Sheep Matters_Aug-Sept 17 (redesigned)

for a variety of traits. Data are
recorded by breeders at premating,
lambing, 8-weeks post
lambing and 21 weeks postlambing.
Modern methods also
use CT scanning to generate data.
EBVs are calculated from these
performance data along with
information about known relatives,
where the effects of environment
(e.g. nutrition, management) are
removed. This analysis uses a
procedure called BLUP (Best Linear
Unbiased Predictor).
An EBV gives an independent
assessment of an individual ram’s
genetic potential relative to a
common baseline. EBVs have been
developed for a range of traits.
A Breeding Index may also be
generated that combines a number
of EBV traits. This aids decisionmaking
around a set of objectives
that require the improvement of
several traits at once. Economic
weightings are applied to the
individual traits that make up the
breeding index to reflect current
market conditions. Commonly
used Indexes include the Terminal
Sire Index (combining growth and
carcass traits to select superior
terminal sires); the Maternal
Index (focusing on early lamb
growth rate, maternal ability and
prolificacy. These indexes are
useful for self-replacing flocks),
and the Hill 2 Index (improves the
overall productivity of hill ewes).
Information about the use of
Breeding Indexes is available from
Signet Breeding Services (5).
‘EBVs are easy to
interpret’
• ●EBVs are expressed in the same
units as the recorded trait (e.g.
kilograms for the 8-week weight).
EBV of zero the greater the genetic
potential of the ram.
For example, a ram with an EBV
of +3 kg for 8-week weight is
estimated to produce lambs that
are 1.5 kg heavier at eight weeks
compared to the baseline EBV of
zero. The baseline represents the
average eight-week weight of the
animals from the same flock in
the year when the EBV was first
produced.
EBVs are published for each trait
that is recorded. This allows a
producer to focus on EBVs that
are pertinent to specific breeding
goals. Further detail on interpreting
EBVs can be found via the Levy
Boards (2,3,6).
Genes Pay
On an average Non-SDA farm
with a breeding flock of 688
and a replacement rate of
22.9% this could potentially
lead to an additional return
of £2211 to the business each
year. The potential additional
return increases to £2520 for
an average SDA farm with a
breeding flock of 814 and a
replacement rate of 26.3%.
Based on average ewe to
ram ratios this means that
knowing the genetic potential
of your rams could increase
your returns by between £769
and £942 per ram over four
breeding years.
Calculations based on data from
Stocktake Report 2016 (4).
• ●Because a lamb only inherits half
its genes from the ram the EBV
must be halved.
• ●Depending on the trait an EBV may
be expressed as a negative or a
positive value.
• ●The further away from the average
Q
2017 AUGUST & SEPTEMBER 11