Breeder Herd
Management

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If you can't measure it, you can't manage it

• Measurement and management are paramount to business success. Actively review production records to identify areas for improvement and monitor success of interventions
• Reproductive performance is a key profit driver and must be balanced with selection for growth and carcass attributes
• Actively manage stocking rate to match available pasture
• Manage heifers and cows so that they calve when feed is most abundant and have strategies to manage cows that calve outside this time period
• Control production limiting diseases through targeted vaccination programs

_{Acknowledgements: Preparation of these guidelines was completed with technical assistance and advice from the following veterinarians and animal scientists working as industry advisors and researchers in the northern Australian beef industry: Ian Braithwaite, Phil Holmes, Geoff Niethe, John Bertram and Tim Schatz}

Helping you manage your herd more effectively

In November 2010, Meat and Livestock Australia released the Northern Beef Situation Analysis (McCosker et al 2010). A follow-up analysis was undertaken in 2013 with similar findings (McLean et al 2013). The CashCow project has also recently been completed. These publications highlight a number of opportunities for significant improvement in the management of northern Australian beef enterprises. The CashCow project has established achievable benchmarks for production in Northern Australian beef herds. These reports identified that the rising costs of production are not being matched by increases in productivity. Reproductive management, calf loss and breeder cow mortality have been identified as key areas of focus for improvement in productivity.

The Northern Beef Management Guidelines aim to help producers manage their herds more effectively and achieve optimum breeder herd performance, especially reproductive performance. These guidelines are intended for the most extensively managed beef herds in Australia. These are typically those in the Gulf and Channel country of Queensland, Northern Territory and Kimberley and Pilbara regions of Western Australia. Each section focuses on one key area of northern cattle herd management and summarises the key aspects producers should consider when managing their herd. They are designed to be easily understood and implemented and provide a pathway to help producers get their herds back on track. A list of reference materials provides more detailed information on these topics.

Zoetis produce a range of animal health products which offer the opportunity to control key production limiting diseases and boost the rate of genetic gain in beef herds. This document makes reference to these various products where appropriate. However, these tools on their own are not silver bullets. The objective of these guidelines is to outline some of the other key issues producers must manage concurrently to make a profit from beef production in northern Australia.

Key goals for Northern Beef Production

The Ultimate Production System

The below diagram illustrates the key areas that should be addressed to successfully manage your herd. Measurement, genetics, nutrition and disease are all discussed in later sections of these guidelines.

All the elements are linked, which means changes to one aspect of the operation can have positive and negative impacts on other aspects of the production system. Producers who achieve optimum productivity and sustainability are ultimately balancing all these aspects of their business.

For example, reducing breeder cow mortality by controlling botulism through effective vaccination, early weaning and strategic supplementation of cows and heifers calving during the dry season will ultimately fail unless the surplus females that are generated are sold. Over time, stocking rates will increase, lowering available pasture, which leads to reduced cow body condition scores and reduced conception rates. Producers who make appropriate changes to their stocking rate and marketing programs profit from the exercise. For those that do not make these associated changes in management and adapt to their changing circumstances, the intervention is a failure, despite its early benefits.

In addition to the above factors, the following factors also need to be considered:

1. Enterprise mix – determining the appropriate enterprise mix is a key factor in determining the success of any beef production enterprise.
2. Target markets, their location relative to the enterprise and other marketing issues need to be considered
3. Human Resource Management is essential. If you are relying on staff to implement your strategies, they need to understand what is expected of them, be well trained and appropriately resourced. In family businesses, equivalent strategies need to be in place to manage the roles of each family member.
4. Timing is critical. To obtain maximum benefit, key activities need to be done at the correct time and in the correct sequence. Where timing is disrupted, such as due to prolonged wet seasons, priority activities still need to be done first
5. Get the next generation off to a good start – heifers are the future of your herd – a good heifer management program is fundamental to a successful breeding operation.

MEASUREMENT

IF YOU CAN’T MEASURE IT, YOU CAN’T MANAGE IT

Objective

To provide a list of key measurements for northern extensive beef producers that will allow them to effectively monitor their enterprise. This allows productivity to be effectively monitored from one year to the next and allows progress to be monitored over the long-term. More importantly, the impact of any management interventions can be measured and monitored.

Key measurements

1. Opening numbers by class of stock
2. Closing numbers by class of stock
3. Sales by $ and heads
4. Purchases by $ and heads
5. Total kg of cattle sold
6. Total operating costs

Key performance indicator

>400mm average annual rainfall – kg beef turned off/Ha.

<400mm average annual rainfall – kg beef turned off/Animal Equivalent (AE).

A spreadsheet tool is now available for determination of Animal Equivalents in northern Australian beef herds (McLean et al 2014).

Key indices (determined using rolling 4 year averages)

Death rate (see table below).

Reproductive rate – for heifers, second calvers and cows (see table below).

Weaner production (kg/cow retained) – Annual total number of calves weaned multiplied by average weaner weight, divided by number of females retained the previous year.

The following benchmarks have been established from CashCow. Refer to the project report for further detail and the geographic bounds of each region (McGowan et al 2014).

The following process allows further problem definition Step 1. Gather stock numbers

1. Females joined = number of heifers/second calvers/cows joined in last 12 month period (less culls not related to pregnancy status)
2. Calves branded = number of calves branded this year from each group*
3. Calves weaned = number of calves weaned this year from each group*
4. If figures are available for a number of years, also gather number of cattle turned off.

_{*Can be combined if branding and weaning occur concurrently.}

• Number of cull heifers and steers and total weight sold in kg.
• Cull cows and bulls and total weight sold in kg.

Step 2. Generate production indices

1. Pregnancy % – pregnant females/females joined x 100
2. Branding % – calves branded/females joined x 100
3. Weaning % – calves weaned/females joined x 100
4. Turn off rate – number sold in a 12 month period/number in total herd. Male and female turn off rate should also be calculated and compared over a 5 year period.
5. Breeder death rate (%) (opening cow numbers - closing cow numbers + cow sales)/opening cow numbers x 100
6. Kg of beef turned off/Ha or AE

Step 3. Compare to goals/benchmarks

(can be varied for each enterprise depending on baseline figures – the following are examples only. Refer to CashCow and other resources for property and animal class specific benchmarks)

1. Pregnancy percentage – 80%
2. Branding – 70%
3. Weaning – 70%
4. Turn off rate >0.3 but will vary with the nature of enterprise. Properties selling grown bullocks will have lower turn off rates than properties selling lighter cattle for live export.
5. Breeder death rate – 2%
6. Kg of beef turned off/Ha or Animal Equivalent – this is a property specific benchmark and will vary greatly depending on the quality of the soil and pasture on a property.

Step 4. Explore losses and areas for improvement

1. Is pregnancy rate too low?
2. What are the losses from pregnancy testing to branding?
3. What are the losses from branding to weaning?
4. What are the losses from weaning to turn off in steers or cull heifers?
5. Are few female cattle being turned off?

Step 5. Explore losses and areas for improvement

• Compare losses between management groups

– Heifers, first calvers and mature cows?

– Different paddocks or properties?

– Different years?

Step 6. Look at timing

• Calving distribution?

Categorise the problem

1. Failure to get pregnant or early abortions
2. Losses from pregnancy testing to Branding
3. Losses from Branding to Weaning
4. Post-weaning losses
5. A combination of the above
6. Heifer or cow (and calf) losses are occurring
7. Too many out of season calves

Genetic gains are cumulative, permanent and obtainable by selection of herd sires from performance-recorded herds, bred in a tropical environment.

The key to the breeding success of any northern beef business is to be able to effectively balance the selection of fertility, growth and carcass traits in both male and female cattle.

Most of the genetic improvement in a beef herd will come through bull selection – 87.5% of the genetics in any herd is due to the genes from the last 3 generations of sires used in that herd. This is because bulls pass on their genes to many calves, while cows will usually not have more than 8 calves in their lifetime.

Recent research has also demonstrated that standardised, readily measured traits in bulls such as scrotal circumference and percent morphologically normal sperm are heritable and genetically correlated with the important female traits of age at puberty and interval from calving to first cycle after calving

Cross-breeding with adapted breeds

Because of the low heritability of female fertility traits, cross-breeding using adapted breeds should be looked at carefully as a shorter-term option to achieving genetic goals.

The most cost-effective way to meet the nutritional requirements of grazing cattle in northern Australia is through the correct management of stocking rate, along with strategic supplementation of phosphorus and protein.

Establish priorities for feed allocation. Generally, the highest priority group will be the replacement heifer group, including calved heifers. Next highest priority will be growing steers.

Objective

Set a sustainable stocking rate that matches stock numbers, based on requirements, to the quantity and quality of pasture available, in a sustainable manner.

Methods

Adequate water of good quality

1. Strategically place water points so maximum distance to water (grazing radius) is no greater than 3-5 km
2. Quality impacts performance. Monitor underground water quality annually. Monitor open water sources for algal blooms

Develop a sustainable grazing system

• Maintain predominance of 3P pasture species – perennial, palatable, productive.
• 30% utilisation by weight. May need to be as low as 15% in areas with very low rainfall.
• Maintain the majority of land in A and B land condition.

Steps

1. Prepare a detailed property plan including determination of long-term carrying capacity for each paddock. Monitor land/resource condition and make adjustments to property plan where necessary to address deficiencies. Plan placement of new infrastructure including fencing and water points.
2. Implement a grazing system – consider incorporation of wet season spelling and prescribed burning.
3. Manage stocking rate.
   

   a. Pasture budget at end of growing season.

   b. Develop a grazing management plan for the dry season.

   c. Adjust stocking rate accordingly.

A pasture budget involves determining how much pasture is available in a paddock at the end of the growing period and then estimating how many cattle that paddock is capable of carrying over the next dry season. The way in which the available pasture is used is the grazing management plan. The methodology for pasture budgeting is covered in Grazing Land Management courses or in courses conducted by Resource Consulting Services. It is recommended that producers complete one of these courses.

Supplementation

The areas of Northern Australia where these guidelines apply are characterised by soils which are phosphorus deficient growing tropical pastures which are seasonally deficient in protein and energy.

Phosphorus

Phosphorus deficiency is common in most of northern Australia unless addressed through appropriate supplementation. Clinical signs include easily broken bones (peg leg) and obvious bone chewing. However, phosphorus deficiency may also severely affect growth rate and reproductive performance of cattle without other obvious clinical signs.

It is critical that phosphorus supplementation occurs when cattle are on good feed so they are able to store phosphorus in their bones for use during the dry season. Wet season supplementation of phosphorus to breeding and growing cattle can provide significant economic returns.

In the dry season, energy and protein deficiency are also common as pastures mature and hay off.

Faecal near infrared spectroscopy (NIRS) allows the determination of current energy and protein intakes in cattle grazing tropical pastures. Faecal phosphorus levels can also be used to determine the intake of phosphorus. Blood testing of a sample of cattle in various risk groups during the late wet or early dry season may also be used to determine blood phosphorus levels and diagnose sub-clinical phosphorus deficiency. This information can be used to tailor supplement programs to suit each property as requirements will differ for different soil and pasture situations. (Dixon et al 2011)

Protein

Protein supplements should be provided during the dry season when the protein content of pasture falls. True protein supplements such as protein meals need to be considered for light weaners and growing cattle and for cows that are lactating during the dry season. Non-protein nitrogen (generally urea based supplements) can be used in older dry cattle provided sufficient dry grass is available.

Energy

In addition to phosphorus supplements during the wet season, supplements that provide energy should be considered for specific groups of cattle during the dry season. Early weaned calves, especially those lighter than 100kg body weight will be the group with the highest requirement. Heifers that are close to reaching their target weight for mating may also benefit from a supplement containing extra energy to get a greater proportion to their target weight for mating. Spike feeding heifers due to calve that are less than the desired body condition score has also increased second calf conception rates. Heifers and cows that calve during the dry season may also require supplements containing energy until their calves are old enough to wean if they are low in body condition at calving and on feed of low quality.

Supplement programs can represent a significant component of operating expenses. Segregation of cattle into groups based on nutritional demand and provision of tailored supplementation programs to each group can lead to significant reductions in operating costs. At the same time, improvements in reproductive performance and young cattle growth rates can be maximised for the least cost.

Goal

To effectively manage the breeder herd to have a surplus of replacement heifers and cull for age breeding cows available for turn off annually.

The only way to do this is to ensure that annual conception rates are high and that breeder mortality rate is low. The main factor affecting this is body condition (BCS), so females should be managed to be in good condition and gaining weight with the aim of being in BCS 3/5 at calving.

Mating system

To achieve high conception and pregnancy rates, heifers and cows should be bred when pasture quality is at its best, which is generally during the wet season. Ideally, bulls should be placed with heifers and cows during this period then subsequently removed. Determination of the most reliable period for wet season rainfall is best done by analysis of long term rainfall records for each specific enterprise. In far northern Australia, February is normally the month with the highest chance of rainfall sufficient to generate significant pasture growth.

Controlled mating is not always practical in northern Australia. For this reason, year round mating is often practiced. However, there are ways to manage year round mated herds so that the majority of calves are born at the desired time and cows get pregnant during the wet season.

The key is to ensure that heifers are mated at the correct time and then managed so that they re-conceive as soon as possible after having their first calf.

A combination of weaning management, drafting cows according to lactation status and pregnancy testing with foetal ageing can then be used to manage the cow herd.

This ensures that most calves are born at the right time and provides special management to those cows that calve out of season.

Heifer management

The future of the herd is the replacement heifer. Managing heifers separate from the main cow herd allows them to receive preferential management to ensure they calve just prior to the onset of the wet season. Heifers that calve at the right time, with appropriate management, will become cows that calve at the right time.

Management of heifers from weaning to selection as replacement breeders

Heifers should be segregated from cows from time of weaning. Ideally weaner heifers (0.5-1.5 years) should be segregated from older heifers ready to be mated (1.5-3.5 years). Careful planning can assist with heifer control. Putting heifers in paddocks with good feed but away from major water courses can ensure paddock integrity and bull control.

Management of heifers from joining onwards

Following joining, pregnant heifers should be kept as a separate group through to calving, weaning and re-conception. Re-conception rates in first lactation heifers in northern Australia are often 25%. This impacts greatly on the sustainability of self-replacing breeding herds. In order to ensure heifers perform to their potential, it’s important that heifers receive preferential treatment until they have their second calf. This allows early weaning and specific supplementation, especially wet season phosphorus, which has a significant impact on their likelihood of re-conceiving after their first calf and maintaining their desired calving pattern.

Critical mating weight

Weight is one of the most significant factors influencing the onset of puberty in heifers and commencement of cycling. Age at puberty can be influenced by selection pressure over time.

The critical mating weight is the minimum weight at which heifers are mated to achieve a high pregnancy rate when first joined. To determine the critical mating weight for heifers in your herd, individually identify and weigh heifers prior to mating and then pregnancy test and record pregnancy status for these same heifers. Pregnancy rates for different pre-mating weight ranges, say 200-225 kg, 226-250 kg, 251-275 kg, 276-300 kg can then be determined. A suitable cut point for critical mating weight can then be determined. This is generally the weight range where pregnancy rates are >80%. This should be repeated over a couple of years and ideally monitored over the long term if efforts are being made to reduce the age at puberty through selection.

A rule of thumb for critical mating weight suitable for most herds would be 300 kg at the start of joining in early January. To achieve this, heifers in the joiner heifer group should weigh a minimum of 250 kg at the 2nd round muster in Oct/Nov prior to joining.

Strategies to attain critical mating weight

To achieve critical mating weight:

• Select heifer paddocks with good quality pasture and manage stocking rate to ensure optimum pasture quantity and quality.
• Supplement heifers to achieve post-weaning growth to critical mating weight. Return on investment in supplement will be high, as heifers will get in calf at the right time and in many cases 12 months earlier than if not supplemented.

Management from mating until entry into the main cow herd

• Control mate heifers for 2 cycles (42 days or 6 weeks) each year from the start of January. If this is not possible due to problems accessing paddocks in the wet season, put bulls out in January and remove at pregnancy testing. Use pregnancy testing to identify heifers conceiving in the desired time period.
• Mate heifers to moderate birth weight bulls to manage dystocia (calving difficulty).
• Heifers should be at their critical mating weight at start of mating. Alternatively, control mate all heifers and select those that become pregnant to select for heifers which achieve puberty at lighter body weights.
• Pregnancy test at first muster. If heifers have been mated for more than 2 cycles, use foetal ageing to identify heifers that are pregnant within the desired time period. Sell or identify for special management heifers that will calve later in the year.
• Wean calves at first muster the following year. Wean calves early if necessary to maintain body condition.
• Heifers should be given preferential access to adequate quantities of good quality pasture to ensure that they have a body weight of >400kg when their calves are weaned, as well as a sufficient condition score (BCS 3/5) for re-conception for their second calf.
• Transfer heifers to the cow herd at 3.5 years of age when pregnant with second calf.

Cow management

Ideally, cows should be control mated from January to April/May each year. However, this is not practical on most properties in northern Australia because of the difficulties of putting bulls out and removing them. The following systems assume bulls are with cows year round and are practical alternatives. Cows that calve outside the optimal calving period are provided with extra care.

Replacement heifer management is paramount. Heifers must be set up to calve at the right time and then managed to maintain this desirable calving pattern. Cows that fall out of this pattern due to extended lactational anoestrus need to be identified and managed to ensure their welfare and subsequently sold.

A number of systems have been developed that incorporate these principles.

System 1.

This system involves segregating the cow herd annually at first muster into three calving groups, A, B and C based on expected month of calving, using a combination of lactational status (wet/dry) and pregnancy status. (Braithwaite and de Witte 1999).

The goal is to have the majority of the cow herd calving in the optimum calving window from October to December (calving group A) with calves weaned by April/May the following year. However, in year round mated herds, cows will continue calving at other times of the year. Two further calving groups are identified, those calving from January to April the following year (calving group B) and those calving from May to September the following year (calving group C).

Calving groups B and C will be lactating at times when feed quality is seasonally poor and will require special care and supplementation. This can occur with much greater ease if they are in the one group. The cost of the supplements these cows require is generally much greater than those required by Group A cows, so considerable savings in supplement cost can be achieved.

A further advantage is that mustering related calf losses can be greatly reduced.

Early weaning can greatly reduce energy demands on cows and reduce or remove the need for supplementation. Segregation also allows radical early weaning, if necessary. Calves weaned off calving group B and C cows may be weaned down to 100kg and in extreme cases down to 60kg, to ensure cow survival.

A further management option this system allows is the option to sell cows in Group C and even Group B early in the year if the wet season fails and feed budgets indicate there will be inadequate feed reserves to carry these cows through the coming dry season.

Cows in northern Australia often have a calving interval which is greater than 12 months due to prolonged periods of lactational anoestrus. In this system, cows which have a >12 month calving interval will progressively drift into other calving groups. A goal can be to have <15% of cows drift from A to B and B to C from one year to the next.

Group C cows are managed to become sale cows in the following year. These cows can typically be marketed early after the wet season to capitalise on relatively high cow prices that occur at this time in most years.

System 2

If segregation is not possible due to lack of infrastructure, problems with wet season damage to fencing or consistently low pregnancy rates in lactating cows, an alternative system is to focus on best practice replacement heifer management, correct stocking rate and weaning management.

Key elements of this system are:

• Cows are mustered twice yearly and drafted according to lactation status (wet/dry) into two groups.
• Calves are weaned twice yearly down to 100kg before cows lose too much body condition. Lighter calves are branded and left on their mothers.
• At the first round muster, dry cows are pregnancy tested and empty dry cows which will be fat enough to sell are culled.
• Pregnancy tested in calf (PTIC) heifers/cows are followed to ensure they wean a calf. Those that fail to wean a calf are identified. If they subsequently fail to wean another calf they are culled.
• If cows are not pregnancy tested, an alternate system is to just wet/dry cows. A cow that comes in dry at two consecutive musters is culled.
• Pregnancy testing reduces the time to identify these poorly productive cows and remove them from the system freeing up available pasture for other cattle.

Where lactational anoestus is a problem, this program can be used as a transition to System 1. Over time, more cows will reconceive while lactating if appropriate selection pressure is applied.

As a transition to System 1, cows may also be sorted according to lactation status into paddocks at the first muster and again at second muster. Cows that are still dry at the second muster can be pregnancy tested.

Managing disease is an important component of risk management for any beef enterprise.

The first step in managing disease on your property is to define where losses are occurring. Refer to the measurement module, which takes you through an approach to better define the problems you may have.

The checklist below can be used to provide a list of potential causes that can then be ruled in or out based on further testing or analysis:

Low pregnancy rate – failure to get pregnant or early abortions

• Incorrect stocking rate leading to low cow/heifer BCS at weaning
• Inadequate wet season phosphorus supplementation esp in calved heifers
• Bull problems
• Vibriosis
• Trichomoniasis
• Pestivirus

Losses from pregnancy testing to branding

• Time of calving.
• Abortions due Leptospirosis or Vibriosis
• Abortions and calf losses due to Leptospirosis or Pestivirus
• Abortions due to genetic defects, toxins or protozoal infections
• Calving difficulty
• Weak calves, mis-mothering and bottle teats
• Mustering at time of calving
• Excessive heat and humidity at calving time
• Vitamin A deficiency
• Calf scours
• Predation by dingoes/wild dogs.

Losses from branding to weaning

• Poor castration technique (if greater losses in male than female calves)
• De-horning related losses
• Clostridial diseases after surgical procedures – tetanus, malignant oedema and blackleg.

Post-weaning losses

• Botulism
• Blackleg
• Coccidiosis (blood scours)
• Pestivirus (loss of persistently infected calves)
• 3-day sickness
• Toxicities (toxic plants, toxic algae in water supplies)

A combination of low pregnancy rate, losses from pregnancy testing to weaning and post-weaning losses

• Pestivirus
• You have multiple disease problems occurring concurrently.

Heifer or cow (and calf) losses are occurring

• Calving difficulty
• 3-day sickness (heifers and second calvers most commonly)
• Botulism.

Too many out of season calves

• Poor heifer management program
• Incorrect stocking rate resulting in low cow/heifer BCS at weaning
• Long lactational anoestrus
• Inadequate phosphorus supplementation
• Bull problems
• Vibriosis
• Trichomoniasis
• Pestivirus
• Leptospirosis.

Losses after surgical procedures (e.g. spaying)

• Blood loss
• Tetanus/Malignant oedema and wound infections.

Solutions for identified disease risks

References

Anon. Beef Cattle Nutrition – An introduction to the essentials. Meat and Livestock Australia, Sydney. 2007.

Anon. Grazing Land Management – Sustainable and productive natural resource management. Meat and Livestock Australia, Sydney. 2007.

Anon. Managing the breeder herd. Practical steps to breeding livestock in northern Australia. Meat and Livestock Australia, Sydney 2006.

Braithwaite ID, de Witte KD. A practical management template for improved decision-making in north Australian beef cattle production. In ‘Proceedings of Australian Assoc of Cattle Veterinarians’, Hobart 1999: 250-261.

Braithwaite ID, de Witte KD. Strategies to optimize beef cattle production in north Australia. In ‘Proceedings of Australian Assoc of Cattle Veterinarians’, Hobart 1999: 237-238.

Dixon, R et al. Phosphorus nutrition and management – overcoming constraints to wider adoption. In ‘Proceedings, Northern Beef Research Update Conference’, Darwin, 2011: 102-109.

Fordyce G. Practical strategies to reach target mating weight in north Australian beef Heifers.

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Hall W. Sustainable pastures in the rangelands, In ‘Proceedings of the Australian Veterinary Association Annual Conference’, Adelaide 2011: E1.5.1.

Holroyd R.G. et al. Bull selection and use in Northern Australia (Bull Power Project), Meat and Livestock Australia, Sydney, DAQ.104, 2000.

Jackson D et al. Phosphorus management of beef cattle in northern Australia. Meat and Livestock Australia, Sydney. 2012.

Johnston DJ et al. Genetics of heifer puberty in two tropical beef genotypes in northern Australia and associations with heifer and steer-production traits. Animal Production Science, 2009, 49: 399–412 Jubb T, Kerr JW, Bolam MJ. Problem definition for veterinarians working with extensive beef herds.

In ‘Proceedings of the Australian Cattle Veterinarians Conference’, Brisbane, 1997: 163-169.

McCosker, T., McLean, I, and Holmes, P, Northern beef situation analysis. Meat and Livestock Australia. Sydney, B.NBP.0518, 2010.

McGowan M. et al. Northern Australian beef fertility project: CashCow. Meat and Livestock Australia, Sydney,B.NBP.0382, 2014.

McLean, I, Holmes, P, Counsell D. The Northern Beef Report, 2013 Northern beef situation analysis. Meat and Livestock Australia, Sydney, B.COM.0348, 2014.

McLean I, Blackley, S. Adult Equivalent Methodology – A methodology to accurately and consistently calculate cattle grazing loads in northern Australia, Meat and Livestock Australia, Sydney,.B.NBP.0779, 2014.

McGowan MR, Fordyce G, Holroyd RG. Recent advances in beef cattle reproduction – how science will improve herd performance. In ‘Proceedings, Northern Beef Research Update Conference’, Darwin, 2011: 11-18.

Schatz TJ, Hearnden MN. Heifer fertility on commercial cattle properties in the Northern Territory, Australian Journal of Experimental Agriculture, 2008, 48: 940-944.