Wednesday, October 29, 2014

Using Sheep Improvement Limited (“SIL”) figures to buy Rams!!!

It’s that time of the year again, so I thought I would outline some of my thoughts on SIL performance figures and what to be aware of when buying rams!!

 Again I would point out that I am ram breeder with my own sale so I am not a neutral commentator, but as such I do think I have  a good practical understanding of the value, reliability and pitfalls of such figures.

 Dual Purpose Production (“DPP”) or Dual Purpose Overall (“DPO”) indexes

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.

 “Dual purpose Adult Size” index (“DPA”)

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!!!   

 Some are genuine for excluding it as the index itself is, in my view, at present a complete waste of time.   Firstly if you don’t weigh your ewes (which is still the majority of breeders) SIL then calculates this DPA figure based on the rams early growth breeding values eg the weaning weight breeding value (‘Wwtbv”) and the live weight 8 (8 months old) breeding value (“lw8bv”): if a ram has a particularly high lw8bv, then SIL will give that ram a high negative DPA based on the assumption that such high early growth will mean bigger adult sheep.    This is true for some sheep, but not all; accordingly the DPA figure is a waste of time because it can’t be relied on.  I had a great example myself with one of my best breeding Romney rams in the last 10 years: he had phenomenal early growth (450 grams a day for 3 months), but he himself as an adult was not a big sheep nor in fact were the majority of his progeny (he actually reduced the size of our ewes), but he had a lousy DPA.   

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.

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