One of the measures to reduce the problem is to put sows and gilts on a 16-hour light/8-hour dark cycle, using at least 200 lux light intensity in the service and dry sow house, says Paul Thompson, veterinary consultant to pig-breeding company, ACMC Ltd.

He also advises re-whitewashing walls to increase light reflection and cleaning skylights and windows. Fluorescent tubes should be checked and repaired, and replacement with higher intensity tubes considered. Light levels can be checked by using hand-held lightmeters.

Producers should discuss with their breeding stock supplier and vet the need to lift service targets over the problem period, which will require pre-planning gilt replacements.