Effects of Heat Stress on Blood Metabolites and Milk Quality in Lactating Holstein and Jersey Cows

Abstract

Heat stress has been linked to numerous changes related to health and metabolism in dairy cattle. The effects of heat stress on milk quality factors and blood metabolites were observed in Holstein and Jersey cows under varying severities of heat stress (n = 12/ 6 = Holstein, 6 = Jersey). Milk quality was assessed using increasing somatic cell count (SCC), conductivity, and bacterial load as indicators of decreased milk quality. Concentrations of some blood metabolites such as calcium (Ca), potassium (K), sodium (Na), blood urea nitrogen (BUN), albumin (Alb), glucose, cholesterol, and non-esterified fatty acids (NEFA) were monitored for changes as well. Many significant differences relating to increases in SCC (p = 0.0936) and conductivity (p = 0.0195) were observed. There were no significant findings relating bacterial load to heat stress of breed. Furthermore, some significant differences concerning blood metabolites, such as Mg (p = 0.0388), will require more research to ascertain a better understanding of the underlying mechanisms. The results uncovered an overall decline in milk quality due to heat stress as well as an unclear relationship between heat stress treatments and variable concentrations of blood metabolites.