Essential Reading:

Laying Hens

Snapshot

The UK laying hen sector monitors total usage on the basis of bird-days* medicated (daily doses**) as a proportion of the estimated total number of bird-days at risk based on Lion Code census figures. On this basis, for 2017 the egg industry reported in VARSS 2017 that its use was 0.57 daily doses/100 bird-days (or % medication days).
An update on progress against specific targets was published in November 2018, with a summary of progress in laying hens as follows:

Under the Lion Code of Practice, the egg industry’s quality assurance scheme which accounts for more than 90% of UK egg production, use of fluoroquinolones at day-old and the use of all 3rd and 4th generation cephalosporins is prohibited.
In response to growing concern with respect to potentially transmissible colistin resistance, Lion subscribers have also agreed to voluntarily cease use of colistin-containing approved products.
Antibiotics are not used routinely in layer flocks.
Vaccines are used to prevent viral diseases, which then prevents any secondary bacterial diseases that might otherwise require antibiotic treatment.
The Lion Code requires the vaccination of all birds, destined to produce Lion eggs, against Salmonella.
The targets published on 27 October 2017 stipulate that total bird/days medicated remains should below 1%, and fluoroquinolone + colistin (HP-CIA) days medicated should remain below 0.05% on an ongoing basis. For more detail on the egg and laying hen sector targets, please refer to the full Targets Task Force Report.

*A bird-day is the standard denominator used to calculate all proportions, or percentages. For the year, it is the mean daily population of birds in the Lion scheme (including breeding birds and pullets in rear) multiplied by 365.

**A daily dose is a single chicken treated with an antibiotic for one day. Courses of treatment will vary with the clinical need, but are typically 3-5 days. So a flock of 5,000 chickens treated with an antibiotic for 3 days is 15,000 daily doses.