benefits in terms of decreased mortality and morbidity (a possible benefit here is a reduction in antibiotic usage due to generally healthier pigs), as such the system is overall more efficient so there are sustainability benefits in terms of resource usage (energy, feed, and water) and these efficiencies result in a lower carbon footprint per Kg of pork produced. The direct and indirect benefits of new technology could be widespread if these new technologies are adopted into the future.

Craig R G Lewis PhD
Genetic Services Manager
PIC Europe

A native of Hereford, England, Craig Lewis is a member of the PIC Global Product Development team, based in Barcelona, overseeing Genetic Services for the European, Russian, and African region and is active in PIC’s global welfare research programme. Additionally, he is responsible for directly managing the genetic programme for a number of PIC’s key customers and internal multipliers. External to PIC, Craig is currently the chair of the steering committee for the European Forum of Farm Animal Breeders (EFFAB) which is a cross species European political lobby association that represents the majority of animal breeding and reproduction organisations within Europe.

If you’d like your own swine questions answered by an expert, please contact the editor Emily Houghton

Emily Houghton

Editor, The Pig Site

Emily Houghton is a Zoology graduate from Cardiff University and was the editor of The Pig Site from October 2017 to May 2020. Emily has worked in livestock husbandry, and has written, conducted and assisted with research projects regarding the synthesis of welfare and productivity of free-range food species.

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