Breeding sheep to eliminate dags and worms. 1.

By Dr Clive Dalton

PART 1


Introduction

• Farmers used genetics to improve fertility in their commercial sheep flocks in the 1970s - 1980s, and this greatly improved income.
  
• But with recent inflation and currency fluctuations, they realise that more lambs are not all profit.
  
• Rising costs, especially for animal health are now a major issue, but veterinary science has not come up with ways to reduce these; so-called progress seems to be to use more!

Dagging and drenching

• These are the two main killers in terms of cost and physical effort, as sheep farmers’ average age is now creeping up towards 60, with fewer young people entering the industry, or who want to spend their time wrestling with today’s 80kg sheep.
• Many sheep farmers have back, hip and knee problems from hauling sheep around, and the veterinary profession are only offering more drug and chemical therapy as future solutions, which will not reduce costs.
• This approach is not sustainable – neither economically nor for the environment.
  
• So the obvious conclusion is that we have to stop, (or at least greatly reduce), dagging and drenching sheep.
  
• If you don’t agree, and are happy to get the handpiece out to clean up sheep like the one below, then don’t read further.

What a prospect to have to clean up this sheep's rear end!

Major mind change needed

Sheep are never keen to cooperate

• Dagging (to prevent blowfly) and drenching (to kill worms) have always been accepted as part of sheep husbandry.
• So has crutching, most of which is done to prevent dags forming.
• You never see these chores featured in a shepherd’s job description: they are taken for granted.
• If the boss had no jobs planned, then he/she could always find some dagging or drenching to do to keep staff active and give the dogs a run!

This advert in a 1970 New Zealand Farmer was certainly convincing.
Back then, nobody thought about long-term implications of the
new wonder chemicals!

Breeding is the solution

• Breeding is the way to get rid of the endless chore of dagging and drenching, which inevitably is followed by more dagging and drenching.
• The chemicals used in drenches cannot be sustainable, and consumers will start to demand ‘drug-free’ products for their health and welfare.
• Genetic gains are cost effective and they are not lost.
• But breeding as a solution has been hard to get through to farmers, as since the modern anthelmintics came on the market in the 1960s, farmers have been bombarded by myths and untruths.
  

Myths & untruths

A typical range of anthelmintic chemotherapy products on the market.
Sold in bright coloured packs with regular promotional specials.

• Breeding is too slow. Breeding for Facial Eczema (FE) resistance for example took nearly 30 years. True but there are reasons – see below.
• Drench is faster, and with the new products on the market that kill everything, the problem of drench resistance has been solved. Not true.
• Vets who sell drench hardly ever mention genetics to their clients. If they do, it’s always as a last resort. Drench sales are a significant part of vets' income and the more they sell the bigger markup they can negotiate from the manufacturer supplying them.
  
• Genetics doesn’t seem to figure strongly in their university training, and in any case they don’t sell rams from their clinics!
• If you start a breeding programme, you’ll be buried in paper and will need a computer. Not true.
  

Breeding for FE resistance – why it took so long?

Hogget with FE which is clearly suffering pain and distress.
It also cannot see as its eye lids are swollen up.

There were plenty of reasons:

• The sporidesmin toxin harvested from the fungus was so horrendously expensive that stud breeders could only afford to dose a few of their rams.
• It’s a very dangerous poison and has to be handled carefully by veterinarians, and if not done correctly valuable animals can be killed.
• Farmers couldn’t afford to drench any females, so halving the overall ‘Selection Differential’ (selection pressure) and slowing up genetic gain, despite the trait being highly heritable (about 25% or the same as fleece weight).
• Selection on the ewe side had to rely on ‘natural challenge’ to the toxin, which varied greatly between seasons.
• Commercial sheep farmers only bought FE tested rams after a bad season, and expected instant solutions the next season. They didn’t have a policy of buying resistant rams every year.
• Farmers turned their purchased FE resistant rams out with their commercial ewes and expected to see rapid gains. This random mating approach could never bring rapid improvement.
• Because tested rams were expensive, farmers only bought one or two, when they should have bought a team of rams to bring about positive change.
• So, many stud breeders gave it away, as there was no profit in the business. Only the dedicated kept going to benefit their own flocks, which they certainly did. Now in bad years they hardly ever see a clinical case of FE.
• With today’s knowledge and technology, success could be achieved in a quarter of the time.
  

How did FE resistance work?

• Scientists worked hard to find out how resistant sheep could break down the toxin’s complex chemical structure in the liver, and get rid of it. It was a fascinating bit of detective work at Ruakura, which I don’t think was fully completed.
• In simple terms, the sheep’s immune system did the work, so breeders were actually selecting for sheep with better genetic immune systems.
• This is very interesting, as the pioneer breeders today (along with their ram buying clients), are finding their sheep don’t get grass staggers (another fungal toxin), and have fewer internal parasites as judged by less drench needed.
• So to select against dags and worms, we need to identify sheep with a high natural (genetic) immune system, and manage them to allow it to be fully expressed.
• It’s a simple objective and is really a repeat of breeding for FE tolerance, but in a very much shorter time.
  

Dags and worms – why fix them in this order?

• Because this is the order in which they cause pain to the farmer.
  
• With dagging you have to wrestle with sheep before staying bent over, to remove a worthless product. And then being in constant contact with faeces is also a health hazard.
• Even if you have modern sheep handling equipment, physical effort is still needed and costs didn’t disappear.
  
• Drenching is not so bad, as you stand upright but with no automatic drenchers invented yet, stretching and being bumped by sheep, and perhaps even being bitten are still hazards!
  

Are these traits inherited?

• Yes they are.
  
• The heritability of dags is around 25% and resistance to worms (also called host resistance) is around 23-25 %.
  
• You will see ‘resilience’ used which is where a sheep can live with worms and still keep performing.
  
• If this is a separate trait, (and scientists state that it is), we don’t want it as these sheep produce dags.
  
• We only want sheep that are Worm-Free and Dag-Free.

Are the traits linked?

• Technically, dags and worm resistance are separate traits so are not linked through common genes.
  
• But there are farmers who have cleaned up the dags in their flocks (measured in barrow loads), and are finding that worms, (measured by the number of drenches given) are very apparent.
  
• This may be entirely environmental and not genetic, but at this stage why worry – it’s saving work and money. So keep an open mind at this stage.

Breeding sheep to eliminate dags and worms. 2.

By Dr Clive Dalton

PART 2

Dag-Free & Worm-Free sheep – where to start?
Commercial sheep farmers have two options if they want to get rid or drastically reduce dags and worms:

Option1. Buy in the genetics (as rams) needed from established ‘stud breeders’.

Option 2. Start a breeding programme in their own flock, which includes breeding their own rams.

Option1. Buy genetics from stud breeders.

Stud rams at public sale. FEC data are rare and Dag information non existent.
All rams are drenched frequently before sale.

• Buying the genetics (as rams) from stud breeders seems the logical choice, as ‘stud breeders with registered flocks have been providing rams (and assumed genetic improvement) for commercial breeders since sheep farming began in New Zealand.
• They record masses of data through Sheep Improvement Ltd (SIL) database via a number of bureaus.
  
• But it’s often this mass of data that scares commercial buyers away. Stud breeders have all worked hard over many generations and none got rich from selling rams.
  
• Few commercial buyers appreciate the costs, dedication and work involved in stud breeding.
  

Selection indexes

SIL Ram selection front page listing all the Indexes
There are 5 indexes and 11 Breeding Values provided.

• The core of the SIL data provided to commercial farmers on the ‘ram selection list’ is in the ‘indexes’ and ‘sub indexes’, and there’s a range of them.
• Breeding Values (BVs) are first calculated for each trait using all the information on the animal and its relatives.
• They are then balanced up for varying genetic relationships between them and finally balanced for the relative economic value of each one. This is to achieve maximum overall gain expressed in cents.
  
• See SIL website for details.
• But geneticists never tell you how long it will take to see this overall and balanced improvement expressed in the index, in the bank account. Time is not built into the index – it cannot be.
• The old genetic principle is well known – ‘that the more traits you select for, the slower is the rate of progress in any individual one’.
• My concern is that today’s sheep farmers don’t have time to wait for these sophisticated indexes with all the various economic traits to bring about improved overall income, of which dags and worms are only a part.
• If you want to fix dags and worms on ‘Fast Track’ because they are killing you and your profits, you need to hit them hard, and not let the rest of the index components slow you down.

Ram selection list showing extensive data on each animal.
This regularly scares ram buyers so they end up picking rams on their looks.

Special concern over dags and worms
The obvious conclusion: Farmers need to get rid of dags and worms on fast track as there’s nothing more important on a sheep farm right now.

Using ‘Independent Culling Levels’

• We need to treat dags and worm resistance as ‘Independent Culling Levels’.
• This is where you select for each trait independently (as they are unrelated), and if an animal fails to reach the pass mark for one trait (whatever level you set the pass mark at), then it fails the whole exam.
  
• It’s like what the old School Certificate used to be – if you failed one critical subject like maths, no matter how good you were at the others – you failed the lot. It was tough.
• Using the index approach, excellence in one trait can compensate for failure in another. This is not good enough to get rid of both dags and worms quickly – which is urgent right now.
  

The BIG problem:
Finding SIL breeders with Dag-Free and Worm-Free sheep

• Very few SIL breeders have taken the option to select for host resistance to worms, and fewer still are selecting against dags to provide Breeding Values (BVs) for these traits.
  
• This is understandable, as their clients are not asking for such rams. The new drench chemicals have now come along as the ultimate solution.
• The BV for worm resistance (called WormFEC™) is based on a flexible protocol, (too flexible in my view) allowing great variation in FEC sampling times and methods, so accuracy for selection purposes has got to be a concern.
• For those with WormFEC™ BVs, not all the lamb crop is always put up for testing, and this is often not made clear. So the choice of rams for sale within a flock can be very limited.
• These BVs only apply within farms and not between them.
• It would be hard to find a stud breeder who had not drenched the sale rams for at least two months before your visit. This is the minimal period needed to get an honest drug-free assessment of how genetically daggy individuals are.
• Farmers are told by stud breeders, technical advisers and stock agents, that if they stop selecting rams for the main economic traits like fertility and growth (wool doesn’t worry them), then these traits will go backwards in their flock.
• This is NOT true; they’ll just stay where they are, until selection moves things ahead again. You’d be hard put to select against these traits to start and lose them.
• Ignoring the other main traits won’t drive you bankrupt for a couple of generations at least till you make a big dent in dags and worms.
  

Obvious conclusion: The choice of getting Dag-Free and Worm-Free rams from SIL breeders is very limited, so you need to look at starting a breeding programme in your own commercial flock.


Option 2. Start a breeding programme in your own flock.


What’s wrong with the idea?
Here’s some facts and fiction that you hear:

• Fiction: Breeding is too much work and you’ll be buried in paper, stuck in the office when you should be outside – presumably dagging and drenching! Not true.
• Fact: All you need to get started is some raddle and some tags (which may as well be numbered). Later on you may need to use your index finger!
• Fiction: The genetics in your flock are not good enough as stud breeders have all the superior genes. Not true. This is biologically impossible.
• Fact: If you’ve been buying rams from the same stud breeder for a number of years, you’ll have all the genes they have. Your flock will genetically be a couple of generations behind that stud.
  

The big positives

Sheep selected and bred on your farm will perform well on your farm.

• You’ll be identifying top genetics in your own farming environment, and that’s a massive advantage. There’s no worry over whether a stud’s sheep will ‘shift well’ and adapt to your farm and management.
• You don’t have to keep trying different studs in different areas to see which suits your environment. On your own farm – what you see is what you get, and you certainly can’t hide how much time and money has been spent on dagging and drench!
• Also, because of the large numbers of animals in a commercial flock, there is a mass of scope for selection and culling, which many smaller studs don’t have. A high proportion of the ram lambs born in many small studs have to be sold as sires to make money.
  

Breeding sheep to eliminate dags and worms. 5.

By Dr Clive Dalton

PART 5

Two-tooth ewes from the A team nucleus

• Now as two-tooths bred from the A team nucleus ewes, they should look a picture due to the intense selection pressure put on them up to now.
• Apart from the odd sample to monitor progress, it’s not worth doing any more FECs, but keep on ruthlessly culling any that get daggy and don’t clear up quickly.
• There would be no harm in doing a FCS now and again to check on any that are not measuring up, especially those getting daggy and not drying up fast.
• Cull any that develop problems like footrot.
  

Planning the two-tooths’ mating
Decision needed: What rams are you going to join with these top two-tooths? They deserve very special consideration after all the work you’ve put into them.

Ram options

Option 1:

Stud breeders rams at pubic auction but few FEC records and no dag data.

• Contact your nearest consultant from Sheep Improvement Ltd (SIL) by phoning 0800-745-435, or Email "mailto:help@sheepimprovement.co.nz" help@sheepimprovement.co.nz
• Ask which breeders have rams for sale with WormFEC™ and Dag Score BVs.
• Take care to check the records and ask the breeder how many rams have been tested and how this was done, as despite the SIL WormFEC™ protocol in the Breeders’ Manual (1994), some breeders have developed a few variations of their own.
• FCS is not accepted by SIL as a correction for FEC. And in any case, the rams will all have been drenched regularly and recently, so you won’t be able to get a true ‘drug-free’ FCS assessment.
• Beware that breeders may advertise that they are breeding for worm resistance or even worm resilience, but their programmes will need questioning.

Lab FEC raw data on rams at a sale - a very rare feature.
The FECs were not being used in an index.

Option 2:

• Failing any success with SIL breeders, the next option is to look at any old sires you have on the farm purchased previously from SIL breeders.
• This could surprise you or shock you - to see what you have spent money on (in all innocence) in previous seasons.
  
• Their mature (genetic) immunity against dags and worms should have been fully developed – if they have any. It would be worthwhile having a look.
• Make sure they have not been drenched for at least two months (preferably three) and first check their FCS. It’s not worth wasting $5 on a FEC if a ram is a scourer.
• Any like this need to be used as terminal sires as you’ll be dagging their progeny for the next five years at least.
• For the marblers or hand grenaders, get a FEC done.
• Don’t contemplate using any animal with a FEC over 500 epg and zero should be a better target.
  

Option 3:
This is the obvious choice - to use your own rams, bred in the A team nucleus flock, and Pathway 2 describes this.

Breeding sheep to eliminate dags and worms. 7.

By Dr Clive Dalton

PART 7

These are the last two pathways where emphasis is on the males.

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


Pathway 3: Selecting males to breed females

• This will happen by using the two-tooth rams bred from the A team nucleus ewes described in Pathway 2.
  
• With all the selection pressure put on their dams, they are bound to be ‘improvers’.
  
• They are your ‘power house’ for flock improvement, because a ram has greater genetic influence than any single female.
• Their mission is to sire as many future females as possible in the flock to spread their genetic potential for resistance to dags and worms.
• These rams are worth big money and if in doubt, ask yourself where you could buy better ones with intense selection against dags and worms?
• Also, they have been intensively selected on your farm, so there are no worries about how their progeny will perform.
• If AI had been a commercial reality, then this would have been the way to use them. But a lot can be done using single-sire natural mating.
• Past experience has shown that really top rams can be single-sired mated with 400 ewes for one cycle. But using a top ram to mate 100 ewes is normal these days.
  

Pathway 4: Selecting males to breed males

• This is the final genetic pathway and comes from using the male lambs produced by the top sires out of the A team ewes.
  
• They will go around the loop again described in Pathway 2.

Inbreeding:

• Inevitably the top sires of one generation will sire the top sires of the next generation, so a build-up of inbreeding is inevitable.
• At low levels (e.g. under 7%) this is not a problem, but when it reaches high levels quickly (> 25%) then problems can be seen such as minor genetic defects like undershot jaw.
  
• When levels get really high (> 50%) they can be major from ‘inbreeding depression’ where fertility and survival are reduced.
• In this programme, a top two-tooth ram which finally comes through, when used on the A team ewes could have a dam in there, and a twin sister.
  
• He could also have a number of half sisters (by his sire out of different dams) which he could also mate.
• However, if this bit of intense inbreeding did cause problems in this early stage, the intense selection and culling programme would identify and eliminate them.
• After a couple of generations of the programme, if there was cause for concern, then one single outcross to rams from a breeder with similar objectives would immediately restore genetic variation to continue making progress.
• Another method for the long term is to divide the A team nucleus into small sub-flocks (on paper and with different coloured tags) and keep moving rams around these in a planned rotation each year.
  

Final points to ponder

• There is no need to panic!
• You certainly cannot go backwards genetically as everything you have done so far is positive! Sheep that don’t produce dags and don’t have worms are ‘efficient converters’ of their feed so are profitable sheep.
• What you have done in your flock should be of great interest to your former ram suppliers, as now you have given them a challenge to come up with genetics that will reduce your animal health costs and increase ‘easy care’.
• Invite them to visit your flock and show them the A team ewes and your sires bred from them. They can go home and plan how to keep your custom in future.
• The wise ones won’t write you off, as you could have genes to help them in future!
• For any vets complaining about your low drench purchases, suggest that if they want to keep on selling drench, they should provide a free dagging service with each container. Not many vets would ever have done a week's dagging!
  

What to do if you hit a worm crisis?

• This could happen of course. An example would be an unexpected outbreak of Barber’s Pole (Haemonchus contortus) worms or some other species depending on where you farm.
• Again, don’t panic as now when you use an appropriate conventional drench, because your sheep have never been drenched and developed any resistance, the drench will be highly effective.
• You won’t need to keep on drenching.

Breeding sheep to eliminate dags and worms. 8.

By Dr Clive Dalton

PART 8

Life cycle of main species of sheep worms

• The main species are 'roundworms', but there are also tape worms, lung worms and liver flukes. Below are Barber's Pole worms (Haemonchus contortus)
  

• Mature worms live in the sheep's gut where they mate and produce eggs.
• These eggs then pass out in dung on to the pasture.
• When conditions are right (warm and moist), they hatch into larvae and go through three main stages - L1 to L3.
• The L3 stage is the critical one as they crawl up the pasture plants to be eaten by another sheep to continue the cycle as mature worms inside the sheep.
• It takes about 21 days for ingested larvae to develop into adults capable of laying eggs.
• These larvae are aquatic creatures and need moisture to survive and travel. Dessication kills them.
• Larvae need a minimum of 2-6 weeks of warm moist conditions to develop successfully.
• Some larvae can live for 6-8 months in cooler temperatures (surviving frosts) and in warmer conditions can die after 2-3 months.
• They can survive droughts by going down 10-20cm.

• KEY POINT: Around 90% of the worm cycle is on the pasture where you can't do much about them - other than get other species of animals to eat them with no ill effects.
• If you want to kill any worms, you have to do it with chemicals when they are inside the sheep. Some drenches only kill the worms and others kill both worms and eggs.

Faecal Egg Counting (FEC)

• A FEC is a good general indicator of a worm burden is the number of eggs passing out of the animal in the faeces.
• This is the basis of a ‘Faecal Egg Count’ that can be done through a vet clinic or on the farm if you have a microscope and the equipment.
  
• Ask your vet for details, or you can buy a commercially available kit with everything you require plus technical support when needed from FECPAK International Ltd, Box 5057, Dunedin, New Zealand.
• The costs through a veterinary clinic can vary depending on quantity.
• To check the quality control of the veterinary laboratory, split some samples and send them in with different numbers. The sub-samples should not vary more than a few hundred eggs per gram.

• Some farmers with a FEC kit share the work and cost with neighbours.
• A FEC shows the number of eggs per gram of faeces (epg) and there are accepted ‘trigger levels’ after which you should take action by drenching – or do nothing.
• You cannot tell the worm species from their eggs, so to identify species the eggs have to be incubated in the lab which takes about 10 days and consequently costs more.

Larvae being incubated in lab

• However the eggs of Nematodirus are larger and very distinctive compared to all other strongyloides worm eggs.
  
• They are always counted separately as Nematodirus worms are not great egg producers so animals can harbour heavy worm burdens and have low (less than 500) epg. This often occurs in lambs.
  

Limitations of a FEC

• A FEC can only be a snapshot of the animal’s worm burden judged by egg output at that time of sampling.
• It’s really a measure of what was going on inside the sheep 3 weeks beforehand.
• With the standard FEC used in the past, the biggest limitation was that samples were not corrected for the Dry Matter intake of the animal or the moisture content of the faeces.
• Despite the limitations of FEC (and still some academic criticism of its interpretations) it’s a very cost-effective tool and in any case it’s the best we have at the moment.
• Whatever its many shortcomings, it's the most cost effective at this time.
  

FEC sampling tips

Paddock (composite) samples

• The easiest way to get a dung sample for FEC is to pick up fresh faeces from the paddock.
• Follow a few sheep around for a while, or go where they have been camping, and make up a composite sample from at least 5 heaps and better still 10.
  
• Mix them well.
• Using composite samples keeps the lab costs down.
• When the lab gets a composite sample, it should give it a further good mix before sub sampling, but check that this will be done.
• The more accurate way for the lab to do a composite FEC is for individual samples to be sent to the lab and an equal weight of sample is taken from each, and a special composite FEC carried out to a sensitivity of 10 epg per pooled sample.
  

Finger sampling

• Use your index finger to draw a sample of faeces from the rectum.
• Rubber gloves are recommended.
  
• The sheep will not like this, and it can take a good push to gain entry if the animal has not been scouring.
  
• You need at least 5 g of faeces so it usually needs a second finger insertion. The sheep won't like this either.
• With many sheep to do, this can be tiring on your fingers so you may have to change hands occasionally.
  

Probe rectal sampling

• You can use a probe made from half inch plastic water pipe to draw out the sample.
• The probe is carefully inserted, and given a 180 degree twist before removal.
  
• You will normally get more than the 5g needed by one insertion of the probe.

Faecal Consistency Score (FCS)

• Australian research from Armidale in NSW has shown that when you get the FEC, you should correct it for moisture content. They showed that the easiest way to judge this was from the form of the faeces.
• The more liquid the faeces, the quicker they pass through the digestive system, and hence the more diluted the 'eggs per gram of faeces' will be when they come out the rear end.
• A healthy sheep with an efficient digestive system passes round ‘marbles’ – even when on lush pasture and crops.
  
• These are formed in the hind gut where water is removed, and the movement of the gut wall (peristalsis) produces the marbles. It’s an amazing bit of physiology!

When to do it?

• It should always be done when collecting a FEC sample and the score built into the animal ID number.
• Or it can be done at any other time.

Scores used

• The Australian researchers used numerical scores but the following descriptions are used below as they are easier to remember:

Photo 1: ‘Marbles’

Photo 2: ‘Hand grenades’


Photo 3: ‘Plops’


Photo 4: ‘Slops’



Photo 5: ‘Scour’



Corrections
The corrections used are very simple and again are easy to remember. Multiply the FEC by 1 to 5 as shown below:

• Marbles x 1
• Hand grenades x 2
• Plops x 3
• Slops x 4
• Scour x 5
  

A quick and easy method
If you don't want to pull out a sample of faeces from the rectum, then all you do is insert your finger and feel what's in there.

• Marbles - you will feel these easily
• Hand grenades - you will feel an empty gut as the handgrenade has just been voided.
• Plops - you will see just a green stain on the end of your finger.
• Slops - your finger will come out quite green.
• Scour- your finger will be covered in green soup!
  

Advantages of marbles

An overnight pile of marbles from a sheep that has defeacated 2-3 times without getting up.
She has got up and no dung has stuck to her wool causing dags.

Faecal marbles have big advantages for sheep, and big disadvantages for larvae:

• Marbles don’t stick to wool and produce dags.
• They fall to the ground and many separate and spread out.
• If the lamb’s tail has not been docked too short, causing damage to the supporting tissue around the anus, when the sheep wags it’s tail during defaecation the marbles are projected away from the body.
• Single marbles or small clusters dry out quickly on the ground leading to larval death through desiccation.
• The surface area of marbles is about six times greater than if the same volume of dung was in a large wet heap.
• The dark green to black colour of the marbles absorbs more UV radiation adding to larval death.
  

Conclusion: Having sheep that pass marbles will be a practical and effective way to reduce the larval population on the paddock.

Breeding implications of FCS correction
Correcting a FEC for FCS has major implications to improve the accuracy of FEC interpretation, when selecting individual animals in breeding programmes.

Example:

• When selecting ram hoggets or two tooths as future sires, if you decided to keep a ram with a FEC of less than 500 epg, you would be fairly happy that he was resistant to worms.
  
• But that would only be correct if he was passing marbles (FCS 1).
• If he was scouring (FCS 5), then multiplying his FEC of 500 x 5 would give a 2,500 epg count and you would certainly not want to keep him as a future sire – even though he may be classed as resistant using FEC alone.
  
• He should be on his way to the dog tucker freezer. The FCS has changed the decision drastically – and for the better.
• So not correcting for faecal moisture can lead to a very wrong genetic assessment of replacements (especially rams) for the flock.
  
• You could easily end up with high-index daggy sheep that will pass those genes on to their progeny, and you would be bending over their rear end and removing dags for the next five years.. That’s not progress!
  

Breeding sheep to eliminate dags and worms. 9.

By Dr Clive Dalton

PART 9

Getting the best from a 'Dag-Free' and 'Worm-Free' ram

This is an outstanding Romney ram. He was named 'The Colonel'.
Every time he has been tested he has had zero FEC, and had a FCS of 1 (marbles). Consequently, he has always remained clean regardless of the feed he was on. His sons have come through showing the similar traits.

If breeding is not for you
If the idea of breeding your own rams is not an option, and you are lucky enough to find a source of genuine Dag-Free and Worm-Free rams, how can you get maximum genetic benefit from them to improve your commercial flock -on 'fast track'.

Don't

• Don't just turn a top ram loose at random in the flock. His genetic influence will be so diluted that you'll never live to see the benefits of eliminating dagging and drenching.

Must do

• It's your job to make sure the ram or rams are mated to ewes that will speed up genetic gain in the flock - so you have to do some intense selection on the females side.
  
• A ram only carries half his superior genes to his offspring, but he has the big advantage of influencing many more offspring than any single female in the flock.

Before you start

• Do not drench any ewe at least two months (more if possible) before joining, no matter how convincing the advertising or sales promotions may be.
  
• Mature ewes with their fully developed immune system should not need drenching, and if any do, then mate them to a terminal sire and cull them after weaning. Don't let their genes into the wider flock.
• You can't identify genetically daggy ewes if they are full of drench.
  

Mating group options
Here are some options from lowest priority to highest from a technical viewpoint. Just do what suits your farm management system best.

• Among each group, look for individuals that are structurally sound and have as clean backsides as possible.
  
• Avoid like the plague any that have been regularly dirty.
• Do a FCS to identify all those with marbles or hand grenades.
• Do a FEC through a lab if you can afford it, and avoid using any ewes over 500 epg.
  

1. Mixed age ewes.
2. Two-tooth ewes.
3. Cast-for-age ewes.
4. Ewes scanning twins before lambing.
5. Ewes that have reared a lamb to weaning - still with milk at their udder.

Mating ratios

• Single sire each ram with 400 selected ewes for one cycle, to try to get as many progeny as possible.
  
• Otherwise don't come down to less than 100 ewes per ram.

What to do with the progeny?
Just make sure you can identify them to put plenty 'selection pressure' on them as described in the earlier parts of this blog.