Investing in weigh scales is helping Southland dairy farmers Julia and Stewart Eden grow bigger heifers which produce more milk.

The couple milk 275 Holstein Friesian cows, which are run as a split-calving herd, at Balfour near Gore.

In 2013, they bought a Te Pari cattle crush fitted with digital scales, enabling them to regularly weigh their replacement heifers.

"Our young stock is weighed and drenched every three weeks from about seven weeks of age," said Julia.

"Buying the scales has been one of the best investments we've ever made."

"Our vets reckon we have the only herd where they can't tell the two-year-old heifers and the cows apart," she said.

Some of the Eden's herd eating silage in a wintering barn. Photo / Supplied
Some of the Eden's herd eating silage in a wintering barn. Photo / Supplied

The Eden's use the target weights in LIC's digital herd management system MINDA to benchmark their heifers. All weights, from seven weeks of age, are entered into the programme.

The Eden's aim to have their heifers weighing 380-400 kilograms by 15 months of age, in time for their first mating.

"Heifers who calve underweight spend their first season using feed to continue growing, instead of producing milk," said Julia.

Prior to moving to their current 199-hectare (effective) farm in 2013, the Eden's had a 1300 cow herd.

"We didn't really weigh young stock on our previous farm. But using the scales to set and hit targets has paid big dividends," said Julia.

"Our Holstein Friesian heifers which calve at target weight produce an average of 80 kgMS more than underweight heifers."

Based on a $7 kgMS payout, that is an extra $560 per heifer in milk income in their first season.

Nationally, the number of heifers not at target weight at calving is startling.

In 2016, Massey University and LIC analysed the weights of 655,964 dairy heifers which had been entered into MINDA Weights.

The heifers were born between 2011-12 and 2014-15.

The research found 65 per cent of the heifers were below target weight pre-calving (22 months of age).

On average they were nearly 42 kilograms below the target. Industry targets show heifers should be at 90 per cent of their mature liveweight pre-calving.

The Eden's milk 275 Holstein Fresian cows. Photo / Supplied
The Eden's milk 275 Holstein Fresian cows. Photo / Supplied

"Several studies have shown that heifers closer to target weights before calving produce more milk," said Vanessa Robinson from DairyNZ.

"Those production benefits aren't just evident in the first lactation, they flow through to the second and third lactations."

"There are also reproductive benefits such as increased six-week in-calf rates and decreased empty rates in the first lactation," she said.

DairyNZ research shows it costs $1400-$2000 to rear a heifer and get her into the milking herd.

"Regular weighing is the best way to ensure heifers are meeting liveweight targets, especially pre-mating and pre-calving," said Robinson.

"A lot of people eyeball their young stock and guess. More often than not they're wrong and the heifers are underweight, which has impacts down the track."

DairyNZ advises people to have a good plan in place with their grazier to combat feed shortages, such as during a drought.

Cows with a mature liveweight of 550 kilograms need to weigh 495 kilograms at 22 months of age.

More information can be found at on DairyNZ's website.