The DA expressed concern about alleged interference in the investigation of cruelty to animals at NCOP chairwoman Thandi Modise's North West farm.
The Veterinary Defence Association had confirmed that one of the surgeons investigating the case had been threatened, Democratic Alliance North West leader Chris Hattingh said.
"The DA, apart from being concerned about the pressure excreted [sic] upon Dr Abbas, will add the latest revelations to our charge... registered at the Buffelshoek SAPS, as evidence of attempts to defeat the ends of justice accumulates," he said in a statement.
Last month, police and inspectors from the National Society for the Prevention of Cruelty to Animals (NSPCA) found starving and dead animals on Modise's farm Modderfontein, near Potchefstroom, North West.
About 85 live pigs had begun cannibalising 58 dead pigs, and were reportedly drinking their own urine. Sheep, geese, goats, and ducks were also among the more than 100 dead animals. Many had to be put down.
It appeared the animals had been without water and food for a week, possibly two. There were no farmworkers on the property, no electricity, and the water pumps were broken.
The Mail & Guardian and Beeld newspapers reported that the vet who performed the post mortems on several pigs' carcasses refused to have anything more to do with the case.
Dr Sameer Abbas, a veterinary surgeon practising in Potchefstroom, also refused to hand over his report to the NSPCA.
The society has laid charges against Modise and people living on the farm.
Hattingh said Modise had promised to co-operate with the investigation.
"We have seen nothing of this co-operation yet. Instead reports of attempts to prevent NSPCA officials from doing their work emerged."
On Tuesday, Modise's farm manager Neo Moepi denied threatening two NSPCA inspectors with violence, claiming he had saved them from harm at the hands of farmworkers.
Earlier that day, Moepi and a farm manager allegedly threatened to kick the inspectors' car and set it alight, and grabbed a cellphone and erased recordings.
The altercation allegedly happened last Friday, when the inspectors visited Modise's farm to evaluate the animals.
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