ALLEGATIONS of inhumane slaughter of horses at a western suburbs knackery have sparked outrage and prompted the Melbourne and Werribee Open Range zoos to source horsemeat from other knackeries.

Secret footage shot by animal activists, the Coalition for Protection of Racehorses, and seen by Fairfax Media, shows several horses being killed at the Laverton Knackery, with at least one animal tied up and dragged along concrete while apparently still alive. The allegations are being investigated by the state's meat regulator, PrimeSafe, as well as the RSPCA after Animals Australia - the group that uncovered cruelty to Australian cattle in Indonesia in 2011 - made a formal complaint.

In a detailed letter to the Department of Primary Industries, Animals Australia claims dozens of breaches of animal cruelty, hygiene, welfare and meat industry laws, which could result in the cancellation or suspension of the business' licence.

In one case, Animals Australia alleges a ''worker shot the horse twice, did not ensure the horse was dead, and then tied the horse to a tractor and dragged him across 60 metres of concrete and gravel after which he was found to still be breathing.