Responding to the statement, Ms Macdonald said: “It’s a total load of lies, the testing has never been validated.
“He’s still standing by such a ridiculous claim because they’ve made errors of judgment and they’ve been caught out.
“If he’s willing to kill a healthy animal in front of the whole world without testing him properly first, then it’s a sorry state of affairs.
“And it will be for the world to see. Because if he sends some poor person down here with a gun to shoot Geronimo then it will get filmed by the world’s media.”
The 50-year-old vet and alpaca breeder, who has a farm in south Gloucestershire, has said she would “stand in the way of any gunman who comes to destroy Geronimo”.
She has repeatedly claimed the tests carried out on the New Zealand-born male alpaca were inaccurate.
And Ms Macdonald added: “They’ve known since 2016 that those tests produce false positives if you give an alpaca more than two shots of tuberculin within a 12-month period.
“If George Eustice or the chief vet aren’t willing to look at the evidence and accept that the drug can produce an immune response that can produce a false positive then they need to take a look at their positions.”
Downing Street later refused to grant a stay of execution for Geronimo, and the Prime Minister’s official spokesman said: “We know how distressing losing animals to TB is for farmers and our sympathies are with Ms Macdonald and everyone with animals affected by this terrible disease.
“The Environment Secretary has looked at this case very carefully, multiple times over the last few years, and has interrogated all the evidence with expert vets alongside the Animal and Plant Health Agency.
“But, sadly, Geronimo has tested positive twice for TB using highly specific, reliable and validated tests.”
Geronimo had four skin tests before he was exported from New Zealand all of which were negative. The animal then had two blood tests and a skin test in the UK which were all positive.
The Department for Environment, Food & Rural Affairs (Defra) said the test has a 0.36% chance of producing a false positive.
However, no trials for how accurate the tests are on alpacas have been carried out.
The alpacas who travelled with Geronimo from New Zealand were all tested and returned negative results. Geronimo currently lives with five other alpacas. Defra has refused to test them.
Ms Macdonald said: “I had no idea this was going to blow up the way it has and I’m so thankful to everyone who is supporting me, including the British Alpaca Society, animal rights groups and a number of celebrities.
Bovine TB causes devastation and distress for farmers and rural communities and that is why we need to do everything we can to reduce the risk of the disease spreading.
“People are genuinely upset and outraged by the behaviour of the Government.
“This is having a massive impact on mine and my family’s mental health and all because Eustice won’t allow samples to be taken from Geronimo to make sure before they kill an innocent and healthy animal that he has actually got TB.
“Because I assure you – he hasn’t got it. And the sad thing is, they’ll realise that only when he’s dead and they’ve carried out a post-mortem on him, and then it’s too late.”
A “Save Geronimo” petition has now gathered 80,000 signatures.
A Defra spokesperson said: “We are sympathetic to Ms Macdonald’s situation – just as we are with everyone with animals affected by this terrible disease.
“It is for this reason that the testing results and options for Geronimo have been very carefully considered by Defra, the Animal and Plant Health Agency and its veterinary experts, as well as passing several stages of thorough legal scrutiny.
“Bovine TB causes devastation and distress for farmers and rural communities and that is why we need to do everything we can to reduce the risk of the disease spreading.”
The online petition to save Geronimo can be found at change.org/p/boris-johnson-save-geronimo-stop-killing-healthy-alpacas-without-valid-science