April 03, 2019

Interpretive Summary: Heat stress and heat abatement effects on Holstein cows.

Interpretive Summary: Heat stress abatement during the postpartum period: effects on whole lactation milk yield, indicators of metabolic status, inflammatory cytokines, and biomarkers of oxidative stress.

By: Dr. Caitlin Vonderohe

Heat stress is a significant issue in dairy cows around the time of calving. In many cases, cows enter a negative energy balance because the increased demands of lactation are not met by feed intake. As a result, early lactation cows are more prone to metabolic disease such as ketosis, milk fever and hepatic lipidosis. Cows are also unable to properly respond to increases in ambient temperature, due in part to the metabolic changes that occur during this time. Heat-stress, coupled with the other physiologic stresses of early lactation may also result in increased circulation of reactive oxygen species and systemic inflammation. A study recently published in the Journal of Animal Science by Safa et al., entitled “Heat stress abatement during the postpartum period: effects on whole lactation milk yield, indicators of metabolic status, inflammatory cytokines, and biomarkers of oxidative stress” explores how heat stress and heat abatement affects production, immune status, and metabolic and oxidative stress in post-partum Holstein dairy cows. 

Forty-six Holstein dairy cows were randomly assigned to one of two treatments, cooling or heat stress, for seven weeks postpartum. Cooling was accomplished with fans and misters, but all other conditions were the same across treatments, including diet. Milk yield was recorded daily, and body condition score was measured weekly throughout the study. Milk samples and blood samples were collected weekly. Milk was analyzed for protein, fat, lactose, and somatic cell count. Blood was analyzed for glucose, beta-hydroxy butyrate, non-esterified fatty acids, total anti-oxidant capacity, reactive oxygen species, tumor necrosis factor-alpha, interleukin 1-alpha, interleukin-2, IgA, Ig-M, and IgG. 

Heat stressed cows hat greater rectal temperature, lower dry matter intake and produced 1,442 kg less milk than the cooled cows. Feed efficiency was improved in the cooled compared to heat stressed cows. Cooled cows had greater plasma glucose, beta-hydroxy butyrate and non-esterified fatty acid levels compared to the heat stressed cows. Heat stressed cows had greater levels of total-antioxidant capacity, and ROS was higher in weeks 1, 5, 6, and 7. However, heat stressed cows had lower levels of TNF-α, IL-1α, and IL-2. Plasma levels of IgM and IgG were higher in cooled cows throughout the study. 

Overall, this study showed that cooling heat-stressed dairy cows can improve dry matter intake, performance, support the cow through the metabolic changes that occur around parturition, and reduce systemic inflammation and reactive oxygen species. The marked benefits of cooling indicate that it is an appropriate management strategy for heat stressed dairy cows to maximize cow health and productivity, particularly in the post-partum period.

To view the full article, visit the Journal of Animal Science.