Abstract
The aim of the present study was to evaluate the changes in physiological responses and serum biochemical panel in crossbred dairy cow populations kept in a hot climate environment. We used a population of 384 dairy cows of genetic groups ½Holstein × ½Guzerá (n = 105) and ¾Holstein × ¼Guzerá (n = 279) derived from the Brazilian semiarid region. The physiological responses analyzed were: respiratory rate (RR, movements/minute), rectal temperature (RT, °C), free thyroxine (T4, µg/mL) and thyroid-stimulating hormone (TSH, µUI/mL). The values of RR, RT, T4, TSH and serum levels of glucose, cholesterol, total protein, urea and creatinine were determined and correlated with milk production for 305 days, correlation lying only with TSH. Significant differences were observed just in milk production, RR and TSH comparing the genetic groups ½Holstein × ½Guzerá and ¾Holstein × ¼Guzerá. In conclusion, ¾Holstein × ¼Guzerá cows showed higher thyroid activity and milk production than ½Holstein × ½Guzerá cows, and may therefore be a better option for dairy production systems in semiarid regions.
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