The aim of this study was to compare biochemical indicators of blood plasma of laying hens housed in three different housing systems (conventional cage system, enriched cage system and deep litter system). In each housing system, 12 ISA Brown laying hens were observed during the laying period from week 22 to 75 of age. Blood samples for determination of biochemical indicators in plasma were collected during this period in week 22, 47 and 75. Indicators of blood plasma metabolic profi le of laying hens of all monitored groups during the laying period ranged in intervals stated for healthy animals. In some cases, signifi cant differences between housing systems were found, however, these differences do not give clear evidence of the infl uence of the housing system on the health of animals. The differences were apparently due to different effi ciency of each group during the laying period.

The aim of this study was to compare the blood plasma mineral profile (Ca, P, K, Mg, Zn, Cu and Se) and egg-shell quality (eggshell weight, eggshell breaking strength and thickness) of laying hens housed in three different housing systems (traditional cage system, enriched cage system and deep litter system). In each housing system, 12 ISA Brown laying hens were observed during the laying period from week 22 to 75 of age. The effect (p < 0.05 and p < 0.01) of age and/or phase of the laying cycle on all mineral concentrations was determined. Eggshell breaking strength decreased (p < 0.001) with the age of birds. The results of this study indicate that the housing systems compared had no significant effect on the blood plasma mineral profile of laying hens under study and the values were within the physiological range. However, a significant effect of housing system on eggshell breaking strength and eggshell weight was found. Improved eggshell quality was obtained in most periods of the laying cycle in the enriched cage systems. Blood minerals, egg-shell quality, standard cage, enriched cage, deep litter floorPassage of the Council Directive 1999/74/EC has resulted in the replacement of traditional cages with enriched cages, litter technologies or aviaries to improve the welfare of laying hens. The shell quality remains one of the most important issues for the technology of further egg handling (Ledvinka et al. 2000). However, some authors pointed out that there are differences in eggshell quality and proportion of cracked eggs between different housing systems (Abrahamsson et al. 1995;Abrahamsson and Tauson 1997;Wall and Tauson 2002). Shell quality can be influenced by many factors including mineral nutrition. Calcium, magnesium and phosphorus are major inorganic constituents of avian eggshells (Cusack et al. 2003). Simons (1976) found small amounts of potassium, copper and zinc in the palisade layer of the eggshell. The presence of sodium, potassium, magnesium, zinc, and copper was confirmed also in the shell membranes (Wedral et al. 1974). The importance of minerals is reflected in changes of arrangement pattern of shell membrane fibres in relation to the structural composition of the eggshell, for example when using copper-and magnesium-deficient diets (Leach and Gross 1983). Traces of magnesium, potassium, copper and zinc were also found in the egg cuticle. Plasma mineral concentrations during the laying period can be influenced by many factors; such as laying rate and energy requirements (Suchý et al. 2001), partial quantitative feed restriction (Sahin and Kucuk 2001), mineral supplements (Eren et al. 2004), ambient temperature (Siegel 1995;Donoghue et al. 1990;Ching 1992;Belay and Teeter 1993; Večerek et al. 2002), production type (Suchý et al. 2004), age of hens (Cerolini et al. 1990;Gyenis et al. 2006), stress (Beisel 1982Combs and Combs 1984; Tufft and Nockles 1991;Klasing 1998), exposure to heavy metals (Zralý et al. 2008), etc.With regard to differences in eggshell quality between different ho...

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