TETRA Ltd started a programme in 2008 to improve existing layer lines of Tetra, and establish new strains selected for better persistency. In a Tetra study, a group of experimental combinations were tested for a longer laying period till 90 weeks of age. Performance test results conducted in cages showed that among the tested Rhode Island type single cross combinations, significant differences were found, the main cause being the variation in persistency of egg production.

The range in hen-housed egg production was between 374 and 345 eggs produced to 80 weeks of age, and between 425 and 385 eggs produced till 90 weeks of age. In the 'Long Life' programme, optimised egg size and improved shell strength will have high priority.

Heterosis was not diminishing although continuous classical RR selection was in practice using the same two Rhode Island parental lines. Because of long-term selection improvement, some traits reached biological limits. Improving early maturity further and increasing peak production did not seem worthwhile. Persistence of lay is a trait of increasing importance. Tetra Ltd started in 2008 a 'Long Life' selection programme to increase the laying period of layers.

In this programme, a modified RR selection programme is practised; the testing of crossbred progeny is extended to the pure parental lines also, previously the total test period lasted until 65 to 72 weeks of age.

Since 2008, considering the goals of the 'Long Life' programme, TETRA Ltd extended the test period to 80 weeks of age or even longer.

Egg production and mortality was recorded daily. Egg quality traits such as weight, shell colour, shell strengths and Haugh units were measured for all hens objectively using the Multiple Egg Quality Testers - using all eggs laid by the hens as they reach 35, 60 and 82 weeks of age.

In the first preliminary test programme in 2008-2009, TETRA Ltd tested the standard layer hybrid and two other experimental crosses, both of them surpassed the standard cross significantly in egg production mainly in persistency. Based on these results and utilizing the experiences gained, with improved lines and new cross combinations in 2010-2012, a new test programme was organized by housing all birds in cages. Each combination had six replicated groups, one group consisted of 15 hens, replicates were randomly allotted in the cage house.

Based on the first 2008-2009 test results, eight cross combinations were produced and tested for the 'Long Life' extended laying period till 90 weeks of age.

The test result shows that there are several cross combinations capable to produce over 410 eggs per hen in extended layer periods to 90 weeks of age, there seems enough genetic variation to improve persistency. Shell colour improvement and reduced variation are important, the heritability is also high in Tetra straits similar to the findings of others. It is necessary to pay much attention to shell strength. Beside the genetic variation, complex nutritional and management practices can also contribute to the improvement of egg shell strength.

As a conclusion of these tests, TETRA Ltd is ready to introduce to the market its new brown layer hybrid named TETRA-SL LL, which is capable of producing more than 400 eggs per hen to 90 weeks of age, proving that it is possible to breed crossbred brown egg layers to improve the economical efficiency of egg production by extending the production period.