Egg white biologically active proteins activity in relation to laying hen's age.

The study was performed in order to determine the activity of biologically active proteins that naturally occur in egg white in relation to the age of the laying hen. For the experiment 240 eggs were collected from 40 hens (20 birds of ISA Brown and 20 birds of Hy-Line). Hens were kept in individual cages and fed with standard fodder. The activity of cystatin, lysozyme, serine proteinases inhibitors (ovomucoid and ovoinhibitor) were measured in egg whites obtained from hens in 35, 40, 45 and 50 weeks of age. The results of the study showed that cystatin had the lowest activity in egg white collected from 35 weeks old hens, whereas eggs collected in 50 weeks of hen’s age expressed the highest activity of cystatin. This relation was proved for both bird’s crossbreeds. No significant differences in cystatin activity were observed between two experimental lines. Similar to the results obtained for cystatin, the lysozyme activity was the lowest at first time of eggs collection, and then it increased from 244 u/mg protein to 273 u/mg protein for ISA Brown and from 235 u/mg protein to 316 u/mg protein for Hy-Line. Activity of trypsin inhibitors analysed in egg white increased together with the hen’s age from 35 to 45 weeks, when the activity of serine proteinases inhibitors reached the maximum point. Activity of mentioned biological components measured in eggs obtained from 50 weeks old hens was significantly lower. A similar trend was estimated for chymotrypsin inhibitor analysed in egg white. HyLine birds produced eggs with higher anti-trypsin and anti-chymotrypsin activity than ISA Brown hens. It is concluded that activities of biologically active proteins in egg white increase with increasing age of the hens to 45 weeks in case of trypsin and chymotrypsin inhibitors, and up to 50 weeks in case of cystatin and lysozyme.