Mature cow weight a balancing act

Determining the optimal cow size for an operation and whether there is more money in producing a larger number of lighter weaners versus less but heavier calves was a key topic at beef producers field day held at Casino last week.

The message was that while there is no ‘perfect size’ formulae for mature cows, and it will always be a balancing act, having an understanding of some key points and research findings can ensure decisions are more strategic and likely to serve producers better in the long term.

North Coast Local Land Services senior agricultural advice officer Nathan Jennings said in today’s beef world there were big variations, both between and within breeds, in mature cow weights (MCW).

Price grids were demanding younger, heavier, better-finished stock and producers were also looking to increase kilograms of beef per hectare to dilute costs, he said.

“So the logical decision is to select for growth and get weight into your cattle young,” he said.

However, selecting for growth also affects MCW potential.

“Higher growth potential at younger ages tends to lead to heavier mature weights and that has implications on the profitability of a breeding operation,” Mr Jennings said.

MCW affects feed demand and costs, breeder fertility and the salvage value of culls.

The feed requirements of a Bos Taurus/Bos Indicus cross cow, dry and empty, at 450 kilograms is 7kg of dry matter per day just for maintenance, given feed of 8 megajoules of metabolisable energy per kg/DM.

“At 550kg, it is 8.2kg/dm and at 650kg it is 10 and this increases significantly as we place them into a reproductive cycle,” Mr Jennings said.

“The bigger they are, the more they need to eat and the better quality the feed has to be.

“Beware taking short-term profitability over long-term sustainability and ask yourself can your farm sustain high-growth genetics and higher mature cow weights profitably year in, year out.”

A study case outlining various MCW scenarios of a 440 hectare NSW/Queensland border property was presented at the field day.

Running 300 females, joined to ten bulls, targeting weaner weights of 250kg at 8 months, the operation currently has a MCW average of 550kg.

The system requires just under 2m kilograms of dry matter to sustain the herd on a native pasture base.

At present pasture is not getting them the whole way and an additional 128 tonnes of feed, at a higher cost, is bought in annually.

If the average MCW was reduced to 500kg, the feed need would be 1.8m kgs and that brings purchased-in feedback to about 8.2t, significantly reducing the level of expected feed shortage.

If the average MCW was lifted to 600kg, the feed requirement is 2,085,157kg, with around a 260t shortage.

An option might be to keep breeding for the heavier cows and increase pasture growth to bridge the gap.

That would require growing 600kg of additional dry matter per hectare, which - assuming rain - would come at a cost of $36,000 in fertiliser costs at current rates.

Another option would be to run heavier cows but less of them to better align the feed requirement with the feed potential of the property. To delete the feed gap, that would mean dropping 30 head.

Back-of-the-envelope gross margin figures show that at the current MCWs, with an 88 per cent weaning rate, 264 calves at 250kg would return $625 a head, 36 culls at $1000 a head with an overall return of $201,000.

Under the 600kg MCW scenario, with 231 calves produced - assuming calves were also 30kg heavier - making $700/head and 32 culls at $1100 head, the return would be $196,700.

By running less head, there are some management and animal health savings, plus one less bull, adding up to an estimated $6780, giving a final return of $203,480.

Mr Jennings said there was also evidence to suggest the number of calves produced per cow could decrease with increasing cow weight.

“This particular case study showed the total weaning weights of calves as a mob decreased over seven years as a result of less calves on the ground,” he said.

“That suggests that as the cows are getting heavier, the weaning rate for the enterprise is decreasing ever so slightly each year and a sound assumption is that the bigger cows are struggling to go back in calf, particularly in the harder seasons.”

While losses in calf weight are certainly offset to a degree by increased values of cull cows as they get heavier, there are other ways to lift the value of cull cows such as increasing muscle score, Mr Jennings said.

Run by the North Coast Local Land Services and Norco Rural, more than 140 producers and industry representatives attended the field day, which also included presentations on everything from cattle markets and saleyard management to buffalo fly control and fencing demonstrations.

Mature cow weight genes are highly heritable.

Research shows that in Bos Taurus breeds 40 to 50 per cent of MCW is due to genes and in Bos Indicus 39 to 55pc.

Nutrition is the other big factor that affects MCW and the big point to note here is that stunting at a younger age in females becomes permanent.

“What that means is you can do a lot of good work in selecting for growth but if your country or system doesn’t support the development of the cattle early you have lost that potential,” said North Coast Local Land Services senior agricultural advice officer Nathan Jennings.