Environmental heat load (HL), a combination of high ambient temperature and humidity, negatively affects livestock production. In the next decades, climate change is predicted to increase the prevalence and intensity of HL. As a consequence, livestock will be increasingly exposed to heat stress, negatively impacting wellbeing and the sustainability of the animal agriculture industry. Due to their increased metabolic rate, high-yielding dairy cows are extremely sensitive to hot environments. In these animals, chronic HL has detrimental effects on feed intake, milk production and reproductive performance. Around parturition, HL contributes to systemic inflammation by increasing the expression of pro-inflammatory cytokines in blood cells, leading to immune dysfunction. Key modulators of the metabolic function such as adipose tissue (AT) are also affected by HL; during seasonal HL, subcutaneous AT of periparturient cows exhibits enrichment of proteins related to the oxidative stress response pathway such as Nrf2-oxidative stress response. The endocannabinoid system (ECS) is a central regulator of whole body metabolism and energy homeostasis, and it is also a potent modulator of inflammatory responses and immune function in mammals. The cannabinoid-2 (CB2) receptor, expressed by various cells of the immune system, can also modulate the release of cytokines and appears to have a critical role in immune regulation and function. Another receptor related to the ECS is the heat-sensitive transient-receptor-potential-cation channel-subfamily-V-member-1 (TRPV1), which is a ligand-gated ion channel that plays a key role in modulation of the sensation of pain and thermal hyperalgesia. We hypothesized that HL during summer may affect the inflammatory state, oxidative stress and the ECS in dairy cows, possibly via TRPV1. We found that seasonal HL during the peripartum period was associated with lower white blood cell counts coupled with increased levels of subacute inflammation and oxidative stress, indicating dysregulation of immune function. In addition, environmental HL, either directly or via reduced feed intake, seems to have a limited effect on ECS components in AT, and the heat-sensitive receptor TRPV1 could be related to the association between HL and the ECS in dairy cows.
Dr. Maya Zachut
Environmental Heat Load Affects Subacute Inflammation, Oxidative Stress and the Endocannabinoid System in Periparturient Dairy Cows
Volcani Institute, Agricultural Research Organization, Israel