Schüller LK, Burfeind O, Heuwieser W
Theriogenology 2014 May;81(8):1050-7
PMID: 24612695
Abstract
The objectives of this retrospective study were to investigate the relationship between temperature-humidity index (THI) and conception rate (CR) of lactating dairy cows, to estimate a threshold for this relationship, and to identify periods of exposure to heat stress relative to breeding in an area of moderate climate. In addition, we compared three different heat load indices related to CR: mean THI, maximum THI, and number of hours above the mean THI threshold. The THI threshold for the influence of heat stress on CR was 73. It was statistically chosen based on the observed relationship between the mean THI at the day of breeding and the resulting CR. Negative effects of heat stress, however, were already apparent at lower levels of THI, and 1 hour of mean THI of 73 or more decreased the CR significantly. The CR of lactating dairy cows was negatively affected by heat stress both before and after the day of breeding. The greatest negative impact of heat stress on CR was observed 21 to 1 day before breeding. When the mean THI was 73 or more in this period, CR decreased from 31% to 12%. Compared with the average maximum THI and the total number of hours above a threshold of more than or 9 hours, the mean THI was the most sensitive heat load index relating to CR. These results indicate that the CR of dairy cows raised in the moderate climates is highly affected by heat stress.
[Conclusions]
Conception rate of lactating dairy cows in the moderate
climate was highly affected by heat stress. The THI of 73 was the most likely threshold for the influence of heat stress on CR, based on the observed relationship between the mean THI at the day of breeding and the resulting CR. Negative effects of heat stress, however, were apparent already at lower levels of THI and 1 hour of mean THI of 73 or more decreased CR significantly. This indicates that dairy cows in themoderate climates might be more affected by heat stress than cows acclimatized to tropical or subtropical climates, which are exposed to a constant heat stress. The CR of lactating dairy cows was negatively affected by heat stress both before and after the day of breeding. The period from Day21 to 1 before the day of breeding was the most sensitive to heat stress. Thus, heat abatement strategies should maintain low and constant THI to avoid fluctuations in heat stress over a period of at least 3 weeks before to 3 weeks after the day of service.
[Introduction]
ドイツの受胎率は35%まで落ちている。高泌乳量の牛は、いっぱい食べているため、暑熱ストレスを受けやすい。牛の密飼いは、暑熱ストレスを増す。
Morton, et al. (J Dairy Sci, 2007) estimated that heat stress defined as
a daily maximum temperature–humidity index (THI) of 72 or more from Day 35 before to Day 6 after the day of breeding decreases CR of lactating dairy cows by around 30% points relative to days of breeding inwhich there was no heat load from Day 35 before to Day 6 after the day of breeding. でも、日内最大THIが72を超える日は多くなってきている。
[Materials and methods]
Ambient temperature (AT) and relative humidity (RH) within the experimental barn were recorded using a
Tinytag Plus 2 logger secured at a beam 3 m from the ground. These data were recorded hourly. Ambient temperaturand RH data were used to calculate the THI, according to the equation reported by Kendall, et al.
:THI=(1.8*AT+32)-((0.55-0.0055*RH)*(1.8*AT-26))
“The association of each THI threshold from 41 to 79 and CR was evaluated in a univariable logistic regression model. Odds ratios including 95% confidence intervals (CI95) were reported for all thresholds, and significance was set at P-value less than 0.05.”
“The relation of the number of hours above determined THI threshold at the day of breeding and the CR was evaluated in a univariable logistic regression model. Odds ratios, including CI95, were reported for all THI thresholds, and significance was set at P-value less than 0.05.”
“The relationship of each heat load index and the CR was evaluated in a univariable logistic regression model. Odds ratios, including CI95, were reported for all heat load indices, and significancewas set at P-value less than 0.05.”
“The relation of each period to the CR was evaluated in a uni- variable logistic regression model. Odds ratios including CI95 were reported for all periods of exposure, and signif- icance was set at P-value less than 0.05.”