Submitted to: Journal of Dairy Science
Publication Type: Abstract Only
Publication Acceptance Date: March 8, 2007
Publication Date: July 8, 2007
Citation: Norman, H.D., Wright, J.R., Cole, J.B. 2007. Effect of temperature and humidity on gestation length. Journal of Dairy Science. 90(Suppl. 1):16(abstr. M38). Technical Abstract: High temperature and humidity have been shown to suppress daily milk and component yields of dairy cows, but their effects on most other performance traits have not been investigated. To determine if monthly differences in GL are caused by temperature and humidity, meteorological data since 1997 recorded at 238 weather stations was used in conjunction with national data for nearly 7 million calvings from 1999 through 2005. Temperature and relative humidity recorded at the weather station closest to the herd were combined into temperature-humidity indexes (THI): THI = (1.8T + 32) – (0.55 – 0.0055H)(1.8T – 28), where T is temperature in °C and H is relative humidity expressed as a percentage, for the week prior to calving and for calving day. Effect of weekly and calving-day THI on GL were compared with a model that accounted for THI, calving day, calving year, calving herd-year, calving month, age-parity, calf birth code (gender and multiple-birth status), lactation length, milk yield, service sire, sire, and cow. All effects were fixed except service sire, sire, and cow. Effect of THI on GL without calving month in the model also was examined. When weekly THI was 36 to 40, 56 to 60, and 76 to 80 with calving month in the model, GL was 279.7, 279.5, and 279.1 d, respectively; without calving month in the model, GL was 280.2, 279.8, and 278.6 d. Excluding calving month from the model resulted in greater variation in GL, which became shorter at an accelerated rate as THI increased. Calving-day THI were less effective than weekly THI in accounting for GL differences. Although the benefit of including THI in the model was rather limited if calving month was already considered, GL still became noticeably shorter when THI was >70. Either calving month or THI can be effective in helping to predict calving dates.