126 T. Szwaczkowski et al.
Effect of <strong><strong>in</strong>breed<strong>in</strong>g</strong> <strong>on</strong> producti<strong>on</strong> <strong>and</strong> reproducti<strong>on</strong> <strong>in</strong> lay<strong>in</strong>g hens 0.421 for H77 <strong>and</strong> N88, respectively). This corroborates the results obta<strong>in</strong>ed by Besbes et al. [1992] <strong>and</strong> Tufvess<strong>on</strong> et al. [1999]. However, Szydłowski <strong>and</strong> Szwaczkowski [2001] reported lower Bayesian estimates of heritability for BW of two Polish stra<strong>in</strong>s of lay<strong>in</strong>g hens. The estimates of heritabilities for age at first egg obta<strong>in</strong>ed by other authors [Sewalem 1998, Szwaczkowski et al. 2001] showed variati<strong>on</strong> rang<strong>in</strong>g from 0.08 to 0.44. Heritabilities of PEF <strong>and</strong> PEH (Tab. 4) are <strong>in</strong> general agreement with results by other authors for different populati<strong>on</strong>s [Sewalem et al. 1998, Szwaczkowski et al. 2000]. From a methodological po<strong>in</strong>t of view it should be <str<strong>on</strong>g>note</str<strong>on</strong>g>d that these data have not been transformed. It is known that some layer <strong>traits</strong> exhibit deviati<strong>on</strong>s from normality. This led to overestimati<strong>on</strong> of mean square of residuals <strong>and</strong>, <strong>in</strong> c<strong>on</strong>sequence, to underestimati<strong>on</strong> of heritability. However, from the breeder’s perspective an <strong>in</strong>terpretati<strong>on</strong> of <strong><strong>in</strong>breed<strong>in</strong>g</strong> <strong>effect</strong>s could be difficult, as transformed are also natural units of <strong>traits</strong> studied. Piotrowski <strong>and</strong> Szwaczkowski [2002] <strong>in</strong>dicated similar estimates of variance comp<strong>on</strong>ents obta<strong>in</strong>ed from untransformed vs transformed data. The results presented here lead to the follow<strong>in</strong>g c<strong>on</strong>clusi<strong>on</strong>s. The <strong><strong>in</strong>breed<strong>in</strong>g</strong> level seems to be relatively low <strong>in</strong> these populati<strong>on</strong>s, undergo<strong>in</strong>g selecti<strong>on</strong>. The <strong><strong>in</strong>breed<strong>in</strong>g</strong> depressi<strong>on</strong>s for the <strong>traits</strong> studied (except per cent of eggs fertilized) are mean<strong>in</strong>gless. The heritability estimates of <strong>productive</strong> <strong>and</strong> re<strong>productive</strong> <strong>traits</strong> corresp<strong>on</strong>d to those reported <strong>in</strong> literature. Acknowledgement. The authors are grateful to Dr. Kar<strong>in</strong> Meyer for supply<strong>in</strong>g a set of DFREML programmes. REFERENCES 1. BESBES B., DUCROCQ V., FOULLEY J.L., PROTAIS M., TAVERNIER A., TIXIER-BOICHARD M., BEAUMONT C., 1992 – Estimati<strong>on</strong> of genetic parameters of egg producti<strong>on</strong> <strong>traits</strong> of lay<strong>in</strong>g hens by restricted maximum likelihood applied to a multiple-trait reduced animal model. Genetics, Selecti<strong>on</strong>, Evoluti<strong>on</strong> 24, 539-552. 2. FLOCK D.K., AMELI H., GLODEK P., 1991 – Inbreed<strong>in</strong>g <strong>and</strong> heterosis <strong>effect</strong>s <strong>on</strong> quantitative <strong>traits</strong> <strong>in</strong> a white leghorn populati<strong>on</strong> under l<strong>on</strong>g-term reciprocal recurrent selecti<strong>on</strong>. British Poultry Science 32, 451-462. 127
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