Post on 30-Mar-2015
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