Mark Jones, Phil Williamson, Mark Purdon and John Price all told the Otago Daily Times (ODT) the careers of young horses were being hindered because the current handicapping system favours multiple race-winning, older horses too much.
Williamson said that extra opportunities to race those older horses came at the expense of developing young stock.
"The older stock can keep racing, but it is probably at the expense of the younger horses coming through."
The Oamaru trotting ace said there were only two options to protect young horses from racing battle-hardened horses that have won multiple races.
"The young horses - the 2 and 3yr-olds - it is hard to race them in this system.
"Because if you win a race, [the horse is] put in to such a tough rating that you can't race them.
"It's either sell them or you can't race.
"A champion can probably overcome it, it probably won't hurt them, because they are just star horses.
"But for the most part, most of the young horses [that] come out at 2 and 3, if they get in the rating system past a maiden, it is just crazy tough."
Despite that, he still had the same concerns his training counterparts did.
Purdon has been so appalled by the state of the current ratings system he nominated Princess Tiffany for the Easter Cup to demonstrate how it treated young horses.
"She has won two races as a 3yr-old filly, and her assessment dictated that she had to race in the Easter Cup.
"That is how appalling the system is.
"It is not bad, it is actually appalling.
"You would wonder how many brains they have got to come up with a system like that where you really hurt young horses."
Purdon agreed with his training colleagues and said the current structure of the rating system effectively promoted the sale of young horses overseas.
Jones said the lack of pathways for up-and-coming horses to learn their trade against like competitors has developed into a sad situation for harness racing.
"When I go to the races now, probably the happiest person I see is the person that has run second in the maiden trot.
"The most disappointed one is the winner, because they think `where the hell do I go now?'.
"They are actually disappointed to win a race that and that is not the way it should be.
"If you have a one-win trotter rated 55, you could be racing horses that have won seven or eight races."
Williamson said that it was clearly a fault of the system when so many young horses become instantly uncompetitive after winning their maiden.
"A horse that wins a maiden race, it then becomes non-competitive at its next start, which I think is not a good thing.
"If you are in winning form you should be able to go to your next start and be competitive, but you are not.
"The owners get a win and think their horses are going great, but I have to say to them hold on, next week if we race we won't be competitive."
Jones said the handicapping of 2yr-olds was so dire that he was advising owners to turn their horses out.
"I have 2-yr-olds now that I am telling my owners to turn them out, because if they win a race they are not going to be racing one-win races.
"I could have an average 2yr-old win an average maiden race and it would be rated higher than a horse that had won eight races.
"Why would you win a race at 2? If you do, you are buggered now.
"I am for a system that caters for lesser horses, because we have all got one of them."
Price said that running a horse down the track so that it could find a rating where it could be competitive was not an option every trainer or owner wants to take.
"The handicapping sub-committee say just race your horse until it drops back to where it is competitive.
"A lot of trainers and owners don't want to do that - you don't want to line up six or seven times to get it back to where it is competitive."
Williamson said running horses until they find a competitive rating goes against what he stands for as a trainer.
That meant horses were kept at home, instead of being out and racing.
"I like to go out there and win and win every race.
"It is hard enough to do, but the aim has got to be there, and the mindset has got to be we have got to be the best we can be.
"If you start driving those young ones that have only had two or three starts in that aggressive manner against horses that have had 60 starts, you are going to come undone."
Each of the trainers that spoke to the ODT said older, experienced horses coming down the ratings created a log jam in the 40-60 rating bracket.
Jones said that has been made worse by the removal of points for placings.
Penalising runners for running placing is considered a vital part of ratings-based handicapping systems used in horse racing codes across the world.
"Our system was designed to get placings," Jones said.
"But at the moment one is going up, four are staying the same and the rest are going down.
"I don't like a system that supports mediocrity and has an incentive to get beat, because it still costs owners money.
"I think the system they have bought on encourages you to be a hobby trainer and have a full time job.
"Us professional trainers are trying to get young horses up and get owners returns, but you can't even do that for them now."
Harness Racing New Zealand chief executive Peter Jensen told the ODT earlier this month that office was open to changing the ratings-based handicapping system for the betterment of the industry.
Jensen said he was aware of concerns trainers from across New Zealand had about the treatment of young and up-and-coming horses under the handicapping system.
The chief executive said improvements to the ratings system that allowed as many horses to race competitively was something to strive for.
"There is a process for reviewing the ratings system, so I don't think it is in a situation ... for good.
"We should be looking at where the opportunities are to continue to improve it.
"In my mind, the ratings system should be, as much as possible, about creating opportunities for horses to race.
"But also, creating even betting fields."
Jensen said concerns trainers and drivers had about the current system could be raised through their representation on the handicapping sub-committee.
The chief executive said any changes to the ratings system could not sacrifice one of its key aims - to provide even betting fields.
"If the ratings system can assist that, that makes good sense, as long as we are creating even betting races when we are doing that.
"What we don't want is dominant favourites as a result of changes to the ratings system.
"Part of the change in Australia - moving towards a ratings system - is because of the predominance of too many short priced favourites.
"None of us want that, it is not good for the industry and for turnover and margin."
