Trainer Brett McDonald, the father of top Sydney jockey James McDonald, has been charged with doping offences by the New Zealand Racing Integrity Unit.

McDonald and stable foreman Tanya Donaldson were on Wednesday charged with administering Phenylbutazone to four horses who competed at the Ruakaka barrier trials on December 9 last year.

One of the affected horses, an unnamed three-year-old, fell during its heat, seriously injuring jockey Chris Dell.

The horse broke both its front legs and was euthanased.

In a media release, the Racing Integrity Unit said the charges followed a detailed two-month investigation and the analysis of post-mortem samples taken from the unnamed horse.

The samples revealed traces of Phenylbutazone, which is a pain killer and has anti-inflammatory properties.

The drug is banned for use on race days and in official barrier trials.