Genetic improvements fuel debate over what makes the ideal cow

While the idea of what makes a good bull or cow will differ from producer to producer, there are several key trends that have emerged in bull and female purchasing over the years as the information available to the breeder which can estimate the true genetic worth of an animal has grown.

Estimated breeding values have made sourcing bulls and females of superior genetic quality to target particular markets far more objective but they have also created a greater need to balance traits and weigh up the advantages and disadvantages of going down various paths.

Cow size, and the rise of crossbreeding, are two areas where there has been plenty of debate.

The question of what is more profitable, big or small cows, has been discussed in depth across most breeds as the mature weight of cows increases genetically, beef consultant John Webb-Ware, from the Mackinnon Project, said.

There is a correlation between mature weight and growth of progeny, so increasing cow size will mean progeny will meet market specifications earlier, potentially sell at the heavier end of specs and be able to target new markets given the trend towards heavier carcase weights - overall it means more valuable progeny.

The disadvantages, however, are in the fact bigger cows have higher feed requirements.

Research shows as cow mature weight lifts from 400 to 700 kilograms, for example, feed demand jumps 59 per cent.

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Dr Webb-Ware said there was a large range in both bodyweight and frame score between breeds.

Overall, however, while mature weight and growth EBVs have increased, birth weight has remained stable, calving ease has improved, days to calving has reduced and rib fat has reduced slightly, he said.

Increasing cow size also has a potential impact on reproductive performance, he said.

Modelling the trade-off has shown larger cow size increases gross margins at low base stocking rates but not a high base.

At a low stocking rate, increasing cow size is likely to increase profitability due to higher weight and sale value of progeny but as stocking rate increases, especially where pasture utilisation exceeds 55pc, the benefits of larger cow size disappears because feed cost increases outweigh the value of extra beef produced, Dr Webb-Ware explained.

He said the Angus breed could be described as a leader in the field of being able to achieve improvement through increased mature cow weight without taking from other traits.

The mature weight of Angus cows has increased genetically by 40kg in the past 20 years, with the current trend showing a lift of 2.5kg per year, according to Angus Australia.

Breed development and extension manager Andrew Byrne said most of that improvement had occurred without compromising calving ease and a focus on improved carcase attributes such as marbling.

Angus Australia last year released research breeding values for mature body condition and mature height last year, which enable consideration to be given to mature cow weight and body composition alongside other traits of importance when making selection decisions.

"The challenge is to breed the modern curve bender, where we continue to put extra growth into Angus cattle but hold mature weight where it is," Mr Byrne said.

To that end, a lift in the submission of weights for mature cows into the TransTasman Angus Cattle Evaluation was needed, he said.

Meanwhile, on the crossbreeding front, getting animals to weight faster via hybrid vigour has been the driver but harder-to-measure traits such as calf survival and fertility have proven big advantages, Dr Webb-Ware said.

On the downside has been the difficulty marketing crossbred animals, particularly in the store market.

"So it has worked better where producers are selling direct to a targetted market," he said.

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