Hematological And Biochemical Parameters In Feedlot Heifers Under Heat Stress: Effect Of Shade Area And Genotype

The aim of the study was to determine the effect of two shade areas per animal on hematological and biochemical concentrations in Zebu and European heifers fattened under heat stress conditions. Five-hundred ten heifers (Zebu, European and its crosses) were randomly assigned to six pens divided in two shade areas: T1) three pens with 100 heifers per pen (shade area: 2.7 m(2)/animal), and T2) three pens with 70 heifers per pen (shade area: 3.7 m(2)/animal). Fifteen blood samples of each genotype per pen were collected three times (days 1, 28 and 66) during the study. To analyze metabolites, electrolytes and thyroid hormones, serum samples were used, while for hematological components fresh blood. Data was analyzed under a 2x2 factorial arrangement in a completely randomized design with repeated measurements. The temperature-humidity index averaged 81.7 units. In T1, both genotypes showed similar glucose concentration (P < 0.05), but in T2 glucose concentrations was higher in Zebu (P < 0.05). The urea level were lower (P < 0.05) in T2 than in T1. The Na+ level in T1 was higher (P < 0.05) than in T2. The Cl- in T1 was lower (P < 0.05) than in T2. The hormone T-3 showed lower concentration (P < 0.05) in T1 compared to T2. No differences were detected for Htc and Hb between genotypes within T1 (P < 0.05), but they were higher in T2 for Zebu heifers (P < 0.05) than Europeans. Overall, the use of greater shade area did not show substantial differences in the physiology of fattening Zebu or European heifers during summer.