Seasonal Variations in the Haemogram of Desert Sheep

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Mohamed, Salwa Ahmed Elsayed
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University of Khartoum
Effects of seasonal changes in thermal environment and age (1.0-3.0 years) of animals on haematological values of 20 Desert ewes in Shambat area were investigated during wet summer, winter and dry summer, successively. There were marked seasonal changes in ambient temperature and relative humidity and the animals experienced the highest heat load during dry summer, then wet summer and the mildest thermal environment was in winter. The results indicated notable changes in most of the parameters. The seasonal variations in RBC count, PCV and Hb concentration were significant and the highest mean values were in winter. Monthly mean values were negatively correlated with monthly mean values of ambient temperature, which could be related to depression of food intake and haemodilution with rise in ambient temperature. Values of RBC count, PCV and Hb concentration were lower in the oldest animals, except one year old animals which maintained also low values. The erythrocyte sedimentation rate (ESR) showed no significant seasonal changes, although the values were higher during dry summer. A positive correlation between the monthly mean values of ESR and the monthly mean values of ambient temperature was observed. ESR was significantly higher in 2-years-old animals compared to the other age groups. The mean values of MCV and MCH were significantly higher during dry summer, while the MCHC values were higher during winter. The oldest animals maintained higher values of MCH and MCV whereas the MCHC value was significantly higher in 2 years-old animals compared to the other age groups. Seasonal fluctuations in total leukocyte counts were significant, with lower values during dry summer. There was also, a low negative correlation between the monthly mean values of total leukocyte counts and the corresponding values of ambient temperature. The response of differential leukocyte counts to seasonal changes in environmental temperature was not consistent. The neutrophils were significantly higher during winter and wet summer. The lymphocytes, eosinophils and basophils were not significantly affected by seasonal change, while monocytes were lower during winter. There was no significant difference between the age groups in total leukocyte count except that the one-year-old animals maintained lower values. There were, also, no significant differences between the age groups in differential leukocyte counts. The concentrations of serum total protein, albumin and globulin were significantly higher during wet summer, a response that could be related to improvement of nutritional status. Concentrations of serum total protein and albumin were not significantly affected by age, but the oldest animals maintained higher globulin concentration which could be associated with increase in intensity of immunological response with age. The results obtained for Desert ewes were discussed and compared with previous findings for sheep and other ruminants. Seasonal variations in the thermal environment influence Desert sheep physiologically and nutritionally. In order to reduce physiological strain and improve the productive performance, Desert sheep could be protected from solar heat load by provision of shade in hot summer conditions. Heat tolerance can be improved by dietary manipulation by offering balanced diets.
Desert Sheep; Animals; Summer