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Implications of genetic selection on yolk proportion on the dry matter content of eggs in a White Leghorn population
Authors:W Icken  C Looft  K Schellander  D Cavero  A Blanco  M Schmutz
Institution:1. Lohmann Tierzucht GmbH, Cuxhaven, Germanyicken@ltz.de;3. Institut für Tierwissenschaften, Tierzucht und Tierhaltung, Rheinische Friedrich-Wilhelms-Universit?t Bonn, Bonn, Germany;4. Lohmann Tierzucht GmbH, Cuxhaven, Germany
Abstract:1. The responses to genetic selection on yolk proportion as a technique for increasing egg dry matter content, an important criterion for the egg-product industry, was investigated in a pedigree flock of White Leghorn hens.

2. Parents were preselected on high and low yolk proportion from a base population. The absolute estimated breeding value for yolk proportion of both groups differed by 3%. The realised selection difference in dry matter content of eggs between groups was more than 1% in the analysed offspring population.

3. Heritability estimates were moderate and dry matter had a lower heritability (h2 = 0.39) than yolk proportion (h2 = 0.44).

4. The genetic correlation between yolk proportion and dry matter content was highly positive (rg = 0.91). Genetic correlations with egg weight were negative and would have to be compensated for in a breeding programme (rg = ?0.76 with yolk proportion and r= ?0.64 with dry matter content). The genetic correlation between the laying performance and yolk proportion was r= 0.28 and close to zero (r= ?0.05) for dry matter content.

5. Easy recording and lower undesirable correlations make yolk proportion more suitable for commercial selection compared with egg dry matter content in layer breeding.
Keywords:
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