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On-farm comparison of layer strains for organic egg production: experimental design and guidelines

Project


Project code: 2804OE005
Contract period: 01.06.2005 - 31.08.2008
Budget: 167,523 Euro
Purpose of research: Applied research

In order to develop guidelines for between-strain comparisons under the conditions of organic egg-production a test of four commercially available strains of layers was simultaneously conducted on 17 organic farms and two test stations. On station stocking density and feed met the requirements for organic egg production, free range was however not possible. Due to practical restrictions (few groups per farm) each farm contributed a pair-wise comparison of two strains (observations from one or, sometimes more, groups per strain). Thus the design was a mixture between a randomised experiment (on station) and an incomplete block design (on farms) with two strains per farm. Field data were collected by farmers and sometimes incomplete (e.g. missing egg numbers for some days). A random-regression model with daily observations was employed in order to cope with that characteristic. Significant interactions between test environment and strains were found for egg production but not for losses and plumage condition. A series of power calculations for various designs (on-farm test only, station-test only and combined) showed that the number of strains compared should be restricted to three, at most four. Experimental power on farm is mainly determined by the total number of groups, but little by the number of groups per farm, as long as two strains are compared per farm. For non-interacting traits a combined test in both environments yields the best efficiency in terms of experimental power given a certain number of groups in test. Per strain the number of groups should be equivalent to at least 15 groups in a completely randomised design (15 effective observations) in order to reach 80% power. Since the level of production traits was higher on station a combined test may provide information both on idle laying capacities of birds on farm and the reaction norm of layer strains.

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