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

Abstract

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.