Ovine Observer

Table 1 Production of the South Australian Selection Demonstration Flocks 2004 drop hoggets. Control values are expressed as the actual performance and the three selection lines are expressed as their values relative to the control

The improvement was greatest for measured performance flock and resulted in a 36% increase in gross margin per hectare compared with the randomly mated control flock. This is a substantial improvement in estimated profitability and was achieved from identifying outside sires for two matings and then a further five years of selection within the flock.

In contrast to the above results, consultants who carry out on-farm benchmarking report that they do not observe consistent differences between profitability between genotypes, whereas differences of 30-40% between genotypes should be easily observed. This raises the question as to why the differences are not being detected. Is the effect of genotype being overridden by the effect of management, or is there a problem with the practical implementation of breeding programs associated with which traits increase profitability in extensive animal production systems? The remainder of the article examines the second issue.

Current genetic selection is based on improving production per head whereas profitability is more closely associated with production per hectare. The difference between the two is associated with the number of animals that can be carried per hectare.

In carrying out economic analysis of different genotypes a range of assumptions have to be made regarding carrying capacity achievable for each genotype. The assumptions made are similar for most genotype evaluations are:

• the feed requirement of animals is proportional to their metabolic liveweight and the foraging ability of animals is similar. This means fewer large animals can be carried than smaller animals and that the level of pasture utilisation is similar regardless of genotype.

• increases in clean fleece weight are achieved without increasing the energy requirement of the animal.

The assumptions may not always be correct, however, the underlying biology is difficult to quantify for more accurate economic analysis.

Sensitivity analysis carried out to determine the importance of these assumptions has shown that varying them within a realistic range has a major effect on the profitability of using different genotypes (Table 3). Further analyses showed that developing a selection index from the values calculated within this range of assumptions would lead to very different breeding directions.

Table 3 Whole farm profit ($) for different pasture and animal production systems based on a standard genotype and changes to profit for more resilient genotypes achieved through increased capacity to consume low quality feed or lower energy requirements for maintenance

It is commonly observed that the number of animals that farmers carry is associated with the number of animals that can be carried in a poor season.

Recent work has shown that there are marked differences between genotypes in their resilience when faced with feed restrictions. Much of the work has revolved around differences in genetic fat and muscle. Animals with higher genetic fat and muscle are more resilient and are able to maintain production when feed supply is short.

While studies suggest that resilience may be a very important trait, so far it has not be widely used for selection.

A recent analysis compared the estimated profitability of a genotype selected for high fleece weight with a genotype selected for improved resilience under two different nutritional scenarios.

• Maintaining ewes at condition score three from joining, day 90 and through to lambing (CS 3-3-3).

• Allowing half a condition score loss during pregnancy from joining in condition score three to lambing in condition score 2.5 (CS 3-2.7-2.5).

The analysis showed the more resilient genotype was $100 000 per annum more profitable when animals were fed to maintain condition and this increased to $250 000 per annum if there was a nutritional challenge and animals were losing 0.5 of a condition score during pregnancy.

This analysis varied the production assumptions outlined above based on some experimental and anecdotal evidence and therefore is not proof that a more resilient genotype is more profitable. However, it suggests that this area needs further work to decide if it is part of the reason for the divergence between theoretical and experimental gains from genetic selection and the on-farm benchmarking observations.

In conclusion, when evaluating the benefits of genetic selection we need to be clear on what is determining the profitability of an enterprise. It may not be production parameters such as clean fleece weight and growth rate as these higher production genotypes require more management to look after those sheep. If stocking rate and the scale of the sheep enterprise is limited by labour requirements and feed costs, then a genotype that reduces these limitations may be more profitable. 

Dorpers: are they really non-seasonal breeders?

Table 4 Number of lambs (live and dead) born each month, 2006 to 2014

At latitude 0, there are 12 hours of light and 12 hours of darkness each day throughout the year. Hence there is no decrease in day length to stimulate onset of oestrus. Perhaps sheep at the equator are non-seasonal breeders, if nothing else influences their oestrous cycle, such as nutrition, disease, temperature, age, stresses of transportation or shearing.

At Merredin, (latitude 31 29’ S), duration of daylight varies from approximately 13.9 hours in December and January to approximately 10.1 hours in June and July. It would be interesting to see the pattern of oestrous cycles of Dorpers at say, Invercargill, New Zealand (46 24’ S) or Bothwell, Tasmania (42 23’ S).

Conclusion

I have no doubt that Dorpers do have the capacity to cycle and conceive in any month of the year. Based on observations of my own sheep, I believe that over time a flock of Dorpers kept at the same location (not close to the equator) will probably tend towards a seasonal polyoestrus pattern. This tendency might not become apparent if breeding stock are often introduced from markedly different latitudes. I suspect that latitude, and hence variability of day length, is an important factor in influencing the length of the breeding season of Dorpers, provided that nutrition and management are always appropriate and that a ram is continuously present. Adverse factors, such as poor nutrition, disease, age, high temperatures and stress of transport or shearing may suppress the occurrence of oestrus cycles.

Managing virulent footrot in sheep and goats in Western Australia

Kirsty Moynihan
Veterinary Officer, Livestock Biosecurity
Department of Agriculture and Food Western Australia, South Perth
Email: kirsty.moynihan@agric.wa.gov.au

There are two forms of footrot in sheep and goats: virulent and benign. They are caused by infection with different strains of the bacterium, Dichelobacter nodosus.

Virulent footrot strains have the potential to cause more severe disease, whereas most benign strains cause a milder form that typically heals once the feet dry out. There are no quarantine restrictions for benign footrot, however producers must be vigilant and not present sheep with any footrot type lesions to saleyards.

Advanced virulent footrot is a painful, crippling condition. It is important to control or eradicate virulent footrot when it occurs in order to reduce production losses and to ensure animal welfare.

Tests for footrot
To test for footrot, a veterinarian or stock inspector takes scrapings of skin from lesions between the toes of infected sheep to be cultured in the laboratory for bacteria. If D.  nodosus bacteria grows in the culture media, isolates are subjected to the gelatin gel test. The gelatin gel test categorises the protease enzymes produced by D.  nodosus on their stability when heated into two groups:

• heat stable (S) strains, which cause virulent footrot
• heat unstable (U) strains that cause benign footrot.
   

• varying degrees of lameness
• separation or under-running of horny material at the junction of the skin and the horn of the hoof, starting at the heel
• usually more than one foot is affected
• both toes of each affected foot are often involved
• loss of body condition and decreased wool production.

Diseases which can be confused with virulent footrot include benign footrot, foot abscess, and scabby mouth. More than one of these diseases may occur in an animal at the same time.

Lameness in several animals should always be checked by a veterinarian as the exotic disease foot-and-mouth disease can make sheep lame. Detecting an exotic disease early will limit the impact of the disease on the livestock industries and Australia’s economy.

Severity of virulent footrot

The severity of virulent footrot lesions depends on three factors:

• the susceptibility of the animal
• environmental conditions
• the strain of bacteria.

If conditions are not favourable to the bacteria, then virulent footrot strains may only cause mild changes. Less severe forms may involve only the soft horn of the inside wall and the sole. This is why it is so important to take a skin scraping from between the toes and to use the gelatin gel test, rather than rely only on visual signs.

Spread of virulent footrot
Infected sheep or goats are the main source of new infections and some will maintain the infection from year to year. The bacteria can survive in deep, unexposed lesions in the foot for many years, but when away from the foot, survival time on the soil or in faeces is quite short. Hot, dry conditions cause bacterial death in a few hours, while in warm, wet conditions the bacteria can survive a maximum of seven to ten days. During dry periods there is minimal spread of disease. Most of the affected feet appear to heal; any bacteria that are shed will die, and they are unlikely to invade and cause damage to uninfected feet. When conditions become wet however, the previously ‘dried out’ lesions in the feet of the chronically infected animals may become active with large numbers of bacteria being shed. Wet feet of clean sheep are then easily infected.

The disease spreads rapidly during warm (greater than ten degrees Celsius) and moist conditions, usually in early spring to summer. Lesions may develop during autumn and summer in some years in high-rainfall areas or where there is an early start to the season.

Although reports are rare, the disease may be spread mechanically, either on the feet of other animals, or by people transferring contaminated mud on boots. This transfer is more likely within an infected property than between properties.  Unwashed livestock transport trucks and sheep handling equipment may occasionally contribute to the spread of footrot. In a small number of cases, cattle have been known to be infected with virulent footrot.

WA Footrot Control Program

Quarantine restrictions

DAFWA inspectors place flocks with virulent footrot under quarantine, restricting movements of sheep and goats from these properties until the infection has been eradicated. 

A permit to move (stating specific conditions) issued by a DAFWA inspector is required for all movements of stock from an infected property. Sales are permitted only if stock are to be sent direct to slaughter. Sheep that are not showing signs of lameness may be consigned for live sheep export under certain conditions.

Management options: eradication or control
Farmers with quarantined flocks first need to decide whether to eradicate or control footrot in their flock. They then, together with their DAFWA inspector, develop a footrot property disease management plan.

Eradication can be achieved by either:

• destocking the property of all sheep and goats
• repeat inspection and culling during the summer period.

If a farmer chooses to control virulent footrot for economic reasons, sheep can still be sold for slaughter under a permit to move. Farmers opting for control are subject to welfare and biosecurity audits.

DAFWA inspectors carry out quarantine release inspections on eligible properties. These occur after each spring until no virulent footrot is found. The inspector then releases the property from quarantine.

Use of footbathing, antibiotics or vaccine at any time before a release inspection must be discussed with a DAFWA footrot case manager as it may affect eligibility for release. Other conditions for eligibility for release from quarantine may also apply.

Footrot vaccine
Use of the serogroup specific vaccine in WA is limited to farms diagnosed with virulent footrot, where it is used to treat the infection, not to prevent footrot. The vaccine is currently only available under an Australian Pesticides and Veterinary Medicines Authority (APVMA) emergency permit and requires written permission from the WA Chief Veterinary Officer before use. Use of the vaccine must be carried out in accordance with the requirements of the Footrot Control Program and discussed with a DAFWA footrot case manager.

Prevention
The greatest risk of introducing footrot into your flock is by buying in infected stock, or having infected stray stock mix with your flock. Sensible precautions to avoid this include:

• buy direct from properties with a known health status
• inspect the feet of animals before buying
• ask for a Sheep Health Statement
• treat sheep returning from agistment as you would purchased stock
• keep newly introduced stock separate from existing stock for as long as possible and examine them regularly
• maintain boundary fences to prevent stray sheep from entering your property.

Footrot treatment to be trialled under WA conditions

Kirsty Moynihan
Veterinary Officer, Livestock Biosecurity
Department of Agriculture and Food Western Australia, South Perth
Email: kirsty.moynihan@agric.wa.gov.au

The Department of Agriculture and Food, Western Australia is trialling a new treatment for virulent footrot developed by the University of Sydney. The vaccine is currently only available under an Australian Pesticides and Veterinary Medicines Authority (APVMA) emergency permit and requires written permission from the WA Chief Veterinary Officer before use. Footrot is an infectious disease of the hoof caused by the bacterium Dichelobacter nodosus, which consists of 10 serogroups. The immune response of the sheep is specific to each serogroup.

The vaccine will only be of use on properties that already have virulent footrot present and needs to be formulated to target the specific serogroups present in the infected flock. The new vaccine targets a maximum of two serogroups of the possible ten. Laboratory testing is used to establish which serogroups are present on the property so that the appropriate vaccine is given.

Sheep receive two vaccinations a month apart. Non-responders are culled and sheep are inspected for the presence of footrot during the optimal disease expression period in late spring/early summer. For a flock infected with more than two serogroups, an initial vaccine is prepared that contains the two predominant serogroups from that flock, then a number of vaccines need to be prepared until all serogroups are eradicated. The use of the vaccine prior to inspection for release from quarantine could affect eligibility for release and must be discussed with a department footrot case manager prior to use. 

More information about virulent footrot and the Footrot Control Program is available on the DAFWA website.

National Livestock Identification System update

Peter Gray
Registrar of Stock and Apiaries
Department of Agriculture and Food Western Australia, Bunbury
Email: nlis.sheep@agric.wa.gov.au

The Department of Agriculture and Food, Western Australia established a sheep and goat National Livestock Identification System (NLIS) helpdesk in December 2014 to help improve the traceability of sheep and goats in WA. Failure to improve the level of traceability of sheep and goats in Western Australia may result in changes to identification regulations, with support growing in the eastern states for electronic tagging.

As a sheep or goat owner, you are required to either record the mob-based movement yourself, or arrange for someone to do it for you, when you:

• buy sheep or goats privately - including rams and private sales through agents

• move stock between your different Property Identification Codes (PICs).

Sheep bought at auction (saleyards, ram sales and clearing sales) will be recorded and uploaded to your PIC by the agent running the sale or the saleyard operator. Sheep and goat movements are recorded on the database as mob-based movements where the originating PIC, the brand on the tags (some may have a PIC), destination PIC, number of stock, NVD/waybill number and date is entered. You can use the NLIS database to check that stock you have received are registered to your PIC. To get started and set up an NLIS user account, visit www.nlis.mla.com.au.

The NLIS was setup to record movements of all sheep across Australia and requires livestock owners along with industry players such as agents, saleyards and abattoirs to register and record all sheep and goat movement on the NLIS database.

Given the thousands of livestock movements taking place daily around Western Australia, an electronic record keeping system is vital to ensure industry and government can readily trace emergency animal diseases or chemical residue issues back to the property of origin, and to other stock that have been in contact, more rapidly.

Case study: early adoption drives accelerated progress at Centre Plus 

Cooperative Research Centre for Sheep Industry Innovation

Website: sheepcrc.org.au

 

A willingness to try something new and to adopt technology early has dramatically changed the Mortimer family’s sheep breeding operation for the better in Central West NSW. The Mortimers, based at ‘Devondale’ at Tullamore in Central West NSW, run the breeding nucleus of 1200 ewes for the Centre Plus Ram Breeding Group.

 

Centre Plus has always been open to new technology and virtually all the technology in use was adopted very early. In the early days it was as simple as micron testing of the ewes. Now they use Australian Sheep Breeding Values (ASBVs) and routine DNA testing. Whenever the latest genetic tools come on the market the Mortimers are looking at them and itching to be involved in using them early.

 

By incorporating advanced genetic measurement tools including DNA testing into the business, the Mortimers have been able to introduce proven genetics to the nucleus flock a full year earlier than under traditional management systems. In order to put selection pressure on objectively measured traits some of the visual selection pressure has been reduced.

 

The breeding objectives for Centre Plus have always been focused on the ‘all purpose Merino’. At the beginning it was growth rate, fertility and lowering micron, while holding fleece weight steady. Over the last decade the focus has moved from reducing micron to increasing fleece weight and improving other traits such as worm egg counts, eye muscle and staple strength. The Mortimers willingness to adopt new technology opened the way for Centre Plus to be an early participant in the Cooperative Research Centre for Sheep Industry Innovation (Sheep CRC) Genomics Pilot Program. The early results of that program revealed the potential gains on offer from DNA testing and as a result Mr Mortimer has since tested 20 per cent of the male drop each year for traits aligned with Centre Plus’s breeding objectives.

At weaning time about 20 of those 100 ram lambs are selected to be potential sires, and they are taken out and fed to reach breeding weight at six months. At that stage, six of those young rams will be chosen to go out into the mating program. Mr Mortimer was also an early user of the Sheep CRC’s DNA test for parentage to give a clearer picture of the genetic make-up of young animals. The Mortimers are using genomic information to select rams at six-months of age and are impressed with how close the performance of the progeny are to the ASBV predictions.  By using six-month-old rams the genetics are also getting into the flock a whole year earlier and allowing them to speed up their genetic gain considerably.

 

There is an understandable wariness in the industry about new technology because it is human nature to be hesitant about relying on a technology when you do not know exactly how it works. The Mortimers’ philosophy is that you have to force yourself to make changes, and back it up with measurements to make sure that it worked as expected.

 

As the Mortimers’ look for the next technological advance to improve their genetic gain they will be keeping a close eye on the improving DNA technology and the Sheep CRC’s work in full sequencing. DNA technology is very exciting because it opens up completely new ways of doing things in sheep breeding and selection.

 

More information on objective selection tools, ASBVs and DNA testing is available at sheepcrc.org.au.

John Karlsson retires

Department of Agriculture and Food, Western Australia

 

John Karlsson, Senior Veterinarian of the Department of Agriculture and Food Western Australia, recently retired after 37 year service to the Australian sheep industry.

He started with the department in 1978 and has always been very passionate about sustainability issues, and breeding for robustness and fitness traits in sheep. At that time, control of internal parasites in sheep had mainly relied on chemical drenches. However, it is now well known that the parasites had and continue to become more resistant to the available drenches - to such an extent that nearly all farms these days experience some form of resistance.

 

In the mid-eighties, John Karlsson realised that chemical control of internal parasites was unsustainable and that alternative methods needed to be found that do not just rely on chemical control. His interest in genetics led him to believe that breeding for worm resistance could be a solution. In 1987, with the assistance and support of 95 Merino farmers who donated sheep, he established the Rylington Merino research flock and was successful in attracting external funding from the International Wool Secretariat to determine the inheritance of worm resistance and whether selection for low faecal worm egg counts could result in improved resistance to worms. Support also came from the Shire of Boyup Brook (who made the Rylington Park farm available for this study), CSIRO and other various research organizations.

 

During the project’s lifetime, John Karlsson measured faecal worm egg count extensively in this flock as well as the production and reproduction traits. Complete pedigrees were diligently recorded on each animal. This unique set of data allowed for the estimation of the heritability of faecal worm egg count and for the genetic and phenotypic relationships between this trait and the production traits that are required to design breeding programs.

A breeding program for low faecal worm egg count was initiated in this flock and the breeding program was continuously updated with the latest scientific information as the genetic parameters estimated in this flock came available. The progress of this selected line was continuously compared against an unselected control line. The results showed that faecal worm egg count is a heritable trait and that selection should be effective to reduce it. However, a significant finding was that the heritability of faecal worm egg count is not constant during the year and that the optimum time to measure worm egg count in a Mediterranean environment is approximately 2-3 months after the start of the winter rainfall (from August to October), rather that it was important to monitor the challenge regularly.

 

The results also showed that sheep can be measured at weaning. This information was used to develop practical breeding methodologies for Mediterranean environments and this has been compiled in a booklet ‘Recommendations for breeding sheep for resistance to worms in a Mediterranean environment’. The success of adopting these methodologies has been clearly demonstrated in the Rylington Merino flock. Selection for low faecal worm egg count has reduced faecal worm egg count by 2.7% per year up to 2000. From then onwards, selection focused on reducing dags and improving production traits. In addition this flock has also shown that selection for low faecal worm egg count does not have a negative effect on the other production traits.

 

The Rylington Merino flock has also been benchmarked for worm resistance in both summer and winter environments. The results have clearly shown that the Rylington Merino flock is currently the most worm resistant flock in Australia and probably in the world. It is therefore a unique genetic resource to determine the underlying mechanisms of worm resistance in Merino sheep and also for biotechnological studies in gene mechanisms.

 

John Karlsson has clearly shown that it is feasible to breed sheep for worm resistance. He has published many scientific papers on this topic and he made a significant contribution to our knowledge of the genetics of worm resistance. He has continuously promoted the concept of breeding for worm resistance amongst ram breeders, farmers and fellow scientists through conferences, workshops, field days and media articles. He has shown that methodologies applicable to summer rainfall regions will not work in Western Australia. He has used the genetic information from the Rylington flock to develop practical methods that ram breeders can use with minimal disruption to their current methods to breed for worm resistance in Mediterranean environments. More and more ram breeders are currently adopting these technologies to make the Western Australian sheep industry more sustainable and less reliant on chemical drenches. In doing so his vision has provided farmers with another tool for successfully running sheep particularly in the high rainfall environments, where the challenge from other land use pursuits is ever eroding the state sheep flock.

 

During the last ten years John was also actively involved in elucidating the underlying causes of breech strike. He managed the Australian Wool Innovation funded breech strike flock with the Rylington Merino flock at the Mt Barker Research Station, which showed that dags, skin wrinkles, urine stain and breech cover were the most important indicator traits for breech strike. These results have been used to develop Australian Sheep Breeding Values (ASBVs) for dags, wrinkles and breech cover, which breeders can obtain from Merinoselect.

 

John’s vision, courage, commitment and determination that it would be possible to breed for worm resistance has been vindicated. He has pursued this dream, which has been realised in the Rylington Merino flock. In 2002 John was awarded the Science and Technology award by the Department of Agriculture.We wish John a very happy retirement and thank him for his service to the Australian sheep industry.