Tracking the development of serum biochemical parameters in two laying hen strains – a comparative study

Abstract. A follow-up, comparative study was designed for the description of differences between two divergent laying hen strains, a Leghorn type and a medium heavy body (MHB) genotype (Hy-Line Brown), in chemical body composition and serum biochemical parameters determined at 3, 4, 6, 8, 10, 12, 14, 18, 20, 25, 30, 52 and 72 weeks of age; each time 5 birds of both genotypes were analysed and exterminated for body composition analysis.

Resulting from the genotype-associated differences, the bodyweight of the populations differed from week 20 on. In the chemical body composition dry matter content was similar, while crude protein was higher on weeks 3, 8, 10, and after 18 weeks in the Leghorns. Crude fat content was higher in the brown birds (weeks 8, 10, 25, 30). Total serum protein and albumin showed slightly increasing trends, while serum creatinine concentration showed a downward trend in both genotypes, the MHB birds having higher values. Triglyceride concentration showed a drastic step-up at 17 weeks by changing to the pre-layer diet, coupled with marked between-genotype differences. This quick increase was matched by concentration drops in total and HDL cholesterol, the serum HDL cholesterol of Leghorns being always lower. Sodium concentration showed an increasing tendency with body DM content (R²=0.914, P<0.001, n=115). The Leghorns tended to show minimally higher Ca concentrations. The γ-GT activity was always higher in MHB birds, indicating a less effective hepatic adaptation to the peak production. Applying discriminant analysis to classify the genotypes, 94.4% of the original grouped cases was correctly classified, using all variables.