March 5, 2010

Breeding sheep to eliminate dags and worms. 3.

By Dr Clive Dalton


Getting started

  • To keep focused when reading further, have your own flock in mind to see what’s possible for you to do.
  • First: Have a slogan on a big card in the woolshed or in the sheep yards for all to see. It should say: ‘We breed sheep that are Dag-Free, Worm-Free & Sustainable’.
  • Keep quoting it and telling everybody you meet what you are doing, especially the stud breeder you have been getting rams from, your stock agent and especially your vet as your drench account will take a massive drop!
  • You’ll need a flock of at least 1000 – 1500 ewes to fast track initial improvement, and it probably wouldn’t be worth starting with fewer than 500 because of the selection pressure needed.
  • But give it a try with a smaller flock, and see how far you get; you may be surprised!

Essential features

First: To keep the job simple and avoid getting bogged in paper.
Second: To keep costs to a bare minimum.

Genetic theory

Thomas Bakewell in the 1700s used the principles used in this exercise to improve Longhorn cattle and Leicester sheep, so they’ve been well tested! He did it by ‘breeding the best to the best’. The challenge is to sort out what’s best. There are four basic ‘pathways’ to do this.

The four pathways to improvement

Text books show these in different orders but they're listed below in the best order to get started:

Pathway 1: Selecting females to breed females.
Pathway 2: Selecting females to breed males.
Pathway 3: Selecting males to breed females.
Pathway 4: Selecting males to breed males.

  • Pathways 1 and 2 put pressure on the females, and 3 and 4 on the males.
  • To maximise overall genetic gain, you must do both.
  • So often the only selection pressure is put on the rams, which is not good enough to see any great change in human years.

Forming an ‘A’ team of females (mothers)
  • To start on Pathways 1 and 2, find the best ewes in the flock as mothers of the next generation of female replacements, and to also breed males from them for use as sires.
  • These ewes need to be identified and kept as a separate ‘A team’ or ‘nucleus’ flock which will get intense selection pressure for traits that keep you in business.
  • Being Dag-Free and Worm-Free will top the list and so will their ‘easy care’ traits.
  • All A team ewes have to keep on performing to stay in the team, because as things progress, there will be plenty top prospects waiting to gain entry.

When to start looking for A team members?
You can start the programme at a number of times through the year, but it’s best when there are no lambs around to get in the way. Mid pregnancy is an ideal time to start.

Top commercial flock of Perendale ewes - a wonderful starting point
for a genetic improvement programme.

Ewes at scanning

  • Identify (ID) the twin-scanned (TS) ewes. Mark them with a raddle that will last till at least lambing, run them separately, and feed them well.
  • Whichever is easiest, select the TS ewes out of the mixed age (MA) flock, or screen the two-tooths to find them.
  • The 5-year-olds are also a great starting point to find some as they have stood the test of time. Don’t be worried about the size of the nucleus at this stage; just get started.
  • Once you’ve got all the TS ewes drafted off, go through and throw out any you don’t like for anything you consider important.
  • Do NOT drench any A team ewes, or any ewes for that matter in the rest of the flock from now on. They shouldn’t need it and it only confuses the picture. Avoid any long-acting drenches like the plague.
  • f there is a health/welfare crisis (confirmed by your vet), only drench individual sheep in the A team, and mark them for culling later. Don’t be persuaded to drench the whole lot even if the drench specials are appealing!

Ewes between scanning and lambing

  • Cull any A team ewes that ‘pack up’, grow dags or have any health/welfare problems.
  • Be ruthless and ‘if in doubt – throw them out’ to tighten the selection pressure on them. To stay into the A team they have to measure up!
  • However, if the whole A team suddenly becomes daggy, don’t panic as that’s an environmental (feed quality) problem and it’s a good ‘challenge’.
  • Use it to ID any ewes that stayed clean during this ‘dag storm’, or got daggy and soon cleaned up. Give them a special mark. The ones that fail to dry up need a special mark too – for culling.

Ewes at lambing

  • Lamb the A team ewes separately and with normal commercial care. If this is ‘easy-care’– then carry on with your normal routine.
  • If you go around the ewes and see any that had trouble – try to remember them, or mark them for culling if you can catch them. If you can catch their lambs, mark them for culling too.
  • Again, be ruthless. Carry the raddle or ear markers at all times!

Ewes at docking of their lambs
  • Do NOT drench any A team ewes, or any others on the farm at docking. They should not need it, regardless of current drench promotions.
  • Mark for culling any TS ewe that didn’t lamb, was wet/dry or that had any other problem. Be ruthless!
  • If there’s a chance that these TS ewes may get mixed with the main flock after docking, and their scanning raddle may have faded, ID them with a numbered plastic tag. The cost is justified at this stage as you don’t want to lose them.

Ewes at weaning of their lambs

  • Mark for culling any A team ewes that have developed physical defects or failed to meet your standards.
  • Check udders, as you’ll be able to find any that went dry early or had mastitis. Teeth are also an obvious feature.
  • Be ruthless, especially on real dirty backsides that never dried up. How dirty is dirty, you’ll have to decide and set your own standards.
  • If you didn’t tag these ewes at docking, then give them a good permanent numbered tag now that you can read from a distance, as you cannot afford to lose these girls after all the work you’ve put into them.

Maintaining the A team nucleus flock
  • You need to decide how big the A team flock should be to provide the number of replacements needed to keep up the pressure on dags and worms.
  • A rough rule of thumb is to have about 7-10% of your total ewe flock in the nucleus. But be flexible at this stage.
  • Keep culling these ewes hard for physical defects and health problems, especially any that get daggy, have flystrike, are lame or have simply packed up.
  • Their problems won’t be all genetic, but be ruthless, as there will a genetic component to their ills somewhere, even if it’s not strong.
  • The target is structurally sound robust ewes with ‘constitution’ that can stand up to your management. If you have any doubts about a sheep, cull it.
  • YOU need to have great confidence in these sheep, as they’ll be great motivators for you and your staff as the programme proceeds.
  • In your doubting moments, go and walk through them and see if you’ve seen any better ones anywhere in the district.

What does it take to stay in the nucleus flock?
  • This is a vitally important part of the exercise. Apply the same simple rules used at the start of the programme.
  • To gain entry into the elite flock in the first place, or to stay there at any subsequent lambing, then a sheep must have completed all of the following:
Scanned twins.
  • Not been wet/dry at docking.
  • To have weaned lambs – judged by udder.
  • To have survived all the culling on constitution, health and structural soundness – and not caused any extra work or cost you money!
  • To have stayed free of dags, or dried up quickly after a ‘dag storm’ caused by feed changes.
  • Have consistently produced marbles or hand grenades.
  • Have had a FEC in the low hundreds.

Where’s the best place to find A team replacements?
  • If because of intense selection and culling, the numbers of ewes in the A team nucleus are now not enough, you may need to do another screening like was done to start the nucleus.
  • Two good age groups to screen for A team replacements to supplement the nucleus are
  1. The 5-year-olds as they have stood the test of time.
  2. The two-tooths as they have a long life ahead, and have already been subject to intense selection pressure.

No comments:

Post a Comment