Their heifer Sherraine Gold Charm-ET VG85 clinched the two-year-old class. Her full sister Sherraine Gold Charas-ET VG87 placed third.
"They are granddaughters of Sherraine Windstar Charm EX3, who was a great brood cow of ours," Cahill said.
"We did embryo work on one of her daughters and ended up with four outstanding two-year-old heifers sired by Braedale Goldwyn."
Another of Charm's granddaughters, Sherraine Fortune Carra EX3, was named the national champion veteran cow.
The 11-year-old won the type and production class at the New Zealand Agricultural Show in Christchurch last November.
She has produced 69,479 litres of milk, or 5,312 kilograms of milksolids (plus excess days), in her lifetime.
"To see Carra take out the coveted veteran class topped off a great week for us," Cahill said.
Sherraine Holsteins entered eight cows in the regional round of judging, which attracted 144 animals from Canterbury/Westland.
Cows were assessed for their structural correctness.
Productive dairy cows with well-attached udders have the potential to live longer and be better for the environment.
Sherraine Holsteins was the only stud nationally to win two of the six classes up for grabs.
The results of the coveted competition were announced over six nights on Holstein Friesian NZ's Facebook page last week.
"They are usually revealed at the association's annual conference, but that was postponed this year due to Covid-19," Cahill said.
"It was quite nerve-racking waiting until 5pm each day to see the results go online. Other breeders messaged to wish us luck."
"I found out we had won the two-year-old class as I was walking the herd off the feed pad," she said.
They also bred Sherraine Doorman Carrie EX, who was named national reserve champion in the four-year-old class.
The national final was judged by Glen Gordon from Australia.
The North Canterbury farm supplies Fonterra year-round and produced 100,000 kgsMS from 144 cows in the 2019-20 season.
The 150-hectare irrigated farm is self-contained with all silage, maize and hay grown on farm.
Three-quarters of the calves born each season are reared using an automatic feeding system, using predominantly whole milk.
The HFNZ Semex On Farm Competition is run annually across eight regions with the aim of promoting Holstein Friesian cattle.
Peter Sherriff judged the regional final in Taranaki.
Full results from the 2020 HFNZ Semex On Farm Competition:
Maughlin Storm two-year-old cow class
1st: Sherraine Gold Charm-ET VG85, Sherraine Holsteins
2nd: Waipiri Solomon Lakota-ET, D & P Fullerton
Comestar Leader three-year-old cow class
1st: Waipiri Cain Kara VG89, D & P Fullerton
2nd: Belbrook Alonzo Jaime VG89, Belbrook Holsteins
Townson Lindy four-year-old cow class
1st: Kauri Glen Atwod Duch1-ET VG89, Kauri Glen Ltd
2nd: Sherraine Doorman Carrie EX, Belbrook Holsteins
Hanoverhill Raider five-year-old cow class
1st: Tahora Aftershk Tootsie EX, Huka View Dairies
2nd: Kauri Glen Fever Prim-ET VG89, Kauri Glen Ltd
Conant-Acres JY Broker mature cow class
1st: Oakdale Guthrie Miss VG89, Valendale Ayrshires/Fusion Genetics
2nd: Bellview Lavanguard Di EX2, Belbrook Holsteins
Comestar Laurie Sheik veteran cow class
1st: Sherraine Fortune Carra EX3, Sherraine Holsteins
2nd: San Ray Goldwyn Toots-ET EX2, Henley Farming Co Ltd