IMPACT OF HEAT STRESS ON REPRODUCTIVE EFFICIENCY AND FERTILITY MARKERS IN DAIRY COWS IN ARID CLIMATES

Abstract

This study investigates the impact of heat stress on reproductive efficiency and fertility markers in dairy cows maintained under arid climatic conditions, where extreme thermal load threatens livestock productivity and reproductive performance. A cross-sectional quantitative study involving six commercial dairy farms encompassed the analysis of oxidative stress biomarkers, assessments of oocyte quality, hormonal profiling, physiological monitoring, as well as the evaluation of embryo development.  The results obtained confirmed chronic exposure to heat stress as continuously high temperature-humidity index (THI) values (>82) were coupled with increased respiratory rates and rectal temperatures.  Reproductive performance was severely compromised with more days available to breed (mean: 147 days), reduced conception rates (down to 25%), and increased pregnancy loss (up to 18 per cent).  Hormonal tests in animals subjected to heat stress showed reduced levels of progesterone, estrogen, LH and FSH that were related to reduced reproductive competence.  Oocyte quality was substantially lower under thermal stress when maturation rates were lowered by 31 percent and degeneration increased threefold compared to controls.  These adverse effects were also corroborated by in vitro embryo development that indicated that heat-stressed cows significantly lower rates of cleavage and blastocyst development (53 and 21 percent, respectively).  Oxidative stress markers were increased lipid peroxidation (MDA) and reduced antioxidant defenses (TAC and SOD activity), which demonstrated that there is a strong mechanistic relationship between oxidative imbalance and reproductive failure.  Correlation analysis confirmed strong associations between THI and reproductive variables of interest and seasonal comparisons revealed that fertility parameters restored partially under cooler conditions.  To enhance resilience and sustain productivity amid climate stress, the findings outlined the grave challenge presented by heat stress on the fertility of dairy cows in arid climates and the need to incorporate multiple approaches to mitigation, which comprises of environmental management, genetic selection, nutritional supplementation, and assisted reproductive technologies.