When you buy rams make sure you
see the SIL printout as to how the indexes are calculated. The reason this is important is there is no
one format: a breeder can get certain sub indexes included or indeed what is
more common at the moment excluded. Accordingly if comparing indexes between
breeders (which is not a good idea for lots of reasons) one of which is that
you may not be comparing apples with apples, it could be apples with oranges.
A number of breeders at present
exclude the DPA from their DPP or DPO indexes.
The DPA is an index which in theory gives you an economic value of the
genetic component of a animal’s size, the lower this figure (i.e. a high
negative number) the worse the DPP or DPO as a high negative figure in theory
means a ram will leave progeny that will have a high mature adult weight, which
many argue we now do not want.
According many breeders exclude this figure as it significantly lifts
the overall index of the ram, which is fine provided they advise you of this,
not so fine if they don’t!!!
Secondly many reading this will
simply say weigh your ewes: but the problem with this is there is a big
difference between a fat 65kg ewe and a skinny 65 kg ewe, which SIL does not
differentiate between when such data is entered. Clearly a big frame skinny ewe is not what
we want, but it is treated the same as the fat one on a DPA index. This is why I still don’t enter such data
into SIL. SIL acknowledges this and is
looking at introducing some sort of system of body condition scoring at the
time of weighing ewes, the problem of course being the subjectivity of the
person scoring the ewe at the time.
In my view still by far the most
reliable way at present of assessing the adult size of ram’s progeny is to look
at the ram himself, big ram (frame wise not necessarily simply heavy ram)
probably big ewes.
Dual Purpose Meat Index (“DPM”) and Terminal Sire Meat Index (“TSM”)
It is defined as being calculated
as an aggregate of hindquarter, forequarter and loin yield percentage.
How do you get such data? From Alliance
viascan: so you have to get the data back on cull progeny and enter that into
SIL. Problem with this: firstly not a
lot of breeders are doing this. Secondly, even if you do, you need a reasonable
sample size to give you some credible data: this use to be 20 to 25 progeny of
a sire (but it seems 15 is being more commonly talked about now). If you only have a few then it could distort
your results and reduce the accuracies.
Without any Viascan data, the index
is calculated by an extrapolation of an eye muscle scan, which may be correct
or not as a good eye muscle does not necessarily mean a good hindquarter (in
fact in my view because of the emphasis on eye muscle scanning in the last 10
years many breeders now have a sheep with a good eye muscle scan and poor or
average hindquarters).
If there is no other data then
they somehow extract a DPM index from the growth figures (wwtbv and lw8bv).
Accordingly I consider this DPM
to be complete waste of time as it can be all to hell. In fact surprisingly I recently found out
that the SILACE analysis (that I get my figures from for my terminal rams)
excludes the viascan data (apparently owing to a lack of such data).
Number of Lambs Born Breeding value
(“nlbbv”)
Again you need to ask how this is
calculated. I personally base my figures
on a SIL analysis where the Reproduction calculations includes LW8 (as I
understand it, the science is clear that there is a correlation between such
size and fecundity). However some
breeders don’t and specifically have nlb bvs based on analyses that exclude LW8
from Reproduction. I reiterate it’s
not wise to be comparing indexes between breeders (unless interalia there are
strong linkages between the flock in questions) but if you are, ensure you are
comparing apples with apples.
The other important thing to
remember is that the ram hogget or 2th you are looking at has nlbbvs which are
a prediction of what genetically he may do.
Until that ram itself has progeny on the ground lambing themselves you
don’t know what sort of fertility he is going to leave. It’s purely an estimate based on his sire,
dam, and siblings etc fertility performance.
SIL Rankings
When looking at the figures check
what their rankings are out of. Generally
most breeders put up rankings based all their male lambs or indeed all animals
born that year. However sometimes
breeders put up rankings simply on those they have retained through the winter
or indeed worse what they are offering for sale. Some only give you rankings and not the
actual breeding values. I think if you
are looking for something in particular to improve on perhaps fertility, wool,
growth etc then you should ask to see the actual values, particularly if the
ranking is based solely on what is being offered for sale as the ranking could
suggest that its much better genetically than what it is.
My basic advice when buying rams,
is first pick a breeder who has breeding policy in line with what you want to
achieve, who you believe in and trust: if you don’t, don’t go there. Secondly select two to three times as many
rams that you want to buy of the type that you like i.e. if you want 4 rams
pick out 8 to 12 that you like the look of.
Thirdly use the figures to whittle them down to the ones you purchase,
focusing on the traits that are important to you. This way you should get a consistent type
with good figures. When using SIL I believe that you should focus more on breeding
values and much less on indexes because as you can see from above, indexes can
be pretty unreliable at times. I
always say if you know what the deficiencies are in SIL it is of use.