Abstract #144

# 144
Effect of pre- and postnatal heat stress on dairy calf thermoregulation and productivity.
B. Dado-Senn*1, L. Vega Acosta2, M. Torres Rivera2, S. L. Field1, M. G. Marrero1, S. Tao3, T. F. Fabris1, G. Ortiz-Colon2, G. E. Dahl1, J. Laporta1, 1Department of Animal Sciences, University of Florida, Gainesville, FL, 2Department of Animal Sciences, University of Puerto Rico, Mayagüez, 3Department of Animal and Dairy Science, University of Georgia, Tifton, GA.

Dairy calves exposed to prenatal heat stress experience compromised growth and immunity compared with those provided with prenatal heat abatement. We hypothesize that heat abatement postnatally will improve calf thermoregulation and growth, particularly if dairy calves were also exposed to heat abatement prenatally. Holstein calves born to heat-stressed (prenatal HT, shade) or cooled (prenatal CL, shade, fans and soakers) dams during late gestation (~46 d, temperature-humidity index; THI ≥ 68) were postnatally exposed to heat stress (postnatal HT, shade) or cooling (postnatal CL, shade and fans at ~4 m/s) for 56 d (THI ≥ 68; HTHT, HTCL, CLHT, and CLCL; n = 12/group). Skin temperature (ST, shaved rump), rectal temperature (RT), and respiration rate (RR) were recorded daily (0700, AM; 1300, AF; and 1900 h, PM) and BW weekly. Feed intake (milk replacer [MR] and grain) was averaged weekly. Calves were allotted up to 10 L of MR and up to 3 g grain via automatic feeder group pens with MR weaning beginning at 42 d. Data were analyzed as a 2 × 2 factorial arrangement by PROC MIXED in SAS. There was an interaction for ST in the AM and PM; CLCL calves had the lowest ST but CLHT calves had the highest (AM: 29.94 vs 32.66 ± 0.12°C; PM: 33.16 vs 35.26 ± 0.14°C, P < 0.01). Rectal temperature was lowered by both pre- and postnatal cooling AM and AF (AM: 38.67 vs 38.84 ± 0.02°C; AF: 38.97 vs 39.12 ± 0.02°C, for CLCL vs HTHT respectively, P < 0.01), whereas only postnatal cooling reduced RT PM (39.18 vs 39.29 ± 0.02°C, P < 0.01). At all times of day, HTCL calves had the lowest RR but HTHT calves exhibited the highest RR (42.64 vs 52.51 ± 0.92 bpm, P < 0.01). Prenatal CL calves tended to weigh more, particularly at birth (42.38 vs 40.51 ± 0.76 kg, P = 0.09), and weaning (80.51 vs 75.84 ± 1.77 kg, P = 0.07) compared with prenatal HT. Milk intake tended to be higher for postnatal CL calves pre-weaning (7.15 vs 6.69 ± 0.18 L/d, P = 0.07), and grain intake increased in postnatal CL calves during weaning (1.39 vs 1.11 ± 0.09 g/d, P = 0.03). This study indicates that a combination of pre- and postnatal heat abatement altered calf thermoregulation accompanied by slight improvements in productivity.

Key Words: heat abatement, calf, growth