Influence of heat stress on white blood cells in Holando Argentino cows

Abstract

The combination of high temperature and humidity, characteristic of the province of Santa Fe, the main dairy production area in Argentina, affects dairy production. The Temperature and Humidity Index (ITH) may be used as an indicator of heat stress. The aim of this investigation was to evaluate heat stress effects on white blood cells in response to the release of plasma cortisol in dairy bovines. The study was carried out in the Milking Parlor Module of the Facultad de Ciencias Agrarias, located at Zavalla (33º 1’ S, 60º 53’ O) during 2013-2014 period. Thirty Holando Argentino dairy cows from second and third lactation milking group were used. Samples were taken during spring (no heat waves) and summer (presence of heat waves) during morning and afternoon milkings. A radioimmunoassay method to dose cortisol was used (Coat-A-Count Cortisol, commercial kit), a blood cell counter (MINDRAY-BC 2800) was used to determine white blood cell total count, and May Grünwald Giemsa stain to determine neutrophil and lymphocyte count. An ITH increase during summer afternoons in coincidence with a significant increase of cortisol levels was observed, a relative decrease in lymphocyte count and an increase in neutrophil count were seen. The neutrophil/lymphocyte ratio also showed a significant increase in summer. It is concluded that heat stress measured by ITH modifies the number and proportion of white blood cells and this could be attributed to plasma cortisol increase.