Evaluation of Production Traits in Two Strains of Layer Chickens under Relaxed Selection
Evaluation of Production Traits in Two Strains of Layer Chickens under Relaxed Selection.
ABSTRACT
This study was conducted to determine strain differences on some production and egg quality traits in 200 birds of synthesized Grand Parent Stock (Male and female lines) under relaxed selection. The hens used were from the same hatch and under the same management practices.
Production traits studied were age at sexual maturity (ASM), body weight at 18 and 20 weeks of age (BW18 and BW20), egg number (EN), average egg weight (AEW), and rate of lay (RL).
Egg weight (Ewt), egg length (El), egg width (Ewdt), albumen weight (Albwt), yolk weight (Ywt), shell weight (Swt) albumen height (Albht), yolk height (Yht), shell thickness (Sth) were measured.
Haugh’s unit (HU) and shell index (SI) were also obtained for egg quality traits. Significant differences (P < 0.05) were obtained for ASM, AEW and BW20 between strains. Male line had higher mean values in ASM (161.50 days) and AEW (43.66g) but Female line had better mean value for ASM (158.79days).
For egg quality traits, significant (P < 0.05) differences were also observed in Ewt, El, Ywt, Swt and HU. Higher mean values were obtained for all traits (Ewt, El, Ywt, and Swt) with the exception of HU in the Female line than the Male line.
Pearson correlation pooled for growth and egg production traits for the two strains showed that ASM had moderate to high negative and significant (P < 0.01) relationship with EN, BW18 and BW20.
INTRODUCTION
The goal of breeders is to improve the performance of their flock. One of the major tools available for this improvement is selection. Selection is the act of choosing those individuals that will become parents of the next generation with the aim of improving the performance of the flock or population.
The various selection methods used based on phenotypic measurement includes: mass selection, progeny testing, tandem selection, independent culling level, and selection index (Bourdon, 2000). Genetic improvement in animals and plants for food consumption has been practised and realised since domestication.
Intensive improvement, increasingly with incorporation of genetic principles, has been undertaken for a century or more (Hill, 2008). Much of this has been highly intensive and effective, notably in poultry. There are consequently concerns that genetic variation is being exhausted and continued gains cannot be expected (Hill, 2008).
The genetics of a metric character centres round the study of its variation (Falconer and Mackay, 1996). It is assumed that genetic variances either remains constant during selection or that any changes in variance can be predicted solely from the variance components of the base population.
Selection experiments have been the basis for testing theories, hypotheses, and predictions of quantitative genetic theory. In addition, selection experiments enable researchers to estimate genetic parameters, test alternate breeding schemes, and study the causes of selection limits and plateaus and develop means to overcome them (Reddy, 1996).
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CSN Team.
