The Otapawa Poll Dorset Progeny Test
By Dr Patricia Johncon, Ag Research, Invermay.

What is Progeny Testing?

Progeny testing is a way to estimate the genetic merit (breeding value) of rams for hard to measure traits, based on the performance of their progeny.

For example We can easily take the weaning weight of a ram lamb and estimate his genetic merit based on his own weaning weight and that if his parents and siblings, but weaning weight is only part of the story we are also interested in the carcass traits. But, if we hope to go on and use a ram lamb as a stud ram we can’t kill him, so we need some other way of estimating his genetic merit for carcass traits.

Though generating progeny from commercial ewes which are killed, we can estimate the rams genetic merit for carcass and other traits based on his progeny and be able to select the top ram to be used extensively across stud ewes to improve the flocks genetic merit for carcass traits and other traits.

The steps involved:

  • Top rams are identified based on their genetic merit for “other traits”
  • These rams are then mated to a group of random, commercial dams
  • Either use: Single sire mating and lambing to determine a lambs sire or
    Multi sire and DNA testing to determine a lambs sire
  • The lambs are then measured for traits of interest: ie growth traits and carcass traits
  • An estimate of the genetic merits of the rams ( a breeding value) is made based on the measurements of their progeny.

Traits of the Future

One of the keys to successful stud breeding is to look into the future and determine what will be important traits in a few years time, as it will take that long to make progress and have rams that are improved for the “new Traits” when there is a market demand for them.

With this in mind Otapawa have identified two traits – Improved Carcass Yield and Feed Efficiency as two traits that are likely to be important in the future.

Improved carcass Yield

Meat processing companies are trialing technologies which will estimate the cut distribution (% leg, % loin etc) and composition (muscle vs fat) of carcass, with the aim being to pay based on this. Carcass yield cannot easily measured on the live ram (can estimate using eye muscle scanning or CT scanning), and so progeny testing offers the best opportunity to obtain accurate Breeding Values for rams.

There are three cuts of interest to try to improve because of their overall contribution to carcass value, the French Rack and Loin are the most valuable cuts in carcass, so by improving the contribution these make to carcass weight you can increase the value of your carcass, for a set carcass weight. The third cut is the leg ( hind legs), although they only have an intermediate value, they make up about 25% of the carcass weight and so further increases to this cut will further add to the importance of the leg.

Feed Efficiency

Stocking rate is one of the key drivers of farm profit, if you can have a higher stocking rate with maintained production you can increase profit. When considering finishing lambs one such way to achieve this is to have lambs which are more efficient at converting their feed into growth, you can either adopt a higher stocking rate and get similar growth rates or maintain current stocking rates and have faster growing lambs for a given amount of feed. Either way your production will improve.

However stimulating feed intake of growing lambs on pasture is not easy, although techniques such as using alkane capsules and measuring content in fecal samples can be used.

So what have Otapawa Been Doing?

Together with Dr Patricia Johnson, who at the time was based at Massey but is now based at Ag Research Invermay, Otapawa set out in 2005 to carry out a progeny test to look at carcass yield and feed efficiency.

The top 10 rams based on growth BVs (some were ram lambs, and others were other sire brought in) were selected and mated to Otapawa commercial Perendale ewes. DNA testing was used to assign sire.

Much of the month of January 2006 was spent fecal sampling the lambs so that the alkane content of faeces and hence the feed intake could be estimated, and ultimately the lambs were sent to slaughter. Unfortunately the company that analyses the alkanes in New Zealand stopped analysing them just as the trial was being completed and so these samples have still not been analysed and so still don’t know whether there is a variation in the efficiency of Otapawa Rams. So this is a trait that will have to get considered further in the future, when better technology is available.

Lambs were drafted for slaughter at target kill weights of 37kgs for ewe lambs and 40 kgs for ram lambs (some progeny tests ensure equal representation of all sires and all slaughters, with variation in kill weight).

Results from the Progeny Test:

Note the BV = Breeding Value, only half of the genetics are passed to the progeny, so if a sire has a 5kg BV you would expect the progeny to be 2.5kg superior for that trait

  • A 3.3kg difference in the weaning weight BVs for sires: eg on average lambs from the best sire weighed 1.75 kgs heavier that the lambs from the worst sire.

But remember that sires were pre-selected on growth – imagine if we had used a really poor sire.

  • This variation in weight was again reflected when the lambs were all weighed mid January before the start of the feed intake trial.
  • The variation in weight meant that there was considerable variation in the number of lambs per sire that had reached target weight at each kill,

At the first kill, the best sires had 45 – 47% of their progeny at the target weight, whilst only 3% had reached the target weight for the worst sire (no that is not a misprint, only one of the 30 of his progeny)
This trend continued such that by the end of the second kill the best sires had 79 – 85% of their progeny killed, whilst the worst sire still only had 37% of his progeny killed.

  • We saw limited variation in the breeding values for carcass weight mainly because we were killing at a fixed weight, and limited variation in dressing out percentage.
  • There was nearly a 2mm difference in the GR BVs for the sires

e.g. on average the lambs from the best sire had 1mm less fat depth that lambs from the worst sire.

  • Looking at carcass yield, we concentrated on looking at the variation in the proportion of carcass weight made up of the French Rack, Loin and Hind Legs. The differences tended to be small, ie the variation in breeding values for the hind legs was only 2%. However, one sire ranked either top or second for all three cuts, which would give this ram a cumulative advantage in overall carcass value

Individual Results

The 2005/2006 Progeny Test Top Sire

A homebred ram lamb Otapawa 162/04 topped the progeny test. This ram lamb ranked near the top for breeding values for all traits measured:

  • 3rd for weaning weight
  • 4th for January weight
  • 1st for % first kill in February
  • 2nd for kill by end of second kill
  • 2nd for carcass weight
  • 4th for dressing out percentage
  • 1st for GR (leanest, less waste)
  • 1st for % carcass in the leg
  • 3rd for % carcass in the Loin
  • 1st for %carcass in the French Rack

Where to next?

A further 10 rams were selected, including 162/04 as a sire to link between the year.

The lambs from those sires are on the ground now and are due to be weaned shortly.

Carcase Yield will once again be assessed.