How many sires?

How many sires?

Drivers
For stud herds recording on DEERSelect the number of sires used in the breeding program (within the the limitations of the stud hind herd size) has two drivers:-

  • the number of progeny required per sire (to enable selection of offspring for the next generation) 
  • the accuracy of the BVs of the progeny. 

Consideration of these factors, along with the size of the breeding hind herd helps to determine the number of progeny weaned per sire.  

Once the number of progeny per sire has been established the type of sires required is next consideration which will determine the number of sires to mate that season. 

Sire types
The first type of sire to consider are link sires, there are two different types of linkage required: between-year and between-herd. 

For between-year linkage, there needs to be at least two sires used that were used in the previous year.  If no year links are used it is difficult for the genetic evaluations to separate out year effects from sire effects.  This means that herd BVs would not be comparable across years, leading to poor selection decisions and, probably, erratic genetic trends.

Between-herd linkage, is required to link recorded herds and allow environmental effects for these herds to be accounted for on DEERSelect.  As for between-year linkage at least two sires should be used for between-herd linkage, preferably these stags would be used in a number of recorded herds in the same year.

So for a herds recording on DEERSelect, for linkage purposes alone, at least four sires are needed.  The target for these four sires should be to wean  20 to 30 progeny each, which means mating around 95 to 140 recorded hinds.

 With link sires determined, that leaves the consideration about “optional” or non-linked stags. Using a similar target of 20-30 progeny weaned per sire, the number of non-link stags able to be used will depend on how many hinds are in the breeding herd.  Likely conception rates need to be factored into equations when planning your number of progeny weaned per sire (e.g. anticipate less weaned progeny per mating for AI than for natural mating).  Sires can be mated to more hinds than required to wean the recommended 20-30 progeny per sire, this will not have any negative impacts in DEERSelect.  So it is perfectly acceptable to breed more than 20-30 progeny per sire for the non-linked sires, so long as acceptable mating ratios are maintained.

Example:

A 200-hind herd,( assuming 85% hinds mated wean a calf) would expect to use a total of 7 sires (4 link and 3 others)

200 x 0.85 = 170 progeny weaned (about 24 progeny per sire).

A 300-hind herd would expect to use 10 sires (4 link and 6 others).

300 x 0.85 = 255 progeny weaned (about 26 progeny per sire).

The number of 20-30 weaned progeny per sire is an optimized figure, which balances various statistical considerations involved in trait collection, and BV estimation for sires and the accuracy of sire BV's. When it comes to accuracy of the progeny BV's, the more half-siblings (half brothers and sisters) produced the greater the accuracy of the BVs. The greater the BV accuracy the better selection decisions. This comes about due to the accuracy of the sire’s BVs; the more progeny, the greater the accuracy of the sire's BVs and the greater the accuracy of their progeny's’ BVs.