Impact of Season and OvSynch + GnRH on Day 5 After Artificial Insemination (AI) on the Heat Detection and Conception Rates of Cooled High-Yielding Holstein Cows.

If global warming persists, new strategies will be necessary to keep high-yielding dairy cows' reproduction at a thermo-neutral level. In this study, two years of data from around 2000 cooled cows from a dairy farm in northeastern Romania were analyzed. In both years, an automated cooling system was used to maintain the temperature-humidity index (THI) within the range of 65-75 when environmental conditions exceeded the upper limit of this range. The univariate analysis shows that there may be a potential association between parity and the heat detection rate (p < 0.25). Additionally, the analysis suggests possible associations between conception rate and season, parity, and 4 + AIs (p < 0.25). These findings warrant further investigation through multivariate analysis. Summer season had the biggest impact (p = 0.001) on poor conception rate, according to the multivariate logistic regression analysis. Notably, the effects on conception rates extended into autumn (p = 0.004) in cooled high-yielding dairy cows. As expected, repeat breeding (4 + AIs) and parity (3 + lact.) impacted reproduction (p = 0.05). However, there was no association between OvSynch and OvSynch + GnRH on day 5 after AI and conception rate (p > 0.05). According to data from the current study, we concluded that the current cooling systems need to be improved to maintain reproduction at a thermo-neutral level for high-yielding dairy cows.