He can’t say he was surprised. Randy Sampson has seen the formula produce results at other racetracks around the country, and he believed it would do the same at Canterbury Park.

The president of the Shakopee track predicted that higher purses would attract larger fields of better-quality horses, which would then stimulate more wagering. Through the first 30 days of a 69-day racing season, things are playing out just as he hoped. Average daily wagering on Canterbury’s races has increased 22.5 percent, and attendance and simulcast handles also have risen.

The track handled more than $1 million on consecutive days on July 3 and 4, which Sampson said was unprecedented in the 19 seasons he has managed Canterbury Park. He is anticipating another big day Saturday for the $125,000 Mystic Lake Mile and $100,000 Lady Canterbury. The richest thoroughbred races of the season thus far, each attracted full fields of 12 horses, with several shipping in from tracks such as Churchill Downs and Arlington Park.

The purse-enhancement agreement signed last summer with the Shakopee Mdewakanton Sioux Community has pushed purses 18 percent higher than last season — and more than twice what was paid out in 2011. That has filled Canterbury’s stables to capacity during a season that also has seen an uptick in average daily attendance (6,306, up 2.1 percent) and average daily total handle ($673,922, up 17.3 percent).

“This is what we’ve been waiting for,’’ Sampson said. “It is a breakthrough for horse racing in Minnesota. And it’s only the first step. We think things will continue to improve.’’

Stall superintendent Mark Stancato was scrambling Thursday to find stable space for the horses shipping in to run Saturday. He said the number of horses on the grounds peaked at 1,591 — 260 more than last season — and all 240 dorm rooms are full. The biggest complaint has been that some horsemen cannot bring in as many horses and workers as they want because there are no more accommodations.

By mid-July, Stancato explained, the number of horses usually declines as trainers move on to other tracks. This year, space remains tight in the 1,600 stalls. “For every two that leave, three want to come in,’’ he said. “It’s a lovely problem to have.’’

It’s also a rare one. National statistics show a downturn in wagering, purses and racing days at American thoroughbred tracks in 2013, with many struggling to fill races. Canterbury’s average field size has increased from 7.33 horses last year to 8.08 this season, making its races more attractive to horseplayers around the country.

Sampson said the track has marketed itself more aggressively through national channels such as the Daily Racing Form and TVG, a cable network that televises races and allows viewers to bet on them. That has helped fuel a 34.1 percent rise in daily out-of-state wagering on Canterbury’s races. And with more money in the betting pools, Sampson said, local players who bet heavily on simulcast racing have begun wagering more on Canterbury’s races.

The increase in the size and quality of the horse population has made it tougher to claim a piece of those fatter purses. Trainer Valorie Lund, in her third season at Canterbury, said some horses that could have won easily in past seasons are not having as much success this year.

Still, Lund noted, the higher purses mean that horses now can earn good money by finishing second or third — something that would have been impossible before. Even though her winning percentage has decreased, she is glad to be in Shakopee this summer.

“It’s a very strong meet,’’ Lund said. “Any time you have bigger fields, it’s good for racing, because it helps that handle go up. And that’s good for everybody. It’s exciting to see what’s happening here.’’