Embryonic lethality / abortion (URB1/LA2-related) - Pig

What does this test analyse?

This DNA test analyses the URB1 variant c.5995del, linked to haplotype LA2, in pigs. The condition is described as embryonic lethality, embryonic death, spontaneous abortion, reduced litter size or URB1/LA2-related reproductive loss.

The variant has been described in Landrace pigs. URB1 is involved in ribosome biogenesis and cellular functions that are essential for growth and embryonic 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 URB1/LA2, carrier-by-carrier matings showed an approximately 15.9% reduction in total number born compared with carrier-by-clear matings. This variant is described as semi-lethal: homozygous animals are strongly underrepresented and embryo survival is clearly reduced.

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 N/N, N/del and del/del. 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 LA2 or URB1-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.