The Loa geneA new fecundity gene in Icelandic

sheep

Jón Vidar Jónmundsson

Emma Eythórsdóttir

Background

• Sheep breeding in Iceland– Lamb meat is the main product– Numbers of sheep have declined

from 900,000 in 1980 to 470,000 in 2002– Local consumption of lamb meat has fallen

from 40-50 kg /capita to 22 kg– Main market is still within the country –

export of lamb increasing to EU and USA

Background

• Breeding work– Recording scheme with long tradition– 246,000 ewes on records in 2002– emphasis on prolificacy – avg. 1.81 lambs/ewe 2002– Recent years – increased emphasis on carcass quality

– increased lean and reduced fat

• Extensive use of AI– 48 rams on stations 2002– 28,500 inseminations – fresh semen

• Strict disease regulations limit movement of stock

Prolificacy of Icelandic sheep

Distribution of litter size in 2002 (ewes)– Barren: 3.13 %– Single:

18.35 %– Twins: 73.26 %– Triplets:

5.08 %– Quad.+: 0.18 %Ewes with litters >2 – increased proportion

due to carriers of the Thoka gene that are spread through the national flock since 1986

Loa from Hafrafellstunga

• Loa 80-092 born in spring 1980 at Hafrafellstunga in NE Iceland (zone 23)

• Farm with complete pedigree records since 1940’s – almost 90% of ewes in the district are on records

• Loa had 32 lambs in nine lambings (2 to 10 yrs old) - always 3 or 4 lambs– 5 ram lambs and 13 ewe lambs were kept for

breeding

Sheep at Hafrafellstunga

Lambing records of Loa’s daughters

Age of ewe

No. 2 3 4

Carrier* 8 2.75 2.33 2.67

Non-carrier 5 2.00 2.00 2.00

Difference 0.75 0.33 0.67

*Carriers defined as ewes with ≥ 1 triplet litter

Lambing records – Loa’s granddaughters

Age of ewe

Sire Daughters No. 2 3 4

88-130 Carrier 44 2.57 2.56 2.95

Non-carrier 52 1.69 1.88 1.85

89-176 Carrier 17 2.35 2.62 2.64

Non-carrier 50 1.58 1.76 1.88

Diffr. 0.82 0.77 0.93

Ewe of the Loa family with 5 lambs

Lambing season 2001 at Hafrafellstunga

Lambing records - granddaughters

• Three of Loa’s sons did not sire daughters with exceptional prolificacy – similar performance as herd average

• Two sons sired daughters that could be classified into two distinct groups – indicating that the sons were heterozygous carriers

• Records for daughters of 89-176 are not precise – may explain uneven no. of carriers vs. non-carriers

Possible relation to the Thoka family?

• Sheep from the Loa family are concentrated at a few local farms in Öxarfjörður – disease free zone – transport of breeding stock from

others zones is prohibited– Pedigree records are complete many generations

back – no relation to sheep from the district where the Thoka family was found

– Loa was born in 1980 – before the first progeny of Thoka carriers used in AI were born in 1985

Information from pedigree records

• Loa’s sire had > 50 daughters in the flock• All her sisters showed good prolificacy but not

exceptional as Loa• Records from maternal line – no indication of

exceptional prolificacy

• Seems to be a new mutation in Loa herself

Conclusions

• New mutation in Loa, inherited as a single gene causes increased prolificacy

• Effect similar to Thoka gene (+ 0.7 lambs per copy)– Very few records available on ewe lambs – effect

unknown

• No relation to the Thoka gene– a few crosses between the families have been made

recently – no records yet

Karl S. Björnsson, farmer at Hafrafellstunga, is gratefully acknowledged for supplying information from his sheep records

Hafrafellstunga

Öxarfirði, NE Iceland