Pre- and postnatal heat stress abatement affects dairy calf thermoregulation and performance

摘要

Prenatal heat stress during late gestation exerts longtermeffects on growth and productivity of the dairycalf. Further, direct exposure to heat stress during thepreweaning period impairs calf thermoregulation andperformance. We examined the effects of heat stressabatement during the prenatal period, postnatal period,or both on calf performance. We hypothesizedthat calves exposed to pre- and postnatal heat stressabatement would perform most optimally in terms ofthermoregulation, growth, and health responses whencompared with calves that are heat-stressed at any timein the pre- or postnatal periods. Holstein calves bornto heat-stressed (HT) or cooled (CL) dams during lategestation (44 ± 5 d; prenatal HT or CL) were exposedto heat stress or cooling postnatally for 56 d (postnatalHT or CL), resulting in 4 treatments: HT-HT, HT-CL,CL-HT, and CL-CL; n = 12/treatment. Calves wereadministered 4 L of pooled colostrum and after 2 d ofage allotted 10 L/d milk replacer and up to 3 kg/d concentratein automatic feeder group pens (n = 6/pen).Postnatal cooling was achieved by 2 fans (average windspeed 2 m/s). Thermoregulatory responses (respirationrate and heart rate; rectal, body, and skin temperature),feed intake, growth parameters including averagedaily gain and medication events were recorded, andblood samples were collected weekly. Thermoregulatoryresponses were lower in postnatal CL calves comparedwith postnatal HT. In the afternoon, HT-HT calveshad the highest respiration rate and rectal temperature,HT-CL calves had the lowest respiration rate, and CLHTcalves had the lowest heart rate compared with theother treatment groups. Prenatal CL calves weighedmore at birth and weaning with a tendency for greateraverage daily gain compared with prenatal HT calves,whereas postnatal CL calves had increased milk replacerand concentrate intake and a tendency for reducedfever, infection, and total medication events relative topostnatal HT. Prenatal HT calves were esophageal tubefed more often than prenatal CL. Blood hematocrit and24-h serum IgG concentration were greater in prenatalCL calves relative to prenatal HT. Prenatal heat stressabatement improves weight gain, hematocrit, and immunoglobulintransfer, whereas postnatal heat stressabatement modulates thermoregulatory responses, feedintake, and calf health. This study is the first to characterizethe combined effects of pre- and postnatal heatstress or active cooling on the dairy calf.