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Performance, physiological response and behavioral of dairy heifers kept under forced ventilation system


National milk production has an important social-economical role, and herd's productivity is a decisive factor for sector's competitiveness. For that, fundamental attention must be destinated to the young animals, because they represent herd's future productive quality. However, climate factor is still a question that represents important losses to the sector. A system that can be employed when environmental temperature is upper critical, consists in increases the ventilation rate, optimizing heat losses by the animals. The research has as principal objective to evaluate the influence of forced ventilation upon performance, physiological and behavioural alterations of holstein dairy heifers in a confinement system. Sixteen heifers will be used, which will be distributed in four treatments: A) Without forced ventilation; B) Forced ventilation during the 24 hours of the day; C) Forced ventilation from 6 am to 6 pm e D) forced ventilation from 6 pm to 6 am. Animals will be divided based on the average weight and body condition score and ramdomly distributed in the treatments. Experimental delineation that will be used is the latin square 4 x 4, repeated twice. Eight experimental periods will be adopted with a duration of 14 days each one, being 9 days of adaptation and 5 to collect data. Climate data (temperature, relative humidity) will be used in the calculation of THI and BGHI. These data will be correlated with animals physiological (rectal temperature, respiratory frequency and skin temperature) and behavioural responses. Performance and intake will be used to evaluate heifers feed efficiency and ponderal growth and to verify the existence of ventilation's effect in thermal stress situations. The results of this research will bring important informations about thermoregulation processes of dairy cattle in heifers stage, as well as the benefits of the use of forced ventilation in this phase. (AU)

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