Activists from the German Animal Welfare Foundation (AWF) said horses on farms in Uruguay, Argentina and Chile are forced to have large bore needles inserted into their jugular vein to extract a powerful hormone which is then injected into pigs to speed up their fertility cycle.

In order to get the hormone, known as pregnant mare’s serum gonadotropin (PMSG), an individual horse can have up to 10 litres of blood a week taken, leaving them at risk of anaemia, hypovolemic shock, miscarriage and death.

NPA chief executive Zoe Davies said: “We are aware that a small number of products containing PMSG are authorised for use in pigs in the UK for the induction and synchronisation of oestrus.

Good management

“However, from extensive enquiries, our understanding is that these products are used very little, if at all, in UK pig production as good management such as boar presence, sow nutrition and proper lighting means that sows naturally return to oestrus after weaning which negates the need to use them.

“It is also important to stress that, as an oestrus synchronisation product for breeding pigs, it would never be used in pigs destined for meat.

“Despite suggestions in the media that this is a story about British pigmeat, we want to make it clear the use of the product is not by any means standard practice in the UK.

“The UK pig industry prides itself on the high standards that underpin our pig production.”

The UK National Office for Animal Health said recovery of the hormone was an authorised practice around the world, but veterinary supervision was required and blood collection limits must be adhered to.