The effects of diurnal heat stress in dairy heifer calves

Abstract

The present study was conducted to examine how dairy heifer calves would respond to a heat stress bout in terms of growth relative to nutrient intake. Nine Holstein and 2 Jersey heifer calves (n = 11) were individually housed and enrolled in a study containing 3 experimental periods (P). Period 1 lasted 7 d during which baseline measurements were obtained. During period 2 (7 d), calves were subjected to diurnal heat stress (dHS) employed by maintaining barn temperature at 33°C (92°F) from 0900 to 2100 h and letting it be equilibrated with outside temperature [24°C (75°F)] during the night. Follow-up measurements were made over 4 d (P3) immediately after dHS. Calves consumed 25% less feed during the day but compensated for it consuming more feed (35%) in night during dHS. Despite DMI (kg/d) being similar between dHS and baseline, ADG and feed efficiency decreased significantly during dHS. These effects are likely consequence of nutrient repartitioning towards the activated immune system and away from productive processes (i.e., growth), as blood haptoglobin increased 3-fold during dHS. Nonetheless, calves exhibited compensatory growth concurrently with increased DMI and drinking water per unit of DMI immediately following dHS. Overall, dHS severely hampers growth and feed efficiency of dairy heifer calves despite unaltered DMI relative to baseline. Understanding nutrient partitioning in calves during and after heat stress could help mitigate the adverse effects and help calves effectively recover from heat stress.