Embryonic lethality / abortion (POLR1B/LA1-related) - Pig

What does this test analyse?

This DNA test analyses the POLR1B variant g.43952776T>G, linked to haplotype LA1, in pigs. The condition is described as embryonic lethality, embryonic death, spontaneous abortion, reduced litter size or POLR1B/LA1-related reproductive loss.

The variant has been described in Landrace pigs. POLR1B encodes a subunit of RNA polymerase I and is important for normal transcription and cell growth during early development. The test is especially relevant for breeding animals, because carriers can appear normal but can produce embryos with two variant copies when bred to another carrier.

What does this embryonic lethality mean?

In carrier-by-carrier matings, about one quarter of embryos can inherit two copies of the variant. For POLR1B/LA1, carrier-by-carrier matings showed an approximately 18.8% reduction in total number born compared with carrier-by-clear matings. Embryos with two copies are generally not expected as live-born animals.

Because the loss usually occurs early in pregnancy, it does not necessarily appear as more stillborn or mummified piglets. The practical effect is mainly seen as smaller litters, repeat empty sows or fertility results that are difficult to explain without genetic information.

Inheritance and result

This trait is inherited as autosomal recessive. A clear animal has no copy of the tested variant. A carrier has one copy and can pass it on without being affected itself. A homozygous combination with two copies causes embryonic lethality or strongly reduced embryo survival.

The result labels for this test are T/T, T/G and G/G. The reported status shows whether the animal is clear, a carrier, or carries two copies of the tested variant.

Practical value of this test

This test is valuable for pig breeders because reproductive loss caused by recessive lethal alleles often remains hidden until two carriers are mated. Identifying carriers early makes breeding plans more precise without unnecessarily removing valuable lines from the population.

Why test?

• Helps reliably distinguish clear animals from carriers before selection or mating decisions.
• Makes it possible to avoid carrier-by-carrier matings and prevent homozygous lethal embryos.
• Supports better litter planning, especially in lines where LA1 or POLR1B-related embryonic lethality occurs.
• Adds useful information for smaller litters, disappointing fertility results or repeated early pregnancy loss.
• Helps combine genetic progress with targeted risk management within the breeding population.