It is possible to simultaneously select for productive and adaptive traits in tropically-adapted cattle, without compromising genetic progress in either, recent Beef CRC research has shown.

Cattle in Northern Australia experience numerous environmental stressors that reduce their growth and reproductive performance and decrease their beef quality. These often include parasites (tick, buffalo fly, worms), seasonally poor nutrition, high heat and humidity and diseases, often transmitted by parasites.

The impact of each stressor on production and animal welfare is often multiplicative rather than additive, particularly when animals are already undergoing physiological stress such as lactation.

Hence under highly stressful conditions, cattle deaths can occur due to the stressors. Under extensive production systems common in the tropics it is generally not possible to control the stressors through management strategies alone.

Therefore the best method of reducing their impact to improve productivity and animal welfare is to breed cattle that are more naturally resistant to productivity decline when challenged, without the need for management intervention.

The impacts of productive and adaptive traits

In every production environment, factors limit beef production, meaning no one breed is best in all environments. Comparative rankings of different cattle breed types for different characteristics in tropical environments are shown in the table below.

Any cattle breeding program designed for the tropics and sub-tropics must consider the impacts of both productive and adaptive traits, even though the adaptive traits (and some productive traits) are very difficult and/or expensive to measure. However the differing impacts of environmental stressors across the breed types indicates that genetic parameters and economic weightings for use in selection indexes must be specific for each breed type and environment.

Comparative rankings of breed types for productive and adaptive traits in tropical environments (more stars = higher value for that trait)

For traits to be included in effective breeding programs, they must be under direct or indirect genetic control. Direct genetic control is assessed by estimating the heritability of traits. Indirect control is achieved through favourable or unfavourable associations (genetic correlations) between different traits.

Beef CRC and earlier research primarily from northern Australia indicates that all the key productive and adaptive traits are at least moderately heritable in tropically-adapted cattle reared in tropical environments, meaning they will respond to genetic improvement through crossbreeding and within-breed selection programs.

In addition, no major antagonistic relationships have been found that would preclude simultaneous genetic improvement of all the traits in tropical beef breeding objectives.

Studies at Belmont Research Station near Rockhampton showed that resistance to parasites and productive attributes such as growth and reproduction are largely genetically (though not phenotypically) independent, meaning selection for parasite resistance will not genetically change productive attributes, or vice versa.

However resistance to heat stress and productive attributes are favourably correlated, particularly in breeds that are not as well-adapted as the Brahman, meaning that selection for growth or reproduction will improve resistance to heat stress and vice versa.

Strategies to optimise adaptation and production

Based on extensive reviews of the scientific literature, the Beef CRC has developed a number of ‘rules of thumb’ to optimally match cattle ‘genotypes’ (breeds or sire lines) to their production and marketing environments. These ‘rules of thumb’ as they apply to crossbreeding systems include:

• Depending on the severity of the environment and the level of stressor challenge, 25pc to 75pc ‘adapted genes’ are required for optimal production. Only exceptionally stressful environments (rare in Australia) require 100pc ‘adapted genes’.
• Adapted genes can be derived from Bos indicus and their derivatives, as well as the tropically adapted Taurus breeds, providing an opportunity to use heterosis from crossbreeding and to maximise productivity without reducing resistance to environmental stressors below levels acceptable for the production environment
• For most tropical environments, optimal levels of productivity and adaptation will be achieved using a combination of multiple breed types (e.g. Bos indicus, tropically adapted Taurus (like Senepol, Belmont Red), British and European).
• The harsher and wetter the environment, the greater the need for Indicus content to ensure sufficient adaptation to parasites (mainly ticks and worms).

Summary

In breeds that are well-adapted to their production environment, there are no major antagonistic relationships to preclude simultaneous genetic improvement of both productive and adaptive traits through selection to maximise herd profitability, CRC research shows.

The major constraint to such genetic improvement is the difficulty and expense of measuring the complete range of economically important productive and adaptive traits required to achieve a balanced breeding objective. This same constraint also applies to genomic selection using DNA-based technologies, which offer new opportunities for tropical beef producers.

Until phenotypes for these traits become available, northern producers can confidently select to improve productive attributes in their cattle, knowing they are unlikely to compromise adaptation of their herds.

Contact: Anne Marie Huey, Department of Agriculture and Food WA, Broome. Email: anne-marie.huey@agric.wa.gov.au

Following the ‘Beef Crash’ of the mid-1970s, the northern Australian beef herd rapidly changed from British breeds such as Shorthorns to being based mostly on a well-adapted high-grade Brahman cow herd.

However, there are very clear productivity and profitability benefits from using new genetic opportunities to improve the Northern Australian beef herd, research shows.

Producers can seek to genetically improve their herds in two ways.

The first is to genetically improve attributes such as beef tenderness and female reproductive performance in high-grade Brahman herds using the CRC’s new genomic prediction equations, due for released at Beef Australia 2012 industry event in Rockhampton in May.

These DNA-based tests will be integrated with BreedPlan EBVs, and will allow seedstock breeders to identify young bulls that are genetically superior for hard-to-measure traits such as carcase and beef quality, feed efficiency and male and female reproductive performance.

Commercial cattle breeders will access the superior genetics by purchasing bulls or semen with genomically-enhanced EBVs, known by abbreviation as gEBVs.

To continue to improve the Brahman breed using gEBVs, ongoing measurement of the traits in cattle that are typical of northern Australian beef production systems is needed.

The Australian Brahman Breeders Association has already accepted this ongoing need and developed its Brahman Information Nucleus to ensure the breed continues to improve well into the future, thereby opening up new and alternative market opportunities for Brahman beef.

Crossbreeding

The second genetic improvement opportunity for Brahman herds in northern Australia is to capitalise on hybrid vigour, or heterosis, through crossbreeding – to either form tropically-adapted composite herds or undertake systematic crossbreeding programs.

Systematic crossbreeding requires considerable management input and may be difficult to implement for many commercial breeders in extensive pastoral environments. However once formed, development of a tropically-adapted composite herd offers the same ease of management as a high-grade Brahman herd.

The critical factor that producers need to consider if choosing to crossbreed is to ensure the herd remains well-adapted to environmental stressors such as ticks, worms, buffalo fly, high temperatures and humidity, endemic diseases and seasonally poor nutrition.

Maintaining sufficient adaptation in northern herds requires a careful choice of breeds to ensure an appropriate mix of ‘adapted’ and ‘productive’ genes. ‘Adapted’ genes are derived from high grade Brahmans and their crosses as well as the tropically adapted Bos taurus (taurine) breeds and their derivatives such as the Belmont Red, Bonsmara, Senepol and Tuli.

Depending on the severity of the environment, most areas of northern Australia need somewhere between 25pc and 75pc ‘adapted’ genes for optimal production. Only exceptionally stressful environments need 100pc ‘adapted’ genes.

This means that beef producers can take advantage of hybrid vigour from crossbreeding to maximise productive performance (carcase and beef quality and reproductive rates) without reducing adaptation below the levels needed for the particular production environment.

For most northern Australian environments, optimal levels of productivity can be achieved using a combination of Brahman, tropically-adapted taurine and British or European breed types, but the harsher and wetter the environment, the greater the need for higher Brahman content.

Clear economic benefit in crossbreeds and composites

The Beef CRC’s research with terminal crossbred and tropically-adapted composite cattle since 1993 shows clear economic benefits can be achieved through crossbreeding.

In 2003, Dr Garry Griffith and Dr Bill Holmes used early CRC results to show that changing 25pc of the Brahman herd in northern Australia to terminal crossbreeds and tropically-adapted composites increased gross margins by $7 and $24 per adult equivalent (AE) respectively, relative to the Brahman for a northern Australian grass-finishing system.

A $7/AE benefit to the terminal cross and the composite was achieved through increased growth rates, whereas the $17/AE additional benefit to the composite herd was derived from improved reproductive performance of the composite cow herd.

When sale steers were finished in a feedlot, terminal crossbred and composite steers realised an additional $38/AE for improved growth rate and feed efficiency (in addition to the initial $7 and $24/AE gross margin).

Conservative figures also showed an extra gross margin of $5/AE could be achieved from a 10c/kg marbling premium in 15pc of crossbred and composite steers (marble score 2 rather than marble score 0 or 1). Applying a 5c/kg premium for 60pc of feedlot-finished crossbred and composite steers achieving MSA 3-star added an additional gross margin of $9/AE.

Since those values were estimated, the Beef CRC has been able to confirm their validity through a major breeding program which evaluated Brahman and tropically adapted composite cattle over a 12-year period.

That program recorded full growth, feed efficiency and carcase and beef quality attributes in steer progeny, while the half-sib sisters of those steers entered the breeding herds on five research stations across Queensland and had very detailed adaptive and reproductive measurements recorded until they had had the opportunity to rear six calves to weaning (i.e. until the cows were about ten years of age).

No major trade-offs between female and steer performance

The cows’ bull calves were all retained so complete measures of bull performance could be obtained to identify early-life indicator traits for female reproductive performance.

The aim of this major program was to identify whether genetic trade-offs existed between reproduction and adaptation of the breeding herds in harsh environments and the ability of sale animals grown and finished in more benign environments to meet premium beef market specifications.

Results from that project show there are no major trade-off between female and steer performance.

The research shows beef producers in harsh northern Australian environments can select to improve carcase and beef quality while simultaneously improving female reproductive performance – very good news for northern producers looking for alternative markets to the live export trade.

An unexplained 10 percent calf loss from when females are pregnancy tested in-calf through to weaning has been identified as a major cause of production inefficiency across northern Australia’s cattle industry.

A mountain of data has now been collected from the $2 million Meat & Livestock Australia-funded Cash Cow project initiated in 2009 which set out to investigate just what are the realistic achievable targets for optimal reproductive performance in northern herds.

Project leader Professor Mike McGowan (University of Queensland School of Veterinary Science) and Dr Geoff Fordyce (Charters Towers) have been working with a huge team of veterinary research scientists and beef extension officers to collect on-farm performance data across two to three reproduction cycles involving 70,000 females on 78 properties.

From all the trial data collected from differing land types across four major regions, it was the northern forest region where production losses were heaviest and deemed most difficult to manage. Half of the properties surveyed recorded a 13pc calf loss from a confirmed pregnancy prior to weaning.

Dr Fordyce said the huge variation in breeder production efficiency was due to herd management inputs and seasonal conditions rather than the class of country which ranged from open downs, southern forest, brigalow and northern forest regions.

“The task now for the Cash Cow team is to identify the major factors contributing to the significant variation in reproductive performance in northern herds and use the data from the top 25pc of herds to set achievable benchmarks,” Dr Fordyce said.

Prof McGowan said a major herd performance issue in the northern forest sector was the ability of the first lactation female to get back into calf.

“In the south region, 45pc of these first lacation females went back into calf whereas in the north just 9pc where pregnancy tested back in calf.

“When looking at mature breeders, the achievable back-in-calf performance from the downs country herds was 70pc whereas in the northern forest just 17pc of cows tested back in calf four months after calving.”

Prof McGowan said when the team looked at the factors influencing breeders not going back into calf, there was a 39pc difference in pregnancy rates between those breeders calving in the December-January period and those calving in the July-August dry season.

At the pregancy diagnosis muster, body score condition (BSC) was recorded and this was a strong predictor of future breeder performance. To lift an animal’s BSC from 2 to 3 would require a liveweight gain of 60kg which is virtually unachievable in the mid to late dry season when pasture protein and energy was at its lowest.

“Pregnancy rates for BSC 2 females were around 20pc whereas those with a BSC 3 were 50pc which showed that planning the time of weaning should focus on the BSC of the breeder and not the weight of the weaner,” Prof McGowan said.

Environmental and seasonal factors also came into play. While wet season phosphorus supplementation was a vital management tool, the reproductive response in northern herds was still being determined.

Calf losses attributed to cows calving in hot weather where temperatures exceed 35 deg C at 20pc humidity also needed further investigation and mustering of small out-of-season calves resulting in mis-mothering was another contributing factor.

Early analysis demonstrates that the Bos indicus females which equate to 75pc of the trial herds had a lower percentage pregnancy rate at four months after calving and had a higher risk of calf loss between pregnancy diagnosis and weaning when compared with the composite Bos taurus content females.

The Cash Cow project aims to define achievable herd performance and use the data collated on-farm to design simple measures in a tool that can be readily accessed by northern producers.