Heat Stress: A Serious Disruptor of the Reproductive Physiology of Dairy Cows

Abstract

Global warming is a significant threat to the sustainability and profitability of the dairy sector, not only in tropical or subtropical regions but also in temperate zones where extreme summer temperatures have become a new and challenging reality. Prolonged exposure of dairy cows to high temperatures compromises animal welfare, increases morbidity, and suppresses fertility, resulting in devastating economic losses for farmers. To counteract the deleterious effects of heat stress, cattl e employ various adaptive thermoregulatory mechanisms including molecular, endocrine, physiological, and behavioral responses. These adaptations involve the immediate secretion of heat shock proteins and cortisol, followed by a complex network of disrupted secretion of metabolic and reproductive hormones such as prolactin, ghrelin, ovarian steroid, and pituitary gonadotrophins. While the strategic heat stress mitigation measures can restore milk production through modifications of the microclimate and nutritional interventions, the summer fertility records remain at low levels compared to those of the thermoneutral periods of the year. This is because sustainment of high fertility is a multifaceted process that requires appropriate energy balance, undisrupted mode of various hormones secretion to sustain the maturation and fertilizing competence of the oocyte, the normal development of the early embryo and unhampered maternal—embryo crosstalk. In this review, we summarize the major molecular and endocrine responses to elevated temperatures in dairy cows, as well as the impacts on maturing oocytes and early embryos, and discuss the consequences that heat stress brings about in dairy cattle fertility.

Advancements in Genetic Biomarkers and Exogenous Antioxidant Supplementation for Safeguarding Mammalian Cells against Heat-Induced Oxidative Stress and Apoptosis

“…The deleterious effects of heat stress (HS) on reproductive function encompass a comprehensive spectrum of repercussions affecting both male and female reproductive components, spanning from the intricate mechanisms of fertilization to the critical stages of early and late embryo–fetal development. Consistently, extensive investigations have collectively unveiled the multifaceted impacts of HS on the reproductive landscape [ 9 , 10 , 11 , 12 , 13 ].…”

“…Specifically, granulosa cells responsible for estradiol production are adversely affected by HS, resulting in decreased estradiol production and subsequent disruption of the estrous cycle in cattle [ 59 , 60 , 61 ]. HS has also been shown to influence corticoid levels, luteinizing hormone (LH), and plasma progesterone in cattle, with alterations in hypothalamus and pituitary gland function leading to changes in the secretion of reproductive hormones [ 9 , 62 , 63 , 64 , 65 , 66 ]. Moreover, HS negatively impacts oocyte quality due to its effects on the hypothalamus and pituitary gland, specifically the LH [ 67 , 68 , 69 ].…”

Heat-Stress Impacts on Developing Bovine Oocytes: Unraveling Epigenetic Changes, Oxidative Stress, and Developmental Resilience

“…Production of the cow is directly correlated to reproductive performance [4]. However, dairy cow reproduction is influenced by many external factors, including nutrition, management, and environmental conditions, and the environmental factor has a vivid impact [5]. Currently, the dairy industry is confronted with substantial difficulties arising from adverse environmental circumstances because of global climate change [6].…”

“…Under severe heat stress, the dietary intake of cattle is reduced, resulting in decreased daily weight gain and milk production [9]. One of the most important effects of heat stress on animal husbandry is the reduction of reproduction rate in cattle, as well as a huge economic loss to the dairy industry [5]. With global warming temperatures rising every year, the detrimental impacts of heat stress on cattle fertility are becoming an increasingly urgent problem [10].…”

Multiview Monitoring of Individual Cattle Behavior Based on Action Recognition in Closed Barns Using Deep Learning

“…They are primarily equipped with sensors that measure the temperature and activity based on motion obtained from accelerometers [ 9 ]. These data provide valuable information for animal behavior [ 10 ], health status [ 11 ], disease [ 12 ], stress [ 13 ], and estrus detection [ 14 ]. Radio frequency identification (RFID) tags are also used to obtain individuals’ identities.…”