Correlation between milk production, days in milk and temperature humidity index in lactating dairy cows in a sub-tropical summer

Thursday, July 24, 2014: 10:00 AM
3501D (Kansas City Convention Center)
Megan L Sullivan , The University of Queensland, Gatton, Australia
John B. Gaughan , The University of Queensland, Gatton, Australia
NH Son , The University of Queensland, Gatton, Australia
Jarrod Lees , The University of Queensland, Gatton, Australia
Angela M Lees , The University of Queensland, Gatton, Australia
Abstract Text:

Heat load is a significant factor that contributes to reductions in milk production in sub-tropical dairy cows. Forty lactating Holstein-Friesian cows were used in a 103 d study investigating the influence of summer conditions on animal responses. The cows were managed within a partial mixed ration system (70% total mixed ration and 30% pasture) and were milked twice daily at 0530 h and 1400 h. Individual milk production (MP) was recorded at each milking. Ambient temperature (TA) and relative humidity (RH), were obtained at 10 min intervals from an automated on-site weather station and temperature humidity index (THI) was calculated based on these data: (THI = 0.8 x TA) + [(RH/100) x (TA - 14.4)] + 46.4). Individual MP were collated and converted into mean MP for the 40 cows. Correlations between MP and mean THI for -1, -2 and -3 d lags were examined using Pearson correlation analysis. The mean MP over the duration of the study was 23.3 kg/cow.d-1 (range 18.9 to 28.3 kg/cow.d-1), and DIM was < 50 d at the commencement of the study. The mean monthly THI for the duration of the study progressively increased: December 71.0 ± 0.07 (range 51.5 to 84.7); January 73.2 ± 0.07 (range 60.2 to 86.4); February 74.1 ± 0.09 (range 59.7 to 87.1). Milk production was negatively correlated with THI (P < 0.01) for 1, 2 and 3 d lags. The correlation between MP for the 1, 2 and 3 d lags and THI on d 0 were -0.57, -0.55 and -0.53. Fluctuations in MP during summer are generally attributed to changes in THI, and this is supported by the current study. However there was a negative correlation (r = -0.72, P < 0.001) between MP and DIM. During the study increasing heat load corresponded with increasing DIM. Reductions in MP due to increasing DIM need to be accounted for, so as not to confound the reductions in MP due to heat load. This study suggests that there is a strong negative correlation between the THI, MP and DIM and the effects are cumulative. 

Keywords: heat stress, milk production, temperature humidity index