Mavstar Simmental stud, Myamyn, took out the prestigious award with its two-year-old cow with calf at foot, Mavstar Maverick Red Star, an April 2020-drop cow by Mavstar Licorice Red L141 and out of Maverick My Girl M164.

She won the award after winning supreme senior champion female in the interbreed judging earlier in the day.

On behalf of the judges Andrew Green, Kyneton, Aimee Bolton, Toowoomba, Qld, and Donna Robson, Adelong, NSW, judge spokesperson Scott Myers said Red Star was "a beautiful, fault-free cow" that was "easy maintenance".

"Our champion cow here, this Simmental female, proves her quality," Mr Myers said.

"She has calved at 24 months, she has a wonderful calf at foot and just a beautiful udder connection.

"If you look at the feet on this female, she is really fault-free."

Ruby Canning, Mavstar, said the win meant the "absolute world" to the family.

"This is just a beautiful accolade to add to what we have won over the years and showcase a home-bred female," she said.

Ms Canning said her grandfather Peter Schembri won a grand champion ribbon with a Simmental cow in 1997.

"To win this year and go all the way to win supreme interbreed is just an honour that we'll never forget," she said.

"I think it was the cow's overall completeness (that pleased the judges), she is a very sound, fertile female and has a great calf at foot."

She said Red Star would probably be flushed and put into an embryo transfer program, with her genetics being used to grow Mavstar's herd.

The Mavstar team exhibited two cows and calves who were both half-sisters, both by one of their home-bred bulls, Mavstar Licorice Red, which Ms Canning said resulted in the females being "well put together and very sound".

Throughout the pandemic, she said the stud worked hard on getting genetics right at home and incorporating new genetics into their operation.

She credited her mum Rita, dad Ross and younger brother Jacob for the effort put in through COVID lockdowns to get their herd to a high quality.

"They're very fertile and sound heifers, and they're really the epitome of what we like to breed as well," she said.

"We actually are really proud of working together at our stud as a family, to breed great cattle and now it's a good time to get them back out there.

"We're also doing some embryo transfer programs at home and we've also got females and bulls, which will be for sale early next year."

The grand champion bull was awarded to Rellum Farms Smooth Operator, from Rellum Farms, Mount Gambier, SA, owned by GC & VJ Muller, which originally won the 16-20 month bull class.