The killing of thousands of conscious sheep has continued for two years since The Age revealed at least four Victorian abattoirs had been granted exemptions to an Australian standard on ritual slaughter to fulfil kosher and halal contracts.

The standard stipulates animals must be electrically stunned unconscious before having their throats slit. The exemptions were granted under a disputed federal guideline.

The former government announced a review of ritual slaughter in 2007. Since then, Agriculture Minister Tony Burke has angered animal welfare groups by refusing to make it public.

The Age obtained a copy of the report, which states that sheep slaughtered without stunning can suffer "panic and terror" and quotes European studies that sheep can remain conscious for up to 20 seconds after having their throats slit.

But the review is non-committal. "The present report makes no judgments about the acceptability of any form of slaughter," the report says. "It is recognised, however, that stunning removes the hazards of pain and distress from the last stage of the slaughter process."

Animal welfare groups have accused the federal and state governments of putting a "cone of silence" over the issue and fear the report will be used to increase the practice.

Although many Muslim export markets accept meat as halal that has been slaughtered with stunning, Animals Australia fears granting further exemptions or changing the standard could lead to commercial pressure on more abattoirs to kill without stunning.

"While we value religious freedom, we do not believe this should extend to practices that inflict suffering on animals," said Animals Australia executive director Glenys Oogjes.

Mr Burke would not say why the report had not been released, but said work was still being carried out through the Primary Industries Ministerial Committee.

A spokesman for Victorian Agriculture Minister Joe Helper said Victoria had been involved in "consultations with representatives of the Jewish and Islamic faiths and animal welfare groups, including the RSPCA".

RSPCA Victoria president Hugh Wirth said such ritual slaughter was widely accepted as inhumane.