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The aim of this study was to evaluate the effects of evaporative cooling at two different frequencies per day on the respiration rate (RR) of lactating dairy cows, considering cow-related factors. Twenty multiparous Israeli Holstein dairy cows housed in a naturally ventilated cowshed were divided randomly into two treatment groups. The cows of both groups were exposed to 3 or 8 cooling sessions per day (3xcool vs. 8xcool, respectively). The RR was observed hourly, with a maximum of 12 measurements per day. Body posture (standing vs. lying) was simultaneously documented. Milk yield was recorded daily. Coat color was determined from a digital photograph. The RR of standing and lying cows was lower in the 8xcool group (60.2 and 51.6 breaths per min (bpm), respectively) than in the 3xcool group (73.1 and 65.6 bpm, respectively). For each increment of five kilograms of milk produced, RR increased by one bpm, and the RR of cows in early days in milk (DIM) was 12.3 bpm higher than that of cows in late DIM. In conclusion, eight cooling sessions per day instead of three lead to a RR abatement in heat-stressed cows under hot conditions, and cow-related factors directly impact the RR during heat stress assessment. [ABSTRACT FROM AUTHOR]

The main objective of this study was to identify the influences of different climatic conditions and cow-related factors on the respiration rate (RR) of lactating dairy cows. Measurements were performed on 84 lactating Holstein Friesian dairy cows (first to eighth lactation) in Brandenburg, Germany. The RR was measured hourly or twice a day with up to three randomly chosen measurement days per week between 0700 h and 1500 h (GMT + 0100 h) by counting right thoraco-abdominal movements of the cows. Simultaneously with RR measurements, cow body postures (standing vs. lying) were documented. Cows' milk yield and days in milk were recorded daily. The ambient temperature and relative humidity of the barn were recorded every 5 min to calculate the current temperature-humidity index (THI). The data were analyzed for interactions between THI and cow-related factors (body postures and daily milk yield) on RR using a repeated measurement linear mixed model. There was a significant effect of the interaction between current THI category and body postures on RR. The RRs of cows in lying posture in the THI < 68, 68 ≤ THI < 72 and 72 ≤ THI < 80 categories (37, 46 and 53 breaths per minute (bpm), respectively) were greater than those of standing cows in the same THI categories (30, 38 and 45 bpm, respectively). For each additional kilogram of milk produced daily, an increase of 0.23±0.19 bpm in RR was observed. Including cow-related factors may help to prevent uncertainties of RR in heat stress predictions. In practical application, these factors should be included when predicting RR to evaluate heat stress on dairy farms. [ABSTRACT FROM AUTHOR]