Iceland is one of the few countries in the world – and the only one in Europe – that uses the controversial method.
In our video report above, a pregnant mare is seen to have a cannula inserted into her neck, with blood drawn at a "blood farm" in Selfoss, in the south of the country. In response to the backlash, farmers at the farm have chosen to remain anonymous.
Pregnant mares' blood is highly sought-after due to the pregnancy hormone PMSG. It is then brought to a lab and used to improve the fertility of other animals, including cows, sheep and pigs. Several litres a week can be extracted from each pregnant mare.
The hormone is processed by the biotech group Isteka, one of the market leaders in Europe. Blood collection is a lucrative business, with farmers able to earn up to 10 million Icelandic kronur (about €70,000) a year.
In 2021, the number of blood farms in Iceland tripled to 199, with nearly 5,400 mares solely bred for their blood.
The release of the video last year led to uproar in Iceland, and police investigations. Many farmers were forced to step away from the business.
Animal Welfare Iceland has called for the practice to be banned entirely, amid claims that the semi-wild horses are kept in a small stalls and in some cases brutalised and beaten.
"Do you think it's okay to take a scared horse and stab it in the neck to make a fertility drug to increase the suffering of other farm animals? Do you think it's okay? I think most people would say no," says Rosa Lif Darradottir, vice-chairman of the organisation.
Arnthor Gudlaugsson, the managing director of Isteka, however, says that the video does not give an accurate picture.
"The video was, let's say, designed a little bit to give an overly negative, in my view, description of the process. There were also instances in the video which indicated bad practice or practice that should have been better," he says.
The scandal sparked debate in Iceland, where many inhabitants learned about the practice for the first time, despite the fact that it has been going on since 1979. Even so, little has changed since then.
"This makes us think about where we stand in our ethics,” says Darradottir.
"To make a fertility drug that is used on farm animals [...] to enhance their fertility beyond their natural capacity, just so that we can have a stable flow of cheap pork [...] The cause is not noble," she says.
Opponents also criticised the amount of blood collected.
"It's purely and simply maltreatment of animals and we have a word for that: animal cruelty," says MP Inga Saeland, who has repeatedly proposed a ban on the practice, but to no avail.
Stricter regulations did, however, enter into force in August, giving authorities more power to monitor the industry and "assess its future" over the next three years.