Predicting rectal temperature and respiration rate responses in lactating dairy cows exposed to heat stress

摘要

Milk production and time effects are consideredrelated to heat stress but they have not yet been combinedin predictive models. In two parts, this studyaimed to develop new models to predict heat stress(rectal temperature and respiration rate) of lactatingdairy cows by inputting predictors, including ambienttemperature (T_a), relative humidity (RH), wind speed(WS), milk yield (MY), and time blocks. In the firstpart of the study, we built the quantitative foundationfor the second part, including the regression relationbetween respiration rate and rectal temperature (toconvert predicted respiration rate to predicted bodytemperature), as well as between rectal temperatureand respiration rate when heat stress was triggered(to recognize whether herds were under stress). In thesecond part, we built models that combined the abovementionedpredictors to predict respiration rate. In partⅠ, data were obtained from 45 high-producing Holsteincows within a Ta range of 9.5 to 30.8°C. We found avery strong correlation between mean respiration rate(MRR) and mean rectal temperature (MRT), whereMRT = 0.021 × MRR + 37.6 (R~2 = 0.925), suggestingthat for each 4.8 breaths per minute (bpm) increase ofMRR, MRT would be expected to increase by 0.1°C.Rectal temperature was determined to be 38.6°C whenheat stress was triggered, which corresponded to a respirationrate of 48 bpm. In part Ⅱ, data were obtainedin 3 stalls within a T_a range of 6.9 to 33.3°C over 3 timeblocks, all of which were the 90 min preceding milking(0630–0800, 1230–1400, and 1830–2000 h). We found anonlinear response of MRR to Ta, which could be linearizedby the quadratic term of Ta. The response of MRRwas the highest in the 0630–0800 h block, followed by1230–1400 h, and finally 1830–2000 h. We proposed amodel combining 3 time blocks (R~2 = 0.836): MRR in0630–0800 h was determined to 56.28 + (−3.40 + 0.11× T_a + 0.02 × RH) × T_a − 0.21 × RH − 2.82 × WS+ 0.62 × MY; MRR in 1230–1400 h and 1830–2000 hwere 4.6 and 10.3 bpm lower than that in 0630–0800 h,respectively (reducing the intercept of the expressionin 0630–0800 h). Compared with temperature-humidityindex equations, the proposed model performed betterat suppressing prediction error, and had better sensitivityand accuracy in recognizing whether heat stress wastriggered.