| Scrapie Canada Updates
August 2005
Tips for using genotype information
to breed for scrapie resistance in sheep
Hossain Farid– Department
of Plant and Animal Sciences, Nova Scotia Agricultural
College
Breeders who participated in the
genotyping project in Nova Scotia and British Columbia
now know the genotype of their ewes and rams at codons
136, 154 and 171 of the prion protein gene.
The question is how should the breeder interpret and
apply the genotype information to increase the natural
resistance of their sheep to scrapie?
One important question is if there
is any relationship between scrapie resistant genotypes
and sheep productivity? There is limited information
on this topic, and published reports are often contradictory.
Some Nova Scotia sheep breeders who took a serious
look at their genotype results last year noticed that
some of their best rams had the susceptible genotype
(QQ171). The same observation was made by at
least one breeder in British Columbia. Is it a bad
luck or is there a negative genetic relationship between
the resistant genotype and performance and/or conformation?
Analysis of the genotype results
of the Nova Scotia purebred sheep indicated that,
in a few breeds, a higher than expected proportion
of breeder rams carried the scrapie susceptible allele
(Q171). This observation suggests that rams
that carried Q171 had some characteristics that appealed
to breeders, i.e. there may in fact be a negative
relationship between resistance to scrapie and conformation
or performance in some breeds. We currently have a
project to look into this issue.
Breeding strategies for your flock
should be based on the fact that, at present, it is
unclear whether scrapie resistance is related to production
performance. Keeping this in mind, below are a few
suggestions on how to use genotype information in
your breeding and selection scheme.
| 1) |
Do not sacrifice
high production for genetic resistance to scrapie.
A low-performing resistant sheep has little market
value. |
2) |
Rams do not transmit the scrapie
agent to your flock, but they have a marked effect
on the genetic status of your flock. Where possible,
use very resistant (AA136RR154RR171) rams. |
3) |
When you are purchasing a
ram, try to obtain a high-performing resistant
(RR171) animal. |
| 4) |
Cull your low-performing susceptible
QQ171 ewes, particularly those with VV136 or VA136
genotypes that are very susceptible, or use such
ewes only for market lamb production. |
5) |
Information on the genotype
of both ewes and rams in your flock provide
you with the opportunity to arrange breeding
strategies that will produce genetically resistant
lambs in the next lambing season, thereby accelerating
the rate of progress toward establishing your
scrapie resistant flock. If you have no RR171
rams, breed high performance QR171 and QQ171
ewes with high performance QR171 rams, and vice
versa, to produce RR171 or QR171 lambs. With
this strategy, it will take longer to establish
a resistant flock, but it will allow you to
maintain a high performance flock.
|
I greatly appreciate constructive
comments from Judith Glibbery from BC and Marg Zillig
from NS.
|
