Performance and physiological responses of naked-neck chickens and their F 1 crosses with commercial layer breeds to long-term high ambient temperature
Department of Animal and Range Sciences, Hawassa University, P.O. Box 05, Hawassa, Ethiopia
Melesse, A., Department of Animal and Range Sciences, Hawassa University, P.O. Box 05, Hawassa, Ethiopia
An experiment was conducted on forty-eight female chickens from each of the following genotypes: Naked-neck (Na, from Ethiopia), New Hampshire (NH), Lohmann White (LW) and F 1 crosses of NaxNH and NaxLW. Twenty four chickens from each genotype were randomly divided and assigned either to high (30-32 °C) or normal ambient temperature (18-20 °C). Body weights were measured during 20 and 68 weeks of age. Eggs were collected once daily while egg weight and feed intake were determined at 28-d intervals. Blood samples were taken from 12 randomly selected birds per genotype and ambient temperature at 38, 51 and 65 weeks age. Total protein levels were measured in plasma whereas differential leukocyte counts were determined from whole blood. Compared with controls, the egg production and feed consumption in commercial layers significantly reduced by 24.2 and 15%, respectively. Surprisingly, heat stress favourably increased body weight in NaxLW genotype by 1.7 and 2.8 % at 20 and 65 weeks, respectively and appeared to be the best F 1 cross combinations. 1 The effect of heat stress was significant for all differential leukocyte counts. Compared with controls, the respective increase in heterophil, basophil and monocyte counts was 19.2, 43.6 and 41% whereas the lymphocyte and eosinophil numbers reduced by 9 and 11.6%, respectively. The hetrophil:lymphocyte (H/L) ratio increased by 45, 18 and 19% at 38, 51 and 65 weeks age, respectively. At high temperature, the highest lymphocyte counts were noted in LW and the lowest in NaxNH whereas heterophil counts were highest in NH and NaxNH resulting in increased H/L ratio. The total plasma protein reduced in all heat stressed chickens although it was only significant at 38 weeks age. It was inferred that the total plasma protein mean values in heat stressed hens declined from 4.12 g/dl at 38 weeks to 2.22 g/dl at 65 weeks. In conclusion, the Na and its F crosses demonstrated better heat stress tolerant than commercial layer chickens as evidenced by measured 1 performance and physiological parameters. These results suggested that differential leukocyte counts, H/L ratio and total plasma protein could be used as a reliable indicator of long-term heat stress in layer chickens. © IDOSI Publications, 2011.
Commercial layer chickens; F 1 crosses; Heat stress; Leukocyte counts; Naked-neck chicken; total plasma protein