EGGSHELL STRENGTH IN MOLTED AND NON-MOLTED LAYERS UNDER SUMMER HEAT STRESS PERIOD
Dragoslav Kocevski, Gjoko Bunevski, Vladimir Djabirski, Vlado Vukovikj, Kocho Porchu, Nedeljka Nikolova, Goran Tashev, Danail Shutevski
"Institute of Animal Biotechnology, Faculty of Agricultural Science and Food, University ""Ss Cyril and Methodius” in Skopje, Republic of Macedonia"
Dragoslav.Kocevski@yahoo.com
An analysis was performed of eggs’ quality parameters in the period of the high-temperature summer (July, August) heat-stress period (egg weight, yolk color, Hough units and eggshell strength) in two flocks of commercial laying hens at advanced age. Each flock consisted of ISA Brown (IB) and DeKalb White (DK) mixed-genetic layers kept in two separate hen-houses equipped with battery cages. The first flock (F1– 7334 DK and 8233 IB) was at the 72nd week of age at the start of the monitored period, and the second one (F2 – 7833 DK and 8815 IB) at the 92nd week of age after being molted at the 70th week of age. In-house environment ventilation as well as hens’ feeding (following technical recommendations) were approximately same for both hen-houses throughout the laying cycle. Eggshell quality of 240 egg samples (30 eggs/month/breed F1 or F2) was analyzed in the laboratory for testing egg quality using Eggshell Gauge (Robotmation Co. Ltd., Tokyo, Japan), a computerized equipment that gives unbiased values. Both genotypes yielded high egg production close to the technological level. Molted ISA Brown layers produce eggs that on average have 400 g/cm 2 stronger shells than the eggs of non-molted layers (mean values of 4,027.63 vs. 3,569.83 g/cm 2 in July and 3,748.67 vs. 3,334.70 g/cm 2 in August). Same tendency was registered in DeKalb White layers’ flock (mean values of 3,743.83 vs. 3,535.67 g/cm 2 in July and 3,400.23 vs. 3,104.53 g/cm 2 in August). The data obtained confirm that heat stress negatively influences shell strength and that molting improves layers’ shell strength production capacity and helps mitigation of heat-stress negative effects.
Keywords: eggshell strength; heat stress; molting; layersovi
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